No abstract

The pathomechanism of familial hypokalemic periodic paralysis (HypoPP) is a mystery, despite knowledge of the underlying dominant point mutations in the dihydropyridine receptor (DHPR) voltage sensor. In five HypoPP families without DHPR gene defects, we identified two mutations, Arg-672→His and →Gly, in the voltage sensor of domain 2 of a different protein: the skeletal muscle sodium channel α subunit, known to be responsible for hereditary muscle diseases associated with myotonia. Excised skeletal muscle fibers from a patient heterozygous for Arg-672→Gly displayed depolarization and weakness in low-potassium extracellular solution. Slowing and smaller size of action potentials were suggestive of excitability of the wild-type channel population only. Heterologous expression of the two sodium channel mutations revealed a 10-mV left shift of the steady-state fast inactivation curve enhancing inactivation and a sodium current density that was reduced even at potentials at which inactivation was removed. Decreased current and small action potentials suggested a low channel protein density. The alterations are decisive for the pathogenesis of episodic muscle weakness by reducing the number of excitable sodium channels particularly at sustained membrane depolarization. The results prove that SCN4A, the gene encoding the sodium channel α subunit of skeletal muscle is responsible for HypoPP-2 which does not differ clinically from DHPR-HypoPP. HypoPP-2 represents a disease caused by enhanced channel inactivation and current reduction showing no myotonia.

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is a hereditary angiopathy caused by mutations in the NOTCH3 gene. The clinical course is highly variable. Little is known about the long-term prognosis and the causes of death in CADASIL patients. Likewise, the impact of gender and NOTCH3 genotype on disease progression remains largely unexplored. We identified 411 subjects (196 men, 215 women) with a definite diagnosis of CADASIL. Age at onset for stroke, immobilization and death as well as the causes of death and clinical status at onset of the cause of death were determined systematically. Weibull regression models were used to calculate times to event, with gender and NOTCH3 genotype as covariates. At the time of the study, 73 patients had died. The median age at onset for stroke was 50.7 years [95% confidence interval (CI) = 48.2-53.1 years] in men and 52.5 years (95% CI = 50.0-54.9 years) in women (P = n.s.). The median ages at onset for inability to walk without assistance [men 58.9 years (95% CI = 56.6-61.3 years); women 62.1 years (59.7-64.4 years)], bedriddenness [men 62.1 years (59.6-64.7 years), women 66.5 years (63.9-69.1 years); and death [men 64.6 years (61.7-67.6 years); women 70.7 years (67.6-73.9 years)] were significantly lower in men than in women (all P < or = 0.01). The median survival time of men was significantly shorter than expected from German life tables (64.6 versus 69.3 years, P = 0.01). In contrast, the median survival time of women was not significantly reduced (70.7 versus 72.2 years). The C117F mutation was associated with a lower age at death and the C174Y mutation with a lower age at onset for stroke, immobilization and death (adjusted P values <0.05). At onset of the cause of death, 78% of the subjects were completely dependent. Sixty-three per cent were confined to bed. Pneumonia was the most frequent cause of death (38%), followed by sudden unexpected death (26%) and asphyxia (12%). We conclude that male sex is a risk factor for early immobilization and death in CADASIL. Our findings suggest possible genotype-phenotype correlations with regard to disease progression. The data presented may serve as source material for counselling CADASIL patients and for designing future interventional trials.

A1A2 Na+/K+-ATPase mutations cause familial hemiplegic migraine type 2 (FHM2). The authors identified three putative A1A2 mutations (D718N, R763H, P979L) and three that await validation (P796R, E902K, X1021R). Ten to 20% of FHM cases may be FHM2. A1A2 mutations have a penetrance of about 87%. D718N causes frequent, long-lasting HM, and P979L may cause recurrent coma. D718N and P979L may predispose to seizures and mental retardation. A1A2 does not play a major role in sporadic HM; only one variant, R383H, occurred in 1 of 24 cases.