LINE1-mediated epigenetic repression of androgen receptor transcription causes androgen insensitivity syndrome

Androgen insensitivity syndrome (AIS) is a difference of sex development (DSD) characterized by different degrees of undervirilization in individuals with a 46,XY karyotype despite normal to high gonadal testosterone production. Classically, AIS is explained by hemizygous mutations in the X-chromosomal androgen receptor (AR) gene. Nevertheless, the majority of individuals with clinically diagnosed AIS do not carry an AR gene mutation. Here, we present a patient with a 46,XY karyotype, born with undervirilized genitalia, age-appropriate testosterone levels and no uterus, characteristic for AIS. Diagnostic whole exome sequencing (WES) showed a maternally inherited LINE1 (L1) retrotransposon insertion in the 5' untranslated region (5'UTR) of the AR gene. Long-read nanopore sequencing confirmed this as an insertion of a truncated L1 element of ≈ 2.7 kb and showed an increased DNA methylation at the L1 insertion site in patient-derived genital skin fibroblasts (GSFs) compared to healthy controls. The insertion coincided with reduced AR transcript and protein levels in patient-derived GSFs confirming the clinical diagnosis AIS. Our results underline the relevance of retrotransposons in human disease, and expand the growing list of human diseases associated with them.