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Relative frequency of hereditary ataxias remains unknown in many regions of Latin America. We described the relative frequency in spinocerebellar ataxias (SCA) due to (CAG)n and to (ATTCT)n expansions, as well as Friedreich ataxia (FRDA), among cases series of ataxic individuals from Peru. Among ataxic index cases from 104 families (38 of them with and 66 without autosomal dominant pattern of inheritance), we identified 22 SCA10, 8 SCA2, 3 SCA6, 2 SCA3, 2 SCA7, 1 SCA1, and 9 FRDA cases (or families). SCA10 was by far the most frequent one. Findings in SCA10 and FRDA families were of note. Affected genitors were not detected in 7 out of 22 SCA10 nuclear families; then overall maximal penetrance of SCA10 was estimated as 85%; in multiplex families, penetrance was 94%. Two out of nine FRDA cases carried only one allele with a GAA expansion. SCA10 was the most frequent hereditary ataxia in Peru. Our data suggested that ATTCT expansions at ATXN10 might not be fully penetrant and/or instability between generations might frequently cross the limits between non-penetrant and penetrant lengths. A unique distribution of inherited ataxias in Peru requires specific screening panels, considering SCA10 as first line of local diagnosis guidelines.

Starting from a proband for whom a family history of neurodegenerative disorder has been reported, clinical and genealogical methods are often used together to reconstruct the pedigree of many large families affected by hereditary diseases. This approach was fundamental in the rebuilding of the N family, the kindred originated from southern Italy affected by early onset autosomal dominant Alzheimer’s disease (AD), that has given an important contribution to the discovery of Presenilin 1, the main gene responsible for AD. The identification of several patients in this pedigree, encompassing 11 generations with several hundred of affected subjects, was achieved through the meticulous study of medical records in the archives of the Provincial Psychiatric Hospital of Girifalco in Italy and in the municipal and parish archives of many towns belonging to the same geographical area. The research on N family triggered several other studies on hereditary neurodegenerative disorders in Southern Italy. Investigation focusing on antique archives and the analysis of phenotypes allowed to reconstruct and clinically detail large pedigrees of hereditary diseases, such as frontotemporal dementia and spinocerebellar ataxia 17, even before the discovery of their causative genes.