Characterization of Mitochondrial DNA Sequence Heteroplasmy in Blood Tissue and Hair as a Function of Hair Morphology*,†,‡

This study characterizes mitochondrial DNA (mtDNA) sequence heteroplasmy in blood tissue and hair as a function of hair morphology. Bloodstains (127 individuals) and head hairs (128 individuals) were typed using the mtDNA LINEAR ARRAY™ assay. A total of 1589 hairs were interpreted: 1478 (93%) were homoplasmic and 111 (7%) exhibited heteroplasmy at one or more positions. Seventy-one percent (82/116) of individuals were homoplasmic, whereas 29% (34/116) exhibited heteroplasmy in at least one hair. The results demonstrate intra- and inter-tissue differences in heteroplasmy within individuals. Sequence heteroplasmy among hairs from each individual varied from 0 to 90%; the frequency does not differ significantly with population group, cosmetic treatment, age, gender, medulla morphology, region of the scalp, hair growth phase, or, when comparing living and deceased donors. However, the results support a correlation between heteroplasmy and hair pigmentation; typically, lighter-pigmented hairs exhibit a higher incidence of sequence heteroplasmy compared to darker hairs.