Novel MBTPS1 Variants and Cutis Laxa Phenotype in the 8th Reported Case of Spondyloepiphyseal Dysplasia, Kondo-Fu Type

Spondyloepiphyseal dysplasia, Kondo-Fu (SEDKF) type is a rare skeletal dysplasia caused by biallelic variants in MBTPS1. To date, only seven SEDKF cases have been reported in the literature. Here, we report the eighth, a 20-year-old male presenting with severe disproportionate short stature, spondyloepiphyseal dysplasia, and the previously unreported feature of cutis laxa, which led to the clinical suspicion of geroderma osteodysplasica. Whole exome sequencing identified compound heterozygosity for a predicted splicing variant and a complete gene deletion in the patient. Functional validation using RNA splicing assays confirmed aberrant splicing, establishing the molecular diagnosis of SEDKF. This case broadens the clinical and molecular spectrum of MBTPS1-related disorders by presenting a novel combination of variants and phenotypic features.