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

SRD5A2 gene polymorphisms affect the risk of breast cancer

Androgens in breast cancer have been studied alone and in correlation with estrogens as estrogen to testosterone ratio. 5-α-reductase is one of the important enzymes participating in androgen metabolism, which affects androgen activity by affecting conversion of testosterone to dihydrotestosterone. We hypothesized that polymorphisms in the SRD5A2 gene (encoding 5-α-reductase) may affect breast cancer risk by affecting total androgen activity. Complete coding region of the SRD5A2 gene was sequenced in a group of 628 patients and 244 control samples from three southern states (Tamil Nadu, Andhra Pradesh, and Karnataka) of India. We observed three common polymorphisms in this gene; namely, A49T, V89L, and (TA)n repeats. A49T locus was monomorphic in the study population, but V89L showed a strong correlation with breast cancer (P = 0.03, OR = 1.40, CI = 1.02-1.91). (TA)0/(TA)9 and (TA)9/(TA)9 genotypes were at a lower risk of breast cancer (P = 0.01, OR = 0.64, CI = 0.46-0.90). We conclude that SRD5A2 genotypes significantly affect breast cancer risk in the South Indian populations.

CYP17, SRD5A2, CYP1B1, and CYP2D6 gene polymorphisms with prostate cancer risk in North Indian population

To investigate the involvement of the CYP17, SRD5A2, CYP1B1, and CYP2D6 variants with prostate cancer, a case-control study of 100 patients and an equal number of age-matched control men was conducted. There appears to be a nonsignificant increase with risk of prostate cancer for individuals carrying one copy of the CYP17 A2 allele (OR, 1.80; 95% CI, 0.99-3.29, P=0.05). The risk was increased in individuals having two A2 alleles (OR; 2.81, 95% CI, 1.06-7.40, P=0.03). Compared with men having the VV genotype of SRD5A2 gene, there was no significant association between the VL genotype and the risk of prostate cancer (OR; 0.54, 95% CI; 0.29-1.03, P=0.06). There was no difference in the occurrence of the genotype LL between controls and prostate cancer patients (OR; 0.90, 95% CI; 0.43-1.89, P=0.79). There was a nonsignificant increased risk of prostate cancer for individuals carrying the CYP1B1Leu/Val genotype (OR, 1.70, 95% CI, 0.91-3.17, P =0.09), which was increased in those having the Val/Val allele (OR, 3.38; 95% CI, 1.13-10.07, P=0.02). Relative to men homozygous for the wild-type allele in CYP2D6 gene, those heterozygous for the B allele had an odds ratio of 1.78 (95% CI, 0.76-4.17, P=0.18) for patients, and for homozygous individuals, it was 1.95 (0.55-6.93, P=0.30). These observations have suggested that the CYP17 A2/A2, CYP1B1 Val/Val, and CYP2D6 genotypes may be associated with an altered risk of prostate cancer, while the CYP2D6 and SRD5A2 V89L polymorphism have no association with its risk in the North Indian population.

Polymorphic changes in the KAL1 gene: not all of them should be classified as polymorphisms

The KAL1 gene has a closely related nonfunctional pseudogene on the Y chromosome; a high degree of X-Y sequence similarity is observed. Some individuals present a T to C substitution at position 1833 (exon 12). Because this nucleotide differs in the X (thymine) and in the Y (cytosine) chromosome, we investigated if this was truly a polymorphism, or if in some cases the Y sequence had been amplified. The complete sequence of exon 12 of KAL1 was analyzed in 11 Kallmann Syndrome (KS) males, in 50 normal males, in 50 normal females, and in 16 patients with Ullrich-Turner Syndrome (UTS). Nucleotide 1833 was found in a heterozygous or a homozygous state in KS, normal males and normal females; UTS patients were always homozygous. Of the 61 males, 17 were heterozygous, while 11 were TT and 33 were CC. With these observations we can not assure whether these patients present a "real" polymorphism. Besides, all males were heterozygous in nucleotides 1678, 1694, 1699, 1708 and 1825, whilst females were homozygous; and in these positions, KAL1 also differs from its pseudogene. These results indicate that we are identifying the X and the Y nucleotide and these variants are not polymorphisms. Sequence variations may be pseudogene products rather than true polymorphisms, so we should always determine if the position where the variation is located differs between KAL1 and its pseudogene, because it has been suggested that the presence of various polymorphisms in affected individuals could be the cause of KS.

Analysis of genetic polymorphisms of steroid 5alpha-reductase type 1 and 2 genes in Korean men with androgenetic alopecia

BACKGROUND

Genetic polymorphisms of steroid 5alpha-reductase have been studied in androgenetic alopecia in Caucasians, but the genes encoding the two isoenzymes were not associated with male pattern baldness. Genetic polymorphisms and ethnic variations have not been studied for Asians, although it is suggested that racial difference could exist and influence clinical phenotypes.

OBJECTIVE

The purpose of our study is to investigate the genetic polymorphisms of steroid 5alpha-reductase type 1 and 2 (SRD5A1 and SRD5A2) genes in Korean population, and to study the association of these polymorphisms with the development, clinical types (female or male pattern) and therapeutic response of androgenetic alopecia.

METHODS

Sixty-six patients with androgenetic alopecia and controls consisted of 92 healthy men were included. Twenty-four patients were treated with finasteride for at least 6 months, and clinical responses were assessed by a simple classification. For type 1 isoenzyme, HinfI and NspI restriction fragment length polymorphisms (RFLPs) were detected using polymerase chain reaction method. For type 2 isoenzyme, RsaI RFLPs detected valine/leucine polymorphisms at codon 89, and MowI RFLPs detected alanine/threonine polymorphisms at codon 49.

RESULTS

We could not find any significant associations of the genetic polymorphisms of these two isoenzyme genes with androgenetic alopecia in Koreans (P>0.05). These polymorphisms were not associated with the clinical types of baldness or the response to finasteride (P>0.05).

CONCLUSION

These results suggest that polymorphisms of SRD5A1 and SRD5A2 genes may not be directly associated with the development of baldness or generation of different clinical phenotypes.

Impact of genetic polymorphisms of 17-hydroxylase cytochrome P-450 (CYP17) and steroid 5alpha-reductase type II (SRD5A2) genes on prostate-cancer risk among the Japanese population

Steroid hormones, especially testosterone, play important roles in the carcinogenesis of prostate cancer, and several studies have reported changes in risk with polymorphisms of genes involved in steroid metabolism. One example is the CYP17 gene, which has a polymorphic T-to-C substitution in the 5'-untranslated region giving rise to A1 (T) and A2 (C) alleles. Steroid 5alpha-reductase type II (SRD5A2), which converts testosterone to the metabolically more active dihydrotestosterone, exhibits 2 polymorphisms: V89L, which substitutes leucine for valine at codon 89, and A49T, which substitutes threonine for alanine at codon 49. We therefore designed a case-control study of 105 prostate-cancer patients and 210 controls with benign prostatic hyperplasia for the purpose of investigating the association between prostate-cancer risk and polymorphisms in the SRD5A2 and CYP17 genes among the Japanese. The frequency of the CYP17 A2/A2 genotype in cases (18.8%) was higher than in controls (14.5%). Compared with the A1/A1 genotype, the odds ratio for the A2/A2 genotype was 2.39 (95% confidence interval 1.04-5.46, p = 0.04). The frequency of the SRD5A2 LL genotype in cases (29.3%) was also slightly higher than in controls (24.6%), but this was not significant. Regarding the A49T polymorphism of SRD5A2, we could not detect the T allele in any of the examined samples. These data suggest a significant association between the CYP17 polymorphism and prostate-cancer risk among the Japanese.

Novel molecular defects in the androgen receptor gene of Mexican patients with androgen insensitivity

The androgen insensitivity syndrome (AIS) is an X-linked form of male pseudohermaphroditism caused by mutations in the androgen receptor (AR) gene. In the present study, we analyzed the AR gene in 8 patients, 4 sporadic and 2 familial cases with the syndrome, using exon-specific polymerase chain reaction, single-stranded conformational polymorphism and sequencing analysis and identified six new single base mutations, including one nonsense mutation at the hinge region of the receptor. These molecular lesions occurred in the steroid-binding domain (SBD) and all but one affected the first nucleotide of their respective codons. A nonsense mutation in exon 4, which converts a glutamine into a premature termination signal (Q657stop), a missense mutation changing arginine instead of glycine (G743R) and a conservative substitution of leucine with valine at amino acid 830 (L830V) were detected in patients with CAIS. Three other missense mutations located in exons 4 (L701I), 5 (A765S), and 6 (Q802R) were present in individuals bearing a partial form of AIS. These data allow us to reaffirm the view that nonsense mutations in the AR results almost invariably in a CAIS phenotype and underly the importance of the SBD for the AR functional activity.

Codon 89 polymorphism in the human 5 alpha-reductase gene in primary breast cancer

The enzyme human steroid 5-alpha reductase type II (SRD5A2) and androgen receptor (AR) are critical mediators of androgen action, suggesting a potential role in hormonally related cancers. The SRD5A2 gene harbours two frequent polymorphic sites, one in the coding region, at codon 89 of exon 1, where valine is substituted by leucine (V89L) and the other in the 3' untranslated region (3' UTR) where a variable number of dinucleotide TA repeat lengths exists. The V89L polymorphism is known to alter the activity of this enzyme. In the present study we examined 144 sporadic breast tumours from Italian patients for the V89L and TA polymorphisms by sequence and fragment analysis, respectively. Tumour extract prostate specific antigen (PSA) concentration as well as a number of well-established clinical and pathological parameters were evaluated. The results show that 53% of the tumours were homozygous for VV alleles, 37% were heterozygous for VL alleles and 10% were homozygous for LL alleles. TA(0) repeats were found in tumours with VV, LL and VL genotypes. TA(9) repeats were only found in VV homozygotes and were totally absent from either LL homozygotes or VL heterozygotes. PSA expression was significantly elevated in tumours with VV genotype. The presence of LL alleles in breast tumours is associated with earlier onset and shorter disease-free (RR = 2.65;P = 0.013) and overall survival (RR = 3.06;P = 0.014) rates. The VV genotype is associated with a more favourable prognosis. Our study suggests that the polymorphism in codon 89 of exon 1 of the human 5 alpha-reductase gene is related with TA repeat genotypes, PSA expression and breast cancer prognosis. More specifically, we found that the LL genotype is also associated with earlier onset and more aggressive forms of breast cancer. Long-term-outcome studies are needed to investigate the relevance of this polymorphism to breast cancer susceptibility.

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.

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.