Clinical Variability and Genotype-Driven Outcomes in CHRND-Related Congenital Myasthenic Syndrome.
BACKGROUND: Congenital myasthenic syndromes (CMS) caused by pathogenic variants in CHRND, encoding the δ-subunit of the nicotinic acetylcholine receptor (AChR), are rare, and data on genotype-phenotype correlations and long-term outcomes are limited. METHODS: We performed a retrospective, multicenter study of nine patients with genetically confirmed CHRND-related CMS from specialized neuromuscular centers. Clinical, electrophysiological, genetic, and therapeutic data were systematically collected. All diagnoses were established by exome sequencing during routine clinical work-up. RESULTS: Eight patients were compound heterozygous and one was homozygous for pathogenic CHRND variants, including nonsense, missense, splice-site variants, and one microdeletion. Disease onset ranged from the neonatal period (n = 7) to adolescence (n = 2). Three patients were followed longitudinally for 22-43 years. Ocular involvement, particularly ptosis and ophthalmoparesis, was present in all patients. Generalized fatigable weakness was common, whereas bulbar and respiratory involvement occurred in a subset and reflected overall disease severity. Genotypes including a null allele or a homozygous missense variant tended to be associated with more severe phenotypes, while compound heterozygous missense variants were linked to a broader and generally milder spectrum, sometimes limited to ocular symptoms. Long-term outcomes ranged from minimal symptoms under therapy to severe motor impairment with respiratory insufficiency, highlighting substantial interindividual variability. CONCLUSIONS: This study expands the phenotypic and genotypic spectrum of CHRND-related CMS and underscores the critical role of genotype in determining disease severity. Comprehensive genetic testing, longitudinal phenotyping, and genotype-informed management are essential for optimal diagnosis and care in this rare disorder.