Compound heterozygous variants in MYBPC1 lead to severe distal arthrogryposis type-1 manifestations

Dominant missense variants in MYBPC1 encoding slow Myosin Binding Protein-C (sMyBP-C) have been increasingly linked to arthrogryposis syndromes and congenital myopathy with tremor. Herein, we describe novel compound heterozygous variants - NM_002465.4:[c.2486_2492del];[c.2663A > G] - present in fibronectin-III (Fn-III) C7 and immunoglobulin (Ig) C8 domains, respectively, manifesting as severe, early-onset distal arthrogryposis type-1, with the carrier requiring intensive care and several surgical interventions at an early age. Computational modeling predicts that the c.2486_2492del p.(Lys829IlefsTer7) variant destabilizes the structure of the Fn-III C7 domain, while the c.2663A > G p.(Asp888Gly) variant causes minimal structural alterations in the Ig C8 domain. Although the parents of the proband are heterozygous carriers for a single variant, they exhibit no musculoskeletal defects, suggesting a complex interplay between the two mutant alleles underlying this disorder. As emerging novel variants in MYBPC1 are shown to be causatively associated with musculoskeletal disease, it becomes clear that MYBPC1 should be included in relevant genetic screenings.