Novel COLQ mutation 950delC in synaptic congenital myasthenic syndrome and symptomatic heterozygous relatives.

The synaptic form of congenital myasthenic syndrome (CMS) is a rare autosomal recessive disease affecting neuromuscular transmission. Mutations in the COLQ gene that encodes the collagenic tail subunit (ColQ) of asymmetric acetylcholinesterase lead to endplate acetylcholinesterase deficiency. We report two children suffering from synaptic CMS due to two compound heterozygous COLQ mutations, IVS1-1G>A and a novel mutation, 950delC. Furthermore, we found familial occurrence of congenital ptosis in heterozygous carriers of 950delC, mimicking a dominant negative effect. Considering the lack of a clear genotype-phenotype-relation in synaptic CMS, several authors speculated on the influence of additional modifying factors. Consequently, involvement of such factors in this report of familial congenital ptosis cannot be excluded.