A Novel Nonsense Mutation in HSD17B3 Gene in a Tunisian Patient with Sexual Ambiguity

Molecular mechanisms underlying the defects of two novel mutations in the HSD17B3 gene found in the Tunisian population

17β-hydroxysteroid dehydrogenase type 3 (17β-HSD3) converts Δ4-androstene-3,17-dione (androstenedione) to testosterone. It is expressed almost exclusively in the testes and is essential for appropriate male sexual development. More than 70 mutations in the HSD17B3 gene that cause 17β-HSD3 deficiency and result in 46,XY Disorders of Sex Development (46,XY DSD) have been reported. This study describes three novel Tunisian cases with mutations in HSD17B3. The first patient is homozygous for the previously reported mutation p.C206X. The inheritance of this mutation seemed to be independent of consanguineous marriage, which can be explained by its high frequency in the Tunisian population. The second patient has a novel splice site mutation in intron 6 at position c.490 -6 T > C. A splicing assay revealed a complete omission of exon 7 in the resulting HSD17B3 mRNA transcript. Skipping of exon 7 in HSD17B3 is predicted to cause a frame shift in exon 8 that affects the catalytic site and results in a truncation in exon 9, leading to an inactive enzyme. The third patient is homozygous for the novel missense mutation p.K202M, representing the first mutation identified in the catalytic tetrad of 17β-HSD3. Site-directed mutagenesis and enzyme activity measurements revealed a completely abolished 17β-HSD3 activity of the p.K202M mutant, despite unaffected protein expression, compared to the wild-type enzyme. Furthermore, the present study emphasizes the importance of genetic counselling, detabooization of 46,XY DSD, and a sensitization of the Tunisian population for the risks of consanguineous marriage.

Disorder of Sex Development Due to 17-Beta-Hydroxysteroid Dehydrogenase Type 3 Deficiency: A Case Report and Review of 70 Different HSD17B3 Mutations Reported in 239 Patients

The 17-beta-hydroxysteroid dehydrogenase type 3 (17-β-HSD3) enzyme converts androstenedione to testosterone and is encoded by the HSD17B3 gene. Homozygous or compound heterozygous HSD17B3 mutations block the synthesis of testosterone in the fetal testis, resulting in a Disorder of Sex Development (DSD). We describe a child raised as a female in whom the discovery of testes in the inguinal canals led to a genetic study by whole exome sequencing (WES) and to the identification of a compound heterozygous mutation of the HSD17B3 gene (c.608C>T, p.Ala203Val, and c.645A>T, p.Glu215Asp). Furthermore, we review all HSD17B3 mutations published so far in cases of 17-β-HSD3 deficiency. A total of 70 different HSD17B3 mutations have so far been reported in 239 patients from 187 families. A total of 118 families had homozygous mutations, 63 had compound heterozygous mutations and six had undetermined genotypes. Mutations occurred in all 11 exons and were missense (55%), splice-site (29%), small deletions and insertions (7%), nonsense (5%), and multiple exon deletions and duplications (2%). Several mutations were recurrent and missense mutations at codon 80 and the splice-site mutation c.277+4A>T each represented 17% of all mutated alleles. These findings may be useful to those involved in the clinical management and genetic diagnosis of this disorder.

The novel founder homozygous V225M mutation in the HSD17B3 gene causes aberrant splicing and XY-DSD

PURPOSE

Mutations in the gene HSD17B3 encoding the 17-beta hydroxysteroid dehydrogenase 3 enzyme cause testosterone insufficiency leading to XY disorders of sex development. In this study the clinical and molecular characteristics of three patients from consanguineous families are elucidated.

METHODS

We identified three patients from two unrelated families with XY DSD and a novel homozygous HSD17B3:c. 673G>A mutation. The effect of the mutation on splicing was determined in RNA extracted from the testis of one patient.

RESULTS

Three patients presented at ages 0.1, 8 and 0.7 years with ambiguous genitalia and an XY Karyotype. Endocrine workup showed normal cortisol and mineralocorticoid levels with a low testosterone/androstenedione ratio. Whole-exome sequencing, carried out in the first family, revealed a homozygous novel mutation in the HSD17B3 gene: c. 673G>A, p. V225M. The same mutation was found by Sanger sequencing in the third unrelated patient. Haplotype analysis of a 4 Mb region surrounding the HSD17B3 gene on chromosome 9 revealed that the mutation resides on the same allele in all three patients. The mutation, being the first nucleic acid on exon 10, affects splicing and causes exon 10 skipping in one of our patients' testes.

CONCLUSION

The novel homozygous c. 673G>A, p. V225M mutation in the 17HSDB3 gene is likely a founder mutation and causes severe XY-DSD. It changes a conserved amino acid residue, and also alters 17HSDB3 gene transcription by causing skipping of exon 10, thereby contributing to an imbalance in the relevant protein isoforms and consequently, significant decreased 17HDSB3 enzymatic activity.

Genomic evidence sheds light on the genetic mechanisms of musk secretion in muskrats

Adult male muskrat (Ondatra zibethicus) has a pair of scent glands which secret musk to attract females during the breeding stage. The goal of the present study was to investigate the genetic mechanisms of musk secretion of muskrats at the whole genome level. Comparative genomics illustrated obvious expansion in 809 gene families, of which nine gene families played pivotal roles in steroid biosynthesis, possibly related to muskrat musk secretion. We identified 1112 positively selected genes (PSGs) in the muskrat, including estrogen receptor 1 (ER1), an important influencing factor to the weight and size of the scented glands of muskrats. HSD17B3, HSD17B4, CYP7B1 and CYP17B1, crucial to steroid hormone biosynthesis, were under strong positive selection in the muskrat, and phylogenetic analysis of HSD and CYP450 classes revealed high gene diversity. Functional enrichment revealed many pathways associated with musk secretion and/or growth and degeneration of scented gland significantly, such as peroxisome, PI3K-Akt signaling pathway, apoptosis, and prostate cancer. Two muskrat-specific missense mutations (Pro237Thr and Ser297Ile) were detected in LIPC, which were reported to be involved cholesterol metabolic process. More importantly, the missense mutations discovered in LIPC were classified as deleterious by PolyPhen-2, possibly affecting the musk secretion of muskrats.

Pig Hsd17b3: Alternative splice variants expression, insertion/deletion (indel) in promoter region and their associations with male reproductive traits

Hydroxysteroid 17-Beta Dehydrogenase 3 (Hsd17b3), primarily expressed in Leydig cells (LCs) of the mammalian testes, is essential for testosterone biosynthesis and male fertility. The aim of our study was to profile the expression, splice variants (SV) and novel insertion/deletion (indel) of Hsd17b3 in boars. Quantitative analysis showed that the expression level of Hsd17b3 in the testis was significantly highest. Among different testicular cell types, the Hsd17b3 mRNA expression level of LCs was significantly higher than that of SSCs (spermatogonial stem cells) and SCs (Sertoli cells). Furthermore, the SV was firstly identified in pigs and it was highly expressed in LCs comparing with SSCs and SCs. In addition, two mutations were identified in pig Hsd17b3 gene promotor and intron, respectively, which were associated with male reproductive traits (P <  0.05). In conclusion, both transcripts of Hsd17b3 gene were highly expressed in pig testes and LCs; the two novel indel variants of Hsd17b3 gene can be used as potential DNA makers for the marker-assisted selection in pigs. All these findings would enrich the study of Hsd17b3 gene in pig genetic breeding.

Development of 17β-hydroxysteroid dehydrogenase type 3 as a target in hormone-dependent prostate cancer therapy

17β-Hydroxysteroid dehydrogenase type 3 (17β-HSD3) is expressed almost exclusively in the testes and specifically converts the weak androgenic androstenedione to active testosterone (T) in the presence of NADPH. Additionally, studies have demonstrated that 17β-HSD3 is over-expressed in hormone-dependent prostate cancer. T, which interacts with the androgen receptor (AR), eventually stimulates the growth of prostate cancer cells. Defects in T synthesis or action impair the development of the male phenotype during embryogenesis and cause the autosomal recessive disorder male pseudohermaphroditism. Affected individuals are often born with female-appearing external genitalia and are reared as females. Since 17β-HSD3 plays a central role in T production, it has been recognized as a promising therapeutic target to reduce the circulating level of androgens and to suppress androgen-sensitive tumor proliferation. In recent decades, improvements have been made in the development of 17β-HSD3 inhibitors. Herein, we give an overview of the main structure and function of human 17β-HSD3 and summarize steroidal and non-steroidal inhibitors of 17β-HSD3, which can be a potential target for prostate cancer.

Novel cases of Tunisian patients with mutations in the gene encoding 17β-hydroxysteroid dehydrogenase type 3 and a founder effect

17β-Hydroxysteroid dehydrogenase type 3 (17β-HSD3) is expressed almost exclusively in the testis and converts Δ4-androstene-3,17-dione to testosterone. Mutations in the HSD17B3 gene causing 17β-HSD3 deficiency are responsible for a rare recessive form of 46, XY Disorders of Sex Development (46, XY DSD). We report novel cases of Tunisian patients with 17β-HSD3 deficiency due to previously reported mutations, i.e. p.C206X and p.G133R, as well as a case with the novel compound heterozygous mutations p.C206X and p.Q176P. Moreover, the previously reported polymorphism p.G289S was identified in a heterozygous state in combination with a novel non-coding variant c.54G>T, also in a heterozygous state, in a male patient presenting with micropenis and low testosterone levels. The identification of four different mutations in a cohort of eight patients confirms the generally observed genetic heterogeneity of 17β-HSD3 deficiency. Nevertheless, analysis of DNA from 272 randomly selected healthy controls from the same geographic area (region of Sfax) revealed a high carrier frequency for the p.C206X mutation of approximately 1 in 40. Genotype reconstruction of the affected pedigree members revealed that all p.C206X mutation carriers harbored the same haplotype, indicating inheritance of the mutation from a common ancestor. Thus, the identification of a founder effect and the elevated carrier frequency of the p.C206X mutation emphasize the importance to consider this mutation in the diagnosis and genetic counseling of affected 17β-HSD3 deficiency pedigrees in Tunisia.

Biochemical analyses and molecular modeling explain the functional loss of 17β-hydroxysteroid dehydrogenase 3 mutant G133R in three Tunisian patients with 46, XY Disorders of Sex Development

Mutations in the HSD17B3 gene resulting in 17β-hydroxysteroid dehydrogenase type 3 (17β-HSD3) deficiency cause 46, XY Disorders of Sex Development (46, XY DSD). Approximately 40 different mutations in HSD17B3 have been reported; only few mutant enzymes have been mechanistically investigated. Here, we report novel compound heterozygous mutations in HSD17B3, composed of the nonsense mutation C206X and the missense mutation G133R, in three Tunisian patients from two non-consanguineous families. Mutants C206X and G133R were constructed by site-directed mutagenesis and expressed in HEK-293 cells. The truncated C206X enzyme, lacking part of the substrate binding pocket, was moderately expressed and completely lost its enzymatic activity. Wild-type 17β-HSD3 and mutant G133R showed comparable expression levels and intracellular localization. The conversion of Δ4-androstene-3,17-dione (androstenedione) to testosterone was almost completely abolished for mutant G133R compared with wild-type 17β-HSD3. To obtain further mechanistic insight, G133 was mutated to alanine, phenylalanine and glutamine. G133Q and G133F were almost completely inactive, whereas G133A displayed about 70% of wild-type activity. Sequence analysis revealed that G133 on 17β-HSD3 is located in a motif highly conserved in 17β-HSDs and other short-chain dehydrogenase/reductase (SDR) enzymes. A homology model of 17β-HSD3 predicted that arginine or any other bulky residue at position 133 causes steric hindrance of cofactor NADPH binding, whereas substrate binding seems to be unaffected. The results indicate an essential role of G133 in the arrangement of the cofactor binding pocket, thus explaining the loss-of-function of 17β-HSD3 mutant G133R in the patients investigated.

A Novel Mutation Causing 17-β-Hydroxysteroid Dehydrogenase Type 3 Deficiency in an Omani Child: First Case Report and Review of Literature

This is the first case report in Oman and the Gulf region of a 17-β-hydroxysteroid dehydrogenase type 3 (17-β-HSD3) deficiency with a novel mutation in the HSD17B3 gene that has not been previously described in the medical literature. An Omani child was diagnosed with 17-β-HSD3 deficiency and was followed up for 11 years at the Pediatric Endocrinology Clinic, Royal Hospital, Oman. He presented at the age of six weeks with ambiguous genitalia, stretched penile and bilateral undescended testes. Ultrasound showed no evidence of any uterine or ovarian structures with oval shaped solid structures in both inguinal regions that were confirmed by histology to be testicular tissues with immature seminiferous tubules only. The diagnosis was made by demonstrating low serum testosterone and high androstenedione, estrone, and androstenedione:testosterone ratio. Karyotyping confirmed 46,XY and the infant was raised as male. Testosterone injections (25mg once monthly) were given at two and six months and then three months before his surgeries at five and seven years of age when he underwent multiple operations for orchidopexy and hypospadias correction. At the age of 10 years he developed bilateral gynecomastia (stage 4). Laboratory investigations showed raised follicle-stimulating hormone, luteinizing hormone, androstenedione, and estrone with low-normal testosterone and low androstendiol glucurunide. Testosterone injections (50mg once monthly for six months) were given that resulted in significant reduction in his gynecomastia. Molecular analysis revealed a previously unreported homozygous variant in exon eight of the HSD17B3 gene (NM_000197.1:c.576G>A.Trp192*). This variant creates a premature stop codon, which is very likely to result in a truncated protein or loss of protein production. This is the first report in the medical literature of this novel HSD17B3 gene mutation. A literature review was conducted to identify the previous studies related to this disorder.