The impact of PYROXD1 deficiency on cellular respiration and correlations with genetic analyses of limb-girdle muscular dystrophy in Saudi Arabia and Sudan.

Next generation sequencing is commonly used to screen for pathogenic mutations in families with Mendelian disorders, but due to the pace of discoveries, gaps have widened for some diseases between genetic and pathophysiological knowledge. We recruited and analyzed 16 families with limb-girdle muscular dystrophy (LGMD) of Arab descent from Saudi Arabia and Sudan who did not have confirmed genetic diagnoses. The analysis included both traditional and next generation sequencing approaches. Cellular and metabolic studies were performed on Pyroxd1 siRNA C2C12 myoblasts and controls. Pathogenic mutations were identified in 8 of the 16 families. One Sudanese family of Arab descent residing in Saudi Arabia harbored a homozygous c.464A>G, p.Asn155Ser mutation in PYROXD1, a gene recently reported in association with myofibrillar myopathy and whose protein product reduces thiol residues. Pyroxd1 deficiency in murine C2C12 myoblasts yielded evidence for impairments of cellular proliferation, migration, and differentiation. Similar results were obtained with overexpression of p.Asn155Ser mutant human PYROXD1 in C2C12 myoblasts. Knockdown of CG10721 (Pyroxd1 fly homologue) in Drosophila yielded a lethal phenotype. Further investigations indicated that Pyroxd1 does not localize to mitochondria, yet Pyroxd1 deficiency is associated with decreased cellular respiration. This study identified pathogenic mutations in half of the LGMD families from the cohort, including one in PYROXD1. Developmental impairments were demonstrated in vitro for Pyroxd1 deficiency and in vivo for CG10721 deficiency, with reduced metabolic activity in vitro for Pyroxd1 deficiency.