Co-occurrence of an HSPG2 Missense Variant and Functional Polymorphisms in Atypical Schwartz–Jampel Syndrome Type 1 with Obesity: A Case Report

Schwartz–Jampel syndrome type 1 (SJS1) is an autosomal recessive chondrodystrophic myotonia, linked to heparan sulfate proteoglycan 2 (HSPG2) variants. We describe a patient with typical features of SJS1, but not obesity. Clinical exome sequencing detected a rare missense variant in HSPG2, confirming our clinical diagnosis, but also two homozygous variants in SDC3 and ADRB3 genes, previously described to be associated with obesity. This additional genetic result could better explain our patient's phenotype. Despite the phenotypic variability associated to HSPG2 variants, it is advisable to carefully check other possible genetic causes underlying clinical signs not strictly related to the classical phenotype of SJS1.