X-Linked Spinal Muscular Atrophy 2 due to a Synonymous Variant in the Gene in a Family with Novel Findings from Turkey.

Spinal muscular atrophy, X-linked 2 (SMAX2) is a rare type of spinal muscular atrophy characterized by muscle weakness, hypotonia, areflexia, myopathic face, tongue fibrillations, contractures, bone fractures, and cryptorchidism. Variants of the gene lead to SMAX2. The gene encodes a protein that activates the ubiquitin pathway which is responsible for protein degradation. Here, we describe a family presenting with hypotonia, muscle weakness, areflexia, contractures, weak cry, in association with other anomalies including myopathic face, scoliosis, tongue fibrillations, and cryptorchidism. Molecular analysis in 2 patients revealed a hemizygous pathogenic variant in the gene (NM_153280.3, NP_695012.1: c.1731C>T [p.Asn577Asn]) inherited from their carrier mothers. Our study presents the first patients from Turkey, widening the phenotypic spectrum of SMAX2 by pectus carinatum, medullary sponge kidney, and frontal cyst.