CRISPR/Cas9 technology generated a glycine to glutamic acid substitution at amino acid 118 (p.G118E). This is a novel variant identified in a male with developmental delay, generalized hypotonia, motor planning difficulty and metatarsus adductus that developed seizures with age. Hemizygous males express RNA levels comparable to wild-type in the cortex but have an approximate 40% reduction in protein. (J:343257)