ADSS1 and myopathy: First described in 2016 by Park and colleagues in a small cohort of Korean patients clinically presenting with distal muscle weakness [1], ADSS1 myopathy is an inborn error of metabolism caused by autosomal recessive mutations of the ADSS1 gene, which encodes a striated muscle-specific isoform of adenylosuccinate synthetase (ADSS1).