Clinical and electrophysiological features of SCN8A variants causing episodic or chronic ataxia.

BACKGROUND: Variants in SCN8A are associated with a spectrum of epilepsies and neurodevelopmental disorders. Ataxia as a predominant symptom of SCN8A variation has not been well studied. We set out to investigate disease mechanisms and genotype-phenotype correlations of SCN8A-related ataxia. METHODS: We collected genetic and electro-clinical data of ten individuals from nine unrelated families carrying novel SCN8A variants associated with chronic progressive or episodic ataxia. Electrophysiological characterizations of these variants were performed in ND7/23 cells and cultured neurons. FINDINGS: Variants associated with chronic progressive ataxia either decreased Na+ current densities and shifted activation curves towards more depolarized potentials (p.Asn995Asp, p.Lys1498Glu and p.Trp1266Cys) or resulted in a premature stop codon (p.Trp937Ter). Three variants (p.Arg847Gln and biallelic p.Arg191Trp/p.Asp1525Tyr) were associated with episodic ataxia causing loss-of-function by decreasing Na+ current densities or a hyperpolarizing shift of the inactivation curve. Two additional episodic ataxia-associated variants caused mixed gain- and loss-of function effects in ND7/23 cells and were further examined in primary murine hippocampal neuronal cultures. Neuronal firing in excitatory neurons was increased by p.Arg1629His, but decreased by p.Glu1201Lys. Neuronal firing in inhibitory neurons was decreased for both variants. No functional effect was observed for p.Arg1913Trp. In four individuals, treatment with sodium channel blockers exacerbated symptoms. INTERPRETATION: We identified episodic or chronic ataxia as predominant phenotypes caused by variants in SCN8A. Genotype-phenotype correlations revealed a more pronounced loss-of-function effect for variants causing chronic ataxia. Sodium channel blockers should be avoided under these conditions. FUNDING: BMBF, DFG, the Italian Ministry of Health, University of Tuebingen.

Improving recognition of Duchenne muscular dystrophy: a retrospective case note review.

BACKGROUND: Over the last 30 years, there has been little improvement in the age of diagnosis of Duchenne muscular dystrophy (DMD) (mean age of 4.5-4.11 years). AIM: To review the diagnostic process for DMD in boys without a family history in order to identify where delays occur and suggest areas for improvement. DESIGN: A retrospective case note review. SETTING: A tertiary centre for neuromuscular diseases in England. PATIENTS: All boys without family history diagnosed with DMD in the last 10 years (n=20). OUTCOME MEASURES: Mean age at four key steps in the diagnostic pathway of DMD. RESULTS: (1) Age at first reported symptoms of DMD was 32.5 (8-72) months (2.7 years). (2) First engagement of a healthcare professional was at 42.9 (10-90) months. (3) Creatine kinase (CK) levels were checked at 50.1 (14-91) months. (4) Diagnosis of DMD was confirmed at 51.7 (16-91) months (4.3 years). The total delay from parental concern to diagnosis was 19.2 (4-50) months (1.6 years). CONCLUSIONS: Our study shows an improvement in the age of diagnosis of DMD although there continues to be a delay in presentation to a health professional and a delay in obtaining a CK test. To reduce these delays, we propose screening for DMD as part of the Child Health Surveillance Programme, in addition to lowering the threshold for CK testing in primary care by promoting a new DMD mnemonic MUSCLE. An earlier diagnosis of DMD will allow timely access to genetic counselling, standards of care and clinical trials.