Neonatal salt-wasting and 11 β-hydroxylase deficiency in a child carrying a homozygous deletion hybrid CYP11B2 (aldosterone synthase)-CYP11B1 (11 β-hydroxylase)

Chimeric Genes Causing 11β-Hydroxylase Deficiency: Implications in Clinical and Molecular Diagnosis

Deficiency of 11β-hydroxylase (11β-OHD) is the second most common cause of congenital adrenal hyperplasia (CAH), accounting for 0.2-8% of all cases. The disease is transmitted as an autosomal recessive trait and the underlying genetic causes of 11β-OHD are primarily small pathogenic variants affecting the CYP11B1 gene coding the 11β-hydroxylase enzyme. However, special events complicate the molecular diagnosis of 11β-OHD such as an unequal crossing over between the CYP11B2 (coding aldosterone synthase enzyme) and CYP11B1 genes. The resulting allele contains a hybrid gene, with a CYP11B2 5'-end and a CYP11B1 3'-end, where the CYP11B1 gene is under the control of the CYP11B2 promoter and thus not responding to the adrenocorticotropin (ACTH) but to angiotensin II and K+. This leads a reduction of cortisol production in 11β-OHD. In particular, CYP11B2/CYP11B1 chimeric genes can be distinguished into two groups depending on the breakpoint site: chimeras with breakpoint after the exon 5 of CYP11B2 preserve the aldosterone synthase activity, the others with breakpoint before exon 5 lose this function. In the last case, a more severe phenotype is expected. The aim of this review was to explore the setting of CYP11B2/CYP11B1 chimeras in 11β-OHD, performing a careful review of clinical literature cases.

Case Report: A combination of chimeric CYP11B2/CYP11B1 and a novel p.Val68Gly CYP11B1 variant causing 11β-Hydroxylase deficiency in a Chinese patient

Introduction

11β-Hydroxylase deficiency (11β-OHD, OMIM#202010) is the second most common form of congenital adrenal hyperplasia (CAH) caused by pathogenic variants in the CYP11B1 gene. Both single nucleotide variations (SNV)/small insertion and deletion and genomic rearrangements of CYP11B1 are important causes of 11β-OHD. Among these variant types, pathogenic CYP11B2/CYP11B1 chimeras only contribute to a minority of cases. Heterozygote cases (chimera combined with SNV) are very rare, and genetic analysis of these cases can be challenging.

Case presentation

We presented a suspected 11β-OHD female patient with incomplete virilization, adrenal hyperplasia, and hypokalemia hypertension. Whole exome sequencing (WES) revealed that the patient carried both a chimeric CYP11B2/CYP11B1 and a novel missense variant, NM_000497.4: c.203T>G, p.Val68Gly (chr8:143961027) in CYP11B1, which were confirmed by CNVplex and Sanger sequencing, respectively. The patient's manifestations and genetic findings confirmed the diagnosis of 11β-OHD, and oral dexamethasone was administered as a subsequent treatment.

Conclusion

This report showed a rare CYP11B2/CYP11B1 chimera combined with a novel missense variant in a 11β-OHD female patient. The result expands variant spectrum of CYP11B1 and suggests that both chimera and CYP11B1 variant screening should be performed simultaneously in suspected cases of 11β-OHD. To our knowledge, this is the first report about CYP11B2/CYP11B1 chimera detected by WES analysis. WES combined with CNV analysis is an efficient method in the genetic diagnosis of this rare and complex disorder.

Molecular Diagnosis of Steroid 21-Hydroxylase Deficiency: A Practical Approach

Adrenal insufficiency in paediatric patients is mostly due to congenital adrenal hyperplasia (CAH), a severe monogenic disease caused by steroid 21-hydroxylase deficiency (21-OHD, encoded by the CYP21A2 gene) in 95% of cases. CYP21A2 genotyping requires careful analyses that guaranty gene-specific PCR, accurate definition of pseudogene-gene chimeras, gene duplications and allele dropout avoidance. A small panel of well-established disease-causing alterations enables a high diagnostic yield in confirming/discarding the disorder not only in symptomatic patients but also in those asymptomatic with borderline/positive results of 17-hydroxyprogesterone. Unfortunately, the complexity of this locus makes it today reluctant to high throughput techniques of massive sequencing. The strong relationship existing between the molecular alterations and the degree of enzymatic deficiency has allowed genetic studies to demonstrate its usefulness in predicting/classifying the clinical form of the disease. Other aspects of interest regarding molecular studies include its independence of physiological variations and analytical interferences, its usefulness in the diagnosis of simple virilizing forms in males and its inherent contribution to the genetic counseling, an aspect of great importance taking into account the high carrier frequency of CAH in the general population. Genetic testing of CYP21A2 constitutes an irreplaceable tool to detect severe alleles not just in family members of classical forms but also in mild late-onset forms of the disease and couples. It is also helpful in areas such as assisted reproduction and preimplantation diagnosis. Molecular diagnosis of 21-OHD under expert knowledge definitely contributes to a better management of the disease in every step of the clinical course.

Detection of Small CYP11B1 Deletions and One Founder Chimeric CYP11B2/CYP11B1 Gene in 11β-Hydroxylase Deficiency

OBJECTIVE

11β-Hydroxylase deficiency (11β-OHD) caused by mutations in the CYP11B1 gene is the second most common form of congenital adrenal hyperplasia. Both point mutations and genomic rearrangements of CYP11B1 are important causes of 11β-OHD. However, the high degree of sequence identity between CYP11B1 and its homologous gene CYP11B2, presents unique challenges for molecular diagnosis of suspected 11β-OHD. The aim of this study was to detect the point mutation, indel, small deletion of CYP11B1 and chimeric CYP11B2/CYP11B1 gene in a one-tube test, improving the genetic diagnosis of 11β-OHD.

METHODS

Optimized custom-designed target sequencing strategy was performed in three patients with suspected 11β-OHD, in which both the coverage depth of paired-end reads and the breakpoint information of split reads from sequencing data were analysed in order to detect genomic rearrangements covering CYP11B1. Long-range PCR was peformed to validate the speculated CYP11B1 rearrangements with the breakpoint-specifc primers.

RESULTS

Using the optimized target sequencing approach, we detected two intragenic/intergenic deletions of CYP11B1 and one chimeric CYP11B2/CYP11B1 gene from three suspected patients with 11β-OHD besides three pathogenic heterozygous point mutation/indels. Furthermore, we mapped the precise breakpoint of this chimeric CYP11B2/CYP11B1 gene located on chr8:143994517 (hg19) and confirmed it as a founder rearrangement event in the Chinese population.

CONCLUSIONS

Our optimized target sequencing approach improved the genetic diagnosis of 11β-OHD.

Insights on the phenotypic heterogenity of 11β-hydroxylase deficiency: clinical and genetic studies in two novel families

PURPOSE

11β-hydroxylase deficiency accounts for 5% of congenital adrenal hyperplasia cases. Diagnosis suspiction is classically based on the association between abnormal virilization, precocious puberty, and hypertension in 46XX or 46XY subjects. We investigated two families with siblings presenting with opposed clinical features, and provided a review of the mechanisms involved in mineralocorticoid-dependent phenotypic heterogeneity.

METHODS

The coding region of the CYP11B1 gene of 4 patients was sequenced and familial segregation was confirmed. Clinical characterization and blood steroid profile were performed.

RESULTS

Family 1 comprised a female and a male siblings who presented in middle childhood with genital ambiguity (Prader II) and precocious puberty, respectively, associated with hypertension. In the second decade of life, the woman had three full-term pregnancies, and then evolved normotensive with no treatment over a 5-year follow up. On the other hand, her brother had hypertensive end-organ damage at age 24. In family 2, a 2.9 year-old boy presented with precocious puberty and hypertension, whereas his 21 days-old sister had genital ambiguity (Prader III) and salt wasting. A homozygous exon 4 splice site mutation was identified (IVS4ds-1G > A; c.799 G > A) in family 1, while a nonsense mutation in exon 6 (p. Q356X; c.1066 C > T) was found in family 2.

CONCLUSION

CYP11B1 mutations were associated with highly variable phenotypes, from mild to severe virilization, and early-onset hypertension or salt wasting. Further analysis of variants in other hypertension-related genes, steroid synthesis and metabolism compensatory pathways, and/or the investigation of chimeric CYP11B genes are needed to clarify the phenotypic heterogeneity in 11β-hydroxylase deficiency.

Clinical perspectives in congenital adrenal hyperplasia due to 11β-hydroxylase deficiency

Congenital adrenal hyperplasia due to 11 beta-hydroxylase deficiency is a rare autosomal recessive genetic disorder. It is caused by reduced or absent activity of 11β-hydroxylase (CYP11B1) enzyme and the resultant defects in adrenal steroidogenesis. The most common clinical features of 11 beta-hydroxylase deficiency are ambiguous genitalia, accelerated skeletal maturation and resultant short stature, peripheral precocious puberty and hyporeninemic hypokalemic hypertension. The biochemical diagnosis is based on raised serum 11-deoxycortisol and 11-deoxycorticosterone levels together with increased adrenal androgens. More than 100 mutations in CYP11B1 gene have been reported to date. The level of in-vivo activity of CYP11B1 relates to the degree of severity of 11 beta-hydroxylase deficiency. Clinical management of 11 beta-hydroxylase deficiency can pose a challenge to maintain adequate glucocorticoid dosing to suppress adrenal androgen excess while avoiding glucocorticoid-induced side effects. The long-term outcomes of clinical and surgical management are not well studied. This review article aims to collate the current available data about 11 beta-hydroxylase deficiency and its management.

Improving the diagnosis of 11β-hydroxylase deficiency using home-made MLPA probes: identification of a novel chimeric CYP11B2/CYP11B1 gene in a Sicilian patient

PURPOSE

11β-Hydroxylase deficiency (11OHD) represents the second most common cause of congenital adrenal hyperplasia. It is caused by mutations in the CYP11B1 gene localized about 40 kb from the CYP11B2 gene with which it shares a homology of 95 %. The asymmetric recombination of these two genes is involved both in 11OHD and in glucocorticoid-remediable aldosteronism (GRA). Our objective was to set up an easy and rapid method to detect these hybrid genes and other kinds of deletions, to improve the molecular diagnosis of 11OHD.

METHODS

A set of 8 specific probes for both the CYP11B1 and the CYP11B2 genes to be used for multiplex ligation-dependent probe amplification (MLPA) analysis was designed to detect rearrangements of these genes.

RESULTS

The method developed was tested on 15 healthy controls and was proved to be specific and reliable; it led us to identify a novel chimeric CYP11B2/CYP11B1 gene in one patient that carried the known A306V mutation on the other allele. Specific amplification and sequencing of the hybrid gene confirmed the breakpoint localization in the second intron.

CONCLUSIONS

The MLPA kit developed enables the detection of deletions, duplications or chimeric genes and represents an optimal supplement to DNA sequence analysis in patients with 11OHD. In addition, it can also be used to show the presence of the opposite chimaera associated with GRA.

Roux-en-Y gastric bypass in the treatment of non-classic congenital adrenal hyperplasia due to 11-hydroxylase deficiency

Non-classic adrenal hyperplasia (NCAH) has been associated with insulin resistance (IR). Therapies such as metformin, thiazolidinediones and lifestyle alterations improve IR and also ameliorate the biochemical and clinical abnormalities of NCAH, much as they do in polycystic ovarian syndrome (PCOS). More recently, bariatric surgery, such as Roux-en-Y gastric bypass (RYGBP), has also been associated with improvement in IR and amelioration of PCOS and may, therefore, be beneficial in NCAH. We report a case of a 39-year-old, deaf-mute, obese woman with NCAH due to 11-hydroxylase deficiency who underwent RYGBP followed by improvement of NCAH manifestations. She was initially treated with metformin and pioglitazone, which lowered serum 11-deoxycortisol from 198 ng/dl (<51) to 26 ng/dl. Five weeks after undergoing RYGBP her body mass index fell from 44.18 kg/m(2) to 39.54 kg/m(2) and, despite not taking metformin or pioglitazone, serum 11-deoxycortisol remained normal at <40 ng/dl. Concurrently and subsequently, her NCAH symptoms, for example, alopecia, hirsutism and irregular menses normalised as well. We conclude that RYGBP, like other interventions that reduce IR, may be another way of treating non-classic 11-hydroxylase deficiency in selected patients.

Mineralocorticoid hypertension

Hypertension affects about 10 - 25% of the population and is an important risk factor for cardiovascular and renal disease. The renin-angiotensin system is frequently implicated in the pathophysiology of hypertension, be it primary or secondary. The prevalence of primary aldosteronism increases with the severity of hypertension, from 2% in patients with grade 1 hypertension to 20% among resistant hypertensives. Mineralcorticoid hypertension includes a spectrum of disorders ranging from renin-producing pathologies (renin-secreting tumors, malignant hypertension, coarctation of aorta), aldosterone-producing pathologies (primary aldosteronism - Conns syndrome, familial hyperaldosteronism 1, 2, and 3), non-aldosterone mineralocorticoid producing pathologies (apparent mineralocorticoid excess syndrome, Liddle syndrome, deoxycorticosterone-secreting tumors, ectopic adrenocorticotropic hormones (ACTH) syndrome, congenitalvadrenal hyperplasia), and drugs with mineraocorticoid activity (locorice, carbenoxole therapy) to glucocorticoid receptor resistance syndromes. Clinical presentation includes hypertension with varying severity, hypokalemia, and alkalosis. Ratio of plasma aldosterone concentraion to plasma renin activity remains the best screening tool. Bilateral adrenal venous sampling is the best diagnostic test coupled with a CT scan. Treatment is either surgical (adrenelectomy) for unilateral adrenal disease versus medical therapy for idiopathic, ambiguous, or bilateral disease. Medical therapy focuses on blood pressure control and correction of hypokalemia using a combination of anti-hypertensives (calcium channel blockers, angiotensin converting enzyme inhibitors, or angiotensin receptor blockers) and potassium-raising therapies (mineralcorticoid receptor antagonist or potassium sparing diuretics). Direct aldosterone synthetase antagonists represent a promising future therapy.

Donor splice mutation in the 11beta-hydroxylase (CypllB1) gene resulting in sex reversal: a case report and review of the literature

BACKGROUND

Mutations in the gene encoding 110-hydroxylase (CYPI]BJ) are the second most common cause of congenital adrenal hyperplasia (CAH), a disorder characterized by adrenal insufficiency and virilization of female external genitalia.

OBJECTIVE

We describe a new case of 1113-hydroxylase CAH caused by donor splice site mutation in the CYPllB1 gene.

PATIENT

A 46,XX patient of Pakistani descent was identified with severe virilization soon after birth. The karyotype was negative for SRY. Pelvic ultrasound showed normal uterus and cervix. Periniogram revealed a 3-cm long urogenital sinus, ACTH stimulation test showed normal 17-hydroxyprogesterone, low cortisol, elevated 11-deoxycortisol and deoxycorticosterone (DOC) levels, consistent with 11beta-hydroxylase deficiency. Glucocorticoid treatment was started on the basis of a low baseline cortisol and severely virilized external genitalia. The patient did not develop salt wasting and/or hypertension.

RESULTS

Analysis of the CYPllBlgene revealed homozygosity for a codon 318+1G--C substitution at the 5'-splice donor site of intron 5 resulting in a missense mutation. The parents of the patients are consanguineous and are heterozygous for the same mutation.

CONCLUSIONS

In a previous reported case a donor splice mutation was identified for the first time at the same position codon 318 of the CYPIIB1 gene. We present this case in detail along with a literature review of 11beta-hydroxylase deficiency CAH.

Rapid second-tier molecular genetic analysis for congenital adrenal hyperplasia attributable to steroid 21-hydroxylase deficiency

BACKGROUND

Neonatal screening for steroid 21-hydroxylase (CYP21) deficiency is performed to identify congenital adrenal hyperplasia (CAH). The immunologic assay for 17alpha-hydroxyprogesterone (17-OHP) has a high rate of false positives. We assessed the potential for increasing the specificity for CAH by use of a second step involving analysis of the CYP21 gene.

METHODS

Between January 1999 and December 2003, a total of 810,000 newborns were screened. Of these, 7920 had to be retested because their 17-OHP values were above the cutoff of the assay. Sixty-one had positive 17-OHP values in their recall samples and were diagnosed as having CAH. We used a rapid assay for common mutations of the CYP21 gene to analyze these 61 samples. In a prospective study, 198 consecutive samples that had increased 17-OHP and 100 samples that had normal 17-OHP concentrations were genotyped.

RESULTS

Fifty-nine of 61 cases diagnosed as having CAH were confirmed genetically as CYP21 deficiencies. One patient had a 3beta-hydroxysteroid dehydrogenase deficiency, and one patient carried no CYP21 mutations. The 198 increased 17-OHP results were designated as false positives after immunologic testing of recall samples. None of these samples exhibited the genetic pattern consistent with CYP21 deficiency.

CONCLUSIONS

If samples with increased 17-OHP values were screened genetically, the number of retests would decrease by approximately 90%, but the overall sensitivity of CAH screening would remain the same. Adding a second-tier genetic step would require a modest increase in costs, but is counterbalanced by fewer recalls, less clinical follow-up, and a reduction in unnecessary worry for families.