Epidemiology and Phenotypic Characteristics of Dual Molecular Diagnosis Cases in Skeletal Abnormality

Background Skeletal abnormality is a heterogeneous group of disorders that affects the composition and structure of bone and cartilage. In our previous studies, we have revealed that a substantial proportion of cases with early-onset scoliosis could be explained by monogenic disorders such as Marfan syndrome and Ehlers-Danlos syndrome. More recently complex phenotypes caused by more than one genetic defect (i.e., dual molecular diagnosis) have also been reported in skeletal abnormalities. To explore the molecular epidemiology and phenotypic characteristics of dual diagnosis in skeletal abnormalities, we described cases with dual molecular diagnosis from the Deciphering disorders Involving Scoliosis and COmorbidities (DISCO) study.Results In total, 1108 patients with skeletal abnormality from the DISCO study underwent Exome Sequencing. We identified eight probands with dual molecular diagnosis, including three (0.7%) from individuals with early-onset scoliosis (EOS), three (0.5%) from individuals with short stature, and two (2%) from individuals with congenital hand/foot deformity (CHFA). Other skeletal abnormalities observed in these individuals included bone fracture and interphalangeal joint contracture. All the eight probands have dual diagnosis of two autosomal dominant (AD) diseases. A total of 16 variants in 12 genes were identified. A substantial rate (5 of 10) of the identified causal variants were of de novo origin. The frequently observed molecular diagnoses (observed in more than one patient) include Osteogenesis Imperfecta Type I (COL1A1, MIM:166200), Neurofibromatosis, Type I (NF1, MIM:162200) and Marfan Syndrome (FBN1, MIM:154700). These patients with dual molecular diagnosis often present blended phenotypes of two diseases, which significantly complicate their diagnostic process. Conclusions This study revealed the molecular epidemiology and complex diagnostic odyssey of dual molecular diagnosis through analyzing the clinical traits of skeletal abnormalities in eight patients.