Study of Ras/MAPK pathway gene variants in Chilean patients with Cryptorchidism

Undiagnosed RASopathies in infertile men

RASopathies are syndromes caused by congenital defects in the Ras/mitogen-activated protein kinase (MAPK) pathway genes, with a population prevalence of 1 in 1,000. Patients are typically identified in childhood based on diverse characteristic features, including cryptorchidism (CR) in >50% of affected men. As CR predisposes to spermatogenic failure (SPGF; total sperm count per ejaculate 0-39 million), we hypothesized that men seeking infertility management include cases with undiagnosed RASopathies. Likely pathogenic or pathogenic (LP/P) variants in 22 RASopathy-linked genes were screened in 521 idiopathic SPGF patients (including 155 CR cases) and 323 normozoospermic controls using exome sequencing. All 844 men were recruited to the ESTonian ANDrology (ESTAND) cohort and underwent identical andrological phenotyping. RASopathy-specific variant interpretation guidelines were used for pathogenicity assessment. LP/P variants were identified in PTPN11 (two), SOS1 (three), SOS2 (one), LZTR1 (one), SPRED1 (one), NF1 (one), and MAP2K1 (one). The findings affected six of 155 cases with CR and SPGF, three of 366 men with SPGF only, and one (of 323) normozoospermic subfertile man. The subgroup "CR and SPGF" had over 13-fold enrichment of findings compared to controls (3.9% vs. 0.3%; Fisher's exact test, p = 5.5 × 10-3). All ESTAND subjects with LP/P variants in the Ras/MAPK pathway genes presented congenital genitourinary anomalies, skeletal and joint conditions, and other RASopathy-linked health concerns. Rare forms of malignancies (schwannomatosis and pancreatic and testicular cancer) were reported on four occasions. The Genetics of Male Infertility Initiative (GEMINI) cohort (1,416 SPGF cases and 317 fertile men) was used to validate the outcome. LP/P variants in PTPN11 (three), LZTR1 (three), and MRAS (one) were identified in six SPGF cases (including 4/31 GEMINI cases with CR) and one normozoospermic man. Undiagnosed RASopathies were detected in total for 17 ESTAND and GEMINI subjects, 15 SPGF patients (10 with CR), and two fertile men. Affected RASopathy genes showed high expression in spermatogenic and testicular somatic cells. In conclusion, congenital defects in the Ras/MAPK pathway genes represent a new congenital etiology of syndromic male infertility. Undiagnosed RASopathies were especially enriched among patients with a history of cryptorchidism. Given the relationship between RASopathies and other conditions, infertile men found to have this molecular diagnosis should be evaluated for known RASopathy-linked health concerns, including specific rare malignancies.

CAG and GGN repeat polymorphisms in the androgen receptor gene of a Chilean pediatric cohort with idiopathic inguinal cryptorchidism

BACKGROUND

Cryptorchidism is one of the most common congenital disorders in boys and it is associated with a higher risk of sub-fertility and testicular cancer. Testicular descent occurs during embryo-fetal development in two phases, transabdominal and inguino-scrotal. In the latter process, androgens play a leading role. The androgen receptor has in its N-terminal domain, two aminoacidic repeats encoded by polymorphic nucleotide repetitions: (CAG)nCAA and GGN. The number of repetitions of these trinucleotides has been associated with different transactivation capacities and sensitivities of the androgen receptor response.

OBJECTIVE

To determine whether pediatric Chilean individuals with idiopathic inguinal cryptorchidism have a different number of CAG and/or GGN repeats polymorphisms compared with controls.

MATERIALS AND METHODS

A total of 109 cases with idiopathic inguinal cryptorchidism (26 bilateral and 83 unilateral) were studied by polymerase chain reaction amplification from DNA extracted from peripheral blood, followed by fragment size analysis by capillary electrophoresis, which were compared with 140 controls.

RESULTS

The CAG26 repeats allele was increased in the total cases (8.3% vs. 1.4%; p = 0.012; odds ratio = 6.21, 95% confidence interval 1.31-29.4), and in bilateral cases compared to controls (11.5% vs. 1.4%; p = 0.028; odds ratio = 9 CI 95% 1.43-56.8). Similarly, CAG > 22 alleles were increased in the total cases (62.4% vs. 49.3%, p = 0.041), and more significantly in bilateral cases (73.1% vs. 49.3%; p = 0.032; odds ratio = 2.79, 95% confidence interval 1.1-7.1). In addition, CAG < 18 alleles were not observed among cases, but were present in 5.7% of controls (p = 0.01). Regarding the GGN repeats, no differences were observed between cases and controls either when analyzing separately unilateral and bilateral cryptorchidism. The joint analysis of the distribution of CAG and GGN alleles showed that the CAG26 allele was present with GGN23, hence the combination CAG26/GGN23 alleles was equally increased in bilateral cases compared with controls (11.5% vs. 1.4%). In contrast, CAG < 18 was preferably observed in the combination CAG < 18/GGN≠23 and was absent in the total cases (4.3% vs. 0%; p = 0.037).

DISCUSSION

These results suggest that greater lengths of CAG alleles may contribute to a diminished androgen receptor function. The CAG26 allele alone or in combination with GGN23 was associated with a higher risk of bilateral cryptorchidism. On the other hand, CAG < 18 and the CAG < 18/GGN≠23 allele combination may reduce the probability of cryptorchidism.

NR5A1 c.991-1G > C splice-site variant causes familial 46,XY partial gonadal dysgenesis with incomplete penetrance

OBJECTIVE

The study aimed to identify the genetic basis of partial gonadal dysgenesis (PGD) in a non-consanguineous family from Estonia.

PATIENTS

Cousins P (proband) 1 (12 years; 46,XY) and P2 (18 years; 46,XY) presented bilateral cryptorchidism, severe penoscrotal hypospadias, low bitesticular volume and azoospermia in P2. Their distant relative, P3 (30 years; 46,XY), presented bilateral cryptorchidism and cryptozoospermia.

DESIGN

Exome sequencing was targeted to P1-P3 and five unaffected family members.

RESULTS

P1-P2 were identified as heterozygous carriers of NR5A1 c.991-1G > C. NR5A1 encodes the steroidogenic factor-1 essential in gonadal development and specifically expressed in adrenal, spleen, pituitary and testes. Together with a previous PGD case from Belgium (Robevska et al 2018), c.991-1G > C represents the first recurrent NR5A1 splice-site mutation identified in patients. The majority of previous reports on NR5A1 mutation carriers have not included phenotype-genotype data of the family members. Segregation analysis across three generations showed incomplete penetrance (<50%) and phenotypic variability among the carriers of NR5A1 c.991-1G > C. The variant pathogenicity was possibly modulated by rare heterozygous variants inherited from the other parent, OTX2 p.P134R (P1) or PROP1 c.301_302delAG (P2). For P3, the pedigree structure supported a distinct genetic cause. He carries a previously undescribed likely pathogenic variant SOS1 p.Y136H. SOS1, critical in Ras/MAPK signalling and foetal development, is a strong novel candidate gene for cryptorchidism.

CONCLUSIONS

Detailed genetic profiling facilitates counselling and clinical management of the probands, and supports unaffected mutation carriers in the family for their reproductive decision making.