First report of THOC6 related intellectual disability (Beaulieu Boycott Innes syndrome) in two siblings from India

Abstract

THOC6 is a newly described causal gene for an autosomal recessive intellectual disability (ID) - Beaulieu Boycott Innes syndrome (BBIS) (OMIM # 613680). It is characterized by ID with dysmorphic facies, genitourinary, cardiac anomalies, and dentition problems. Here, we report the first two siblings of BBIS from the Indian subcontinent with previously unreported skeletal anomalies such as Sprengel shoulder, calcaneo valgus deformity, radioulnar dysostosis, and overlapping toes. Whole exome sequencing (WES) identified previously reported three missense variants (p.Trp100Arg, p.Val234Leu, p.Gly275Asp) in THOC6. THOC6 is a subunit of TRanscription and EXport (TREX) complex involved in mRNA transcription, processing, and nuclear export of spliced mRNAs and has a potential role in neurodevelopment. Till date, only 12 patients with BBIS have been reported. This report reviews the phenotypic and genetic data of known BBIS cases in addition to the new phenotypic features, thereby expanding the phenotype of this rare syndrome.

Keywords: Beaulieu boycott innes syndrome; Chromosomal microarray; Intellectual disability; THOC6; Whole exome sequencing.