RESUMO
Congenital myasthenic syndromes (CMS) are a group of inherited disorders caused by mutations in genes encoding proteins essential for neuromuscular transmission. CMS is characterized by fatigable muscle weakness with onset at birth or in early childhood; rarely, symptoms may present later. The most frequently involved proteins are choline acetyltransferase, the endplate species of acetylcholinesterase and the acetylcholine receptor subunits. Defects in the cholinergic receptor nicotinic delta subunit (CHRND) are a rare cause for CMS but they should be considered in patients with a severe, early onset disease, with respiratory distress. We describe two sisters, clinically and genetically diagnosed with CMS, carrying two heteroallelic variants in the CHRND gene: c.730C>T; p.(Arg244Cys) and c.1304T>C; p.(Leu435Pro). The first variant has already been described yet no clinical relevance has been proved; the second one, is a novel variant documented here for the first time. These two cases expand the clinical spectrum of CMS linked to CHRND mutations.