Severe loss-of-function mutations in the adrenocorticotropin receptor (ACTHR, MC2R) can be found in patients diagnosed with salt-losing adrenal hypoplasia

Severe adrenal insufficiency in six neonates with normal newborn screening for CAH

BACKGROUND

Newborn screening (NBS) reduces the risk of mortality in congenital adrenal hyperplasia (CAH), mainly due to the salt-wasting form of 21-hydroxylase deficiency. There is limited knowledge regarding the results of NBS in non-CAH primary adrenal insufficiency (non-CAH PAI).

PATIENTS AND METHODS

Clinical and NBS for CAH data of neonates who were diagnosed with non-CAH PAI between January and December 2022 were examined.

RESULTS

Patients (n = 6, 4 females) were presented with severe hyperpigmentation (n = 6), hypoglycemia (n = 4), hyponatremia (n = 3), hyperkalemia (n = 1), respiratory distress syndrome (n = 1) between 3rd hour to 2 months of life. All had normal NBS results. The median first-tier 17-hydroxyprogesterone (17OHP) concentration in NBS for CAH was 0.14 ng/mL (range; 0.05-0.85). Molecular studies revealed biallelic mutations in the MC2R (n = 4; 3 homozygous, 1 compound heterozygous), MRAP (n = 1) and STAR (n = 1) genes. Glucocorticoid with or without mineralocorticoid replacement was initiated once the diagnosis of non-CAH PAI was established.

CONCLUSION

Neonates with non-CAH PAI have always normal NBS due to persistently low 17OHP, even when these newborn infants are severely symptomatic for adrenal insufficiency. Clinicians should be alert for signs of adrenal insufficiency in neonates, even if the patient has a 'normal' screening for CAH, so as not to delay diagnosis and treatment. This fact should be kept in mind particularly in countries where these conditions are more common than elsewhere.

A Rare Presentation of Homozygous Pathogenic Variant in MC2R Gene with Salt-Wasting Crisis in a Neonate

Introduction

Familial glucocorticoid deficiency (FGD) is a rare autosomal recessive disease resulting from isolated glucocorticoid deficiency or unresponsiveness to adrenocorticotropic hormone. Patients with FGD usually present in infancy or early childhood with hyperpigmentation, recurrent infections, and hypoglycemia. The salt-wasting crisis is rare.

Case Presentation

A term female neonate was admitted to the neonatal intensive care unit due to respiratory distress. On physical examination, she had generalized hyperpigmentation. Initial laboratory work-up yielded normal serum electrolytes and glucose. Hyponatremia and hyperkalemia emerged on follow-up. The patient was diagnosed as having primary adrenal insufficiency (PAI) with elevated plasma adrenocorticotropin hormone and reduced cortisol levels and hydrocortisone. We started on oral sodium (5 mEq/kg/day) and fludrocortisone (FC) (0.2 mg/day) treatment to the patient. Ultrasonography revealed hypoplastic adrenal glands. Molecular genetic analysis revealed a previously reported homozygous pathogenic variant NM_000529.2: c.560delT (p.V187fs*29) in the MC2R gene. FC dose was tapered to 0.05 mg/day on the third month of life and was stopped at tenth months of age with maintenance of normal serum electrolytes and clinical findings.

Conclusion

FGD due to MC2R gene mutation may rarely present with a salt-wasting crisis in the neonatal period. Identifying the causative gene with the pathogenic variant in PAI may serve to individualize a treatment plan.

Genetic and phenotypic spectrum of non-21-hydroxylase-deficiency primary adrenal insufficiency in childhood: data from 111 Chinese patients

BACKGROUND

Primary adrenal insufficiency (PAI) is a rare but life-threatening condition. Differential diagnosis of numerous causes of PAI requires a thorough understanding of the condition.

METHODS

To describe the genetic composition and presentations of PAI. The following data were collected retrospectively from 111 patients with non-21OHD with defined genetic diagnoses: demographic information, onset age, clinical manifestations, laboratory findings and genetic results. Patients were divided into four groups based on the underlying pathogenesis: (1) impaired steroidogenesis, (2) adrenal hypoplasia, (3) resistance to adrenocorticotropic hormone (ACTH) and (4) adrenal destruction. The age of onset was compared within the groups.

RESULTS

Mutations in the following genes were identified: NR0B1 (n=39), STAR (n=33), CYP11B1 (n=12), ABCD1 (n=8), CYP17A1 (n=5), HSD3B2 (n=4), POR (n=4), MRAP (n=2), MC2R (n=1), CYP11A1 (n=1), LIPA (n=1) and SAMD9 (n=1). Frequent clinical manifestations included hyperpigmentation (73.0%), dehydration (49.5%), vomiting (37.8%) and abnormal external genitalia (23.4%). Patients with adrenal hypoplasia typically presented manifestations earlier than those with adrenal destruction but later than those with impaired steroidogenesis (both p<0.01). The elevated ACTH (92.6%) and decreased cortisol (73.5%) were the most common laboratory findings. We generated a differential diagnosis flowchart for PAI using the following clinical features: 17-hydroxyprogesterone, very-long-chain fatty acid, external genitalia, hypertension and skeletal malformation. This flowchart identified 84.8% of patients with PAI before next-generation DNA sequencing.

CONCLUSIONS

STAR and NR0B1 were the most frequently mutated genes in patients with non-21OHD PAI. Age of onset and clinical characteristics were dependent on aetiology. Combining clinical features and molecular tests facilitates accurate diagnosis.

Familial Glucocorticoid Deficiency: the changing landscape of an eponymous syndrome

Familial Glucocorticoid Deficiency encompasses a broad spectrum of monogenic recessive disorders that theoretically solely abrogate cortisol biosynthesis. In reality, delineating clear genotype-phenotype correlations in this disorder is made complicated by marked phenotypic heterogeneity even within kindreds harbouring identical variants. Phenotypes range from isolated glucocorticoid insufficiency to cortisol deficiency plus a variety of superimposed features including salt-wasting and hypoaldosteronism, primary hypothyroidism, hypogonadism and growth defects. Furthermore, mutation type, domain topology and perceived enzyme activity do not always predict disease severity. Given the high burden of disease and implications of a positive diagnosis, genetic testing is crucial in the management of patients warranting detailed delineation of genomic variants including viable functional studies.

The melanocortin receptor signaling system and its role in neuroprotection against neurodegeneration: Therapeutic insights

The melanocortin signaling system consists of the melanocortin peptides, their distinctive receptors, accessory proteins, and endogenous antagonists. Melanocortin peptides are small peptide hormones that have been studied in a variety of physiological and pathological conditions. There are five types of melanocortin receptors, and they are distributed within the central nervous system and in several tissues of the periphery. The G protein-coupled melanocortin receptors typically signal through adenylyl cyclase and other downstream signaling pathways. Depending on the ligand, surface expression of melanocortin receptor, receptor occupancy period, related proteins, the type of cell, and other parameters, the signaling pathways are complicated and pleiotropic. While it is known that all five melanocortin receptors are coupled to Gs, they can also occasionally couple to Gq or Gi. Both direct and indirect neuroprotection are induced by the melanocortin signaling system. Targeting several of the components of the melanocortin signaling system (ligands, receptors, accessory proteins, signaling effectors, and regulators) may provide therapeutic opportunities. Activation of the melanocortin system improves different functional traits in neurodegenerative diseases. There is a potential for additional melanocortin system interventions by interfering with dimerization or dissociation. This review aims to discuss the melanocortin receptor signaling system and its role in neuroprotection, as well as its therapeutic potential.

A rare homozygous variant of MC2R gene identified in a Chinese family with familial glucocorticoid deficiency type 1: A case report

Background

Melanocortin-2 receptor (MC2R), a member of the G protein-coupled receptor family, is selectively activated by adrenocorticotropic hormone (ACTH). variants in MC2R are associated with family glucocorticoid deficiency 1 (FGD1).

Case presentation

We first reported a Chinese family with two affected siblings with a homozygotic variant of c.712C>T/p.H238Y in MC2R, presenting with skin hyperpigmentation, hyperbilirubinemia, and tall stature. These individuals showed novel clinical features, including congenital heart defects, not been found in other FGD1 patients.

Conclusions

We reported a Chinese family with affected siblings having a homozygotic variant of c.712C>T/p.H238Y in MC2R.Our report may expand the genetic and clinical spectrum of FGD1.

A Novel Mutation in Melanocortin Receptor 2 and a Reported Mutation in Melanocortin Receptor 2 Accessory Protein: Three Chinese Cases with Familial Glucocorticoid Deficiency

Background

Familial glucocorticoid deficiency (FGD) is a rare autosomal recessive disease characterized by glucocorticoid deficiency without mineralocorticoid deficiency. We report 3 Chinese patients with MRAP or MC2R mutations.

Case Reports

Patient 1 presented with hyperpigmentation. Endocrine investigations revealed low serum cortisol levels and elevated adrenocorticotropic hormone (ACTH) levels. Furthermore, low serum sodium was evident. She was diagnosed with FGD type 2 due to a homozygous mutation in MRAP (c.106+1delG), revealed through exome sequencing (ES). After 2-year treatment with hydrocortisone, skin hyperpigmentation was improved. Patient 2 initially presented with hyponatremia. Low cortisol levels and high levels of ACTH were subsequently detected; he was subjected to a hydrocortisone treatment during which he experienced repeated hypoglycemic attacks and pigmentation. ES revealed the same mutation as in patient 1 in MRAP (c.106+1delG), thus he was diagnosed with FGD type 2. After 6 years of age, his symptoms remarkably improved, and there was no episode of hypoglycemia. Patient 3 mainly presented with hyperpigmentation, hypoglycemic attack, and tall stature. Laboratory findings were normal except for low serum cortisol levels and high ACTH levels. She was diagnosed with FGD type 1 as ES revealed a novel homozygous mutation in MC2R (c.712C>A, p.His238Tyr). After nearly 2 years of hydrocortisone replacement therapy, the excessive growth was reduced to near normal, and the skin color returned to normal.

Conclusions

Three patients were diagnosed with FGD (one with FGD type 1 and two with FGD type 2). They all presented with hyperpigmentation and hypoglycemia; however, compared with patient 1, the clinical manifestations of patient 2 were more complicated. Patient 3 had later onset and taller stature than patients 1 and 2. A novel mutation in patient 3 expands the mutation spectrum of MC2R.

An Update on Genetics of Adrenal Gland and Associated Disorders

The intricacies of human adrenal development have been under scrutiny for decades. Each year marks the identification of new genes and new interactions between gene products that ultimately will act to produce the fully functioning adult gland. Due to the complexity of this process, genetic missteps may lead to a constellation of pathologies. Recent years have identified several novel genetic causes of adrenal dysgenesis and provided new insights into previously delineated processes. SF1, DAX1 (NR0B1), CDKN1C, SAMD9, GLI3, TPIT, MC2R, MRAP, NNT, TXNRD2, AAAS, and MCM4 are among the genes which have had significant contributions to our understanding of the development and function of both adrenals and gonads. Collection and elucidation of these genetic and clinical insights are valuable tools for clinicians who diagnose and manage cases of adrenal dysfunction.

Targeting trafficking as a therapeutic avenue for misfolded GPCRs leading to endocrine diseases

G protein-coupled receptors (GPCRs) are plasma membrane proteins associated with an array of functions. Mutations in these receptors lead to a number of genetic diseases, including diseases involving the endocrine system. A particular subset of loss-of-function mutant GPCRs are misfolded receptors unable to traffic to their site of function (i.e. the cell surface plasma membrane). Endocrine disorders in humans caused by GPCR misfolding include, among others, hypo- and hyper-gonadotropic hypogonadism, morbid obesity, familial hypocalciuric hypercalcemia and neonatal severe hyperparathyroidism, X-linked nephrogenic diabetes insipidus, congenital hypothyroidism, and familial glucocorticoid resistance. Several in vitro and in vivo experimental approaches have been employed to restore function of some misfolded GPCRs linked to endocrine disfunction. The most promising approach is by employing pharmacological chaperones or pharmacoperones, which assist abnormally and incompletely folded proteins to refold correctly and adopt a more stable configuration to pass the scrutiny of the cell's quality control system, thereby correcting misrouting. This review covers the most important aspects that regulate folding and traffic of newly synthesized proteins, as well as the experimental approaches targeted to overcome protein misfolding, with special focus on GPCRs involved in endocrine diseases.

Genetic Analysis of Pediatric Primary Adrenal Insufficiency of Unknown Etiology: 25 Years' Experience in the UK

CONTEXT

Although primary adrenal insufficiency (PAI) in children and young people is often due to congenital adrenal hyperplasia (CAH) or autoimmunity, other genetic causes occur. The relative prevalence of these conditions is poorly understood.

OBJECTIVE

We investigated genetic causes of PAI in children and young people over a 25 year period.

DESIGN SETTING AND PARTICIPANTS

Unpublished and published data were reviewed for 155 young people in the United Kingdom who underwent genetic analysis for PAI of unknown etiology in three major research centers between 1993 and 2018. We pre-excluded those with CAH, autoimmune, or metabolic causes. We obtained additional data from NR0B1 (DAX-1) clinical testing centers.

INTERVENTION AND OUTCOME MEASUREMENTS

Genetic analysis involved a candidate gene approach (1993 onward) or next generation sequencing (NGS; targeted panels, exomes) (2013-2018).

RESULTS

A genetic diagnosis was reached in 103/155 (66.5%) individuals. In 5 children the adrenal insufficiency resolved and no genetic cause was found. Pathogenic variants occurred in 11 genes: MC2R (adrenocorticotropin receptor; 30/155, 19.4%), NR0B1 (DAX-1; 7.7%), CYP11A1 (7.7%), AAAS (7.1%), NNT (6.5%), MRAP (4.5%), TXNRD2 (4.5%), STAR (3.9%), SAMD9 (3.2%), CDKN1C (1.3%), and NR5A1/steroidogenic factor-1 (SF-1; 0.6%). Additionally, 51 boys had NR0B1 variants identified through clinical testing. Although age at presentation, treatment, ancestral background, and birthweight can provide diagnostic clues, genetic testing was often needed to define the cause.

CONCLUSIONS

PAI in children and young people often has a genetic basis. Establishing the specific etiology can influence management of this lifelong condition. NGS approaches improve the diagnostic yield when many potential candidate genes are involved.

Increased longevity due to sexual activity in mole-rats is associated with transcriptional changes in the HPA stress axis

Sexual activity and/or reproduction are associated with a doubling of life expectancy in the long-lived rodent genus Fukomys. To investigate the molecular mechanisms underlying this phenomenon, we analyzed 636 RNA-seq samples across 15 tissues. This analysis suggests that changes in the regulation of the hypothalamic–pituitary–adrenal stress axis play a key role regarding the extended life expectancy of reproductive vs. non-reproductive mole-rats. This is substantiated by a corpus of independent evidence. In accordance with previous studies, the up-regulation of the proteasome and so-called ‘anti-aging molecules’, for example, dehydroepiandrosterone, is linked with enhanced lifespan. On the other hand, several of our results are not consistent with knowledge about aging of short-lived model organisms. For example, we found the up-regulation of the insulin-like growth factor 1/growth hormone axis and several other anabolic processes to be compatible with a considerable lifespan prolongation. These contradictions question the extent to which findings from short-lived species can be transferred to longer-lived ones.

Pediatric Primary Adrenal Insufficiency: A 21-year Single Center Experience

OBJECTIVE

Primary adrenal insufficiency (PAI) is a rare but potentially life-threatening condition. In childhood, PAI is usually caused by monogenic diseases. Although congenital adrenal hyperplasia (CAH) is the most common cause of childhood PAI, numerous non-CAH genetic causes have also been identified.

METHODS

Patients aged 0-18 years and diagnosed with PAI between 1998 and 2019 in a tertiary care hospital were retrospectively evaluated. After the etiologic distribution was determined, non-CAH PAI patients were evaluated in detail.

RESULTS

Seventy-three PAI patients were identified. The most common etiology was CAH (69.9%, n=51). Non-CAH etiologies accounted for 30.1% (n=22) and included adrenoleukodystrophy (ALD; n=8), familial glucocorticoid deficiency (n=3), Triple A syndrome (n=5), autoimmune adrenalitis (n=1), adrenal hypoplasia congenital (n=1), IMAGe syndrome (n=1), and other unknown etiologies (n=3). The median age at the time of AI diagnosis for non-CAH etiologies was 3.52 (0.03-15.17) years. The most frequent symptoms/clinical findings at onset were hyperpigmentation of skin (81.8%), symptoms of hypoglycemia (40.9%), and weakness/fatigue (31.8%). Hypoglycemia (50.0%), hyponatremia (36.4%) and hyperkalemia (22.7%) were prominent biochemical findings. Diagnosis of specific etiologies were proven genetically in 13 of 22 patients. A novel p.Q301* hemizygous frameshift mutation of the DAX1 gene was identified in one patient.

CONCLUSION

Etiology was determined in 86.3% of children with non-CAH PAI through specific clinical and laboratory findings with/ without molecular analysis of candidate genes. ALD was the most common etiology. Currently, advanced molecular analysis can be utilized to establish a specific genetic diagnosis for PAI in patients who have no specific diagnostic features.

Case Report: Neonatal Cholestasis as Early Manifestation of Primary Adrenal Insufficiency

Neonatal cholestasis (NC) may be due to multiple surgical and non-surgical causes, some of which are potentially fatal. The list of potential causes of NC is long, and the systematic search for each of them is challenging in infants, especially when overt signs of underlying disease are lacking. Endocrinological diseases as causes of NC are rare and sometimes misdiagnosed. We report the case of an infant with prolonged cholestatic jaundice due to adrenal insufficiency suspected because of a single episode of hypoglycemia occurring at birth in the absence of clinical signs of adrenal impairment. Clinical exome analysis identified a new homozygous variant in MC2R gene as a putative responsible for familial glucocorticoid deficiency (FGD). Adrenal insufficiency should always be considered in all cholestatic infants, even in the absence of specific symptoms, since early recognition and treatment is essential to prevent life-threatening events.

Current Insights Into Adrenal Insufficiency in the Newborn and Young Infant

Adrenal insufficiency (AI) is a potentially life-threatening condition that can be difficult to diagnose, especially if it is not considered as a potential cause of a child's clinical presentation or unexpected deterioration. Children who present with AI in early life can have signs of glucocorticoid deficiency (hyperpigmentation, hypoglycemia, prolonged jaundice, poor weight gain), mineralocorticoid deficiency (hypotension, salt loss, collapse), adrenal androgen excess (atypical genitalia), or associated features linked to a specific underlying condition. Here, we provide an overview of causes of childhood AI, with a focus on genetic conditions that present in the first few months of life. Reaching a specific diagnosis can have lifelong implications for focusing management in an individual, and for counseling the family about inheritance and the risk of recurrence.

Tall stature in children and adolescents

Tall stature is usually defined as a height beyond 97^th percentile or more than 2 SD above the mean height for age and sex in a defined population. Familiar tall stature, also known as constitutional tall stature, is the most common cause of tall stature. Overnutrition, obesity, also usually causes overgrowth. Tall stature by itself is not a pathological condition, however, there are a number of disorders associated with tall stature. Some genetic disorders and syndromes may be associated with mental retardation and various complications. Therefore, recognition of tall stature and revealing the underlying pathogenic causes and making the diagnosis are important not to miss the serious conditions and to provide adequate medical care and genetic counseling. Pathological causes for tall statute include endocrine disorders, such as excessive growth hormone secretion, hyperthyroidism, precocious puberty and lipodystrophy, chromosome disorders, such as Trisomy X (47, XXX female), Klinefelter Syndrome (47, XXY), XYY syndrome (47, XYY male) and fragile X syndrome, and syndromes and metabolic disorders, such as Marfan Syndrome, Beckwith-Wiedemann Syndrome, Simpson-Golabi-Behmel Syndrome, Sotos Syndrome and homocystinuria. Children may require growth-reductive treatment if the predicted adult height would be excessive and unacceptable. Some hormonal, high doses of sex steroids, or surgical, bilateral percutaneous epiphysiodesis of the distal femur and proximal tibia and fibula, treatment is currently available to reduce adult height.

ACTH signalling and adrenal development: lessons from mouse models

The melanocortin-2-receptor (MC2R), also known as the ACTH receptor, is a critical component of the hypothalamic-pituitary-adrenal axis. The importance of MC2R in adrenal physiology is exemplified by the condition familial glucocorticoid deficiency (FGD), a potentially fatal disease characterised by isolated cortisol deficiency. MC2R mutations cause ~25% of cases. The discovery of a MC2R accessory protein MRAP, mutations of which account for ~20% of FGD, has provided insight into MC2R trafficking and signalling. MRAP is a single transmembrane domain accessory protein highly expressed in the adrenal gland and essential for MC2R expression and function. Mouse models helped elucidate the action of ACTH. The Mc2r-knockout (Mc2r - / - ) mice was the first mouse model developed to have adrenal insufficiency with deficiencies in glucocorticoid, mineralocorticoid and catecholamines. We recently reported the generation of the Mrap - / - mice which better mimics the human FGD phenotype with isolated glucocorticoid deficiency alone. The adrenal glands of adult Mrap - / - mice were grossly dysmorphic with a thickened capsule, deranged zonation and deranged WNT4/beta-catenin and sonic hedgehog (SHH) pathway signalling. Collectively, these mouse models of FGD highlight the importance of ACTH and MRAP in adrenal progenitor cell regulation, cortex maintenance and zonation.

The Importance of Melanocortin Receptors and Their Agonists in Pulmonary Disease

Melanocortin agonists are ancient neuropeptides that have steroidogenesis and anti-inflammatory properties. They activate melanocortin receptors (MCR), a family of five seven-transmembrane G-protein coupled receptors. MC1R and MC3R are mainly involved in immunomodulatory effects. Adrenocorticotropin hormone (ACTH) and alpha-Melanocortin stimulating hormone (α-MSH) reduce pro-inflammatory cytokines in several pulmonary inflammatory disorders including asthma, sarcoidosis, and the acute respiratory distress syndrome. They have also been shown to reduce fibrogenesis in animal models with pulmonary fibrosis. By understanding the functions of MCR in macrophages, T-helper cell type 1, and T-helper cell type 17, we may uncover the mechanism of action of melanocortin agonists in sarcoidosis. Further translational and clinical research is needed to define the role of ACTH and α-MSH in pulmonary diseases.

Isolated glucocorticoid deficiency: Genetic causes and animal models

Hereditary adrenocorticotropin (ACTH) resistance syndromes encompass the genetically heterogeneous isolated or Familial Glucocorticoid Deficiency (FGD) and the distinct clinical entity known as Triple A syndrome. The molecular basis of adrenal resistance to ACTH includes defects in ligand binding, MC2R/MRAP receptor trafficking, cellular redox balance, cholesterol synthesis and sphingolipid metabolism. Biochemically, this manifests as ACTH excess in the setting of hypocortisolaemia. Triple A syndrome is an inherited condition involving a tetrad of adrenal insufficiency, achalasia, alacrima and neuropathy. FGD is an autosomal recessive condition characterized by the presence of isolated glucocorticoid deficiency, classically in the setting of preserved mineralocorticoid secretion. Primarily there are three established subtypes of the disease: FGD 1, FGD2 and FGD3 corresponding to mutations in the Melanocortin 2 receptor MC2R (25%), Melanocortin 2 receptor accessory protein MRAP (20%), and Steroidogenic acute regulatory protein STAR (5-10%) respectively. Together, mutations in these 3 genes account for approximately half of cases. Whole exome sequencing in patients negative for MC2R, MRAP and STAR mutations, identified mutations in minichromosome maintenance 4 MCM4, nicotinamide nucleotide transhydrogenase NNT, thioredoxin reductase 2 TXNRD2, cytochrome p450scc CYP11A1, and sphingosine 1-phosphate lyase SGPL1 accounting for a further 10% of FGD. These novel genes have linked replicative and oxidative stress and altered redox potential as a mechanism of adrenocortical damage. However, a genetic diagnosis is still unclear in about 40% of cases. We describe here an updated list of FGD genes and provide a description of relevant mouse models that, despite some being flawed, have been precious allies in the understanding of FGD pathobiology.

Novel Melanocortin 2 Receptor Variant in a Chinese Infant With Familial Glucocorticoid Deficiency Type 1, Case Report and Review of Literature

Familial glucocorticoid deficiency type 1 (FGD1) is an autosomal recessive disorder caused by mutations in the melanocortin 2 receptor (MC2R) gene, characterized by a low or undetectable serum cortisol level and a high adrenocorticotropic hormone (ACTH) level. Clinical manifestations include hypoglycemia, seizure, skin hyperpigmentation, hyperbilirubinemia, cholestasis, and a tall stature. Some dysmorphic features such as, a prominent forehead, hypertelorism, a broad nasal bridge, and small tapering fingers, have been reported. Children with FGD1 may have other isolated endocrine abnormalities. To date, no patient with FGD1 has been reported in mainland China. Here we report on a Chinese patient with FGD1 having a novel MC2R gene variant, a mild transverse palm crease, hypertelorism, and subtle/transient endocrine abnormalities relating to all three zones of the adrenal cortex and thyroid gland. We also reviewed cases with dysmorphic features or additional endocrine abnormalities.

Rare monogenic causes of primary adrenal insufficiency

PURPOSE OF REVIEW

Monogenic disorders play significant roles in the pathogenesis of childhood-onset primary adrenal insufficiency (PAI). The most common form of PAI is congenital adrenal hyperplasia (CAH), which includes the enzymatic defects of the steroidogenic pathway. This review focuses on less common forms of monogenic PAI (i.e. non-CAH monogenic PAI) with particular attention on their cause, clinical phenotypes and genetic epidemiology.

RECENT FINDINGS

Non-CAH monogenic PAI can be classified into three major categories: first, adrenocorticotropic hormone resistance, second, impaired adrenal redox homeostasis and third, defective organogenesis of the adrenal glands. The clinical phenotypes of the mutation-carrying patients vary depending on the responsible gene, and they are partially explained by the tissue RNA expression patterns. Genetic epidemiology studies conducted in Turkey and Japan showed that about 80% of PAI of unknown cause was monogenic.

SUMMARY

Genetic basis of non-CAH monogenic PAI had been less clearly understood than CAH; however, significant advances have been made with use of new research techniques such as next-generation sequencing. Understanding of these rare forms of PAI may contribute to clarifying the physiology and pathology of the adrenal glands.

ACTH Receptor (MC2R) Specificity: What Do We Know About Underlying Molecular Mechanisms?

Coincidentally, the release of this Research Topic in Frontiers in Endocrinology takes place 25 years after the discovery of the adrenocorticotropic hormone receptor (ACTHR) by Mountjoy and colleagues. In subsequent years, following the discovery of other types of mammalian melanocortin receptors (MCRs), ACTHR also became known as melanocortin type 2 receptor (MC2R). At present, five types of MCRs have been reported, all of which share significant sequence similarity at the amino acid level, and all of which specifically bind melanocortins (MCs)-a group of biologically active peptides generated by proteolysis of the proopiomelanocortin precursor. All MCs share an identical -H-F-R-W- pharmacophore sequence. α-Melanocyte-stimulating hormone (α-MSH) and adrenocorticotropic hormone (ACTH) are the most extensively studied MCs and are derived from the same region. Essentially, α-MSH is formed from the first 13 amino acid residues of ACTH. ACTHR is unique among MCRs because it binds one sole ligand-ACTH, which makes it a very attractive research object for molecular pharmacologists. However, much research has failed, and functional studies of this receptor are lagging behind other MCRs. The reason for these difficulties has already been outlined by Mountjoy and colleagues in their publication on ACTHR coding sequence discovery where the Cloudman S91 melanoma cell line was used for receptor expression because it was a "more sensitive assay system." Subsequent work showed that ACTHR could be successfully expressed only in endogenous MCR-expressing cell lines, since in other cell lines it is retained within the endoplasmic reticulum. The resolution of this methodological problem came in 2005 with the discovery of melanocortin receptor accessory protein, which is required for the formation of functionally active ACTHR. The decade that followed this discovery was filled with exciting research that provided insight into the molecular mechanisms underlying the action of ACTHR. The purpose of this review is to summarize the advances in this fascinating research field.

Congenital primary adrenal insufficiency and selective aldosterone defects presenting as salt-wasting in infancy: a single center 10-year experience

Background

Salt-wasting represents a relatively common cause of emergency admission in infants and may result in life-threatening complications. Neonatal kidneys show low glomerular filtration rate and immaturity of the distal nephron leading to reduced ability to concentrate urine.

Methods

A retrospective chart review was conducted for infants hospitalized in a single Institution from 1^st January 2006 to 31^st December 2015. The selection criterion was represented by the referral to the Endocrinology Unit for hyponatremia (serum sodium <130 mEq/L) of suspected endocrine origin at admission.

Results

Fifty-one infants were identified. In nine infants (17.6 %) hyponatremia was related to unrecognized chronic gastrointestinal or renal salt losses or reduced sodium intake. In 10 infants (19.6 %) hyponatremia was related to central nervous system diseases. In 19 patients (37.3 %) the final diagnosis was congenital adrenal hyperplasia (CAH). CAH was related to 21-hydroxylase deficiency in 18 patients, and to 3β-Hydroxysteroid dehydrogenase (3βHSD) deficiency in one patient. Thirteen patients (25.5 %) were affected by different non-CAH salt-wasting forms of adrenal origin. Four familial cases of X-linked adrenal hypoplasia congenita due to NROB1 gene mutation were identified. Two unrelated girls showed aldosterone synthase deficiency due to mutation of the CYP11B2 gene. Two unrelated infants were affected by familial glucocorticoid deficiency due to MC2R gene mutations. One girl showed pseudohypoaldosteronism related to mutations of the SCNN1G gene encoding for the epithelial sodium channel. Transient pseudohypoaldosteronism was identified in two patients with renal malformations. In two infants the genetic aetiology was not identified.

Conclusions

Emergency management of infants presenting with salt wasting requires correction of water losses and treatment of electrolyte imbalances. Nevertheless, the differential diagnosis may be difficult in emergency settings, and sometimes hospitalized infants presenting with salt-wasting are immediately started on steroid therapy to avoid life-threatening complications, before the correct diagnosis is reached. Physicians involved in the management of infants with salt-wasting of suspected hormonal origin should remember that, whenever practicable, a blood sample for the essential hormonal investigations should be collected before starting steroid therapy, to guide the subsequent diagnostic procedures and in particular to address the analysis of candidate genes.

Rare Causes of Primary Adrenal Insufficiency: Genetic and Clinical Characterization of a Large Nationwide Cohort

CONTEXT

Primary adrenal insufficiency (PAI) is a life-threatening condition that is often due to monogenic causes in children. Although congenital adrenal hyperplasia occurs commonly, several other important molecular causes have been reported, often with overlapping clinical and biochemical features. The relative prevalence of these conditions is not known, but making a specific diagnosis can have important implications for management.

OBJECTIVE

The objective of the study was to investigate the clinical and molecular genetic characteristics of a nationwide cohort of children with PAI of unknown etiology.

DESIGN

A structured questionnaire was used to evaluate clinical, biochemical, and imaging data. Genetic analysis was performed using Haloplex capture and next-generation sequencing. Patients with congenital adrenal hyperplasia, adrenoleukodystrophy, autoimmune adrenal insufficiency, or obvious syndromic PAI were excluded.

SETTING

The study was conducted in 19 tertiary pediatric endocrinology clinics.

PATIENTS

Ninety-five children (48 females, aged 0-18 y, eight familial) with PAI of unknown etiology participated in the study.

RESULTS

A genetic diagnosis was obtained in 77 patients (81%). The range of etiologies was as follows: MC2R (n = 25), NR0B1 (n = 12), STAR (n = 11), CYP11A1 (n = 9), MRAP (n = 9), NNT (n = 7), ABCD1 (n = 2), NR5A1 (n = 1), and AAAS (n = 1). Recurrent mutations occurred in several genes, such as c.560delT in MC2R, p.R451W in CYP11A1, and c.IVS3ds+1delG in MRAP. Several important clinical and molecular insights emerged.

CONCLUSION

This is the largest nationwide study of the molecular genetics of childhood PAI undertaken. Achieving a molecular diagnosis in more than 80% of children has important translational impact for counseling families, presymptomatic diagnosis, personalized treatment (eg, mineralocorticoid replacement), predicting comorbidities (eg, neurological, puberty/fertility), and targeting clinical genetic testing in the future.

Primary Adrenocortical Insufficiency Case Series: Genetic Etiologies More Common than Expected

BACKGROUND/AIMS

Primary adrenal insufficiency (AI) is an important cause of morbidity in children. Our objectives were: (1) to describe the clinical presentation of children with new-onset primary AI, and (2) to identify monogenic causes of primary AI in children.

METHODS

Chart review and mutation detection in candidate genes were conducted for 11 patients with primary AI.

RESULTS

The likely cause of AI was determined in 9 patients. One had a homozygous MC2R mutation associated with familial glucocorticoid deficiency. Two had the same homozygous mutation in the AIRE gene which is associated with type 1 autoimmune polyglandular syndrome. One patient had a heterozygous change in this gene of undetermined significance. Five were homozygous for the previously reported p.R188C STAR mutation causing nonclassic lipoid congenital adrenal hyperplasia, representing the largest cohort of such patients from a single geographic area. In the remaining 2 patients, no clear etiology was identified.

CONCLUSIONS

We recommend genetic testing for patients who have negative anti-adrenal antibodies or suggestive family history. Diagnosing a genetic etiology can provide information about prognosis and treatment, and is therefore beneficial for patients. Our high proportion of patients with nonclassic lipoid congenital adrenal hyperplasia likely represents a founder effect.

Stress-induced Aldosterone Hyper-Secretion in a Substantial Subset of Patients With Essential Hypertension

CONTEXT

Aldosterone (ALD) secretion is regulated mainly by angiotensin II, K(+), and adrenocorticotropic hormone (ACTH). Mineralocorticoid receptor antagonists (MRAs) have effectively been used for the treatment of patients with hypertension who do not have primary aldosteronism (PA).

OBJECTIVE

We tested whether chronic stress-related ACTH-mediated ALD hypersecretion and/or zona glomerulosa hypersensitivity could be implicated in the pathogenesis of essential hypertension (ESHT).

PATIENTS AND METHODS

One hundred thirteen hypertensives without PA and 61 normotensive controls underwent an ultralow-dose (0.03-μg) ACTH stimulation and a treadmill test. Patients with ALD hyper-response according to the cutoffs obtained from controls received treatment with MRAs and underwent genomic DNA testing for the presence of the CYP11B1/CYP11B2 chimeric gene and KCNJ5 gene mutations. A control group of 22 patients with simple ESHT received treatment with MRAs.

RESULTS

Based on the cutoffs of ALD and aldosterone-to-renin ratio (ARR) post-ACTH stimulation obtained from controls, 30 patients (27%) exhibited an ALD but not cortisol (F) hyper-response (HYPER group). This group had no difference in basal ACTH/renin (REN) concentrations compared with controls and the 83 patients with hypertension (73%) without an ALD hyper-response to ACTH stimulation. Patients in the HYPER group demonstrated significantly higher ALD concentrations, ARR, and ALD/ACTH ratio (AAR) in the treadmill test. Treatment with MRAs alone produced normalization of blood pressure in these patients whereas patients with hypertension with neither PA nor ALD hyper-response to ACTH stimulation who served as a control group failed to lower blood pressure. Also, two novel germline heterozygous KCNJ5 mutations were detected in the HYPER group.

CONCLUSIONS

A number of patients with hypertension without PA show ACTH-dependent ALD hyper-secretion and benefit from treatment with MRAs. This could be related to chronic stress via ACTH hyper secretion and/or gene-mutations increasing the zona glomerulosa responsiveness to excitatory stimuli.

Progress in aldosteronism: a review of the prevalence of primary aldosteronism in pre-hypertension and hypertension

Primary aldosteronism (PA) secondary to excessive and/or autonomous aldosterone secretion from the renin-angiotensin system accounts for ∼10% of cases of hypertension and is primarily caused by bilateral adrenal hyperplasia (BAH) or aldosterone-producing adenomas (APAs). Although the diagnosis has traditionally been supported by low serum potassium levels, normokalaemic and even normotensive forms of PA have been identified expanding further the clinical phenotype. Moreover, recent evidence has shown that serum aldosterone correlates with increased blood pressure (BP) in the general population and even moderately raised aldosterone levels are linked to increased cardiovascular morbidity and mortality. In addition, aldosterone antagonists are effective in BP control even in patients without evidence of dysregulated aldosterone secretion. These findings indicate a higher prevalence of aldosterone excess among hypertensive patients than previously considered that could be attributed to disease heterogeneity, aldosterone level fluctuations related to an ACTH effect or inadequate sensitivity of current diagnostic means to identify apparent aldosterone excess. In addition, functioning aberrant receptors expressed in the adrenal tissue have been found in a subset of PA cases that could also be related to its pathogenesis. Recently a number of specific genetic alterations, mainly involving ion homeostasis across the membrane of zona glomerulosa, have been detected in ∼50% of patients with APAs. Although specific genotype/phenotype correlations have not been clearly identified, differential expression of these genetic alterations could also account for the wide clinical phenotype, variations in disease prevalence and performance of diagnostic tests. In the present review, we critically analyse the current means used to diagnose PA along with the role that ACTH, aberrant receptor expression and genetic alterations may exert, and provide evidence for an increased prevalence of aldosterone dysregulation in patients with essential hypertension and pre-hypertension.

Whole-Exome Sequencing in the Differential Diagnosis of Primary Adrenal Insufficiency in Children

Adrenal insufficiency is a rare, but potentially fatal medical condition. In children, the cause is most commonly congenital and in recent years a growing number of causative gene mutations have been identified resulting in a myriad of syndromes that share adrenal insufficiency as one of the main characteristics. The evolution of adrenal insufficiency is dependent on the variant and the particular gene affected, meaning that rapid and accurate diagnosis is imperative for effective treatment of the patient. Common practice is for candidate genes to be sequenced individually, which is a time-consuming process and complicated by overlapping clinical phenotypes. However, with the availability, and increasing cost effectiveness of whole-exome sequencing, there is the potential for this to become a powerful diagnostic tool. Here, we report the results of whole-exome sequencing of 43 patients referred to us with a diagnosis of familial glucocorticoid deficiency (FGD) who were mutation negative for MC2R, MRAP, and STAR the most commonly mutated genes in FGD. WES provided a rapid genetic diagnosis in 17/43 sequenced patients, for the remaining 60% the gene defect may be within intronic/regulatory regions not covered by WES or may be in gene(s) representing novel etiologies. The diagnosis of isolated or familial glucocorticoid deficiency was only confirmed in 3 of the 17 patients, other genetic diagnoses were adrenal hypo- and hyperplasia, Triple A, and autoimmune polyendocrinopathy syndrome type I, emphasizing both the difficulty of phenotypically distinguishing between disorders of PAI and the utility of WES as a tool to achieve this.

The melanocortin receptors and their accessory proteins

The five melanocortin receptors (MCRs) named MC1R-MC5R have diverse physiological roles encompassing pigmentation, steroidogenesis, energy homeostasis and feeding behavior as well as exocrine function. Since their identification almost 20 years ago much has been learnt about these receptors. As well as interacting with their endogenous ligands the melanocortin peptides, there is now a growing list of important peptides that can modulate the way these receptors signal, acting as agonists, antagonists, and inverse agonists. The discovery of melanocortin 2 receptor accessory proteins as a novel accessory factor to the MCRs provides further insight into the regulation of these important G protein-coupled receptor.

Neonatal presentation of familial glucocorticoid deficiency resulting from a novel splice mutation in the melanocortin 2 receptor accessory protein

BACKGROUND

Familial glucocorticoid deficiency (FGD) is a rare autosomal recessive disorder characterised by isolated glucocorticoid deficiency. Mutations in the ACTH receptor/melanocortin 2 receptor (MC2R), the MC2R accessory protein (MRAP) or the STAR protein (STAR) cause FGD types 1, 2 and 3, respectively, accounting for ~50% of all cases.

PATIENT AND METHODS

We report a neonate of Indian origin, who was diagnosed with FGD in the first few days of life. He presented with hypoglycaemic seizures and was noted to have generalised intense hyperpigmentation and normal male genitalia. Biochemical investigations revealed hypocortisolaemia (cortisol 0.223 μg/dl; NR 1-23 μg/dl) and elevated plasma ACTH (170 pg/ml). Serum electrolytes, aldosterone and plasma renin activity were normal. Peak cortisol following a standard synacthen test was 0.018 μg/dl. He responded to hydrocortisone treatment and continues on replacement. Patient DNA was analysed by direct sequencing. The effect of the novel mutation was assessed by an in vitro splicing assay using wild type and mutant heterologous minigenes.

RESULTS

A novel homozygous mutation c.106+2_3dupTA was found in the MRAP gene. Both parents were heterozygous for the mutation. In an in vitro splicing assay, the mutation resulted in the skipping of exon 3.

CONCLUSION

We have identified a novel MRAP mutation where disruption of the intron 3 splice-site results in a prematurely terminated translation product. This protein (if produced) would lack the transmembrane domain that is essential for MC2R interaction. We predict that this would cause complete lack of ACTH response thus explaining the early presentation in this case.

[Overgrowth with and without obesity: clinical and molecular principles]

Somatic overgrowth is a complex and heterogeneous pathology that is only partially understood, although developments in molecular biology have allowed the discovery of the aetiological basis of some of these conditions. The differential diagnosis of a patient with a possible variant of normality, a chromosomopathy, a dysmorphic syndrome, a metabolic or an endocrine disease is essential. The initial clinical evaluation should include a correct anamnesis and physical examination, as well as complementary laboratory and image analyses that will help to orient the diagnosis. This should include a full blood counts and complete biochemical analysis, determinations of IGF-I, IGFBP-3, free T4, TSH and homocystinuria, as well as a karyotype and an X-ray of the left hand and wrist. These results should be very beneficial in orienting the diagnosis. Additional molecular studies should be performed when a monogenic disease is suspected. Cardiological, ophthalmological, skeletal, psychological and psychiatric studies should be performed if the clinical information and previously mentioned complementary studies so indicate. In this review, the aetiological basis and the diagnostic-therapeutic principles in the most common causes of overgrowth, will be analysed.

The molecular biology, biochemistry, and physiology of human steroidogenesis and its disorders

Steroidogenesis entails processes by which cholesterol is converted to biologically active steroid hormones. Whereas most endocrine texts discuss adrenal, ovarian, testicular, placental, and other steroidogenic processes in a gland-specific fashion, steroidogenesis is better understood as a single process that is repeated in each gland with cell-type-specific variations on a single theme. Thus, understanding steroidogenesis is rooted in an understanding of the biochemistry of the various steroidogenic enzymes and cofactors and the genes that encode them. The first and rate-limiting step in steroidogenesis is the conversion of cholesterol to pregnenolone by a single enzyme, P450scc (CYP11A1), but this enzymatically complex step is subject to multiple regulatory mechanisms, yielding finely tuned quantitative regulation. Qualitative regulation determining the type of steroid to be produced is mediated by many enzymes and cofactors. Steroidogenic enzymes fall into two groups: cytochrome P450 enzymes and hydroxysteroid dehydrogenases. A cytochrome P450 may be either type 1 (in mitochondria) or type 2 (in endoplasmic reticulum), and a hydroxysteroid dehydrogenase may belong to either the aldo-keto reductase or short-chain dehydrogenase/reductase families. The activities of these enzymes are modulated by posttranslational modifications and by cofactors, especially electron-donating redox partners. The elucidation of the precise roles of these various enzymes and cofactors has been greatly facilitated by identifying the genetic bases of rare disorders of steroidogenesis. Some enzymes not principally involved in steroidogenesis may also catalyze extraglandular steroidogenesis, modulating the phenotype expected to result from some mutations. Understanding steroidogenesis is of fundamental importance to understanding disorders of sexual differentiation, reproduction, fertility, hypertension, obesity, and physiological homeostasis.

Effects of melanocortins on adrenal gland physiology

The melanocortin-2-receptor (MC(2) receptor), also known as the ACTH receptor, is a critical component of the hypothalamic-pituitary-adrenal axis. The importance of MC(2) receptor in adrenal physiology is exemplified by the condition familial glucocorticoid deficiency, a potentially fatal disease characterised by isolated cortisol deficiency. MC(2)receptor mutations cause ~25% of cases. The discovery of a MC(2) receptor accessory protein MRAP, mutations of which account for ~15%-20% of familial glucocorticoid deficiency, has provided insight into MC(2) receptor trafficking and signalling. MRAP is essential for the functional expression of MC(2) receptor. MRAP2, a novel homolog of MRAP, can also facilitate MC(2) receptor cell surface expression and function. Like MRAP, MRAP2 is a small transmembrane domain glycoprotein capable of homodimerising. In addition, MRAP/MRAP2 can heterodimerise. The presence of MRAP2 adrenal expression suggests a possible role for MRAP2 in adrenal physiology, which has yet to be elucidated. Importantly, new data shows that the MRAPs can interact with all the other melanocortin receptors (MC(1,3,4,5) receptor). In contrast to MC(2) receptor, this interaction results in reduced melanocortin receptor surface expression and signalling. MRAP2 is predominantly expressed in brain. Hypothalamic expression has been demonstrated for both MRAP and MRAP2. The ability of MRAPs to modulate different members of the melanocortin receptor family in a bidirectional manner is intriguing. Furthermore, central nervous system expression of MRAPs points to a role beyond MC(2) receptor mediated adrenal steroidogenesis.

Familial glucocorticoid deficiency due to compound heterozygosity of two novel MC2R mutations

Familial glucocorticoid deficiency (FGD) is a rare autosomal recessive disorder characterized by isolated glucocorticoid deficiency. Mutations in the ACTH receptor (melanocortin 2 receptor, MC2R) or the MC2R accessory protein (MRAP) cause FGD types 1 and 2, respectively. A 2-year-old adopted Chinese girl presented with hypertonic seizures associated with hypoglycemia, skin hyperpigmentation, muscle weakness and mild jaundice. Hormonal analyses revealed high ACTH, low serum cortisol along with normal blood electrolytes. On hydrocortisone supplementation, the disease symptoms disappeared and the child recovered, although further episodes occurred with infection. To date, her physical and neurocognitive development progress is normal. A clinical diagnosis of FGD was given. We undertook MC2R and MRAP mutation screening. Two novel MC2R mutations were identified: p.D107G localized in the transmembrane region, predicted to be trafficking-competent but is unable to bind to ACTH, and p.R145C, situated in the second intracellular loop, predicted to be trafficking-defective.

Aldosterone and arterial hypertension

In the setting of primary aldosteronism, elevated aldosterone levels are associated with increased blood pressure. Aldosterone concentrations within the normal range, however, can also alter blood pressure. Furthermore, the aldosterone-to-renin ratio, an indicator of aldosterone excess, is associated with hypertension, even in patients without excessive absolute aldosterone levels. In this Review we assess the data on the role of aldosterone in the development and maintenance of hypertension. We provide an overview of the complex crosstalk between genetic and environmental factors, and about aldosterone-mediated arterial hypertension and target organ damage. The discussion is organized according to major targets of aldosterone action: the collecting duct in the kidney, the vasculature and the central nervous system. The antihypertensive efficacy of mineralocorticoid-receptor blockers, even in patients with aldosterone values in the normal range, supports the evidence that aldosterone plays a part in blood pressure elevation in the absence of primary aldosteronism.

Isolated Addison's disease is unlikely to be caused by mutations in MC2R, MRAP or STAR, three genes responsible for familial glucocorticoid deficiency

BACKGROUND

Familial glucocorticoid deficiency (FGD) is a rare autosomal recessive disease caused by ACTH resistance and leads to isolated glucocorticoid deficiency. Although FGD patients typically have normal mineralocorticoid secretion, subtle alterations in the renin-angiotensin-aldosterone axis have been reported in a subset of patients at presentation. Anecdotally, some patients with FGD have been initially diagnosed as having Addison's disease (AD), with implications for treatment and genetic counselling. Currently, mutations in three genes: the ACTH receptor (MC2R); the melanocortin 2 receptor accessory protein (MRAP); and the steroidogenic acute regulatory protein (STAR) are known to give rise to FGD types 1-3. We investigated a cohort of autoantibody-negative AD patients for mutations in these genes.

METHODS

Forty patients with known AD without evidence of autoimmune disease were screened for mutations in MC2R, MRAP and STAR. In addition, patients were genotyped for the MC2R promoter polymorphism previously associated with reduced responsiveness to ACTH.

RESULTS

No mutations in MC2R, MRAP or STAR were identified in any patient. The frequencies of the MC2R promoter polymorphism were similar to those reported in healthy controls.

CONCLUSIONS

FGD does not appear to be underdiagnosed in the AD population. However, in approximately 50% of patients with FGD, no genetic cause has yet been identified and it is possible that the other, as yet unidentified, genes giving rise to FGD may be implicated in AD.

The molecular basis of adrenocorticotrophin resistance syndrome

Adrenocorticotrophin resistance syndromes comprise familial glucocorticoid deficiency (FGD) and triple A syndrome, which are rare autosomal recessive diseases with distinct clinical features and molecular etiologies. Mutations of melanocortin-2 receptor (MC2R) have been described in segregation with FGD in 25% of patients. More recently melanocortin-2 receptor accessory protein (MRAP), a small single-transmembrane domain protein, was described as an essential protein for the traffic of MC2R and its expression on the plasma membrane. About 20% of FGD patients carry homozygous mutations of MRAP. The ALADIN protein (for alacrima/achalasia/adrenal insufficiency/neurologic disorder) was identified as the molecular basis of triple A syndrome. The elucidation of the genetic basis of the ACTH resistance syndrome has contributed to the better understanding of MC2R function. However, in some patients the molecular etiology is not yet known and awaits further genetic studies.

Diagnosis of diseases of steroid hormone production, metabolism and action

Biochemical tests have been the basis for investigations of disorders affecting steroid hormones. In recent years it has been possible however to study the genes that determine functional enzymes, cofactors, receptors, transcription factors and signaling systems that are involved in the process. Analyses of mutations are available as a diagnostic service for only a few of these genes although research laboratories may be able to provide a service. Both biochemical and genetic research have brought to light new disorders. Some genes for transcription factors involved in the development of the endocrine organs have also been identified and patients with defects in these processes have been found. This paper will review general aspects of adrenal disorders with emphasis on clinical and laboratory findings. As with all endocrine investigations there are few single measurements that provide a definitive answer to a diagnosis. Timing of samples in relation to age, gender and time of day needs to be considered.

Homozygous nonsense and frameshift mutations of the ACTH receptor in children with familial glucocorticoid deficiency (FGD) are not associated with long-term mineralocorticoid deficiency

OBJECTIVE

Familial glucocorticoid deficiency (FGD) is a rare autosomal recessive disease characterized by isolated glucocorticoid deficiency with preserved mineralocorticoid secretion. Mutations in the ACTH receptor (MC2R) account for approximately 25% of all FGD cases, but since these are usually missense mutations, a degree of receptor function is frequently retained. A recent report, however, suggested that disturbances in the renin-aldosterone axis were seen in some patients with potentially more severe MC2R mutations. Furthermore, MC2R knock out mice have overt aldosterone deficiency and hyperkalaemia despite preservation of a normal zona glomerulosa. We wished to determine whether a group of patients with severe nonsense mutations of the MC2R exhibited evidence of mineralocorticoid deficiency, thereby challenging the conventional diagnostic feature of FGD which might result in diagnostic misclassification.

DESIGN

Clinical review of patients with nonsense MC2R mutations.

PATIENTS

Between 1993 and 2008, 164 patients with FGD were screened for mutations in the MC2R. Totally 42 patients (34 families) were found to have mutations in the MC2R. Of these, 6 patients (4 families) were found to have homozygous nonsense or frameshift mutations.

RESULTS

Mild disturbances in the renin-angiotensin-aldosterone axis were noted in four out of six patients, ranging from slightly elevated plasma renin levels to low aldosterone levels, although frank mineralocorticoid deficiency or electrolyte disturbance were not found. No patient required fludrocortisone replacement.

CONCLUSION

Severe nonsense and frameshift MC2R mutations are not associated with clinically significant mineralocorticoid deficiency and are thus unlikely to require long-term mineralocorticoid replacement.

The genetics of familial glucocorticoid deficiency

Familial glucocorticoid deficiency is an autosomal recessive disorder resulting from defects in the action of adrenocorticotropic hormone (ACTH) to stimulate glucocorticoid synthesis in the adrenal. Production of mineralocorticoids by the adrenal is normal. Patients present in early life with low or undetectable cortisol and--because of the failure of the negative feedback loop to the pituitary and hypothalamus--grossly elevated ACTH levels. About half of all cases result from mutations in the ACTH receptor (melanocortin 2 receptor) or from mutations in the melanocortin 2 receptor accessory protein (MRAP), but other genetic causes of this potentially lethal disorder remain to be discovered.

Functional consequence of a novel Y129C mutation in a patient with two contradictory melanocortin-2-receptor mutations

CONTEXT

Familial glucocorticoid deficiency (FGD) is a rare autosomal recessive disease, characterised by isolated glucocorticoid deficiency in the absence of mineralocorticoid deficiency. Inactivating mutations in the ACTH receptor (melanocortin-2-receptor, MC2R) are well described and account for approximately 25% of cases. By contrast, activating MC2R mutations are extremely rare.

PATIENT

We report a child of Saudi Arabian origin who was diagnosed with FGD following hypoglycaemic episodes that resulted in spastic quadriplegia.

METHODS AND RESULTS

MC2R gene analysis revealed an unusual combination of two homozygous missense mutations, consisting of the novel mutation Y129C and the previously described F278C activating mutation. Parents were heterozygous at both of these sites. In vitro analysis of the Y129C mutation using a fluorescent cell surface assay showed that this mutant was unable to reach the cell surface in CHO cells stably transfected with MC2R accessory protein (MRAP), despite the demonstration of an interaction with MRAP by co-immunoprecipitation. The double mutant Y129C-F278C also failed to traffic to the cell surface.

CONCLUSION

The tyrosine residue at position 129 in the second intracellular loop is critical in MC2R folding and/or trafficking to the cell surface. Furthermore, the absence of cell surface expression of MC2R would account for the lack of activation of the receptor due to the F278C mutation located at the C-terminal tail. We provide a novel molecular explanation for a child with two opposing mutations causing severe FGD.

Characterization of mice deficient in melanocortin 2 receptor on a B6/Balbc mix background

We have previously reported that Melanocortin 2 receptor (MC2R(-/-)) deficient mice on B6 N5 generations exhibited macroscopically detectable adrenal glands with markedly atrophied zona fasciculata (zF) and lack of detectable levels of corticosterone, and reduced serum concentrations of aldosterone and epinephrine. All MC2R(-/-) mice on B6/N8 background die within 2 days after birth, while about half of the MC2R(-/-) mice on B6/Balbc mix background survived to adulthood. Both male and female MC2R(-/-) mice were fertile, suggesting that normal development and function of reproductive organs. MC2R(-/-) mice delivered from MC2R(-/-) dams failed to survive due to lung failure, suggesting that fetal or maternal corticosterone is essential for lung maturation. MC2R(-/-) mice failed to activate the hypothalamic-pituitary-adrenal axis in response to both immune and non-immune stimuli. MC2R(-/-) mice maintained glomerular structure and achieved electrolyte homeostasis by the activation of the renin-angiotensin-aldosterone system under low aldosterone and undetectable levels of corticosterone.

Altered corticosteroid biosynthesis in essential hypertension: A digenic phenomenon

Aldosterone plays an important role in electrolyte and blood pressure homeostasis. Our studies have focused on the role of aldosterone in essential hypertension. We have shown that plasma aldosterone and ARR are heritable characteristics and that aldosterone concentrations in older subjects are inversely correlated with birthweight and positively correlated with blood pressure. Aldosterone levels are also associated with polymorphic variation in the CYP11B2 gene, which encodes aldosterone synthase, the enzyme responsible for aldosterone production. Interestingly, CYP11B2 polymorphisms are also associated with less efficient activity of 11beta-hydroxylase, encoded by the neighbouring, highly homologous CYP11B1 gene. We propose that a digenic effect leads to increased aldosterone production, with inefficient 11beta-hydroxylation causing a long-term increase in ACTH drive to the adrenal gland and enhanced expression of CYP11B2, thereby resulting in chronically raised aldosterone secretion in response to factors such as angiotensin II and potassium. In susceptible subjects this is likely, over many years, to result in hypertension with relative aldosterone excess.

CBP/p300-interacting transactivator, with Glu/Asp-rich C-terminal domain, 2, and pre-B-cell leukemia transcription factor 1 in human adrenal development and disease

CONTEXT

Disorders of adrenal development result in significant morbidity and mortality. However, the molecular basis of human adrenal development, and many forms of disease, is still poorly understood.

OBJECTIVES

We evaluated the role of two new candidate genes, CBP/p300-interacting transactivator, with Glu/Asp-rich C-terminal domain, 2 (CITED2), and pre-B-cell leukemia transcription factor 1 (PBX1), in human adrenal development and disease.

DESIGN

CITED2 and PBX1 expression in early human fetal adrenal development was assessed using RT-PCR and in situ hybridization. The regulation of CITED2 and PBX1 by steroidogenic factor-1 (SF-1) and dosage-sensitive sex reversal, adrenal hypoplasia congenital, critical region on the X chromosome, gene-1 (DAX1) was evaluated in NCI-H295R human adrenocortical tumor cells by studying promoter regulation. Finally, mutational analysis of CITED2 and PBX1 was performed in patients with primary adrenal disorders.

RESULTS

CITED2 and PBX1 are expressed in the human fetal adrenal gland during early development. Both genes are activated by SF-1 in a dose-dependent manner in NCI-H295R cells, and, surprisingly, PBX1 is synergistically activated by SF-1 and DAX1. Mutational analysis failed to reveal significant coding sequence changes in individuals with primary adrenal disorders.

CONCLUSIONS

CITED2 and PBX1 are likely to be important mediators of adrenal development and function in humans, but mutations in these genes are not common causes of adrenal failure in patients in whom a molecular diagnosis remains unknown. The positive interaction between DAX1 and SF-1 in regulating PBX1 may be an important mechanism in this process.

A novel variant of familial glucocorticoid deficiency prevalent among the Irish Traveler population

CONTEXT

Familial glucocorticoid deficiency (FGD) is an autosomal recessive disorder characterized by distinct clinical, biochemical, and genetic abnormalities. The prevalence of FGD is unknown, with the likelihood that cases remain undiagnosed. We noted a significant proportion of our FGD cases are Irish Travelers. Irish Travelers are an endogamous nomadic group ethnically and genetically distinct from Roma gypsies.

AIMS

The objective of the study was to describe the clinical features and assess the prevalence of FGD amongst Irish Travelers in the Republic of Ireland and describe their phenotype.

METHODS

Diagnosis of FGD was based on clinical features, high ACTH, and low cortisol concentrations with normal renin and aldosterone concentrations and exclusion of other causes of adrenal failure. Data from the Republic of Ireland Census 2006 were used.

RESULTS

We identified 21 cases of FGD, generating an overall prevalence of one in 201,898. We report nine Irish Travelers (five females) with FGD related to a new gene negative for melanocortin-2 receptor and melanocortin-2 receptor accessory protein mutations. Of a total population of 22,557 Travelers, this yields a disease prevalence of one in 2506 with a carrier frequency of one in 25 in this group and represents a prevalence of one in 665 and a carrier frequency of one in 13 in the 4- to 15-yr Traveler age group. All nine children had a later onset of FGD due to the fact that their initial investigations revealed normal cortisol (422-575 nmol/liter) and ACTH (<34 ng/liter) concentrations.

CONCLUSION

We report a high prevalence of FGD among Irish Travelers. Their subtle phenotype and initial normal biochemistry may delay the early diagnosis of FGD.

A lifetime of aldosterone excess: long-term consequences of altered regulation of aldosterone production for cardiovascular function

Up to 15% of patients with essential hypertension have inappropriate regulation of aldosterone; although only a minority have distinct adrenal tumors, recent evidence shows that mineralocorticoid receptor activation contributes to the age-related blood pressure rise and illustrates the importance of aldosterone in determining cardiovascular risk. Aldosterone also has a major role in progression and outcome of ischemic heart disease. These data highlight the need to understand better the regulation of aldosterone synthesis and its action. Aldosterone effects are mediated mainly through classical nuclear receptors that alter gene transcription. In classic epithelial target tissues, signaling mechanisms are relatively well defined. However, aldosterone has major effects in nonepithelial tissues that include increased synthesis of proinflammatory molecules and reactive oxygen species; it remains unclear how these effects are controlled and how receptor specificity is maintained. Variation in aldosterone production reflects interaction of genetic and environmental factors. Although the environmental factors are well understood, the genetic control of aldosterone synthesis is still the subject of debate. Aldosterone synthase (encoded by the CYP11B2 gene) controls conversion of deoxycorticosterone to aldosterone. Polymorphic variation in CYP11B2 is associated with increased risk of hypertension, but the molecular mechanism that accounts for this is not known. Altered 11beta-hydroxylase efficiency (conversion of deoxycortisol to cortisol) as a consequence of variation in the neighboring gene (CYP11B1) may be important in contributing to altered control of aldosterone synthesis, so that the risk of hypertension may reflect a digenic effect, a concept that is discussed further. There is evidence that a long-term increase in aldosterone production from early life is determined by an interaction of genetic and environmental factors, leading to the eventual phenotypes of aldosterone-associated hypertension and cardiovascular damage in middle age and beyond. The importance of aldosterone has generated interest in its therapeutic modulation. Disadvantages associated with spironolactone (altered libido, gynecomastia) have led to a search for alternative mineralocorticoid receptor antagonists. Of these, eplerenone has been shown to reduce cardiovascular risk after myocardial infarction. The benefits and disadvantages of this therapeutic approach are discussed.

Adrenal gland development and defects

The network regulating human adrenal development is complex. Studies of patients with adrenal insufficiency due to gene mutations established a central role for transcription factors GLI3, SF1 and DAX1 in the initial steps of adrenal formation. Adrenal differentiation seems to depend on adrenocorticotropic hormone (ACTH) stimulation and signalling, including biosynthesis and action of POMC, PC1, TPIT, MC2R, MRAP and ALADIN, all of which cause adrenocortical hypoplasia when mutated in humans. Studies of knockout mice revealed many more factors involved in adrenal development; however, in contrast to rodents, in humans several of those factors had no adrenal phenotype when mutated (e.g. WT1, WNT4) or, alternatively, human mutations have not (yet) been identified. Tissue profiling of fetal and adult adrenals suggested 69 genes involved in adrenal development. Among them were genes coding for steroidogenic enzymes, transcription and growth factors, signalling molecules, regulators of cell cycle and angiogenesis, and extracellular matrix proteins; however, the exact role of most of them remains to be elucidated.

Melanocortin 2 receptor is required for adrenal gland development, steroidogenesis, and neonatal gluconeogenesis

ACTH (i.e., corticotropin) is the principal regulator of the hypothalamus-pituitary-adrenal axis and stimulates steroidogenesis in the adrenal gland via the specific cell-surface melanocortin 2 receptor (MC2R). Here, we generated mice with an inactivation mutation of the MC2R gene to elucidate the roles of MC2R in adrenal development, steroidogenesis, and carbohydrate metabolism. These mice, the last of the knockout (KO) mice to be generated for melanocortin family receptors, provide the opportunity to compare the phenotype of proopiomelanocortin KO mice with that of MC1R-MC5R KO mice. We found that the MC2R KO mutation led to neonatal lethality in three-quarters of the mice, possibly as a result of hypoglycemia. Those surviving to adulthood exhibited macroscopically detectable adrenal glands with markedly atrophied zona fasciculata, whereas the zona glomerulosa and the medulla remained fairly intact. Mutations of MC2R have been reported to be responsible for 25% of familial glucocorticoid deficiency (FGD) cases. Adult MC2R KO mice resembled FGD patients in several aspects, such as undetectable levels of corticosterone despite high levels of ACTH, unresponsiveness to ACTH, and hypoglycemia after prolonged (36 h) fasting. However, MC2R KO mice differ from patients with MC2R-null mutations in several aspects, such as low aldosterone levels and unaltered body length. These results indicate that MC2R is required for postnatal adrenal development and adrenal steroidogenesis and that MC2R KO mice provide a useful animal model by which to study FGD.