alt=image showing how two carriers can produce one in four offspring with<unk> . This is called an autosomal-recessive pattern of inheritance.<unk>  is an autosomal-recessive disorder that affects a gene (FXN) on chromosome 9, which produces an important protein called frataxin. In 96% of cases, the mutant FXN gene has 90–1,300 GAA trinucleotide repeat expansions in intron 1 of both alleles. This expansion causes epigenetic changes and formation of heterochromatin near the repeat. The length of the shorter GAA repeat is correlated with the age of onset and disease severity. The formation of heterochromatin results in reduced transcription of the gene and low levels of frataxin. People with FDRA might have 5-35% of the frataxin protein compared to healthy individuals. Heterozygous carriers of the mutant FXN gene have 50% lower frataxin levels, but this decrease is not enough to cause symptoms. In about 4% of cases, the disease is caused by a (missense, nonsense, or intronic) point mutation, with an expansion in one allele and a point mutation in the other. A missense point mutation can have milder symptoms. Depending on the point mutation, cells can produce no frataxin, nonfunctional frataxin, or frataxin that is not properly localized to the mitochondria.
Friedreich's ataxia
Spinocerebellar ataxia type 6
Stratton Parker syndrome
Autosomal recessive cerebellar ataxia type 1
Spinocerebellar ataxia type-13
Sandhoff disease
Jokela type spinal muscular atrophy
Parkes Weber syndrome