These families were identified through a population-based nationwide survey for hereditary ataxias, to the best of our knowledge the largest ever performed. We can thus conclude that AOA4 is the most frequent form of AOA in the Portuguese population (it affects nearly 40% of the families identified) and the most frequent recessive ataxia in this population, after Freidreich ataxia.8 Mean age at onset (4.3 years) for individuals with AOA4 is closer to that of individuals with AOA1 (6.9 ± 4.7 years) than to that of those with AOA2 (14.6 ± 3.4), although it is lower than both.16,17 Clinical presentation, with marked extrapyramidal manifestations and its rapid progression, also more closely resembles that of AOA1 than that of AOA2. Additionally, in individuals with AOA4, albumin may be low or normal and cholesterol levels are normal or high, a similar situation to what is seen in individuals with AOA1 after some years of disorder progression. On the other hand, α-fetoprotein was elevated in some individuals with AOA4, which seems to always be the case in those with AOA2.