Friedreich's ataxia (FRDA) is an autosomal recessive, degenerative disease that involves the central and peripheral nervous systems and the heart. A gene, X25, was identified in the critical region for the FRDA locus on chromosome 9q13. This gene encodes a 210-amino acid protein, frataxin, that has homologs in distant species such as Caenorhabditis elegans and yeast. A few FRDA patients were found to have point mutations in X25, but the majority were homozygous for an unstable GAA trinucleotide expansion in the first X25 intron.

Hereditary spastic paraplegia (HSP) is characterized by progressive weakness and spasticity of the lower limbs due to degeneration of corticospinal axons. We found that patients from a chromosome 16q24.3-linked HSP family are homozygous for a 9.5 kb deletion involving a gene encoding a novel protein, named Paraplegin. Two additional Paraplegin mutations, both resulting in a frameshift, were found in a complicated and in a pure form of HSP. Paraplegin is highly homologous to the yeast mitochondrial ATPases, AFG3, RCA1, and YME1, which have both proteolytic and chaperon-like activities at the inner mitochondrial membrane. Immunofluorescence analysis and import experiments showed that Paraplegin localizes to mitochondria. Analysis of muscle biopsies from two patients carrying Paraplegin mutations showed typical signs of mitochondrial OXPHOS defects, thus suggesting a mechanism for neurodegeneration in HSP-type disorders.

Friedreich's ataxia is the most common inherited ataxia. Ninety‐six percent of patients are homozygous for GAA trinucleotide repeat expansions in the first intron of the frataxin gene. The remaining cases are compound heterozygotes for a GAA expansion and a frataxin point mutation. We report here the identification of 10 novel frataxin point mutations, and the detection of a previously described mutation (G130V) in two additional families. Most truncating mutations were in exon 1. All missense mutations were in the last three exons coding for the mature frataxin protein. The clinical features of 25 patients with identified frataxin point mutations were compared with those of 196 patients homozygous for the GAA expansion. A similar phenotype resulted from truncating mutations and from missense mutations in the carboxy‐terminal half of mature frataxin, suggesting that they cause a comparable loss of function. In contrast, the only two missense mutations located in the amino‐terminal half of mature frataxin (D122Y and G130V) cause an atypical and milder clinical presentation (early‐onset spastic gait with slow disease progression, absence of dysarthria, retained or brisk tendon reflexes, and mild or no cerebellar ataxia), suggesting that they only partially affect frataxin function. The incidence of optic disk pallor was higher in compound heterozygotes than in expansion homozygotes, which might correlate with a very low residual level of normal frataxin produced from the expanded allele. Ann Neurol 1999;45:200–206

BDNF promoter/exon IV is frequently hypermethylated in the Wernicke area of the postmortem brain of suicide subjects irrespective of genome-wide methylation levels, indicating that a gene-specific increase in DNA methylation could cause or contribute to the downregulation of BDNF expression in suicide subjects. The reported data reveal a novel link between epigenetic alteration in the brain and suicidal behavior.