Distal spinal muscular atrophy (DSMA) is also known as distal hereditary motor neuronopathy (dHMN or HMN). Properly, DSMA refers to the autosomal recessive forms of HMN: DSMA1 (IGHMBP2 mutations), DSMA2, DSMA3 (no identified genes) and DSMA4 (PLEKHG5 mutations).
HMN showing autosomal dominant inheritance include distal HMN types I and II (HMN2A and HMN2B), characterized by juvenile and adult onset, respectively; HMN type V (HMN5), characterized by upper limb involvement; and HMN VII (HMN7A and HMN7B), with vocal cord paralysis. HMN2A is caused by mutation in the HSPB8 gene, HMN2B by mutation in the HSPB1 gene and HMN2C by mutation in the HSPB3 gene. A distal hereditary motor neuronopathy with pyramidal features has been classified as ALS4, due to mutations in the SETX gene. There are also an X-linked form (SMAX3, ATP7A gene mutations) and a congenital autosomal dominant form (TRPV4 gene mutations).
HMN showing autosomal dominant inheritance include distal HMN types I and II (HMN2A and HMN2B), characterized by juvenile and adult onset, respectively; HMN type V (HMN5), characterized by upper limb involvement; and HMN VII (HMN7A and HMN7B), with vocal cord paralysis. HMN2A is caused by mutation in the HSPB8 gene, HMN2B by mutation in the HSPB1 gene and HMN2C by mutation in the HSPB3 gene. A distal hereditary motor neuronopathy with pyramidal features has been classified as ALS4, due to mutations in the SETX gene. There are also an X-linked form (SMAX3, ATP7A gene mutations) and a congenital autosomal dominant form (TRPV4 gene mutations).
