The IVS1-2A>G mutation in the SRD5A2 gene predominates in Cypriot patients with 5α reductase deficiency

Genetic diagnosis of endocrine disorders in Cyprus through the Cyprus Institute of Neurology and Genetics: an ENDO-ERN Reference Center

The report covers the current and past activities of the department Molecular Genetics-Function and Therapy (MGFT) at the Cyprus Institute of Neurology and Genetics (CING), an affiliated Reference Center for the European Reference Network on Rare Endocrine Conditions (Endo-ERN).The presented data is the outcome of > 15 years long standing collaboration between MGFT and endocrine specialists from the local government hospitals and the private sector. Up-to-date > 2000 genetic tests have been performed for the diagnosis of inherited rare endocrine disorders. The major clinical entities included Congenital Adrenal Hyperplasia (CAH) due to pathogenic variants in CYP21A2 gene and Multiple Endocrine Neoplasia (MEN) type 2 due to pathogenic variants in the RET proto-oncogene. Other rare and novel pathogenic variants in ANOS1, WDR11, FGFR1, RNF216, and CHD7 genes were also found in patients with Congenital Hypogonadotropic Hypogonadism. Interestingly, a few patients with Disorders of Sexual Differentiation (DSD) shared rare pathogenic variants in the SRD5A2, HSD17B3 and HSD3B2 while patients with Glucose and Insulin Homeostasis carried theirs in GCK and HNF1A genes. Lastly, MGFT over the last few years has established an esteemed diagnostic and research program on premature puberty with emphasis on the implication of MKRN3 gene on the onset of the disease and the identification of other prognosis biomarkers.As an Endo-ERN member MGFT department belongs to this large European network and holds the same humanistic ideals which aim toward the improvements of health care for patients with rare endocrine conditions in respect to improved and faster diagnosis.

Pathogenic and Low-Frequency Variants in Children With Central Precocious Puberty

Background

Central precocious puberty (CPP) due to premature activation of GnRH secretion results in early epiphyseal fusion and to a significant compromise in the achieved final adult height. Currently, few genetic determinants of children with CPP have been described. In this translational study, rare sequence variants in MKRN3, DLK1, KISS1, and KISS1R genes were investigated in patients with CPP.

Methods

Fifty-four index girls and two index boys with CPP were first tested by Sanger sequencing for the MKRN3 gene. All children found negative (n = 44) for the MKRN3 gene were further investigated by whole exome sequencing (WES). In the latter analysis, the status of variants in genes known to be related with pubertal timing was compared with an in-house Cypriot control cohort (n = 43). The identified rare variants were initially examined by in silico computational algorithms and confirmed by Sanger sequencing. Additionally, a genetic network for the MKRN3 gene, mimicking a holistic regulatory depiction of the crosstalk between MKRN3 and other genes was designed.

Results

Three previously described pathogenic MKRN3 variants located in the coding region of the gene were identified in 12 index girls with CPP. The most prevalent pathogenic MKRN3 variant p.Gly312Asp was exclusively found among the Cypriot CPP cohort, indicating a founder effect phenomenon. Seven other CPP girls harbored rare likely pathogenic upstream variants in the MKRN3. Among the 44 CPP patients submitted to WES, nine rare DLK1 variants were identified in 11 girls, two rare KISS1 variants in six girls, and two rare MAGEL2 variants in five girls. Interestingly, the frequent variant rs10407968 (p.Gly8Ter) of the KISS1R gene appeared to be less frequent in the cohort of patients with CPP.

Conclusion

The results of the present study confirm the importance of the MKRN3-imprinted gene in genetics of CPP and its key role in pubertal timing. Overall, the results of the present study have emphasized the importance of an approach that aligns genetics and clinical aspects, which is necessary for the management and treatment of CPP.

Genetic Analysis of 25 Patients with 5α-Reductase Deficiency in Chinese Population

Background

A deficiency in steroid 5α-reductase type 2 is an autosomal recessive disorder. Affected individuals manifested ambiguous genitalia, which is caused by decreased dihydrotestosterone (DHT) synthesis in the fetus.

Methods

We analyzed 25 patients with 5α-reductase deficiency in China. Seventeen of the 25 patients (68%) were initially raised as females. Sixteen patients changed their social gender from female to male after puberty.

Results

Eighteen mutations were identified in these patients. p.Gly203Ser and p.Gln6∗ were found to be the most prevalent mutations. On the basis of the genotype of these patients, we divided them into different groups. There was no significant difference in hormone levels and external masculinization score (EMS) in patients with or without these prevalent mutations. Twelve common single-nucleotide polymorphisms (SNPs) near the p.Gln6∗ mutation were chosen for haplotype analysis. Three haplotypes were observed in 6 patients who had the p.Gln6∗ mutation (12 alleles).

Conclusion

We analyzed mutations of the SRD5A2 gene in Chinese patients with 5α-reductase deficiency. Although hotspot mutations exist, no founder effect of prevalent mutations in the SRD5A2 gene was detected in the Chinese population.

Mutational analysis of SRD5A2: From gene to functional kinetics in individuals with steroid 5α-reductase 2 deficiency

Human steroid 5α-reductase 2 (SRD5A2) plays a determinative role in the masculinization of external genitalia. To date, approximately 114 different mutations of the SRD5A2 gene have been reported; however, little information is available about their impact on catalytic function or their three-dimensional (3D) structures. We determined the effect of point mutations on the testosterone-depend kinetic constants (K_m,app and V_max,app) and structural characteristics of SRD5A2 from Mexican patients with 46,XY-steroid 5α-reductase 2 deficiency. PCR-SSCP assays identified ten distinct gene variants and sequencing analysis identified missense mutations [p.V3I, p.S14R, p.A52T, p.F118L, p.R145W, p.R171S, p.L226P, p.F229S, p.S245Y, and p.A248V]. Mutations were re-created by site-directed mutagenesis and expressed in HEK293 cells. Functional studies demonstrated that 8 variants led to partial (K_m,app = 0.16-2.6 μM; V_max,app = 224-2640 pmol/mg P/min) or complete losses of activity compared to the wild-type enzyme (K_m,app = 0.7 μM; V_max,app = 4044 pmol/mg P/min). All the mutations were assessed using multiple software tools and the results predicted that all of the mutations were associated with disease or damage. Mapping mutations on the model of a 3D structure of SRD5A2 demonstrated alterations in contact sites with their proximal amino acids. Our data show that mutations affect the catalytic efficiency (V_max/K_m) or result in residual enzymatic activity, which could be due to erroneous interactions between amino acid residues, the substrate testosterone, or NADPH.

Molecular genetics and phenotype/genotype correlation of 5-α reductase deficiency in a highly consanguineous population

CONTEXT AND OBJECTIVES

5-α reductase deficiency is a rare 46,XY disorder of sex development. We present detailed phenotypic and genotypic features of a cohort of 24 subjects from a highly consanguineous population of Saudi Arabia SUBJECTS AND METHODS: We studied the clinical presentation and hormonal profiles of 24 subjects diagnosed with 5-α reductase deficiency and performed genetic testing on DNA isolated from their peripheral blood using polymerase chain reaction and direct sequencing of the SRD5A2.

RESULTS

All subjects had 46,XY karyotype and presented with atypical appearance of external genitalia ranging from clitoromegaly, micophallus with hypospadias, undescended testes to completely normally looking female genitalia. Thirteen (54%) of them had severe under virilization and were assigned female sex at birth. The other 11 subjects were raised as males. Stimulated Testosterone:Dihydrotestosterone ratio was high in all 16 subjects in whom it was measured. The genetic testing revealed 2 nonsense mutations (p.R103X and p.R227X) in 2 unrelated subjects, 3 missense mutations (p.P181L, p.A228T, p.R246Q) in 11 subjects and a splice site mutation (IVS1-2A > G) in 11 other subjects. There was significant phenotypic variability even in subjects with the same mutation and also within the same family.

CONCLUSION

This is the first and largest report of the clinical and molecular genetics of 5-α reductase deficiency from the Middle East. It shows weak genotype/phenotype correlation and significant phenotypic heterogeneity. IVS1-2A > G mutation is the most common mutation and is likely to be a founder mutation in this part of the world.

Multiple endocrine neoplasia 2 in Cyprus: evidence for a founder effect

PURPOSE

Multiple endocrine neoplasia type 2 (MEN2) affects patients with RET proto-oncogene mutations. This cohort study refers to patients who were diagnosed with familial medullary thyroid carcinoma (MTC) and underwent RET genetic testing in Cyprus between years 2002 and 2017.

METHODS AND PATIENTS

Forty patients underwent RET testing by Sanger sequencing of exons 10-11 and 13-16. Genotyping with STR genetic markers flanking the RET gene along with Y-chromosome genotyping and haplogroup assignment was also performed.

RESULTS

RET mutations were identified in 40 patients from 11 apparently unrelated Cypriot families and two non-familial sporadic cases. Nine probands (69.2%) were heterozygous for p.Cys618Arg, one (7.7%) for p.Cys634Phe, one (7.7%) for the somatic delE632-L633 and two (15.4%) for p.Met918Thr mutations. The mean age at MTC diagnosis of patients carrying p.Cys618Arg was 36.8 ± 14.2 years. The age of pheo diagnosis ranged from 26 to 43 years and appeared simultaneously with MTC in 5/36 (13.9%) cases. The high frequency of the p.Cys618Arg mutation suggested a possible ancestral mutational event. Haplotype analysis was performed in families with and without p.Cys618Arg. Six microsatellite markers covering the RET gene and neighboring regions identified one core haplotype associated with all patients carrying p.Cys618Arg mutation.

CONCLUSIONS

The mutation p.Cys618Arg is by far the most prevalent mutation in Cyprus followed by other reported mutations of variable clinical significance. The provided molecular evidence speculates p.Cys618Arg mutation as an ancestral mutation that has spread in Cyprus due to a possible founder effect.

5-α-Reductase type 2 deficiency: is there a genotype-phenotype correlation? A review

5-α-Reductase type 2 enzyme catalyzes the conversion of testosterone into dihydrotestosterone, a potent androgen responsible for male sexual development during the fetal period and later during puberty. Its deficiency causes an autosomal recessive disorder of sex development characterized by a wide range of under-virilization of external genitalia in patients with a 46,XY karyotype. Mutations in the SRD5A2 gene cause 5-α-Reductase deficiency; although it is an infrequent disorder, it has been reported worldwide, with mutational heterogeneity. Furthermore, it has been proposed that there is no genotype-phenotype correlation, even in patients carrying the same mutation. The aim of this review was to perform an extensive search in various databases and to select those articles with a comprehensive genotype and phenotype description of the patients, classifying their phenotypes using the external masculinization score (EMS). Thus, it was possible to objectively compare the eventual genotype-phenotype correlation between them. The analysis showed that for most of the studied mutations no correlation can be established, although the specific location of the mutation in the protein has an effect on the severity of the phenotype. Nevertheless, even in patients carrying the same homozygous mutation, a variable phenotype was observed, suggesting that additional genetic factors might be influencing it. Due to the clinical variability of the disorder, an accurate diagnosis and adequate medical management might be difficult to carry out, as is highlighted in the review.

Late Diagnosis of 5-α-Reductase Type 2 Deficiency in an Adolescent Girl with Primary Amenorrhoea

Deficiency of the 5-α-reductase enzyme has been found to affect male sexual development. We report an 18-year-old patient who was referred to an endocrinology clinic in Jizan, Saudi Arabia, in April 2014 with primary amenorrhoea, virilisation and a lack of secondary sex characteristics. As female external genitalia were present at birth, she had been raised as a female. Magnetic resonance imaging revealed no uterine or ovarian tissue in the pelvis and the presence of a scrotal sac. She was diagnosed with 5-α-reductase type 2 deficiency, a 46,XY disorder of sexual development. Typically, affected males have pseudovaginal perineoscrotal hypospadias and ambiguous genitalia at birth. Individuals who have been raised as female manifest characteristics of virilisation at puberty, including deepening of the vocal tone, phallus enlargement, scrotal hyperpigmentation and increased muscle mass.

Association of SRD5A2 gene mutations with risk of hypospadias in the Iranian population

BACKGROUND

Hypospadias is one of the most common forms of congenital malformation of the male external genitalia worldwide. The ratio in the Iranian population is one in 250 live male births. The conversion of testosterone to dihydrotestosterone (DHT) in the presence of steroid 5α-reductase 2, which is encoded by SRD5A2 gene, plays an important role in the normal development of the male reproductive system.

METHODS

We examined whether SRD5A2 gene mutations (V89L and A49T polymorphisms) are associated with the risk of hypospadias in the Iranian population. We performed exons sequencing for SRD5A2 gene in 109 hypospadias patients.

RESULTS

We identified two new mutations in the subgroups of affected cases: including a substitution of the nucleotide T > A in the codon 73 [c.219T > A (p.Leu73_Ser74insHisPro)] and an insertion of an extra A nucleotide in the codon 77 [c.229insA* (p.Gly77*)]. Additionally, we performed PCR-RFLP for the two identified polymorphisms and revealed that V89L [OR = 5.8, 95% CI (3.8-8.8), p value < 0.001] and A49T [OR = 10.16, 95% CI (3.94-26.25), p value < 0.001] are significantly associated with hypospadias occurrence in patients. Our haplotype analysis further indicated that the Leu-Ala haplotype increases risk of hypospadias; conversely, the Val-Ala haplotype decreases the risk of hypospadias in the studied patients.

CONCLUSIONS

This study demonstrates that polymorphisms in the SRD5A2 gene could be considered as a risk factor for hypospadias disease emergence.

Phenotypic and molecular characteristics in eleven Chinese patients with 5α-reductase Type 2 deficiency

CONTEXT

Steroid 5α-reductase type 2 deficiency (5α-RD2) is a male-limited, autosomal recessive inherited disease. Affected 46, XY individuals usually present with ambiguous genitalia at birth. An early and precise diagnosis is of great value to the long-term prognosis of the disease.

OBJECTIVE

To describe the clinical features and molecular determinants in 11 Chinese patients with the SRD5A2 gene mutation and to investigate the functional alteration arising from a novel splicing site mutation identified in one of the patients.

SUBJECTS AND METHODS

Eleven subjects born with abnormal external genitalia from 10 unrelated families were recruited. Among them, nine patients who were reared as girls underwent virilization and gender change after puberty. Genotyping analysis of the SRD5A2 gene was performed in each of the patients. Haplotype analysis was performed in five patients with a prevalent mutation of p.G203S to illustrate the founder effect in China. Functional impairment of the new variant was explored by an in vitro splicing study and enzymatic activity assay.

RESULTS

Nine mutations in the SRD5A2 gene were detected in the eleven patients. In addition to the previously reported p.G203S, p.R227Q, p.N193S, p.R246Q, p.Q6X, p.A228V, c.655delT and IVS1-2 A>G, a novel splicing site mutation (IVS4 + 2 T>C) was identified. From an in vitro functional study, this mutation was found to result in a skipping of exon 4 in the course of mRNA splicing, leading to a truncated protein of 205 amino acids that lacks the catalysing activity. Two siblings with the same compound heterozygous mutation (IVS1-2A>G/p.G203S) exhibited differing phenotypes and opposite patterns of gender rearing. A prevalent variation p.V89L combined with c.655delT was revealed to cause a mild phenotype of 5α-RD2 with a micropenis.

CONCLUSION

This cohort study describes the phenotypic, biochemical and long-term outcome in 11 Chinese patients with 5α-RD2 deficiency and defines the genotypic spectrum of SRD5A2 mutations in China.

Diagnosis of 5α-Reductase 2 Deficiency: Is Measurement of Dihydrotestosterone Essential?

BACKGROUND

5α-Reductase 2 deficiency (5ARD) is a known cause of 46,XY disorders of sex development (DSD). Traditionally, the diagnosis relies on dihydrotestosterone (DHT) measurement, but the results are often equivocal, potentially leading to misdiagnosis. We reviewed alternative approaches for diagnosis of 5ARD.

METHODS

We conducted a retrospective review of the results of urinary steroid profiling (USP) by GC-MS and mutational analysis of SRD5A2 [steroid-5-alpha-reductase, alpha polypeptide 2 (3-oxo-5 alpha-steroid delta 4-dehydrogenase alpha 2)] by PCR and direct DNA sequencing of all 46,XY DSD patients referred to our laboratory with biochemical and/or genetic findings compatible with 5ARD. We also performed a literature review on the laboratory findings of all 5ARD cases reported in the past 10 years.

RESULTS

Of 16 patients diagnosed with 5ARD between January 2003 and July 2012, 15 underwent USP, and all showed characteristically low 5α- to 5β-reduced steroid metabolite ratios. Four patients had DHT measured, but 2 did not reach the diagnostic cutoff. In all 12 patients who underwent genetic analysis, 2 mutations of the SRD5A2 gene were detected to confirm the diagnosis. Twenty-four publications involving 149 patients with 5ARD were published in the review period. Fewer than half of these patients had DHT tested. Nearly 95% of them had the diagnosis confirmed genetically.

CONCLUSIONS

5ARD can be confidently diagnosed by USP at 3 months postnatally and confirmed by mutational analysis of SRD5A2. Interpretation of DHT results may be problematic and is not essential in the diagnosis of 5ARD. We propose new diagnostic algorithms for 46,XY DSD.

RET proto-oncogene mutations are restricted to codon 618 in Cypriot families with multiple endocrine neoplasia 2

BACKGROUND

RET germline mutations predispose to the development of inherited cancer syndrome multiple endocrine neoplasia type 2 (MEN2). Several variants of the RET proto-oncogene including G691S and S904S have been suggested to act as genetic modifiers at the age of onset ofMEN2.

AIM

The aim of this study is to characterize clinically and molecularly 7 Cypriot patients with familial medullary thyroid carcinoma (FMTC) and 1 with MEN2A and also to determine the allelic frequencies of the RET variants G691S and S904S.

SUBJECTS AND METHODS

Seven probands from FMTC families and 1 from MEN2A were screened for the presence of RET mutations and the G691S and S904S variants. Additionally, 226 healthy Cypriots, who served as controls were analysed in an attempt to compare the frequencies of G691S and S904S RET variants to those observed in the 8 patients.

RESULTS

The clinical diagnosis of the probands was based on clinical presentation and supported with biochemical findings. The germline C618R mutation of exon 10 was identified in all 8 probands and in 15 relatives from 7 different families. No significant difference in the G691S/S904S variants allele frequencies between patients (4/16 or 25%) and controls (124/452 or 27.4%) was found.

CONCLUSIONS

Mutational screening of the RET gene identified a common mutation (C618R) in all 8 (7 FMTC and 1 MEN2A) unrelated Cypriot patients which may be explained by a founder effect. Additionally, no association of the G691S/S904S variants was linked with the disease.