A novel SLC35D1 variant causing milder phenotype of Schneckenbecken dysplasia in a large pedigree.

SLC35D1 gene encodes UDP-glucuronic acid/UDP-n-acetylgalactosamine dual transporter protein and transports organic or inorganic molecules across cellular membranes. SLC35D1 gene pathogenic variants causes Schneckenbecken dysplasia (SHNKND) which is a rare lethal autosomal recessive disorder characterized by the snail-like pelvis, flattening of vertebral bodies, short and broad long bones with a dumbbell-like appearance, thoracic hypoplasia. Only six cases with homozygous SLC35D1 variants have been reported to date, and all of these cases were lost in the perinatal period. Here we report different family members with a novel SLC35D1 variant who presented a milder phenotype of SHNKND. The affected patients have common clinical features such as short stature, mild mesomelia, shortening of the lower extremity, genu valgum, and narrow thorax. Exome sequencing of the proband revealed a homozygous missense variant of SLC35D1 gene, c.401 T > C (p. Met134Thr). The affected siblings, their two cousins, and their paternal uncle with a similar phenotype were also homozygous for the variant. This is the first case report of a family with a novel likely pathogenic variant (p. Met134Thr) and mild phenotypic features. It has the largest family with different ages of patients (ages ranged 4-31 years old) reported to date. The present report supports the evidence that the p. Met134Thr variant is responsible for a milder phenotype than previously reported cases with SLC35D1 pathogenic variants.