Molecular analysis of the CTSK gene in a cohort of 33 Brazilian families with pycnodysostosis from a cluster in a Brazilian Northeast region
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2016
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Background: Pycnodysostosis is an autosomal recessive skeletal dysplasia, the prevalence of which is estimated to be low (1 per million). Nevertheless, in recent years we have found 27 affected individuals from 22 families in Ceara State, a region of the Brazilian Northeast, giving a local prevalence of 3 per million. This local prevalence associated with a high parental consanguinity, suggesting a possible founder effect, prompted us to perform a molecular investigation of these families to test this hypothesis. Methods: The CTSK gene was sequenced by the Sanger method in the patients and their parents. In addition to 18 families from Ceara, this study also included 15 families from other Brazilian regions. We also investigated the origin of each family from the birthplace of the parents and/or grandparents. Results: We have studied 39 patients, including 33 probands and 6 sibs, from 33 families with pycnodysostosis and identified six mutations, five previously described (c.436G>C, c.580G>A, c.721C>T, c.830C>T and c.953G>A) and one novel frameshift (c.83dupT). This frameshift variant seems to have a single origin in Ceara State, since the haplotype study using the polymorphic markers D1S2344, D1S442, D1S498 and D1S2715 suggested a common origin. Most of the mutations were found in homozygosity in the patients from Ceara (83.3 %) while in other states the mutations were found in homozygosity in half of patients. We have also shown that most of the families currently living outside of Ceara have northeastern ancestors, suggesting a dispersion of these mutations from the Brazilian Northeast. Conclusions: The high frequency of pycnodysostosis in Ceara State is the consequence of the high inbreeding in that region. Several mutations, probably introduced a long time ago in Ceara, must have spread due to consanguineous marriages and internal population migration. However, the novel mutation seems to have a single origin in Ceara, suggestive of a founder effect.
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European Journal Of Medical Research. London, v. 21, p. -, 2016.