What causes paramyotonia in the United Kingdom? Common and new SCN4A mutations revealed.

OBJECTIVE

To study the clinical and genetic features in a large cohort of UK patients with sodium channel paramyotonia congenita.

METHODS

We conducted a UK-wide clinical and molecular genetic study of patients presenting with a phenotype suggestive of paramyotonia congenita.

RESULTS

We identified 42 affected individuals (28 kindreds). All cases met our core criteria for a clinical diagnosis of paramyotonia congenita. Seventy-five percent of patients (32 patients/20 kindreds) had SCN4A mutations. Twenty-nine subjects from 18 kindreds had exon 22 and 24 mutations, confirming these exons to be hot spots. Unexpectedly, 3 of these subjects harbored mutations previously described with potassium-aggravated myotonia (G1306A, G1306E). We identified two new mutations (R1448L and L1436P). Ten cases (8 kindreds) without mutations exhibited paramyotonia congenita with prominent pain and weakness.

CONCLUSIONS

This study identifies two new mutations, confirms SCN4A as a common cause of paramyotonia congenita in the UK, and suggests further allelic and possibly genetic heterogeneity.