C07 Intergenerational cag stability across chromosome 4 haplogroups

Background Variation in the prevalence of Huntington’s disease (HD) is associated with differences in chromosome 4 haplogroup proportions between populations. No data have been published on mutant HTT (mHTT) repeat stability in different haplogroups. Aim To study intergenerational CAG repeat stability in different mHTT haplotypes. Methods A previously identified Finnish cohort of 207 HD patients and data on mHTT repeat lengths obtained from the diagnostic laboratories were used as a basis to identify parent-offspring pairs using several national registries. DNA remaining from diagnostic testing was analysed to determine haplogroups defined by the SNPs rs762855 and rs4690073. Haplogroup A haplotypes were further defined using four additional SNPs, rs2857936, rs363096, rs2276881 and rs362307. (Warby et al. 2009) The SNPs were determined either with restriction fragment analysis, allele specific amplification using locked nucleic acid primers or by sequencing. Results mHTT haplogroup and CAG repeat could be phased in 49 transmissions (haplogroup A, 38; haplogroup C, 10; other haplogroup, 1). The mean change in the length of CAG repeats differed between haplogroups A and C in paternal inheritances (p=0.038), but not in maternal inheritances (p=0.17). The change in haplogroup C was negative in paternal as well as maternal transmissions (p=0.74 for difference; figure 1), whereas the repeats in haplogroup A expanded in paternal transmissions in comparison to maternal transmissions (p=0.008). The difference was most obvious in haplotype A1 inheritances (p=0.022).Abstract C07 Figure 1 The mean change (%) in the length of CAG repeats in haplogroups A and C in paternal and maternal transmissions Conclusions Intergenerational stability of the CAG repeat differed between mHTT haplogroups in a sex-dependent manner.