Clinical and genetic features of congenital myasthenic syndrome due to the muscle acetylcholine receptor genes

Objective

The adult nicotinic acetylcholine receptor in muscle is a pentameric complex composed of four transmembrane subunits, and these are encoded by CHRNA1, CHRNB1, CHRND, and CHRNE, respectively. There were only a few case reports of congenital myasthenic syndromes due to CHRNA1, CHRNB1, and CHRND. We aimed to share phenotypic and genotypic features of the patients.

Methods

The clinical features, genetic variants, treatment, and follow-up of congenital myasthenic syndromes patients due to CHRNA1, CHRNB1, CHRND and CHRNE were retrospectively reviewed. In addition, a questionnaire-based survey using pediatric quality of life inventory 3.0 neuromuscular module (PedQL™3.0NMM) was conducted on the caregivers.

Results

Fourteen patients were enrolled in this study. The variants in CHRNE were the most prevalent (42.9 %), followed by variants in CHRNA1(21.4 %), CHRND (21.4 %), and CHRNB1 (14.3 %), respectively. Symptoms presented at birth in 10 patients (71.4 %) and during infancy in the remaining four patients (28.6 %). The patients due to CHRNA1, CHRNB1, and CHRND had an earlier onset(p = 0.01). The initial clinical feature in 6 patients with CHRNE variants was ptosis. In the patients with CHRNA1, CHRNB1, and CHRND variants, the most common initial presentation was feeding difficulties in 6 of 8. Pyridostigmine was beneficial in 12 (92.3 %) patients. Salbutamol was then tried in 10 patients, and only two patients stopped it for no more effects. The mean score of PedQL™3.0 in 10 patients under therapy was 76.50 ± 11.66.

Conclusions

All patients had very early onset, and most had ocular, limb, and bulbar symptoms. The patients due to CHRNA1, CHRNB1, and CHRND had an early age at onset and more severe initial symptoms. Most of the patients got some benefit from therapy and had satisfactory results of the life quality survey.