Genetic Architecture of Azoospermia-Time to Advance the Standard of Care.

BACKGROUND: Crypto- and azoospermia (very few/no sperm in the semen) are main contributors to male factor infertility. Genetic causes for spermatogenic failure (SPGF) include Klinefelter syndrome and Y-chromosomal azoospermia factor microdeletions, and CFTR mutations for obstructive azoospermia (OA). However, the majority of cases remain unexplained because monogenic causes are not analysed. OBJECTIVE: To elucidate the monogenic contribution to azoospermia by prospective exome sequencing and strict application of recent clinical guidelines. DESIGN, SETTING, AND PARTICIPANTS: Since January 2017, we studied crypto- and azoospermic men without chromosomal aberrations and Y-chromosomal microdeletions attending the Centre of Reproductive Medicine and Andrology, Münster. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: We performed exome sequencing in 647 men, analysed 60 genes having at least previous limited clinical validity, and strictly assessed variants according to clinical guidelines. RESULTS AND LIMITATIONS: Overall, 55 patients (8.5%) with diagnostic genetic variants were identified. Of these patients, 20 (3.1%) carried mutations in CFTR or ADGRG2, and were diagnosed with OA. In 35 patients (5.4%) with SPGF, mutations in 20 different genes were identified. According to ClinGen criteria, 19 of the SPGF genes now reach at least moderate clinical validity. As limitations, only one transcript per gene was considered, and the list of genes is increasing rapidly so cannot be exhaustive. CONCLUSIONS: The number of diagnostic genes in crypto-/azoospermia was almost doubled to 21 using exome-based analyses and clinical guidelines. Application of this procedure in routine diagnostics will significantly improve the diagnostic yield and clinical workup as the results indicate the success rate of testicular sperm extraction. PATIENT SUMMARY: When no sperm are found in the semen, a man cannot conceive naturally. The causes are often unknown, but genetics play a major role. We searched for genetic variants in a large group of patients and found causal mutations for one in 12 men; these predict the chances for fatherhood.

Sequence Variants in TBX6 Are Associated with Disorders of the Müllerian Ducts: An Update.

Müllerian anomalies comprise the Mayer-Rokitansky-Küster-Hauser syndrome as well as fusion defects of the müllerian ducts. Recurrent micro-aberrations like deletions in 16p11.2 encompassing TBX6 were found to be causative in these patients. TBX6 encodes a transcription factor which plays a role in paraxial mesoderm differentiation/specification. In previous studies, we and other groups found possibly pathogenic variants in TBX6 in patients with müllerian anomalies. Since we suggested TBX6 as a strong candidate, we performed sequential analysis of the TBX6 gene in additional 125 patients with müllerian anomalies, and 2 possibly pathogenic missense variants and 1 nonsense substitution in TBX6 in 4/125 patients were found. The missense variant c.484G>A, which we have described in a previous study, was reidentified but with no higher frequency as in our controls. We detected 3 possibly pathogenic variants in TBX6 and could show that the variant c.484G>A is not causative for disorders of the müllerian ducts in the non-Finnish European population. In summary, we present increasing evidence for association of variants in TBX6 with malformations of the müllerian ducts.

Four Novel NR5A1 Mutations in 46,XY Gonadal Dysgenesis Patients Including Frameshift Mutations with Altered Subcellular SF-1 Localization.

46,XY gonadal dysgenesis (46,XY GD) is a disorder of sexual development caused by mutations in genes involved in early gonadal development (bipotential gonads) and testis differentiation. In 46,XY GD individuals, mutations of the SRY gene are detected most frequently, followed by mutations in the NR5A1 (SF-1) gene, but in a lot of cases, the underlying molecular mechanism remains elusive. In this study, we retrospectively performed sequence analyses of the NR5A1 (SF-1) gene in 84 patients with complete, partial, and syndromic forms of 46,XY GD. In total, 7 heterozygous mutations were found in 6 of 84 patients (7.1%). Among these, we identified 4 mutations that, to the best of our knowledge, have not been reported before (c.268G>T, c.369del, c.871-1G>C, and c.893T>C). Transfection of different mutations revealed altered subcellular localization of the mutant SF-1 protein in the case of the frameshift mutations, indicating an impaired protein function. In conclusion, we present 4 novel mutations of the NR5A1 gene associated with 46,XY GD together with in vitro data pointing towards a possible functional impairment of the mutant SF-1 proteins.

Variations in RBM8A and TBX6 are associated with disorders of the müllerian ducts.

OBJECTIVE: To identify genetic causes of malformations of the müllerian ducts. DESIGN: Retrospective laboratory study. SETTING: University hospital. PATIENT(S): A total of 167 patients with disorders of the müllerian ducts: 116 patients with Mayer-Rokitansky-Küster-Hauser syndrome and 51 patients with fusion disorders of the müllerian ducts. The control group was composed of 94 fertile women with at least one child. INTERVENTION(S): Sequential analysis of RBM8A and TBX6 in a group of 167 clinically well-defined patients with disorders of the müllerian ducts. MAIN OUTCOME MEASURE(S): Identification of rare variants in RBM8A and TBX6. RESULT(S): In total, we detected four RBM8A variants in 13 patients with disorders of the müllerian ducts and two heterozygous TBX6 variants in 5 of 167 patients. CONCLUSION(S): Mutations of RBM8A and TBX6 are associated with disorders of the müllerian ducts.

DMRT1 mutations are rarely associated with male infertility.

OBJECTIVE: To study a potential association between male infertility and DMRT1 mutations. DESIGN: Retrospective sequencing study. SETTING: University hospital. PATIENT(S): 171 patients with cryptozoospermia (sperm concentration<0.1 million/mL, n=40) or nonobstructive azoospermia (n=131), and 215 normozoospermic controls. INTERVENTION(S): Sequence analysis of DMRT1. MAIN OUTCOME MEASURE(S): Identification of rare variants in DMRT1 that are associated with male infertility. RESULT(S): In total, we detected four putative pathogenic mutations in six patients (3.5%) and less frequently in two controls (0.9%). CONCLUSION(S): Point mutations of DMRT1 may be rarely associated with male infertility.

Comprehensive sequence analysis of the NR5A1 gene encoding steroidogenic factor 1 in a large group of infertile males.

The steroidogenic factor 1 (SF1) protein, encoded by the NR5A1 gene, plays a central role in gonadal development and steroidogenesis. Mutations in NR5A1 were first described in patients with primary adrenal insufficiency and 46,XY disorders of sexual development and later also in men with hypospadias, bilateral anorchia and micropenis and women with primary ovarian insufficiency. Recently, heterozygous missense mutations were found in 4% of infertile men with unexplained reduced sperm counts living in France, but all mutation carriers were of non-Caucasian ancestry. Therefore, we performed a comprehensive NR5A1 sequence analysis in 488 well-characterised predominantly Caucasian patients with azoo- or severe oligozoospermia. Two-hundred-thirty-seven men with normal semen parameters were sequenced as controls. In addition to several synonymous variants of unclear pathogenicity, three heterozygous missense mutations predicted to be damaging to SF1 protein function were identified. The andrological phenotype in infertile but otherwise healthy mutation carriers seems variable. In conclusion, mutations altering SF1 protein function and causing spermatogenic failure are also found in men of German origin, but the prevalence seems markedly lower than in other populations.