Child Neurology: KMT2B -Related Dystonia in a Young Child With Worsening Gait Abnormality

Abstract

KMT2B gene related dystonia (DYT-KMT2B) is a primarily childhood onset movement disorder that usually starts with lower limb dystonia progressing into generalized dystonia. Our patient described here experienced difficulty gaining weight, laryngomalacia and feeding difficulties during infancy and later developed gait difficulties, frequent falls and toe walking. Gait assessment revealed prominent bilateral intoeing and intermittent ankle inversion posturing, as well as extension of left leg. At times, the gait appeared to be spastic. Whole exome sequencing revealed a novel de novo heterozygous likely pathogenic variant, c.7913 T>A (p.V2638E), in the KMT2B gene located in chromosome 19. This variant, which has not been previously published as pathogenic or benign in the literature, can be added to the repertoire of KMT2B mutations causing inherited dystonias.