[Mitochondrial recessive ataxia syndrome (MIRAS) and valproate toxicity]. / Mitokondriaalinen resessiivinen ataksia- syndrooma ja valproaattihoidon toksisuus.

The clinical phenotypes vary considerably and can be divided into three groups: 1) childhood-onset encephalopathy and hepatopathy, 2) juvenile onset refractory epilepsy and migraine-like headaches, and 3) adult-onset ataxia and neuropathy with additional symptoms such as psychiatric symptoms and cognitive impairment. The life-threatening MIRAS epilepsy should be actively treated, as it is associated with poor prognosis. The form of MIRAS, starting as acute, treatment resistant epilepsy, is important to diagnose, since valproate therapy almost always leads to acute liver failure requiring liver transplantation.

Mitochondrial DNA polymerase W748S mutation: a common cause of autosomal recessive ataxia with ancient European origin.

Mutations in the catalytic subunit of the mitochondrial DNA polymerase gamma (POLG) have been found to be an important cause of neurological disease. Recently, we and collaborators reported a new neurodegenerative disorder with autosomal recessive ataxia in four patients homozygous for two amino acid changes in POLG: W748S in cis with E1143G. Here, we studied the frequency of this allele and found it to be among the most common genetic causes of inherited ataxia in Finland. We identified 27 patients with mitochondrial recessive ataxia syndrome (MIRAS) from 15 Finnish families, with a carrier frequency in the general population of 1 : 125. Since the mutation pair W748S+E1143G has also been described in European patients, we examined the haplotypes of 13 non-Finnish, European patients with the W748S mutation. Haplotype analysis revealed that all the chromosomes carrying these two changes, in patients from Finland, Norway, the United Kingdom, and Belgium, originate from a common ancient founder. In Finland and Norway, long, common, northern haplotypes, outside the core haplotype, could be identified. Despite having identical homozygous mutations, the Finnish patients with this adult- or juvenile-onset disease had surprisingly heterogeneous phenotypes, albeit with a characteristic set of features, including ataxia, peripheral neuropathy, dysarthria, mild cognitive impairment, involuntary movements, psychiatric symptoms, and epileptic seizures. The high carrier frequency in Finland, the high number of patients in Norway, and the ancient European founder chromosome indicate that this newly identified ataxia should be considered in the first-line differential diagnosis of progressive ataxia syndromes.

Adult-onset ataxia and polyneuropathy caused by mitochondrial 8993T-->C mutation.

The 8993T-->C mutation in mitochondrial DNA (mtDNA) has been described previously to be associated with infantile- or childhood-onset phenotypes, ranging from Leigh's syndrome to neurogenic weakness, ataxia, and retinitis pigmentosa syndrome. We report a kindred with adult-onset slowly progressive ataxia and polyneuropathy and with the heteroplasmic 8993T-->C mutation. Our findings suggest that the 8993T-->C mtDNA mutation should be considered in the differential diagnosis of nondominant adult-onset ataxia and axonal neuropathy.