Novel RNF113A Variant Underlying X-Linked Trichothiodystrophy With Presumed Mosaicism in an Unaffected Mother

This case report describes two brothers in their 30s with a novel hemizygous variant c.635G>A p.Gly212Asp in the RNF113A gene, associated with X-linked trichothiodystrophy (TTD). The brothers exhibit features consistent with TTD, such as intellectual disability, microcephaly, growth failure, dysmorphic features, severe myopia, and a tiger-tail banding pattern in their hair. However, they do not show endocrinological abnormalities, recurrent infections, genital abnormalities, or abnormal MRI findings, indicating these are not universal features of RNF113A-related TTD. The variant was not found in their mother's tested tissues, suggesting she may have low-level somatic or germline mosaicism. This case underscores the importance of genetic counseling and reproductive testing for families with presumed de novo variants.