Mutations of the 5 alpha-reductase type 2 gene in eight Mexican patients from six different pedigrees with 5 alpha-reductase-2 deficiency

Genetic control of typical and atypical sex development

Sex development relies on the sex-specific action of gene networks to differentiate the bipotential gonads of the growing fetus into testis or ovaries, followed by the differentiation of internal and external genitalia depending on the presence or absence of hormones. Differences in sex development (DSD) arise from congenital alterations during any of these processes, and are classified depending on sex chromosomal constitution as sex chromosome DSD, 46,XY DSD or 46,XX DSD. Understanding the genetics and embryology of typical and atypical sex development is essential for diagnosing, treating and managing DSD. Advances have been made in understanding the genetic causes of DSD over the past 10 years, especially for 46,XY DSD. Additional information is required to better understand ovarian and female development and to identify further genetic causes of 46,XX DSD, besides congenital adrenal hyperplasia. Ongoing research is focused on the discovery of further genes related to typical and atypical sex development and, therefore, on improving diagnosis of DSD.

The Genotype-Phenotype Correlation in Human 5α-Reductase Type 2 Deficiency: Classified and Analyzed from a SRD5A2 Structural Perspective

The phenotype of the 5α-reductase type 2 deficiency (5αRD2) by the SRD5A2 gene mutation varies, and although there have been many attempts, the genotype-phenotype correlation still has not yet been adequately evaluated. Recently, the crystal structure of the 5α-reductase type 2 isozyme (SRD5A2) has been determined. Therefore, the present study retrospectively evaluated the genotype-phenotype correlation from a structural perspective in 19 Korean patients with 5αRD2. Additionally, variants were classified according to structural categories, and phenotypic severity was compared with previously published data. The p.R227Q variant, which belongs to the NADPH-binding residue mutation category, exhibited a more masculine phenotype (higher external masculinization score) than other variants. Furthermore, compound heterozygous mutations with p.R227Q mitigated phenotypic severity. Similarly, other mutations in this category showed mild to moderate phenotypes. Conversely, the variants categorized as structure-destabilizing and small to bulky residue mutations showed moderate to severe phenotypes, and those categorized as catalytic site and helix-breaking mutations exhibited severe phenotypes. Therefore, the SRD5A2 structural approach suggested that a genotype-phenotype correlation does exist in 5αRD2. Furthermore, the categorization of SRD5A2 gene variants according to the SRD5A2 structure facilitates the prediction of the severity of 5αRD2 and the management and genetic counseling of patients affected by it.

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.

New insights into 5α-reductase type 2 deficiency based on a multi-centre study: regional distribution and genotype-phenotype profiling of SRD5A2 in 190 Chinese patients

BACKGROUND

The 5α-reductase type 2 (5α-RD2) deficiency caused by mutations in the steroid 5α-reductase 2 (SRD5A2) gene results in variable degrees of undervirilisation in patients with 46,XY disorders of sex development. This study aims to profile the regional distribution and phenotype-genotype characteristics of SRD5A2 in a large Chinese 5α-RD2 deficiency cohort through multi-centre analysis.

METHODS

190 subjects diagnosed with 5α-RD2 deficiency were consecutively enrolled from eight medical centres in China. Their clinical manifestations and genetic variants were analysed.

RESULTS

Hypospadias (isolated or combined with microphallus and/or cryptorchidism) was fairly common in the enrolled subjects (66.32%). 42 variants, including 13 novel variants, were identified in SRD5A2. Homozygous and compound heterozygous mutations presented in 38.42% and 61.58% of subjects, respectively, and predominated in exons 1, 4 and 5. The most prevalent variant was c.680G > A (52.37%), followed by c.16C > T, (10.79%), c.607G > A, (9.21%) and c.737G > A, (8.95%). However, their distributions were different: c.680G > A was more common in South China than in North China (62.62% vs 39.16%, p < 0.001), whereas the regional prevalence of c.16C > T was reversed (6.07% vs 16.87%, p = 0.001). Furthermore, c.680G > A prevailed in cases with normal meatus (68.75%) or distal hypospadias (66.28%), compared with those with proximal hypospadias (35.54%, p < 0.001). However, cases with proximal hypospadias showed a higher frequency of c.16C > T (20.48%) than those with normal meatus (3.13%) or distal hypospadias (3.49%, p < 0.001).

CONCLUSIONS

This study profiled variable phenotypic presentation and wide mutational spectrum of SRD5A2, revealing its distinctive regional distribution in Chinese patients and further shaping the founder effect and genotype-phenotype correlation of SRD5A2.

Genotype-phenotype correlation, gonadal malignancy risk, gender preference, and testosterone/dihydrotestosterone ratio in steroid 5-alpha-reductase type 2 deficiency: a multicenter study from Turkey

BACKGROUND

Studies regarding genetic and clinical characteristics, gender preference, and gonadal malignancy rates for steroid 5-alpha-reductase type 2 deficiency (5α-RD2) are limited and they were conducted on small number of patients.

OBJECTIVE

To present genotype-phenotype correlation, gonadal malignancy risk, gender preference, and diagnostic sensitivity of serum testosterone/dihydrotestosterone (T/DHT) ratio in patients with 5α-RD2.

MATERIALS AND METHODS

Patients with variations in the SRD5A2 gene were included in the study. Demographic characteristics, phenotype, gender assignment, hormonal tests, molecular genetic data, and presence of gonadal malignancy were evaluated.

RESULTS

A total of 85 patients were included in the study. Abnormality of the external genitalia was the most dominant phenotype (92.9%). Gender assignment was male in 58.8% and female in 29.4% of the patients, while it was uncertain for 11.8%. Fourteen patients underwent bilateral gonadectomy, and no gonadal malignancy was detected. The most frequent pathogenic variants were p.Ala65Pro (30.6%), p.Leu55Gln (16.5%), and p.Gly196Ser (15.3%). The p.Ala65Pro and p.Leu55Gln showed more undervirilization than the p.Gly196Ser. The diagnostic sensitivity of stimulated T/DHT ratio was higher than baseline serum T/DHT ratio, even in pubertal patients. The cut-off values yielding the best sensitivity for stimulated T/DHT ratio were ≥ 8.5 for minipuberty, ≥ 10 for prepuberty, and ≥ 17 for puberty.

CONCLUSION

There is no significant genotype-phenotype correlation in 5α-RD2. Gonadal malignancy risk seems to be low. If genetic analysis is not available at the time of diagnosis, stimulated T/DHT ratio can be useful, especially if different cut-off values are utilized in accordance with the pubertal status.

Characterising SRD5A2 Gene Variants in 37 Indonesian Patients with 5-Alpha-Reductase Type 2 Deficiency

The 5-alpha-reductase type 2 deficiency (5ARD2) is an autosomal recessive condition associated with impairment in the conversion of testosterone to dihydrotestosterone. This condition leads to undervirilisation in 46,XY individuals. To date, there have been more than 100 variations identified in the gene responsible for 5ARD2 development (steroid 5-alpha-reductase 2, SRD5A2). However, few studies have examined the molecular characterisation of Indonesian 5ARD2 cases. In the current study, we analysed 37 subjects diagnosed with 46,XY DSD (disorders of sex development) with confirmed variations in the SRD5A2 gene. We examined results from testosterone/dihydrotestosterone (T/DHT) and urinary etiocholanolone/androsterone (Et/An) ratios, as well as from molecular and clinical analyses. Twelve variants in the SRD5A2 gene were identified, and 6 of which were novel, namely, c.34-38delGinsCCAGC, p.Arg50His, p.Tyr136 ^∗ , p.Gly191Arg, p.Phe194Ile, and p.Ile253Val variants. Moreover, we determined that 20 individuals contained harmful mutations, while the remaining 17 variants were benign. Those containing harmful mutations exhibited more severe phenotypes with median external genitalia masculinisation scores (EMS) of 3 (1.5-9) and were more likely to be diagnosed at a later age, reared as female, and virilised at pubertal age. In addition, the respective sensitivities for detecting severe 5ARD2 cases using T/DHT (cutoff: 10) and urinary Et/An ratios (cutoff: 0.95) were 85% and 90%, whereas mild cases were only identified with 64.7% and 47.1% sensitivity, respectively. Although we were unable to identify clear correlations between genotypic and phenotypic characteristics in this study, we clearly showed that individuals who were homozygous or compound heterozygous for any of the harmful mutations were more likely to exhibit classic 5ARD2 phenotypes, lower EMS, female assignment at birth, and virilisation during puberty. These results serve to inform the development of improved clinical and molecular 5ARD2 diagnostic approaches, specifically in Indonesian patients.

Clinical and molecular characterization of 5α-reductase type 2 deficiency due to mutations (p.Q6X, p.R246Q) in SRD5A2 gene

Early diagnosis and optimal management for steroid 5α-reductase type 2 deficiency (5α-RD2) patients are major challenges for clinicians and mutation analysis for the 5α-reductase type 2 (SRD5A2) gene is the golden standard for the diagnosis of the disease. In silico analysis of this enzyme has not been reported due to the lack of appropriate model. Moreover, the histological and pathological changes of the gonads are largely unknown. In the present study, a 5α-RD2 patient born with abnormal external genitalia was studied and mutation analysis for SRD5A2 gene was conducted. Moreover, we constructed the homology modeling of 5α-reductase using SWISS-MODEL, followed by the molecular docking study. Furthermore, immunohistochemical staining of Ki67 for the testes tissue was conducted to investigate the potential pathological characteristics. The patient had male (46, XY) chromosomes but presented female characteristics, and the mutation analysis identified a heterozygotes mutation (p.Q6X, p.R246Q) in SRD5A2 gene. In silico analysis elucidated the potential effect of the mutation on enzyme activity. Immunohistochemical staining for the excised testes showed that 30%-50% of the germ cells were Ki67 positive, which indicated the early neoplastic potential. In conclusion, we analyzed the genotype-phenotype correlations of 5α-RD2 caused by a heterozygotes mutation (p.Q6X, p.R246Q). Importantly, we conducted the homology modeling and molecular docking for the first time, which provided a homology model for further investigations. Immunohistochemical results suggested gonadectomy or testis descent should be performed early for 5α-RD2 patient, as delayed treatment would have maintained the testes in a tumorigenic condition.

Genotype-phenotype correlation and identification of two novel SRD5A2 mutations in 33 Chinese patients with hypospadias

Hypospadias, a common congenital malformation of male external genitalia, is characterized mainly by an aberrant opening of the urethra on the ventral side of the penis. Depending on the severity of the disease, it can be classified into three types: anterior, middle, and posterior. In our study, 33 patients with hypospadias were recruited, including eight with anterior hypospadias and 25 with posterior hypospadias. We performed mutation analysis of the SRD5A2, AR and HSD17B3 genes in these patients. Eight different SRD5A2 mutations were detected in 15 patients with posterior hypospadias (60%, 15/25), including six previously described mutations (p.Q6X, Q71X, p.L20P, p.G203S, p.R227Q, and p.R246Q) and two novel mutations (p.G196R and p.L73Pfs^∗17). One AR gene mutation (p.A597T) was found in a patient and no HSD17B3 mutations were detected. Additionally, we carried out routine semen analyses in all adult patients. Combing mutation analysis with semen examination results, showed that whole five adult patients who carried SRD5A2 mutations had abnormal semen quality. In summary, all the detected mutations were responsible for the clinical features observed in these 16 patients. Our data suggest that mutations of the SRD5A2 gene are the main causes of posterior hypospadias and seem to affect the semen quality of adult patients, whereas mutations in AR and HSD17B3 gene were rare in these hypospadias patients. Our study expanded the SRD5A2 mutation spectrum in the Han Chinese population and provided useful information for genetic and reproductive counselling for patients with hypospadias.

Reprint of "Steroid 5α-reductase 2 deficiency"

Dihydrotestosterone is a potent androgen metabolite formed from testosterone by action of 5α-reductase isoenzymes. Mutations in the type 2 isoenzyme cause a disorder of 46,XY sex development, termed 5α-reductase type 2 deficiency and that was described forty years ago. Many mutations in the encoding gene have been reported in different ethnic groups. In affected 46,XY individuals, female external genitalia are common, but Mullerian ducts regress, and the internal urogenital tract is male. Most affected males are raised as females, but virilization occurs at puberty, and male social sex develops thereafter with high frequency. Fertility can be achieved in some affected males with assisted reproduction techniques, and adults with male social sex report a more satisfactory sex life and quality of life as compared to affected individuals with female social sex.

Steroid 5α-reductase 2 deficiency

Dihydrotestosterone is a potent androgen metabolite formed from testosterone by action of 5α-reductase isoenzymes. Mutations in the type 2 isoenzyme cause a disorder of 46,XY sex development, termed 5α-reductase type 2 deficiency and that was described forty years ago. Many mutations in the encoding gene have been reported in different ethnic groups. In affected 46,XY individuals, female external genitalia are common, but Mullerian ducts regress, and the internal urogenital tract is male. Most affected males are raised as females, but virilization occurs at puberty, and male social sex develops thereafter with high frequency. Fertility can be achieved in some affected males with assisted reproduction techniques, and adults with male social sex report a more satisfactory sex life and quality of life as compared to affected individuals with female social sex.

46,XY disorder of sexual development resulting from a novel monoallelic mutation (p.Ser31Phe) in the steroid 5α-reductase type-2 (SRD5A2) gene

Inactivating mutations of the 5α-steroid reductase type-2 (SRD5A2) gene result in a broad spectrum of masculinization defects, ranging from a male phenotype with hypospadias to a female phenotype with Wolffian structures. Molecular studies of the SRD5A2 revealed a new heterozygous gene variant within the coding region that results in phenotypic expression. A c.92C>T transition changing serine to phenylalanine at codon 31 of exon 1 (p.Ser31Phe) was identified in a patient with 46,XY disorder of sexual development who displayed glandular hypospadias with micropenis and bilateral cryptorchidism. The restoration of the p.Ser31Phe mutation by site-directed mutagenesis and transient expression assays using cultured HEK-293 cells showed that this novel substitution does not abolish but does deregulate the catalytic efficiency of the enzyme. Thus, the maximum velocity (V_max) value was higher for the mutant enzyme (22.5 ± 6.9 nmol DHT mg protein⁻¹ h⁻¹) than for the wild-type enzyme (9.8 ± 2.0 nmol DHT mg protein⁻¹ h⁻¹). Increased in vitro activity of the p.Ser31Phe mutant suggested an activating effect. This case provides evidence that heterozygous missense mutations in SRD5A2 may induce the abnormal development of male external genitalia.

Ambiguous external genitalia due to defect of 5-α-reductase in seven Iraqi patients: prevalence of a novel mutation

We report on seven Iraqi patients with 46,XY karyotype and ambiguous genitalia characterized by perineo-scrotal hypospadias, bifid scrotum, clitoris like phallus, palpable testes in inguinal canal and pseudovagina. Patients were raised five as females and two as males. They are all unrelated with the exception of two couples of brothers. The diagnosis of 5-α-reductase-2 deficiency syndrome was first hypothesized on clinical grounds and then confirmed by molecular analysis. Direct sequencing analysis of the SRD5A2 gene revealed in five patients a novel homozygous frame-shift mutation (c.453delC) and in two related patients a previous reported missense mutation. The presence of the same mutation in unrelated patients of the same population suggests a possible founder effect. This report brings the 5-α-reductase-2 deficiency syndrome to the attention of clinical geneticists and child surgeons and discusses the appropriate clinical and surgical strategies for treating these patients.

Practical approach to steroid 5alpha-reductase type 2 deficiency

The aim of this article is to review the literature on steroid 5alpha-reductase type 2 deficiency (5α-RD2) to provide clinicians with information to guide their management of patients with this disorder. The 5alpha-reductase type 2 is encoded by the 5alpha-reductase type 2 gene (SRD5A2) on chromosome 2 and is predominantly expressed in external genital tissues and the prostate. Mutations of the SRD5A2 gene leads to an uncommon autosomal recessive disorder affecting sexual differentiation in individuals with 46,XY karyotype; their phenotype can range from almost normal female structures to a distinct male phenotype with ambiguous genitalia at birth. These phenotypes result from impaired conversion of testosterone to dihydrotestosterone due to mutations in the SRD5A2 gene. Patients exhibit virilization at puberty without breast development, which is often accompanied by gender identity change from female to male. More than 40 mutations have been reported in all five exons of the SRD5A2 gene. Phenotype-genotype correlations for 5α-RD2 have not been well established. The newborn phenotypes of male pseudohermaphrodites with 5α-RD2, partial androgen insensitivity syndrome (PAIS), or 17β-hydroxysteroid dehydrogenase type 3 (17β-HSD3) enzyme deficiency may be indistinguishable. We conclude that steroid 5α-RD2 should be included in the differential diagnosis of newborns with 46,XY DSD. It is important that the diagnosis be made in infancy by biochemical and molecular studies before gender assignment or any surgical intervention because these patients should be considered males at birth.

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

BACKGROUND

5α steroid reductase deficiency (5αSRD) is an autosomal recessive enzymatic deficiency and mutations in the 5α steroid reductase type 2 gene (SRD5A2) result in male pseudohermaphrodism caused by decreased dihydrotestosterone (DHT) synthesis.

AIM

To identify the specific mutations of the SRD5A2 gene in Cypriot patients with 5αSRD.

SUBJECTS AND METHODS

Five unrelated patients with 46,XY karyotype were examined. Four of them were born with ambiguous genitalia and 1 patient, who was raised as girl, presented with primary amenorrhea. The hCG test was informative (elevated testosterone/DHT) of 5αSRD in 3 out of 4 subjects. Sequencing of the SRD5A2 gene was completed for all patients. Genomic DNA was also isolated from a total of 204 healthy unrelated Cypriot subjects. Screening for the IVS1-2A>G mutation was performed by using direct sequencing and restriction enzyme analysis.

RESULTS

The IVS1-2A>G was identified in homozygosity in 3 patients and in a compound heterozygote state in the other 2 patients, in combination with p.P181L and p.R171S in exon 3, respectively. The carrier frequency in the Cypriot population for the IVS1-2A>G mutation was estimated to be 0.98% or 2 in 204.

CONCLUSIONS

The same IVS1-2A>G mutation in the SRD5A2 gene seems to characterize all Cypriot patients with 5αSRD diagnosed so far. Furthermore this relatively rare genetic defect, which has only been reported previously in a single case in the Eastern Mediterranean region, is very likely to be the result of a founder effect.

Five novel mutations of SRD5A2 found in eight Chinese patients with 46,XY disorders of sex development

Individuals with male karyotype (46,XY) affected by 5α-reductase type 2 deficiency, a rare autosomal recessive inherited disorder, can have an almost female phenotype or partially virilized external genitalia. Mutations in the steroid-5-α-reductase (SRD5A2) gene, leading to functional impairment of 5α-reductase type 2, are responsible for this disorder. Our present study analyzed SRD5A2 gene mutations in eight unrelated 46,XY Chinese patients with disorders of sex development. Direct sequencing of genomic DNA for SRD5A2 gene revealed the presence of one homozygous (p.Q6X) and seven compound heterozygous mutations (p.G203S/R227Q, p.L20P/R227Q, p.Q6X/p.A228V, p.C222Ffs232X/p.R246Q, p.W140X/F219Sfs278X, p.Q71X/L185Tfs192X and p.Q6X/p.N193S) in our patients. Among them, p.C222Ffs232X, p.A228V, p.Q71X, L185Tfs192X and p.W140X mutations have not been previously reported. These novel mutations may provide us new insights into the molecular mechanism of 5α-reductase type 2 deficiency. Seven out of eight patients had at least one variant in exon 4, and 8 of 12 (66.7%) mutations were located in exon 4. The expanded mutation database of the SRD5A2 gene should benefit patients in the diagnosis and treatment of this disease.

Genetic analysis of the SRD5A2 gene in Indian patients with 5alpha-reductase deficiency

BACKGROUND

5alpha-Reductase deficiency (5RD) is an uncommon autosomal recessive disorder of sexual differentiation. It results from impaired conversion of testosterone to dihydrotestosterone due to mutations in the steroid 5alpha-reductase type 2 gene (SRD5A2). Mutations in SRD5A2 have not been previously reported in Indian patients with 5RD.

AIM

To delineate the clinical features and mutations in the SRD5A2 gene in Indian patients with 5RD.

PATIENTS AND METHODS

The SRDSA2 gene was sequenced in two unrelated patients with elevated testosterone/dihydrotestosterone ratio and in one patient with classical clinical features and virilization at puberty (in whom the ratio could not be measured due to prior gonadectomy). The prevalence of SRD5A2 mutations was also studied in 52 healthy ethnic control subjects by PCR-RFLP.

RESULTS

Two patients, both from the north Indian state of Uttar Pradesh, carried the homozygous missense mutation p.R246Q in exon 5. Parents of both probands were heterozygous for the mutation. The mutation was absent in 52 control subjects. The third patient, with severe perineoscrotal hypospadias and micropenis, was detected to have a novel heterozygous missense mutation p.Q56H, as well as the homozygous polymorphism p.V89L, both in exon 1. The p.Q56H mutation was absent in 52 control subjects.

CONCLUSION

p.R246Q is a common SRD5A2 mutation in 5RD patients from the Indian subcontinent.

Novel compound heterozygous mutations in the SRD5A2 gene from 46,XY infants with ambiguous external genitalia

Dihydrotestosterone is crucial for normal development of external genitalia and prostate in the male embryo. Autosomal recessive mutations in the 5 alpha-reductase type 2 (SRD5A2) gene disrupt the synthesis of dihydrotestosterone in the urogenital tract and give rise to genetic males with undervirilized external genitalia that may be female-like or ambiguous. In this study, three unrelated 46,XY children (0.5, 3, and 8 years old) who presented severe undermasculinization at birth were examined for genetic abnormalities in the SRD5A2 gene. Coding sequence abnormalities were ascertained by exon-specific polymerase chain reaction (PCR), single-stranded conformational polymorphism (SSCP), and sequencing analysis. Functional properties of the mutant alleles were investigated by means of site-directed mutagenesis assays. DNA molecular studies showed that all three patients were compound heterozygotes for SRD5A2 mutations. Patient 1 had a point mutation 547G --> A in exon 3 (G183S) and a novel dinucleotidic mutation 634,635CC --> TG in exon 4 (P212X). This double change results in premature termination signal (TGA) at codon 212, which predicts the expression of a truncated 211-amino acid protein. Patient 2 was the carrier of mutations G115D in exon 3 and S210F in exon 4. Patient 3 had two substitution mutations in exon 1, including a novel G --> C transversion at nucleotide 169 (E57Q) and a G --> A transition at nucleotide 254 (G85D). In transitory transfection assays, the recombinant cDNAs harboring mutations E57Q and G85D showed residual 5 alpha-reductase activity, whereas those with mutations G115D, S210F, and P212X were devoid of activity. In contrast, the G183S substitution affected the catalytic activity of the enzyme by decreasing its affinity for testosterone substrate. We describe six different mutations of the SRD5A2 gene detected in three children with genital ambiguity. These genotypes are consistent with the clinical phenotype of steroid 5 alpha-reductase 2 deficiency. Our data suggest that the combined gene variants (E57Q/G85D, G115D/S210F, and G183S/P212X) result in subfunctional or nonfunctional enzymes, causing masculinization defects in these patients. This further underscores that exon 4 of SRD5A2 may be a site prone to inactivating mutations.

Detection of the G34R mutation in the 5 alpha reductase 2 gene by allele specific PCR and its linkage to the 89L allele among Egyptian cases

The 5 alpha-reductase type 2 deficiency is an autosomal recessive disorder of sexual development among 46,XY individuals. In Egypt, there is a prevalence of a G34R disease underlying mutation. This study aimed to devise a rapid diagnostic method based on allele specific PCR (AS-PCR) and a linked polymorphism (V89L). The results showed that one set of primers was capable to differentiate between normal, heterozygous, and affected individuals efficiently. All 34R mutation carrying sequences had 100% linkage to the 89L allele, contrasting normal ones with low 89L frequencies. This linkage infers a founder effect among Egyptians having G34R mutation.

Identification of mutations in the SRD5A2 gene in Thai patients with male pseudohermaphroditism

OBJECTIVE

To describe two unrelated Thai patients with suspected 5alpha-reductase type 2 deficiency and perform mutation analysis of the SRD5A2 gene.

DESIGN

Case report.

SETTING

A pediatric endocrinology clinic at a university hospital.

PATIENT(S)

Two unrelated patients with 46,XY karyotype, born with ambiguous genitalia, were studied. One was reared as a boy and the other was reared as a girl.

INTERVENTION(S)

The entire coding regions of the SRD5A2 gene were assessed by polymerase chain reaction (PCR) and sequencing analysis.

MAIN OUTCOME MEASURE(S)

Molecular characterization of the SRD5A2 gene.

RESULT(S)

Four different pathogenic mutations (three missense and one nonsense) were identified. These were located at exon 1 (p.Q6X and p.L20P), exon 3 (p.G183S), and exon 4 (p.G203S). The T>C transition (c.59T>C) resulting in a leucine-to-proline substitution at codon 20 (p.L20P) has not been previously described and was not detected in 100 unaffected, ethnic-matched control chromosomes. In addition, p.G183S, previously identified only among patients from mixed African-European ancestry and in the Dominican Republic, was also detected in a Thai patient.

CONCLUSION(S)

This study demonstrates that the SRD5A2 gene is responsible for 5alpha-reductase type 2 deficiency across different populations and emphasizes the important role of genetic testing for the definite diagnosis and genetic counseling before gender assignment or any surgical intervention.

Gender identity of children and young adults with 5alpha-reductase deficiency

Male pseudohermaphroditism (46,XY DSD) due to 5alpha-reductase deficiency has been recognized for the last few decades. There is scant literature on this entity in India. We compiled data on five patients with this disorder. Four of our five patients were reared as females. Our assessment of these children reveals that they had male gender identity from childhood. Three of the four reared as females chose to change gender role at adolescence, while the fourth is still prepubertal. We conclude that all these patients had male gender identity from early childhood. The parents took note of this only after the appearance of male secondary sexual characteristics at puberty, thereby giving an impression of change in gender identity and gender role.

[5alpha-reductase type 2 deficiency: experiences from Campinas (SP) and Salvador (BA)]

OBJECTIVE

To report the experience regarding patients with steroid 5alpha-reductase type 2 deficiency from three different clinical services in Brazil.

CASUISTIC AND METHODS

Twenty five patients with clinical and hormonal features of 5alpha-reductase deficiency from 23 families (15 from Bahia, 7 from São Paulo and 1 from Minas Gerais) were included in this study. Clinical, hormonal and molecular data were evaluated. The molecular analysis of the five exons of the SRD5A2 gene was done by automatic or manual sequencing of PCR products.

RESULTS

In ten families, SRD5A2 mutations were found in homozygosis (5 with G183S, 2 with R246W, 1 with G196S, 1 with del642T, 1 with 217_218insC), in three in compound heterozygosis (1 with Q126R/IVS3+1G>A, 1 with Q126R/del418T, 1 with Q126R/G158R) while other three were heterozygous, with only one deleterious mutation (1 with G196S, 1 with A207D, and 1 with R246W). In seven cases, no sequencing abnormalities were detected. The G183S substitution was the most frequently found among miscegenated patients (Afro-Euro-Brazilians) from Bahia. Hormonal and clinical findings did not differ between patients with or without mutations, exception made to a higher frequency of consanguinity and greater severity of genital ambiguity in the first group.

CONCLUSION

Our results reinforce the importance of molecular investigation for the diagnosis of this disease and point out to the finding of a very frequent mutation (G183S) in our series, especially in patients with mixed ethnic background from Bahia, and the description of mutations that have only been reported in Brazilian patients so far.

A heterozygous mutation in the desert hedgehog gene in patients with mixed gonadal dysgenesis

Aetiology of mixed gonadal dysgenesis (MGD) has not been completely elucidated. Molecular analyses have failed to demonstrate the presence of mutations in sex-determining region on Y chromosome (SRY); it has been suggested that these individuals may bear mutations in other genes involved in the testis-determining pathway. Desert hedgehog's (DHH) importance regarding male sex differentiation has been demonstrated in various studies we describe here, for the first time, two cases of MGD in which a monoallelic single base deletion in DHH is associated with the disorder. Genomic DNA was isolated from paraffin-embedded gonad tissue from 10 unrelated patients with MGD and three controls; in addition to, DNA from peripheral blood leukocytes in 100 controls. Coding sequence abnormalities in DHH were assessed by exon-specific PCR, single-stranded conformation polymorphism (SSCP) and direct sequencing. In two patients, a heterozygous 1086delG in exon 3 was found. Comparing previously described mutations in DHH to the one observed in this study, we can affirm that the phenotypic spectrum of patients with gonadal dysgenesis due to mutations in DHH is variable. This study continues to demonstrate the importance that DHH has in mammalian male sexual differentiation, providing extended evidence that DHH constitutes a key gene in gonadal differentiation.

A novel missense mutation of 5-alpha reductase type 2 gene (SRD5A2) leads to severe male pseudohermaphroditism in a Turkish family

OBJECTIVES

To analyze the steroid 5-alpha reductase type 2 gene (SRD5A2) in 2 siblings with severe male pseudohermaphroditism suspected to have 5-alpha reductase deficiency in a Turkish family.

METHODS

Two female siblings of a family with 7 children were referred to the urology department because of bilateral inguinal masses. The patients had presented after birth with ambiguous genitalia, but no further diagnostic procedures had been performed, and they were raised as girls until the ages of 13 and 15 years. At this time, both had striking ambiguity of the genitalia, with a clitoris-like phallus, severely bifid scrotum, pseudovaginal perineoscrotal hypospadias, a rudimentary prostate, and inguinal testes. Karyotype was 46,XY. Basal and stimulated levels of serum testosterone (T), dihydrotestosterone (DHT), and T/DHT ratio indicated 5-alpha reductase deficiency. Molecular genetic analysis was performed on deoxyribonucleic acid from peripheral blood leukocytes by single-stranded conformational polymorphism analysis and direct sequencing.

RESULTS

Analysis of the SRD5A2 gene revealed a new homozygous missense mutation in exon 2. At codon 123, we identified a GGA to AGA change resulting in a missense amino acid change from glycine to arginine (G123R). Both parents and the 2 healthy sisters and 3 brothers were all heterozygous at codon 123 for the same mutation.

CONCLUSIONS

We report a novel homozygous missense mutation in exon 2 of the 5-alpha reductase type 2 gene that led to severe undervirilization in 2 siblings.

Gender change in 46,XY persons with 5alpha-reductase-2 deficiency and 17beta-hydroxysteroid dehydrogenase-3 deficiency

Individuals with 5alpha-reductase-2 deficiency (5alpha-RD-2) and 17beta-hydroxysteroid dehydrogenase-3 deficiency (17beta-HSD-3) are often raised as girls. Over the past number of years, this policy has been challenged because many individuals with these conditions develop a male gender identity and make a gender role change after puberty. The findings also raised doubts regarding the hypothesis that children are psychosexually neutral at birth and emphasized the potential role of prenatal brain exposure to androgens in gender development. If prenatal exposure to androgens is a major contributor to gender identity development, one would expect that all, or nearly all, affected individuals, even when raised as girls, would develop a male gender identity and make a gender role switch later in life. However, an estimation of the prevalence of gender role changes, based on the current literature, shows that gender role changes occur frequently, but not invariably. Gender role changes were reported in 56-63% of cases with 5alpha-RD-2 and 39-64% of cases with 17beta-HSD-3 who were raised as girls. The changes were usually made in adolescence and early adulthood. In these two syndromes, the degree of external genital masculinization at birth does not seem to be related to gender role changes in a systematic way.

Mutation analysis of five candidate genes in Chinese patients with hypospadias

Hypospadias is the displacement of the urethral meatus from the tip of the glans to the ventral side of the phallus. During fetal development, SRY, SOX9, WT1, SRD5A2 and AR are important at different stages in the differentiation and development of the male genital system. Mutations in these genes impair masculinization and may be associated with hypospadias. In order to explore these possibilities, we employed polymerase chain reaction and direct sequencing to analyze the coding regions of these five genes in 90 Chinese hypospadias patients. We found a total of 16 different mutations in SRD5A2, AR and WT1 in 24 of these 90 patients. Seven mutations are novel. No mutation was found in SRY or SOX9. SNP V89L found in SRD5A2 was statistically significant between patients and controls. Our results indicated that mutations in SRD5A2, AR and WT1 were associated with hypospadias. In conclusion, mutations are frequently found in genes that control androgen action and metabolism, but are seldom found in genes active in the early phase of sex determination and differentiation. Mutations in AR, SRD5A2 or WT1 seem to be associated not only with hypospadias but also with micropenis.

New mutations, hotspots, and founder effects in Brazilian patients with steroid 5alpha-reductase deficiency type 2

Mutations of the steroid 5alpha-reductase type 2 (SRD5A2) gene in 46,XY subjects cause masculinization defects of varying degrees, due to reduced or impaired enzymatic activity. In this study, sequence abnormalities of the SRD5A2 gene were assessed by polymerase chain reaction with specific primers and automated sequencing analysis in DNA samples from 20 patients with suspected steroid 5alpha-reductase type 2 deficiency from 18 Brazilian families. Eleven subjects presented SRD5A2 homozygous single-base mutations (two first cousins and four unrelated patients with G183S, two with R246W, one with del642T, one with G196S, and one with 217_218insC plus the A49T variant in heterozygosis), whereas four were compound heterozygotes (one with Q126R/IVS3+1G>A, one with Q126R/del418T, and two brothers with Q126R/G158R). Three patients were heterozygous for A207D, G196S, and R266W substitutions. The V89L polymorphism was found in heterozygosis in one of them (with A207D) and in one case with an otherwise normal gene sequence. The A49T variant was also detected in heterozygosis in the second case without other sequencing abnormalities. Four patients harbor yet non-described SRD5A2 gene mutations: a single nucleotide deletion (del642T), a G158R amino acid substitution, a splice junction mutation (IVS3+1G>A), and the insertion of a cytosine (217_218insC) occurring at a CCCC motif. This is the first report of a single-nucleotide insertion in the coding sequence of the SRD5A2 gene. In addition to these new mutations, this investigation reveals the prevalence of G183S substitution among a subset of African-Brazilian patients and presents evidences of the recurrence of already known mutations.

5alpha-reductase 2 gene mutations in three unrelated patients of Greek Cypriot origin: identification of an ancestral founder effect

INTRODUCTION

5alpha-Steroid reductase deficiency (5alphaSRD) is an autosomal recessive enzymatic deficiency. Mutations in the 5alpha-steroid reductase type 2 gene (SRD5A2) result in male pseudohermaphroditism caused by decreased dihydrotestosterone (DHT) synthesis--a key hormone of virilization of male external genitalia.

AIM

To study for the first time patients from the Greek Cypriot population, describe their clinical characteristics, and identify the genetic mutations of the SRD5A2 gene.

PATIENTS AND METHODS

Three unrelated patients with 46,XY karyotype born with ambiguous genitalia were examined. Patient 1 was raised as a girl and was diagnosed with partial androgen insensitivity syndrome, based on the clinical picture and incomplete laboratory investigation at the age of 4 years, and underwent gonadectomy. For this patient sequencing analysis of all five exons of the SRD5A2 gene and exons 2 to 8 of the androgen receptor (AR) gene was performed. Patients 2 and 3 were also born with ambiguous genitalia. The hCG test for these two patients was informative of 5alphaSRD, as it showed elevated T/DHT ratio after stimulation. Despite genetic counseling, both families decided to raise their infants as females because of severe under-virilization. Sequencing of the SRD5A2 gene was also completed for both patients.

RESULTS

No mutations were found in the AR sequence for patient 1. Patients 1 and 3 were found homozygous for the mutation A/G at splice junction intron 1/exon 2 and patient 2 was found heterozygous for the same A/G substitution and also heterozygous for an additional mutation, Pro181Leu, in exon 3.

CONCLUSIONS

The same mutation in the SRD5A2 gene was identified in three unrelated patients, in both homozygous and heterozygous form. This splice mutation was previously reported in Turkish patients. This underlying genetic abnormality may be characteristic for the Eastern Mediterranean region and is likely due to an ancestor effect.

Gender identity in XY intersexuality

The following syndromes of XY intersexuality are reviewed: 5alpha-reductase-2 deficiency, 17beta-hydroxysteroid dehydrogenase-3 deficiency, and complete and partial androgen insensitivity with attention focused on issues of gender identity. Each syndrome, with its unique presentation, provides an opportunity to explore the relative effects of nature (androgens) versus nurture (sex of rearing) in gender identity development. The phenomenon of gender role reversal in these conditions is described and theories on the determinants of gender identity formation are proposed. Issues of importance to psychiatrists in treating patients who have these conditions also are discussed.

Molecular epidemiology of hypospadias: Review of genetic and environmental risk factors

Hypospadias is one of the most common congenital anomalies in the United States, occurring in approximately 1 in 125 live male births. It is characterized by altered development of the urethra, foreskin, and ventral surface of the penis. In this review, the embryology, epidemiology, risk factors, genetic predisposition, and likely candidate genes for hypospadias are described. Recent reports have identified increases in the birth prevalence of mild and severe forms of hypospadias in the United States from the 1960s to the present. Studies in consanguineous families and small case series have identified allelic variants in genes controlling androgen action and metabolism that cause hypospadias, but the relevance of these findings to the general population is unknown. Concern has also focused on whether exposure to endocrine disrupting chemicals (EDC) with antiandrogenic activity is the cause of this increase. Hypospadias is believed to have a multifactorial etiology in which allelic variants in genes controlling androgen action and metabolism predispose individuals to develop this condition. When genetic susceptibility is combined with exposure to antiandrogenic agents, a threshold is surpassed, resulting in the manifestation of this birth defect. A clear role for exposure to antiandrogenic environmental chemicals has yet to be established in the etiology of hypospadias, although results from laboratory animal models indicate that a number of environmental chemicals could be implicated. Molecular epidemiology studies that simultaneously examine the roles of allelic variants in genes controlling androgen action and metabolism, and environmental exposures are needed to elucidate the risk factors for these anomalies and the causes of the increased rate of hypospadias.

Molecular analysis of 5alpha-reductase type 2 gene in eight unrelated egyptian children with suspected 5alpha-reductase deficiency: prevalence of the G34R mutation

OBJECTIVE

Analysis of the 5alpha-reductase type 2 (SRD5A2) gene in Egyptian patients with suspected 5alpha-reductase (5alphaR) deficiency.

PATIENTS AND METHODS

Eight unrelated patients, originating from different geographical areas of Egypt, were referred to the Department of Pediatrics. Six prepubertal and two postpubertal patients presented with ambiguous genitalia. Four were being reared as females while the others were being reared as males. Six patients were products of consanguineous marriages. All patients had 46,XY karyotype. Basal and post-human chorionic gonadotrophin (hCG) stimulation plasma levels of testosterone and dihydrotestosterone were determined. Sequencing of five exons of the SRD5A2 gene was carried out.

RESULTS

All patients had normal male testosterone levels, both basal and post-hCG stimulation. The T/DHT ratio was available for six patients and showed values that ranged from normal to high. Three different homozygous mutations were identified. One patient carried a Y235F substitution and two had a N160D substitution. Interestingly, all five of the other patients had the G34R mutation. The parents were heterozygous for the mutations, although the mother of one patient was homozygous for the G34R mutation.

CONCLUSION

Among eight unrelated Egyptian children with 5alpha-reductase deficiency, the G34R mutation was identified in five patients. The high consanguinity rate in Egypt suggests a common ancestor with a founder gene effect in cases of G34R mutation.

Mutations of the 5alpha-steroid reductase type 2 gene in six Turkish patients from unrelated families and a large pedigree of an isolated Turkish village

We describe six Turkish patients with 5alpha-steroid reductase type 2 deficiency from unrelated Turkish families and a large pedigree of one of these patients who reside north-west of Anatolia. Patients NA, KS, BD and SY presented for evaluation of bilateral inguinal masses with female phenotypes. Patient ABE had penoscrotal hypospadias with male phenotype. Homozygous mutation of the 5alphaSR2 gene was identified in five of these patients by genomic DNA analysis. These mutations were Leu55Gln in exon 1 (in patients FG, BD and ABE), deltaMet157 in exon 3 (in patient NA), and splice junction abnormality in intron 1 (in patient SY). One individual (patient KS) was found to be a compound heterozygous carrier of two different mutations, Leu55Gln in exon 1 and Arg171Ser in exon 3. Patient FG had a large pedigree with the Leu55Gln mutation in exon 1. The pedigree of this family with marital consanguinity is remarkable, and possibly due to the isolation of this family because of economic and social problems. A further 85 individuals belonging to this family were analyzed for exon 1 Leu55Gln mutations in the 5alphaSR2 gene. Forty-two of these 85 individuals (49.41%) had this alteration; 11 were homozygous (8 genetic male, 3 genetic female) and 31 heterozygous (18 genetic male, genetic female) for this mutation. It was interesting to see asymptomatic homozygous female carriers. In conclusion, according to our results and those of other Turkish patients reported by different investigators, 5aSR2 gene mutation analysis, especially for Leu55Gln in exon 1 and deltaMet157 in exon 3, must be carried out in Turkish patients with male pseudohermaphroditism. Homozygous asymptomatic female carriers must be taken into consideration in this clinical entity, especially in a closed population, because of the risk of transmitting the disease to their offspring.

Evidence that steroid 5alpha-reductase isozyme genes are differentially methylated in human lymphocytes

The synthesis of dihydrotestosterone (DHT) is catalyzed by steroid 5alpha-reductase isozymes 1 and 2, and this function determines the development of the male phenotype during embriogenesis and the growth of androgen sensitive tissues during puberty. The aim of this study was to determine the cytosine methylation status of 5alpha-reductase isozymes types 1 and 2 genes in normal and in 5alpha-reductase deficient men. Genomic DNA was obtained from lymphocytes of both normal subjects and patients with primary 5alpha-reductase deficiency due to point mutations in 5alpha-reductase 2 gene. Southern blot analysis of 5alpha-reductase types 1 and 2 genes from DNA samples digested with HpaII presented a different cytosine methylation pattern compared to that observed with its isoschizomer MspI, indicating that both genes are methylated in CCGG sequences. The analysis of 5alpha-reductase 1 gene from DNA samples digested with Sau3AI and its isoschizomer MboI which recognize methylation in GATC sequences showed an identical methylation pattern. In contrast, 5alpha-reductase 2 gene digested with Sau3AI presented a different methylation pattern to that of the samples digested with MboI, indicating that steroid 5alpha-reductase 2 gene possess methylated cytosines in GATC sequences. Analysis of exon 4 of 5alpha-reductase 2 gene after metabisulfite PCR showed that normal and deficient subjects present a different methylation pattern, being more methylated in patients with 5alpha-reductase 2 mutated gene. The overall results suggest that 5alpha-reductase genes 1 and 2 are differentially methylated in lymphocytes from normal and 5alpha-reductase deficient patients. Moreover, the extensive cytosine methylation pattern observed in exon 4 of 5alpha-reductase 2 gene in deficient patients, points out to an increased rate of mutations in this gene.

Androgens, androgen receptors, and male gender role behavior

Studies of genetic males with single gene mutations that impair testosterone formation or action and consequently prevent development of the normal male phenotype provide unique insight into the control of gender role behavior. 46,XY individuals with either of two autosomal recessive mutations [17 beta-hydroxysteroid dehydrogenase 3 (17 beta-HSD3) deficiency or steroid 5 alpha-reductase 2 (5 alpha-R2) deficiency] have a female phenotype at birth and are raised as females but frequently change gender role behavior to male after the expected time of puberty. In contrast, genetic males with mutations that impair profoundly the function of the androgen receptor are also raised as females and have consistent female behavior as adults. Furthermore, the rare men with mutations that impair estrogen synthesis or the estrogen receptor have male gender role behavior. These findings indicate that androgens are important determinants of gender role behavior (and probably of gender identity) and that this action is mediated by the androgen receptor and not the result of conversion of androgen to estrogen. The fact that all genetic males with 17 beta-HSD3 or 5 alpha-R2 deficiency do not change gender role behavior indicates that other factors are also important determinants of this process.

Uniparental disomy in steroid 5alpha-reductase 2 deficiency

Steroid 5alpha-reductase 2 deficiency is an autosomal recessive form of male pseudohermaphroditism caused by mutations in the SRD5A2 gene. In this study, we performed DNA analyses in two unrelated subjects bearing the enzyme deficiency and found differences in the mode of transmission for the disease. The data showed that in both families the fathers were carriers for an E197D mutation, whereas the mothers were carriers for a P212R mutation. Patient 1 was identified as compound heterozygote because he had both alterations (E197D/P212R). On the contrary, patient 2 was found to be homozygous, but only for the paternal mutation. Because this finding could not be explained on the basis ofnonpaternity or a chromosomal abnormality, the presence of uniparental disomy was suggested. The reduction to homozygosity for the E197D mutation, as confirmed by restriction analysis, supported this view. The results of our study give evidence of the first case of 5alpha-reductase deficiency resulting from uniparental disomy and also disclose an alternate mechanism whereby this enzymatic disorder can derive from a single parent.

Partial sequencing and tissue distribution of the canine isoforms of steroid 5alpha-reductase type I and type II

BACKGROUND

The dog is regarded to be a valid model to test the effects of 5alpha-reductase inhibitors on prostatic growth. However, limited information is available on the characteristics or even existence of 5alpha-reductase isozymes in this species.

METHODS

Here, we set out to clone the cDNA of the dog isoforms of 5alpha-reductase type I and type II by a degenerate cloning strategy and to assess the tissue distribution of both transcripts and the enzymatic activity of the isozymes.

RESULTS

We identified two clones with homology to the human 5alpha-reductase isoforms type I and type II to be expressed in dog prostate. At the amino-acid level, these partial clones were found to exhibit a homology with their human counterparts of 83% and 88%, respectively. The expression levels of 5alpha-reductase mRNA were screened by RT-PCR in a number of dog tissues. No correlation was found between tissue mRNA expression and enzymatic 5alpha-reductase activities.

CONCLUSIONS

The present study describes the partial cloning of the dog 5alpha-reductase isozymes and their tissue distribution. These results provide additional data for the use of the dog as an animal model to investigate the role of 5alpha-reductase isozymes in steroid metabolism.

Identification of missense mutations in the SRD5A2 gene from patients with steroid 5alpha-reductase 2 deficiency

BACKGROUND AND OBJECTIVE

Mutations of the steroid 5alpha-reductase type 2 (SRD5A2) gene in karyotypic males result in a spectrum of external genitalia phenotypes ranging from complete female to nearly complete male. Here we performed genomic DNA analyses from individuals bearing the enzyme deficiency in order to detect the molecular abnormalities.

PATIENTS

Four unrelated 46,XY patients of Mexican origin with ambiguous external genitalia were studied. A fertile, phenotypically normal male was also included.

MEASUREMENTS

Coding sequence abnormalities of the SRD5A2 gene were assessed by exon-specific polymerase chain reaction, single-stranded conformational polymorphism and sequencing analysis.

RESULTS

Five different missense mutations (two of them novel mutations) were identified. Three subjects presented homozygous single base mutations. These were located at exon 2 (G115D), exon 4 (P212R) and exon 5 (R246Q), and such changes have been described previously. The fourth patient was a compound heterozygote who presented two mutations located in exons 1 and 2. We found a hitherto unreported G --> A transition at the second nucleotide of codon 85 in exon 1 (GGC --> GAC), substituting glycine for aspartic acid (G85D). This patient also presented an identical alteration at codon 115 of exon 2, which was carried by his father (G115D). Finally, in another subject who was included originally as a control, we found a C --> A transversion (yet undescribed) at codon 245 in exon 5 (S245Y).

CONCLUSIONS

Four different single base mutations that cause amino acid substitutions were detected in the steroid 5alpha-reductase type 2 gene of affected individuals. One patient and a normal control had two previously undescribed mutations. Although in the latter individual we cannot exclude the possibility that the base change is a genetic polymorphism, the molecular screening of 100 chromosomes suggests strongly that the change at codon 245 does represent a heterozygous mutation. Further studies, including the recreation of the mutations, will help to reveal the biochemical consequences resulting from these changes.

New frameshift mutation in the 5alpha-reductase type 2 gene in a Brazilian patient with 5alpha-reductase deficiency

Male pseudohermaphroditism caused by steroid 5alpha-reductase deficiency is an autosomal recessive disorder. The enzyme steroid 5alpha-reductase 2 (encoded by the SRD5A2 gene) catalyses the conversion of testosterone to dihydrotestosterone, which is required for normal differentiation of the external male genitalia. This report describes the molecular analysis of the 5alpha-reductase type 2 gene in a Brazilian patient who was raised as a female, underwent a reversal of gender role behavior, and is now a married man. This patient is a compound heterozygote bearing an A-->G mutation within exon 2, changing codon 126 from Glu to Arg on one allele and a novel single base deletion (418delT) causing a frameshift mutation at codon 140 in the same exon, on the other allele. This last mutation probably leads to the synthesis of a truncated protein, because a premature termination signal is created at codon 159.

Natural potent androgens: lessons from human genetic models

Male pseudohermaphroditism due to 17 beta-hydroxysteroid dehydrogenase-3 (17 beta-HSD-3) deficiency and 5 alpha-reductase-2 (5 alpha-RD-2) deficiency provides natural human genetic models to elucidate androgen actions. To date, five 17 beta-HSD isozymes have been cloned that catalyse the oxidoreduction of androstenedione and testosterone and dihydrotestosterone (DHT), oestrone and oestradiol. Mutations in the isozyme 17 beta-HSD-3 gene are responsible for male pseudohermaphroditism due to 17 beta-HSD deficiency. The type 3 isozyme preferentially catalyses the reduction of androstenedione to testosterone and is primarily expressed in the testes. Fourteen mutations in the 17 beta-HSD-3 gene have been identified from different ethnic groups. Affected males with the 17 beta-HSD-3 gene defect have normal wolffian structures but ambiguous external genitalia at birth. Many are raised as girls but virilize at the time of puberty and adopt a male gender role. Some develop gynaecomastia at puberty, which appears to be related to the testosterone/oestradiol ratio. Two 5 alpha-reductase (5 alpha-RD) isozymes, types 1 and 2, have been identified, which convert testosterone to the more potent androgen DHT. Mutations in the 5 alpha-RD-2 gene cause male pseudohermaphroditism, and 31 mutations in the 5 alpha-RD-2 gene have been reported from various ethnic groups. Such individuals also have normal wolffian structure but ambiguous external genitalia at birth and are raised as girls. Virilization occurs at puberty, often with a gender role change. The prostate remains infantile and facial hair is decreased. Balding has not been reported.

Codon 89 polymorphism of the human 5alpha-steroid reductase type 2 gene

The existence of a genetic polymorphism within the coding region of the human 5alpha-steroid reductase type 2 (5alpha-SR2) gene is reported in a Mexican population. Genotypic variation was assessed in 100 unrelated, healthy volunteers (50 males; 50 females), using single-stranded conformational polymorphism and direct sequencing analysis. Examination of exon 1 DNAs disclosed the presence of sequences encoding for valine (GTA) or leucine (CTA) at codon 89 of the gene. Of the subjects screened, 45% were homozygous for GTA (89Val), 50% had a heterozygous pattern GTA/CTA (89Val/89Leu) and the remaining 5% were homozygous for CTA (89Leu). These data support the view that the G/C condition at codon 89 of the 5alpha-SR2 gene represents a silent polymorphism which does not alter phenotypical development in the human.