Monosomy of several genes as a results of partial or full chromosome arm deletion contributes to the development of a complex phenotype which makes diagnosis and possible therapy difficult. Our study explores if individuals with partial or full deletion of chromosome 18 short arm, resulting in the monosomy of SMCHD1 (and several other) gene, can develop facioscapulohumeral muscular dystrophy (FSHD). Digenic inheritance of SMCHD1 mutations and a specific chromosome 4 variant leads to the development of FSHD. We show that monosomy of SMCHD1, regardless of the other deleted genes on chromosome 18, together with a specific chromosome 4 variant leads to muscle  phenotype beside the known 18 p deletion features. (By Dr. Judit Balog, http://jmg.bmj.com/content/early/2018/03/21/jmedgenet-2017-105153 )