A truncating variant in the THOC6 gene with new findings in a patient with Beaulieu-Boycott-Innes syndrome.

Beaulieu-Boycott-Innes syndrome (BBIS; MIM#613680) is a rare, autosomal recessive neurodevelopmental genetic disorder associated with pathogenic variants in the THOC6 gene (*615403). Intellectual disability, dysmorphic facial features, developmental delay, structural cardiac and genitourinary anomalies, and dental caries are suggestive findings of the syndrome. Exome sequencing (ES) may facilitate the diagnosis of this syndrome, whose clinical features can be nonspecific. Here we report a BBIS patient with a homozygous truncating variant (NM_024339.5:c.299G>A; p.Trp100Ter) in the THOC6 gene, diagnosed by ES analysis. The patient's variant is novel and some features such as clivus dysplasia, occult spina bifida, tapered fingers, and upturned fleshy earlobes have not been reported in the literature before. This new case report will expand the knowledge of BBIS and provide more information about the genetic variants and phenotypic spectrum. Also, new cases with THOC6 variants will define the core clinical features and common phenotypes of the BBIS over time.