Frequency of Foclor V (1691 G-A) Mutotion in Turkish Populotion Dear Sir, A mutation in the Factor V gene (1691G-+ A in exon 10) was identified that formed the molecular explanation for the phenotype of APC-resistance in the large majority of affected individuals (1). This mutation, which is associated with a significant increase in tluombotic risk, has been found in 30-5070 of selected families with thrombophilia and in 20Vo of consecutive patients with venous tluombosis (2,3).The prevalence of the FV: Q506 allele is between2To and l07o in Western societies but it varies widely depending on the geographic location and the ethnic background of the population. However, the mutated allele is not found in certain populations, such as the Japanese, Chinese, Africans and native Americans (a-6).

Mutations in the Connexin 26 (GJB2/Cx26) gene are responsible for more than half of all cases of prelingual non-syndromic recessive deafness in many Caucasian populations. To determine the importance of Cx26 mutations as a cause of deafness in Turks we screened 11 families with prelingual non-syndromic deafness, seven (64%) of which were found to carry the 35delG mutation. We subsequently screened 674 Turkish subjects with no known hearing loss and found twelve 35delG heterozygotes (1.78%; 95% confidence interval: 0.9%-3%) but no examples of the 167delT mutation. To search for possible founder effects, we typed chromosomes carrying the 35delG mutation for closely linked polymorphic markers in samples from Turkey and United States and compared the allele frequencies with those of hearing subjects. The data showed a modest degree of disequilibrium in both populations. Analyses of two pedigrees from Turkey demonstrated both conserved and different haplotypes, suggesting possible founder effects and multiple origins of the 35delG mutation.

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These results confirmed the presence of autonomic dysregulation in children with breath-holding spells. Iron deficiency may have an impact on this autonomic dysregulation. Ventricular repolarization was unaffected in patients with breath-holding spells.

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