The spectrum of hypopituitarism caused by PROP1 mutations

Comparison of clinical characteristics of a pediatric cohort with combined pituitary hormone deficiency caused by mutation of the PROP1 gene or of other origins

The most commonly identified genetic cause of combined pituitary hormone deficiency (CPHD) is PROP1 gene mutations. The aim of the study was to compare selected clinical features of patients with CPHD caused by variants of the PROP1 gene (CPHD-PROP1) and patients with inborn CPHD of other etiology (CPHD-nonPROP1).

MATERIAL AND METHODS

The retrospective analysis included childhood medical records of 74 patients (32 female) with CPHD, including 43 patients (23 female) with the mutation in the PROP1 gene.

RESULTS

Patients with CPHD-PROP1 compared to the CPHD-nonPROP1 presented with the following: significantly higher median birth weight (0.21 vs. - 0.29 SDS, p = 0.019), lower growth velocity within 3 years preceding growth hormone administration (- 2.7 vs. - 0.8 SDS, p < 0.001), higher mean maximal blood concentration of growth hormone within the stimulation process (1.2 vs. 1.08 ng/mL, p = 0.003), lower TSH (1.8 vs. 2.4 µIU/mL, p < 0.001), significantly lower prolactin concentrations (128 vs. 416.3 µIU/mL, p < 0.001), and less frequent typical signs of hypogonadism at birth in boys (n = 6; 30% vs. n = 12, 54%, p < 0.001). Secondary adrenal insufficiency was less frequent in CPHD-PROP1 (20 vs. 25 cases, p = 0.006) and occurred at a later age (13.4 vs. 10.4 years). MRI of the pituitary gland in CPHD-PROP1 revealed a small pituitary gland (21 cases), pituitary gland enlargement (eight cases), and one pituitary stalk interruption and posterior lobe ectopy, while it was normal in nine cases.

CONCLUSION

Patients with the PROP1 mutations present a clinical picture significantly different from that of other forms of congenital hypopituitarism. Certain specific clinical results may lead to the successful identification of children requiring diagnostics for the PROP1 gene mutation.

Overview of Congenital Hypopituitarism for the Neonatologist

Congenital hypopituitarism is the deficiency in 1 or more hormones produced by the anterior pituitary or released by the posterior pituitary and has an estimated incidence of 1 in 4,000 to 10,000. Due to the critical role the pituitary plays in growth, metabolic, and reproductive processes, early diagnosis is essential to prevent devastating and often preventable outcomes. However, in neonates with congenital hypopituitarism, symptoms are often nonspecific and tend to overlap with other disease processes, making diagnosis extremely challenging in the neonatal period. This review highlights the embryology and organogenesis of the pituitary gland, genetic causes of hypopituitarism, clinical presentations in the neonatal period, and methods to diagnose and treat select deficiencies with a focus on anterior pituitary hormones.

A new approach to the diagnosis of short stature

Growth is the task of children. We review the normal process of linear growth from the fetus through adolescence and note that growth is the result of age- and gender-dependent interactions among key genetic, environmental, dietary, socioeconomic, developmental, behavioral, nutritional, metabolic, biochemical, and hormonal factors. We then define the wide range of normative data at each stage of growth and note that a pattern within this range is generally indicative of good general health and that growth significantly slower than this range may lead to growth faltering and subsequent short stature. Although not often emphasized, we detail how to properly measure infants and children because height velocity is usually determined from two height measurements (both relatively large values) to calculate the actual height velocity (a relatively much smaller number in comparison). Traditionally the physiology of growth has been taught from an endocrine-centric point-of-view. Here we review the hypothalamic-pituitary-end organ axes for the GH/IGF-1 and gonadal steroid hormones (hypothalamic-pituitary-gonadal axis), both during "mini"-puberty as well as at puberty. However, over the past few decades much more emphasis has been placed on the growth plate and its many interactions with the endocrine system but also with its own intrinsic physiology and gene mutations. These latter, whether individually (large effect size) or in combination with many others including endocrine system-based, may account in toto for meaningful differences in adult height. The clinical assessment of children with short stature includes medical, social and family history, physical exam and importantly proper interpretation of the growth curve. This analysis should lead to judicious use of screening laboratory and imaging tests depending on the pre-test probability (Bayesian inference) of a particular diagnosis in that child. In particular for those with no pathological features in the history and physical exam and a low, but normal height velocity, may lead only to a bone age exam and reevaluation (re-measurement), perhaps 6 months later. he next step depends on the comfort level of the primary care physician, the patient, and the parent; that is, whether to continue with the evaluation with more directed, more sophisticated testing, again based on Bayesian inference or to seek consultation with a subspecialist pediatrician based on the data obtained. This is not necessarily an endocrinologist. The newest area and the one most in flux is the role for genetic testing, given that growth is a complex process with large effect size for single genes but smaller effect sizes for multiple other genes which in the aggregate may be relevant to attained adult height. Genetics is a discipline that is rapidly changing, especially as the cost of exome or whole gene sequencing diminishes sharply. Within a decade it is quite likely that a genetic approach to the evaluation of children with short stature will become the standard, truncating the diagnostic odyssey and be cost effective as fewer biochemical and imaging studies are required to make a proper diagnosis.

Genetic causes of hypopituitarism

Hypopituitarism in neonates is rare, but has life-threatening complications if untreated. This review describes the features of hypopituitarism and the evidence for which infants in whom a genetic cause should be suspected. Importantly, neonates are often asymptomatic or present with non-specific symptoms. Hypopituitarism can be due to abnormal gland development as a result of genetic defects, which result from mutations in gene coding for transcription factors which regulate pituitary development. The mutations can be divided into those causing isolated hypopituitarism or those causing syndromes with associated hypopituitarism. The latter involve mutations in transcription factors which regulate pituitary, as well as extra-pituitary development. There is a paucity of evidence as to which patients should be investigated for genetic mutations, but detailed clinical and biochemical phenotyping with magnetic resonance imaging of the pituitary gland could help target those in whom genetic investigations would be most appropriate.

Hypopituitarism other than sellar and parasellar tumors or traumatic brain injury assessed in a tertiary hospital

Objective:

Data regarding the etiology, clinical and biochemical patterns in hypopituitarism is scant for Pakistan. We describe the characteristics of patients with hypopituitarism other than sellar and parasellar tumors or traumatic brain injury from a tertiary care center in Pakistan.

Methods:

We conducted a retrospective descriptive study in the Aga Khan University Hospital, Karachi, Pakistan. We studied all patients presenting with hypopituitarism, between January 2004 and December 2013. Clinical, hormonal and imaging data pertinent to the study was collected according to inclusion criteria.

Results:

Forty-two patients presented to the endocrinology clinics at the Aga Khan University Hospital during the study period. Thirty-seven patients (88.1%) were females. Mean age ± standard deviation of the participants was 53.8 ± 14.7 years. Sixteen patients had secondary infertility and all were females; a majority of patients in this group had Sheehan’s syndrome (n=8) followed by empty sella syndrome (n=3), partial empty sella syndrome (n=2), idiopathic cause (n=2) and tuberculoma (n=1). Eighteen females (48.6%) reported inability to lactate.

Conclusions:

Non-traumatic hypopituitarism was more common in women, with Sheehan syndrome being the most common cause of hypopituitarism in our study (35.7%). Secondary hypothyroidism was the most common hormonal deficiency. The most commonly reported symptom was weakness.

Identification of a Novel PROP1 Mutation in a Patient with Combined Pituitary Hormone Deficiency and Enlarged Pituitary

Growth hormone deficiency (GHD) can be present from the neonatal period to adulthood and can be the result of congenital or acquired insults. In addition, GHD can be classified into two types: isolated growth hormone deficiency (IGHD) and combined pituitary hormone deficiency (CPHD). CPHD is a disorder characterized by impaired production of two or more anterior and/or posterior pituitary hormones. Many genes implicated in CPHD remain to be identified. Better genetic characterization will provide more information about the disorder and result in important genetic counselling because a number of patients with hypopituitarism represent familial cases. To date, PROP1 mutations represent the most common known genetic cause of CPHD both in sporadic and familial cases. We report a novel mutation in the PROP1 gene in an infant with CPHD and an enlarged pituitary gland. Close long-term follow-up will reveal other possible hormonal defects and pituitary involution.

Congenital Hypopituitarism

Mutations of growth hormone genes and pituitary transcription factors account for a small proportion of cases of severe congenital hypopituitarism. Most cases show characteristic MRI findings of pituitary stalk interruption syndrome. Clinical suspicion should prompt assessment of cortisol, free T4, thyroid-stimulating hormone, and growth hormone levels together with MRI of the hypothalamic and pituitary regions.

Models of GH deficiency in animal studies

Growth hormone (GH) is a peptide hormone released from pituitary somatotrope cells that promotes growth, cell division and regeneration by acting directly through the GH receptor (GHR), or indirectly via hepatic insulin-like growth factor 1 (IGF1) production. GH deficiency (GHD) can cause severe consequences, such as growth failure, changes in body composition and altered insulin sensitivity, depending of the origin, time of onset (childhood or adulthood) or duration of GHD. The highly variable clinical phenotypes of GHD can now be better understood through research on transgenic and naturally-occurring animal models, which are widely employed to investigate the origin, phenotype, and consequences of GHD, and particularly the underlying mechanisms of metabolic disorders associated to GHD. Here, we reviewed the most salient aspects of GH biology, from somatotrope development to GH actions, linked to certain GHD types, as well as the animal models employed to reproduce these GHD-associated alterations.

Cancerous leptomeningitis and familial congenital hypopituitarism

People are at higher risk of cancer as they get older or have a strong family history of cancer. The potential influence of environmental and behavioral factors remains poorly understood. Earlier population and case control studies reported that upper quartile of circulating IGF-I is associated with a higher risk of developing cancer suggesting possible involvement of the growth hormone (GH)/IGF system in initiation or progression of cancer. Since GH therapy increases IGF-1 levels, there have been concerns that GH therapy in hypopituitarism might increase the risk of cancer. We report a 42-year-old female patient who presented with subacute onset of symptoms of meningitis and with the absence of fever which resulted in death 70 days after the onset of symptoms. The patient together with her younger brother was diagnosed at the age of 5 years with familial congenital hypopituitarism, due to homozygous mutation c.150delA in PROP1 gene. Due to evolving hypopituitarism, she was replaced with thyroxine (from age 5), hydrocortisone (from age 13), GH (from age 13 until 17), and sex steroids in adolescence and adulthood. Her consanguineous family has a prominent history of malignant diseases. Six close relatives had malignant disease including her late maternal aunt with breast cancer. BRCA 1 and BRCA 2 mutational analysis in the patient's mother was negative. Histology after autopsy disclosed advanced ovarian cancer with multiple metastases to the brain, leptomeninges, lungs, heart, and adrenals. Low circulating IGF-1 did not seem to protect this patient from cancer initiation and progression in the context of strong family history of malignancies.

Two coexisting heterozygous frameshift mutations in PROP1 are responsible for a different phenotype of combined pituitary hormone deficiency

The role of genetic background in childhood-onset combined pituitary hormone deficiency (CPHD) has been extensively studied. The major contributors are the PROP1, POU1F1, LHX3, LHX4 and HESX1 genes coding transcription factors implicated in pituitary organogenesis. The clinical consequences of mutations encompass impaired synthesis of a growth hormone (GH) and one or more concurrent pituitary hormones (i.e. LH, FSH, TSH, PRL). Manifestation of the disorder may vary due to various mutation impacts on the final gene products or an influence of environmental factors during pituitary organogenesis. We describe the clinical and molecular characteristics of two brothers aged 47 and 39 years presenting an uncommon manifestation of congenital hypopituitarism. Sequencing of the PROP1, POU1F1, LHX3, LHX4 and HESX1 genes was performed to confirm the genetic origin of the disorder. A compound heterozygosity in the PROP1 gene has been identified for both probands. The first change represents a mutational hot spot (c.150delA, p.R53fsX164), whereas the second is a novel alteration (p.R112X) that leads to protein disruption. Based on precise genetic diagnosis, an in silico prediction of a p.R112X mutation on protein architecture was performed. The resulting clinical phenotype was surprisingly distinct compared to most patients with genetic alterations in PROP1 reported in the current literature. This may be caused by a residual activity of a newly identified p.R112X protein that preserves over 70 % of the homeodomain structure. This examination may confirm a key role of a DNA-binding homeodomain in maintaining PROP1 functionality and suggests a conceivable explanation of an unusual phenotype.

Genesis of two most prevalent PROP1 gene variants causing combined pituitary hormone deficiency in 21 populations

Two variants (c.[301_302delAG];[301_302delAG] and c.[150delA];[150delA]) in the PROP1 gene are the most common genetic causes of recessively inherited combined pituitary hormones deficiency (CPHD). Our objective was to analyze in detail the origin of the two most prevalent variants. In the multicentric study were included 237 patients with CPHD and their 15 relatives carrying c.[301_302delAG];[301_302delAG] or c.[150delA];[150delA] or c.[301_302delAG];[ 150delA]. They originated from 21 different countries worldwide. We genotyped 21 single-nucleotide variant markers flanking the 9.6-Mb region around the PROP1 gene that are not in mutual linkage disequilibrium in the general populations--a finding of a common haplotype would be indicative of ancestral origin of the variant. Haplotypes were reconstructed by Phase and Haploview software, and the variant age was estimated using an allelic association method. We demonstrated the ancestral origin of both variants--c.[301_302delAG] was carried on 0.2 Mb-long haplotype in a majority of European patients arising ~101 generations ago (confidence interval 90.1-116.4). Patients from the Iberian Peninsula displayed a different haplotype, which was estimated to have emerged 23.3 (20.1-29.1) generations ago. Subsequently, the data indicated that both the haplotypes were transmitted to Latin American patients ~13.8 (12.2-17.0) and 16.4 (14.4-20.1) generations ago, respectively. The c.[150delA] variant that was carried on a haplotype spanning about 0.3 Mb was estimated to appear 43.7 (38.4-52.7) generations ago. We present strong evidence that the most frequent variants in the PROP1 gene are not a consequence of variant hot spots as previously assumed, but are founder variants.

Case seminar: a young female with acute hyponatremia and a sellar mass

In familial cases of combined pituitary hormone deficiency the most common mutations are that of Prophet of Pit 1 (PROP1) gene. PROP1 mutations are associated with deficiencies of growth hormone, thyrotropin, prolactin, and gonadotropins (follicle-stimulating hormone and luteinizing hormone), with evolving adrenocorticotropin (ACTH) deficiency in some cases. On imaging in most patients the pituitary gland is hypoplastic, but occasionally transient pituitary enlargement is found. We report a 22-year-old female initially diagnosed at age 12 with familial hypopituitarism due to PROP1 mutation, who presented with coma and respiratory arrest (acute hyponatremia). She was urgently treated in Intensive Care Unit of Emergency Center with hypertonic saline and stress doses of hydrocortisone, which resulted in the fast increase of plasma osmolality resulting in the osmotic demyelination syndrome. Simultaneously and incidentally on computed tomography scan a large sellar and suprasellar mass were reported as possible Rathke's cleft cyst or craniopharyngioma. Once the patient was stable, ACTH deficiency was documented. She remained replaced with hydrocortisone and subsequently underwent transphenoidal surgery. The removed sellar content revealed no pituitary adenoma or pituitary cells, but only an eosinophilic, colloid-like mass, and necrotic acellular debris. Her sister with hypopituitarism had an empty sella. Genetic testing in both sisters revealed the same homozygous c.150delA mutation in PROP1 gene. Here we report two sisters with the same PROP1 mutation who presented in adulthood with different pituitary morphology, one of them with a large sellar and suprasellar mass, in which transphenoidal surgery provided an extremely rare opportunity for a histopathological analysis of the sellar content. Due to the lack of endocrine care during the transition period hypocortisolism which evolved, a consequence of PROP1 mutation, was not recognized. Empirical use of hydrocortisone in the Intensive Care in our patient with life-threatening acute hyponatremia was appropriate but because glucocorticoid therapy on its own corrects hyponatremia even after stopping hypertonic saline infusion, the risk for over-correction of hyponatremia in ACTH deficiency is high.

The role of homeodomain transcription factors in heritable pituitary disease

The anterior pituitary gland secretes hormones that regulate developmental and physiological processes, including growth, the stress response, metabolic status, reproduction and lactation. During embryogenesis, cellular determination and differentiation events establish specialized hormone-secreting cell types within the anterior pituitary gland. These developmental decisions are mediated in part by the actions of a cascade of transcription factors, many of which belong to the homeodomain class of DNA-binding proteins. The discovery of some of these regulatory proteins has facilitated genetic analyses of patients with hormone deficiencies. The findings of these studies reveal that congenital defects-ranging from isolated hormone deficiencies to combined pituitary hormone deficiency syndromes-are sometimes associated with mutations in the genes encoding pituitary-acting developmental transcription factors. The phenotypes of affected individuals and animal models have together provided useful insights into the biology of these transcription factors and have suggested new hypotheses for testing in the basic science laboratory. Here, we summarize the gene regulatory pathways that control anterior pituitary development, with emphasis on the role of the homeodomain transcription factors in normal pituitary organogenesis and heritable pituitary disease.

[Genetic background of inherited multiple pituitary hormone deficiency. Mutations of PROP1 gene in Hungary]

In this work I analysed the outcome of growth hormone replacement treatment in patients with inherited form of multiple pituitary hormone deficiency and examined diseased-causing mutations of pituitary transcription factor genes which may underlie this disorder. The results showed that after treatment for a longer than 7-year period with a growth hormone preparation available under well-controlled distribution, the mean height of children with growth hormone deficiency reached the normal national reference range adjusted for age and sex. After establishment of clinical criteria for screening PROP1 gene mutations, I performed mutational analysis of all coding exons of this gene in 35 patients with inherited form of multiple pituitary hormone deficiency. With these studies, diseases-causing PROP1 gene mutations were detected in 15 of the 35 patients (43%). It was also found that more than 80% of mutant alleles were accounted for by those containing the 150delA and 301-302delGA mutations of the PROP1 gene. Importantly, these findings indicated a high relevance of mutational "hot spots" of the PROP1 gene in Hungarian patients with inherited form of multiple pituitary hormone deficiency and they also offered an opportunity for the development of rational and cost-effective screening strategy. When clinical and hormonal findings of patients with and without PROP1 gene mutations were compared, results showed that growth hormone deficiency was diagnosed at earlier age of life in patients with PROP1 gene mutations, but the severity of growth retardation at the time of diagnosis of growth hormone deficiency or the age of patients at the time of manifestation of other pituitary hormone deficiencies (TSH, LH, FSH and ACTH) were similar in the two groups of patients. In 15 patients inherited form of multiple pituitary hormone deficiency who had no PROP1 gene mutations, exon 6 of the POU1F1 gene containing a mutational "hot spot" was also examined but no mutations were found. Thus, these results do not support a significant role of the mutational "hot spot" of the POU1F1 gene in Hungarian patients with inherited form of multiple pituitary hormone deficiency. Finally, I introduced a method for the detection of mutations of the PITX2 gene, a pituitary transcription factor that plays a role not only in pituitary development and differentiation but also in the lateralization of organs. With the use of this method, I performed mutational analysis of all coding exons of this gene in an exceptionally unique patient who had both situs inversus totalis and inherited form of multiple pituitary hormone deficiency, but no mutation was found. Thus, the findings in this patient failed to indicate that mutation of the PITX2 gene is involved in the pathomechanism of situs inversus totalis associated with inherited form of multiple pituitary hormone deficiency.

ARX spectrum disorders: making inroads into the molecular pathology

The Aristaless-related homeobox gene (ARX) is one of the most frequently mutated genes in a spectrum of X-chromosome phenotypes with intellectual disability (ID) as their cardinal feature. To date, close to 100 families and isolated cases have been reported to carry 44 different mutations, the majority of these (59%) being a result of polyalanine tract expansions. At least 10 well-defined clinical entities, including Ohtahara, Partington, and Proud syndromes, X-linked infantile spasms, X-linked lissencephaly with ambiguous genitalia, X-linked myoclonic epilepsy and nonsyndromic intellectual disability have been ascertained from among the patients with ARX mutations. The striking intra- and interfamilial pleiotropy together with genetic heterogeneity (same clinical entities associated with different ARX mutations) are becoming a hallmark of ARX mutations. Although males are predominantly affected, some mutations associated with malformation phenotypes in males also show a phenotype in carrier females. Recent progress in the study of the effect of ARX mutations through sophisticated animal (mice) and cellular models begins to provide crucial insights into the molecular function of ARX and associated molecular pathology, thus guiding future inquiries into therapeutic interventions.

Molecular mechanisms of pituitary organogenesis: In search of novel regulatory genes

Defects in pituitary gland organogenesis are sometimes associated with congenital anomalies that affect head development. Lesions in transcription factors and signaling pathways explain some of these developmental syndromes. Basic research studies, including the characterization of genetically engineered mice, provide a mechanistic framework for understanding how mutations create the clinical characteristics observed in patients. Defects in BMP, WNT, Notch, and FGF signaling pathways affect induction and growth of the pituitary primordium and other organ systems partly by altering the balance between signaling pathways. The PITX and LHX transcription factor families influence pituitary and head development and are clinically relevant. A few later-acting transcription factors have pituitary-specific effects, including PROP1, POU1F1 (PIT1), and TPIT (TBX19), while others, such as NeuroD1 and NR5A1 (SF1), are syndromic, influencing development of other endocrine organs. We conducted a survey of genes transcribed in developing mouse pituitary to find candidates for cases of pituitary hormone deficiency of unknown etiology. We identified numerous transcription factors that are members of gene families with roles in syndromic or non-syndromic pituitary hormone deficiency. This collection is a rich source for future basic and clinical studies.

Mutations in the nuclear localization sequence of the Aristaless related homeobox; sequestration of mutant ARX with IPO13 disrupts normal subcellular distribution of the transcription factor and retards cell division

Background

Aristaless related homeobox (ARX) is a paired-type homeobox gene. ARX function is frequently affected by naturally occurring mutations. Nonsense mutations, polyalanine tract expansions and missense mutations in ARX cause a range of intellectual disability and epilepsy phenotypes with or without additional features including hand dystonia, lissencephaly, autism or dysarthria. Severe malformation phenotypes, such as X-linked lissencephaly with ambiguous genitalia (XLAG), are frequently observed in individuals with protein truncating or missense mutations clustered in the highly conserved paired-type homeodomain.

Results

We have identified two novel point mutations in the R379 residue of the ARX homeodomain; c.1135C>A, p.R379S in a patient with infantile spasms and intellectual disability and c.1136G>T, p.R379L in a patient with XLAG. We investigated these and other missense mutations (R332P, R332H, R332C, T333N: associated with XLAG and Proud syndrome) predicted to affect the nuclear localisation sequences (NLS) flanking either end of the ARX homeodomain. The NLS regions are required for correct nuclear import facilitated by Importin 13 (IPO13). We demonstrate that missense mutations in either the N- or C-terminal NLS regions of the homeodomain cause significant disruption to nuclear localisation of the ARX protein in vitro. Surprisingly, none of these mutations abolished the binding of ARX to IPO13. This was confirmed by co-immunoprecipitation and immmuno fluorescence studies. Instead, tagged and endogenous IPO13 remained bound to the mutant ARX proteins, even in the RanGTP rich nuclear environment. We also identify the microtubule protein TUBA1A as a novel interacting protein for ARX and show cells expressing mutant ARX protein accumulate in mitosis, indicating normal cell division may be disrupted.

Conclusions

We show that the most likely, common pathogenic mechanism of the missense mutations in NLS regions of the ARX homeodomain is inadequate accumulation and distribution of the ARX transcription factor within the nucleus due to sequestration of ARX with IPO13.

Pituitary enlargement in patients with PROP1 gene inactivating mutation represents cystic hyperplasia of the intermediate pituitary lobe. Histopathology and over 10 years follow-up of two patients

Patients with a PROP1 inactivating mutation present combined pituitary hormone deficiency (CPHD) and pituitary maldevelopment. A retrospective analysis of 31 CPHD patients with a PROP1 mutation revealed two individuals, aged 18 and 4.5 years, who had undergone subtotal surgery to remove pituitary tumors, 16.8 x 12 mm and 9 x 10 x 12 mm in size. Histological reassessment of tissue samples revealed epithelial cells, partially oxyphilic, forming gland-like microcystic structures, most of them filled with eosinophilic colloid. These structures were directly linked with fragments of the posterior lobe. Neither atypia nor any traces of proliferation activity (Ki-67 LI=0%) were noted. Immunohistochemistry showed the presence of all hormonal phenotypes of cells. These findings corresponded to the intermediate lobe of the pituitary gland. For this type of pathology we propose the term 'cystic hyperplasia of the intermediate pituitary lobe' and suggest PROP1 gene assessment in patients with CPHD in order to avoid unnecessary neurosurgical interventions.

Discovery of transcriptional regulators and signaling pathways in the developing pituitary gland by bioinformatic and genomic approaches

We report a catalog of the mouse embryonic pituitary gland transcriptome consisting of five cDNA libraries including wild type tissue from E12.5 and E14.5, Prop1(df/df) mutant at E14.5, and two cDNA subtractions: E14.5 WT-E14.5 Prop1(df/df) and E14.5 WT-E12.5 WT. DNA sequence information is assembled into a searchable database with gene ontology terms representing 12,009 expressed genes. We validated coverage of the libraries by detecting most known homeobox gene transcription factor cDNAs. A total of 45 homeobox genes were detected as part of the pituitary transcriptome, representing most expected ones, which validated library coverage, and many novel ones, underscoring the utility of this resource as a discovery tool. We took a similar approach for signaling-pathway members with novel pituitary expression and found 157 genes related to the BMP, FGF, WNT, SHH and NOTCH pathways. These genes are exciting candidates for regulators of pituitary development and function.

Molecular analysis of novel PROP1 mutations associated with combined pituitary hormone deficiency (CPHD)

OBJECTIVE

Homozygous mutations in the gene encoding the pituitary transcription factor PROP1 are associated with combined pituitary hormone deficiency (CPHD) in both mice and humans with a highly variable phenotype with respect to the severity and time of initiation of pituitary hormone deficiency. We have ascertained three pedigrees with PROP1 mutations from a large cohort of patients with variable degrees of CPHD who were screened for mutations in PROP1.

RESULTS

Affected individuals from all three pedigrees were found to harbour novel PROP1 mutations. We have identified two siblings in one family who were homozygous for an intronic mutation (c.343-11C > G) that disrupts correct splicing resulting in the loss of exon 3 from the PROP1 transcript. Two siblings from a second, unrelated family are compound heterozygotes for two point mutations in the coding region, a missense mutation (p.R125W) that leads to impaired transcriptional activation, and a deletion of a single nucleotide (c.310delC) resulting in a frameshift and nonfunctional mutant protein. Additionally, we identified a homozygous deletion of the PROP1 locus in two patients born to consanguineous parents.

CONCLUSION

Mutations in PROP1 are a frequent cause of familial CPHD. We have described four novel mutations in PROP1 in 3 pedigrees, all resulting in PROP1 deficiency by different mechanisms. The phenotypic variation observed in association with PROP1 mutations both within and between families, together with the evolving nature of hormone deficiencies and sometimes changing pituitary morphology indicates a need for continual monitoring of these patients.

Mechanisms related to the pathophysiology and management of central hypothyroidism

Central hypothyroidism (CH) is defined as hypothyroidism due to insufficient stimulation of the thyroid gland by TSH, for which secretion or activity can be impaired at the hypothalamic or pituitary levels. Patients with CH frequently present with multiple other pituitary hormone deficiencies. In addition to classic CH induced by hypothalamic-pituitary tumors or Sheehan syndrome, novel causes include traumatic brain injury or subarachnoid hemorrhage, bexarotene (a retinoid X receptor agonist) therapy, neonates being born to mothers with insufficiently controlled Graves disease, and lymphocytic hypophysitis. Growth hormone therapy, which may be used in children and adults, is now also recognized as a possible cause of unmasking CH in susceptible individuals. In addition, mutations in genes, such as TRHR, POU1F1, PROP1, HESX1, SOX3, LHX3, LHX4 and TSHB, have been associated with CH. The difficulty in making a clear diagnosis of CH is that the serum TSH levels can vary; values are normal in most cases, but in some might be low or slightly elevated. Levels of endogenous T(4) in serum might also be subnormal. Appropriate doses of levothyroxine for T(4) replacement therapy have not been confirmed, but might need to be higher than presently used empirically in patients with CH and should be adjusted according to age and other hormone deficiencies, to achieve free T(4) concentrations in the upper end of the normal range.

Panhypopituitarism: genetic versus acquired etiological factors

OBJECTIVE

Mutations in the genes encoding pituitary transcription factors (mainly PROP1, POUF1 and HESX1) are responsible for familial combined pituitary hormone deficiency (CPHD) and septo-optic dysplasia (SOD) while only a low percentage of mutations are the cause of sporadic forms. Indeed, it has been suggested that environmental rather than genetic factors could be important in the pathogenesis of CPHD.

PATIENTS AND METHODS

Thirty-six sporadic patients diagnosed with CPHD or SOD were included in the study. All coding exons and intron-exon boundary regions of PROP1, POUF1 and HESX1 were amplified by PCR and subsequently sequenced.

RESULTS

Two novel missense mutations in the HESX1 gene (Q117P, K176T) were identified in two patients. Polymorphisms in PIT1 and PROP1 were also detected. A higher percentage of breech delivery in male patients with CPHD versus females was observed.

CONCLUSIONS

The low percentage of mutations found in the most common transcription factors involved in CPHD show that a better characterization of hormonal and morphological phenotypes is necessary for patients with CPHD included in genetic studies, and other genetic or non-genetic factors have to be taken into account.

High prevalence of PROP1 gene mutations in Hungarian patients with childhood-onset combined anterior pituitary hormone deficiency

Combined pituitary hormone deficiency is characterized by the impaired production of pituitary hormones, commonly including growth hormone. The pathomechanism of the childhood-onset form of this disorder may involve germline mutations of genes encoding pituitary transcription factors, of which PROP1 gene mutations have been studied most extensively. However, controversy exists about the significance of PROP1 gene mutations, as both low and high frequencies have been reported in these patients. Because the different results may be related to differences in patient populations and/or the variability of clinical phenotypes, we performed the present study to examine the prevalence and spectrum of PROP1 gene mutations in 35 patients with non-acquired childhood-onset growth hormone deficiency combined with at least one other anterior pituitary hormone deficiency. Genetic testing indicated the presence of disease-causing mutations in exons 2 and 3 of the PROP1 gene in 15 patients (43% of all patients; homozygous mutations in 10 patients and compound heterozygous mutations in 5 patients). Comparison of clinical data of patients with and without PROP1 gene mutations failed to show significant differences, except an earlier growth retardation detected in patients with PROP1 gene mutations. In one patient with PROP1 gene mutation, radiologic imaging showed an enlargement of the anterior lobe of the pituitary, whereas the other patients had hypoplastic or normal pituitary gland. All patients with PROP1 gene mutations had normal posterior pituitary lobe by radiologic imaging. These results indicate that using our inclusion criteria for genetic testing, PROP1 gene mutations can be detected in a high proportion of Hungarian patients with non-acquired childhood-onset growth hormone deficiency combined with at least one other anterior pituitary hormone defect.

Long-term follow-up of combined pituitary hormone deficiency in two siblings with a Prophet of Pit-1 gene mutation

Combined pituitary hormone deficiency (CPHD) is a rare disorder resulting from an impaired pituitary function due to different causes, characterized by impaired secretion of growth hormone (GH) and one or more of the other anterior pituitary hormones. To date, 16 distinct human Prophet of Pit-1 (Prop1) gene mutations have been identified in patients with CPHD, inducing a phenotype involving GH, follicle-stimulating hormone (FSH), luteinizing hormone (LH), prolactin and thyroid-stimulating hormone (TSH), and rarely adrenocorticotropic hormone, deficiency. Herein we present two siblings of different sexes from a family with parental consanguinity presenting the 301-302delAG mutation in the Prop1 gene. The female presented failure of growth from the age of 6 years and was treated for 10 years with GH, ending in a final height (standard deviation score) of -0.28. TSH deficiency was manifested after the initiation of GH and was treated with thyroxine while puberty was initiated with conjugated estrogens. The male presented TSH deficiency since childhood, treated with thyroxine, and growth failure at the age of 14 years, treated for a period of 2 years with GH. Puberty was initiated with increasing doses of testosterone, while human chorionic gonadotropin was added in order to achieve increased testicular volume. In conclusion, these two siblings of different sexes with CPHD carrying the 301-302delAG mutation in the Prop1 gene presented a variable phenotype characterized by GH, TSH, LH and FSH deficiency.

PROP1 gene analysis in Portuguese patients with combined pituitary hormone deficiency

OBJECTIVE

Mutations of the PROP1 gene lead to combined pituitary hormone deficiency (CPHD), which is characterized by a deficiency of GH, TSH, LH/FSH, PRL and, less frequently, ACTH. This study was undertaken to investigate the molecular defect in a cohort of patients with CPHD.

DESIGN, PATIENTS AND MEASUREMENTS

A multicentric study involving 46 cases of CPHD (17 familial cases belonging to seven kindreds and 29 sporadic cases) selected on the basis of clinical and hormonal evidence of GH deficiency, central hypothyroidism and hypogonadotrophic hypogonadism, in the absence of an identified cause of hypopituitarism. Mutations of PROP1 were investigated by DNA sequencing. Clinical, hormonal and neuroradiological data were collected at each centre.

RESULTS

PROP1 mutations were identified in all familial cases: five kindreds presented a c. 301-302delAG mutation, one kindred presented a c. 358C --> T (R120C) mutation and one presented a previously unreported initiation codon mutation, c. 2T --> C. Of the 29 sporadic cases, only two (6.9%) presented PROP1 germline mutations (c. 301-302delAG, in both). Phenotypic variability was observed among patients with the same mutations, particularly the presence and age of onset of hypocortisolism, the levels of PRL and the results of pituitary imaging. One patient presented a sellar mass that persisted into adulthood.

CONCLUSIONS

This is the first report of a mutation in the initiation codon of the PROP1 gene and this further expands the spectrum of known mutations responsible for CPHD. The low mutation frequency observed in sporadic cases may be due to the involvement of other unidentified acquired or genetic causes.

An uncommon phenotype with familial central hypogonadism caused by a novel PROP1 gene mutant truncated in the transactivation domain

CONTEXT

PROP1 gene mutations are usually associated with childhood onset GH and TSH deficiencies, whereas gonadotroph deficiency is diagnosed at pubertal age.

OBJECTIVES

We report a novel PROP1 mutation revealed by familial normosmic hypogonadotropic hypogonadism. We performed in vitro transactivation and DNA binding experiments to study functional consequences of this mutation.

SETTING

Three brothers were followed in the Department of Endocrinology of a French university hospital.

PATIENTS

These patients from a consanguineous kindred were referred for cryptorchidism and/or delayed puberty.

RESULTS

Initial investigations revealed hypogonadotropic hypogonadism. One of the patients had psychomotor retardation, intracranial hypertension, and minor renal malformations. The brothers reached normal adult height and developed GH and TSH deficiencies after age 30. A novel homozygous nonsense mutation (W194X) was found in the PROP1 gene, indicating that the protein is truncated in its transactivation domain. Transfection studies confirmed the deleterious effect of this mutation, whose transactivation capacity was only 34.4% of that of the wild-type. Unexpectedly altered DNA-binding properties suggested that the C-terminal end of the factor plays a role in protein-DNA interaction.

CONCLUSIONS

PROP1 mutations should be considered among the growing number of genetic causes of initially isolated hypogonadotropic hypogonadism. This report extends the phenotype variability associated with PROP1 mutations.

Mutations within the transcription factor PROP1 are rare in a cohort of patients with sporadic combined pituitary hormone deficiency (CPHD)

OBJECTIVE

Mutations within the pituitary-specific paired-like homeobox gene PROP1 have been described in 50-100% of patients with familial combined pituitary hormone deficiency (CPHD). We screened a cohort of sporadic (n = 189) and familial (n = 44) patients with hypopituitarism (153 CPHD and 80 isolated hormone deficiencies) for mutations within the coding sequence of PROP1.

DESIGN AND PATIENTS

Patients with congenital hypopituitarism were recruited from the London Centre for Paediatric Endocrinology as well as several national and international centres. The pituitary phenotype ranged from isolated growth hormone deficiency (IGHD) to panhypopituitarism. Clinical data, including endocrine and neuro-radiological studies were obtained from patient records, and DNA was collected and screened for mutations within PROP1 using PCR and single-stranded conformation polymorphism (SSCP) analysis. Positive results on SSCP were sequenced directly.

RESULTS

The prevalence of PROP1 mutations in unselected sporadic cases of hypopituitarism was lower (1.1%) than in familial cases (29.5%). PROP1 mutations can be associated with a highly variable phenotype, and both pituitary hypoplasia and pituitary hyperplasia. We describe the waxing and waning of a pituitary mass over 20 months in association with a PROP1 mutation that is predicted to lead to complete loss of function. Additionally, we have identified a possible founder mutation in CPHD patients from the Indian subcontinent.

CONCLUSIONS

PROP1 mutations are rare in sporadic cases of CPHD, although the prevalence rises if there is a positive family history or if the patients are carefully selected with respect to the endocrine and neuroradiological phenotype. There is considerable phenotypic variability in families with the same mutation, indicating the role of other genetic or environmental factors on phenotypic expression. Finally, the pituitary enlargement that is observed in patients with PROP1 mutations can wax and wane in size before eventual involution.

Genetic control of pituitary development and hypopituitarism

The pituitary gland functions as a relay between the hypothalamus and peripheral target organs that regulate basic physiological functions, including growth, the stress response, reproduction, metabolism and lactation. The development of the pituitary gland has been studied extensively in mice, and has begun to be explored in zebrafish, an animal model system amenable to forward genetics. Multiple signaling molecules and transcription factors, expressed in overlapping but distinct spatial and temporal patterns, are required at various stages of pituitary development. Defects in this precisely regulated genetic program lead to diverse pituitary dysfunction. The animal models have greatly enhanced our understanding of molecular mechanisms underlying pituitary development in addition to congenital pituitary disorders in humans.

Mutation analysis of POUF-1, PROP-1 and HESX-1 show low frequency of mutations in children with sporadic forms of combined pituitary hormone deficiency and septo-optic dysplasia

OBJECTIVES

Mutations in the genes encoding the transcription factors PROP1 and POUF-1 (Pit-1) have been reported as common causes of combined pituitary hormone deficiency (CPHD), and HESX1 mutations have been identified in children with septo-optic dysplasia (SOD). There are few data on UK children. We have performed mutation analysis in a large cohort of affected children within the West Midlands region to assess the feasibility of a screening strategy for molecular diagnosis in CPHD and SOD.

DESIGN AND PATIENTS

The three coding exons of PROP1, and six exons of POUF-1 in 27 children from 26 families with CPHD, and three exons of HESX1 in 23 children from 22 families with SOD were directly sequenced from a well-characterized regional cohort.

RESULTS

We identified a C to T transition in exon 6 of POUF-1, resulting in a known missense mutation (R271W) in a mother and daughter from one family with CPHD. We also found a novel homozygous T to C transition in exon 6 of POUF-1, resulting in a missense mutation (F233L) in a twin with CPHD. This mutation was excluded in 100 ethnically matched control alleles. We did not identify any mutations in the PROP1 gene or HESX1. The median maternal age at delivery for the CPHD children was 27 years, compared to 21 years for the mothers of SOD children (P = 0.04).

CONCLUSIONS

Mutations in POUF-1, PROP1 and HESX1 are rare causes of CPHD and SOD, respectively, in children from the West Midlands. In particular, we did not confirm the reported 'hotspot' in PROP1. A screening strategy that targets familial cases is highly likely to increase the mutation yield. The young maternal age at conception of children with SOD and potential teratogen exposure indicate the predominance of environmental factors in this condition compared with CPHD.

A novel PROP1 gene mutation (157delA) in Japanese siblings with combined anterior pituitary hormone deficiency

OBJECTIVE

The majority of cases of combined anterior pituitary hormone deficiency (CPHD) reported in Japanese patients have PIT1 abnormality. This study describes for the first time a homozygous mutation of the PROP1 gene in two Japanese siblings with CPHD born to consanguineous parents.

PATIENTS

Two siblings were growth retarded at 3 years of age and developed hypothyroidism. Pituitary function tests showed combined deficiency of GH, TSH, PRL and gonadotrophins. The size of their pituitary glands decreased with age, as demonstrated by magnetic resonance imaging (MRI).

RESULTS

The PROP1 gene was analysed by polymerase chain reaction (PCR) followed by direct sequencing. Both children were homozygous for a novel single base deletion at codon 53 (157delA), while their parents were heterozygous. This mutation, if translated, predicts the production of a protein lacking the paired-like homeodomain required for DNA binding, suggesting that the mutation was the direct cause of CPHD in these patients.

CONCLUSIONS

157delA is the first reported Japanese PROP1 gene mutation. In Japan, PROP1 abnormality appears to be a less frequent cause of CPHD than does PIT1 abnormality, whereas PROP1 abnormality predominates in CPHD patients of Caucasian and European origin.

Pituitary hypoplasia and respiratory distress syndrome in Prop1 knockout mice

Mutations in Prophet of PIT1 (Prop1), one of several homeodomain transcription factors that are required for the development of the anterior pituitary gland, are the predominant cause of MPHD (multiple pituitary hormone deficiency) in humans. We show that deletion of Prop1 in mice causes severe pituitary hypoplasia with failure of the entire Pit1 lineage and delayed gonadotrope development. The pituitary hormone deficiencies cause secondary endocrine problems and a high rate of perinatal mortality due to respiratory distress. Lung atelectasis in mutants correlates with reduced levels of NKX2.1 and surfactant. Lethality of mice homozygous for either the null allele or a spontaneous hypomorphic allele is strongly influenced by genetic background. Prop1-null mice are an excellent model for MPHD and may be useful for testing the efficacy of pharmaceutical intervention for neonatal respiratory distress.

Conserved amino acid sequences confer nuclear localization upon the Prophet of Pit-1 pituitary transcription factor protein

Prophet of Pit-1 (PROP1) is a homeodomain transcription factor essential for development of the mammalian anterior pituitary gland. Studies of human patients and animal models with mutations in their Prop1 genes have established that PROP1 is required for the correct development or sustained function of the hormone-secreting cells that regulate physiological pathways controlling growth, reproduction, metabolism, and the stress response. By comparative analysis of mammalian Prop1 genes and their encoded proteins, including cloning the ovine Prop1 gene and its products, we demonstrate that two conserved basic regions (B1 and B2) of the PROP1 protein located within the homeodomain are required for nuclear localization, DNA binding, and target gene activation. Interestingly, missense mutations in the human Prop1 gene causing amino acid changes in both the B1 and B2 regions have been associated with combined pituitary hormone deficiency (CPHD) diseases, suggesting that disruption of nuclear localization may be part of the molecular basis of such diseases. The ovine Prop1 gene has three exons and two introns, a different structure compared with that of the bovine gene. Two alleles of the ovine gene were found to encode protein products with different carboxyl terminal domain sequences. We demonstrate that the two alleles are distributed in different breeds of sheep. Finally, we show for the first time that the PROP1 protein is associated with the nuclear matrix.

Rational use of the laboratory for childhood and adult growth hormone deficiency

No laboratory test has sufficient diagnostic sensitivity and specificity to serve as a gold standard for the diagnosis for GHD: therefore, test results must be interpreted after assessment of risk for GHD is determined on clinical grounds. Growth data are particularly crucial for diagnosis of childhood GHD;history of known pituitary damage and presence or absence of other pituitary hormone deficiencies are the critical elements for the diagnosis of adult GHD. New reference preparations are available for GH and IGF-I and should greatly aid interassay comparisons when the preparations are universally adopted.GH stimulation testing remains a key part of the diagnosis of adult GHD, but is currently being de-emphasized for the diagnosis of pediatric GHD. Better interassay comparative data and organized clinical collaboration between clinicians and test manufacturers/laboratories to set rational clinical diagnostic cutoffs would improve greatly the clinical usefulness of GH stimulation testing. The availability of statistically sound age- and sex-related normative data for IGF-I and IGFBP3 make these key tests for the diagnosis of childhood GHD. Although IGF-I may not be a perfect test for the diagnosis of adult GHD, it may be sufficiently informative in many cases to warrant using it ona routine basis. IGF-I also has a role in monitoring the safety of adult patients who are on GH treatment; studies are underway to determine if IGF-I may be useful in the future for optimization of GH dosaging.

Transcriptional control during mammalian anterior pituitary development

The mammalian anterior pituitary gland is a compound endocrine organ that regulates reproductive development and fitness, growth, metabolic homeostasis, the response to stress, and lactation, by actions on target organs such as the gonads, the liver, the thyroid, the adrenals, and the mammary gland. The protein and peptide hormones that control these physiological parameters are secreted by specialized pituitary cell types that derive from a common origin in the early ectoderm. Collectively, the broad physiological importance of the pituitary gland, its intriguing organogenesis, and the clinical and agricultural significance of its actions, have established pituitary development as an excellent model system for the study of the gene-regulatory cascades that guide vertebrate cell determination and differentiation. We review the transcriptional pathways that regulate the commitment of the individual pituitary cell lineages and that subsequently modulate trophic hormone gene activity in the differentiated cells of the mature gland.

Clinical Characteristics and Molecular Analysis of PIT1, PROP1,LHX3, and HESX1 in Combined Pituitary Hormone Deficiency Patients with Abnormal Pituitary MR Imaging

BACKGROUND/AIMS

Many genes encoding pituitary transcription factors involved in the formation of the pituitary gland are identified. Different mutations in these genes have been reported in patients with familial combined pituitary hormone deficiency (CPHD). This study was undertaken to analyze PIT1, PROP1, LHX3, and HESX1 in 12 CPHD patients with abnormal pituitary magnetic resonance imaging (MRI). Since embryonic development of the pituitary requires the coordinated expression of specific transcription factors, we postulated the presence of mutations in PIT1, PROP1, LHX3, and HESX1 genes.

METHODS

Anterior pituitary function was evaluated. Each gene was PCR amplified exon by exon, and subsequently sequenced.

RESULTS

In all cases, MRI examination showed abnormal pituitary gland development featuring ectopic neurohypophysis, hypoplastic anterior lobe, empty sella, and septo-optic dysplasia. Endocrinologically, all patients revealed multiple pituitary hormone deficiency including growth hormone, thyroid stimulating hormone, luteinizing hormone, follicular stimulating hormone and adrenocorticotropin. They were all sporadic cases without a positive family history. None of disease-causing specific mutations were identified in PIT1, PROP1, LHX3, and HESX1 genes of 12 sporadic CPHD patients with abnormal pituitary imaging. However, 2 novel polymorphisms were found in PROP1 gene: IVS1+3 A-->G and 27 T-->C (Ala9Ala) in exon 1. Their allele frequencies in patients and normal controls were not statistically different. Overall, allele frequencies of these polymorphisms were as follows: for the IVS1+3 A-->G polymorphism, the allele frequency of A was 54%, and 46% for G, with 58% of an A/G heterozygosity. For the 27 T-->C (Ala9Ala) polymorphism, the allele frequency of T was 46%, and 54% for G, with 42% of a T/C heterozygosity.

CONCLUSIONS

Mutations of PIT1, PROP1, LHX3, and HESX1 genes are very rare in sporadic CPHD patients with abnormal pituitary MRI.