Haplotype analysis of the DM1 locus in the Serbian population

Origin of the myotonic dystrophy type 1 mutation in Mexican population and influence of Amerindian ancestry on CTG repeat allelic distribution

Myotonic dystrophy type 1 is caused by expansion of a CTG trinucleotide repeat situated in the DMPK gene. Worldwide genetic studies suggest a single or limited number of mutational events cause the disease. However, distribution of CTG alleles and disease incidence varies among ethnicities. Due to the great ethnic diversity of the Mexican population, the present study was aimed at analyzing the impact of different lineages in shaping the CTG-repeat allelic distribution in the contemporary Mexican-Mestizo population as well as to shed light on the DM1 ancestral origin. Distribution of CTG-repeat alleles was similar among Mestizo and Amerindian subpopulations with (CTG)_11-13 being the most frequent alleles in both groups, which implies that Mexican-Mestizo allelic distribution has been modeled by Amerindian ancestry. We diagnosed a relatively high number of cases, consistent with the high frequency of large-normal alleles found in Mexican subpopulations. Haplotype analysis using various polymorphic-markers in proximity to DMPK gene indicates that a single founder mutation originates myotonic dystrophy type 1 in Mexico; however, Y-STR haplogroups data and the presence of pre-mutated and large normal alleles in Amerindians support the hypothesis that both European and Amerindian ancestral chromosomes might have introduced the disease to the Mexican population, which was further disseminated through mestizaje.

DMPK-associated myotonic dystrophy and CTG repeats in Alabama African Americans

Myotonic dystrophy type 1 (DM1) is a result of a CTG expansion in the 3'-untranslated region of the DMPK gene. DM1 is rare among African blacks who have fewer large CTG repeats in the normal range than other racial/ethnic groups. Neither the prevalence of DM1 nor the relationship of CTG expansion to clinical status in African Americans (AAs) is well documented. We describe two AA brothers with DM1, each of whom had CTG repeats of 5/639; their father was reported to have DM1 and had CTG repeats of 5/60. Other family members had CTG repeats of 5-14. An unrelated AA patient from a second kinship also had DM1; an analysis revealed CTG repeats of 27/191. In 161 Alabama AA control subjects, we observed 18 CTG alleles from 5 to 28 repeats; the most common allele had five CTG repeats. The frequency of CTG repeats >or=15 were greater (p < 0.0003) in Pygmy, Amhara Ethiopian, Ashkenazi Jewish, North African Jewish, Israeli Muslim Arab, European white, and Japanese populations than in the Alabama AA population. These data suggest that the risk for DM1 in AAs is intermediate between that of African blacks and whites of European descent.