Salih myopathy and Feingold syndrome type 1 caused by the TTN and MYCN mutation in an infant with congenital hypotonia

Salih myopathy (SALMY)—also known as early-onset myopathy with fetal cardiomyopathy—is an autosomal recessive, sporadic motor developmental disorder caused by recessive mutations in the TTN gene. The TTN gene is located on chromosome 2q31.2 and encodes proteins essential for striated muscle function. Affected individuals often present with muscle weakness during the neonatal period or early infancy, delayed motor development, joint and neck contractures, spinal rigidity, scoliosis, and cardiac dysfunction. Feingold syndrome type 1 (FGLDS1) is an autosomal dominant, sporadic neurodevelopmental disorder caused by a heterozygous mutation in the MYCN gene located on chromosome 2p24.1. The MYCN gene is a transcription factor that regulates neurogenesis and differentiation. The syndrome’s clinical features include digital, renal, and cardiac abnormalities, microcephaly, facial dysmorphism, gastrointestinal atresia, and intellectual disability. We report describes a 19-month-old Korean female presenting with compound heterozygous TTN mutations, c.46816_46820delinsCAATGGTTTT (p.E15606fs) and c.104724_104731dup (p.Y34911fs) and a de novo MYCN mutation, c.853C>T (p.R285W) identified through whole genome sequencing. She presented with congenital heart defects, general hypotonia, macrocephaly, facial dysmorphism, distal arthrogryposis, intellectual disability, and developmental delay. This is the first reported case of concurrent SALMY and FGLDS1 attributable to TTN and MYCN mutations.