CASE PRESENTATION: Five patients with female phenotypes presented in early adulthood with primary amenorrhoea with varying degrees of puberty. One was tall with breast development. Another was very short with clitoromegaly and multiple co-morbidities. The other three had no secondary sexual characteristics. They were examined, after which hormonal profile, karyotyping, ultrasound examination and magnetic resonance imaging were done to assess the site of gonads. Gonadectomy was performed once their 46 XY karyotype was confirmed. Results of histopathological examination of their gonads ranged from dysgenetic gonads to having testicular tissues and malignancy.

OBJECTIVE: We sought to investigate the incidence of gene mosaicism in patients with PIDs.

METHODS: The amplicon-based deep sequencing method was used in the 3 parts of the study that establish (1) the allele frequency of germline variants (n = 100), (2) the incidence of parental gonosomal mosaicism in families with PIDs with de novo mutations (n = 92), and (3) the incidence of mosaicism in families with PIDs with moderate-to-high suspicion of gene mosaicism (n = 36). Additional investigations evaluated body distribution of postzygotic mutations, their stability over time, and their characteristics.

RESULTS: The range of allele frequency (44.1% to 55.6%) was established for germline variants. Those with minor allele frequencies of less than 44.1% were assumed to be postzygotic. Mosaicism was detected in 30 (23.4%) of 128 families with PIDs, with a variable minor allele frequency (0.8% to 40.5%). Parental gonosomal mosaicism was detected in 6 (6.5%) of 92 families with de novo mutations, and a high incidence of mosaicism (63.9%) was detected among families with moderate-to-high suspicion of gene mosaicism. In most analyzed cases mosaicism was found to be both uniformly distributed and stable over time.