Comparison of mitochondrial A3243G mutation loads in easily accessible samples from a family with maternally inherited diabetes and deafness

The mitochondrial A3243G mutation is most commonly related to the MELAS syndrome, but can cause many different clinical manifestations at various ages. Here, we present a family with maternally inherited diabetes and deafness (MIDD), the proband of which exhibits hearing loss, diabetes mellitus, cardiomyopathy and short stature. Four easily accessible samples (whole blood, hair roots, buccal scrapings and urinary sediment) from the proband and her 3 sons were simultaneously analyzed for heteroplasmic percentages of the A3243G mutation in their DNA. More than 10 subclones were sequenced and the percentage of clones possessing the A3243G mutation was calculated. The proportion of mutant genomes varied widely among the four samples tested. Blood DNA consistently had the lowest percentage of mutation load, while urinary sediment tended to have the highest. The 3 sons have not exhibited hearing disability or diabetes mellitus thus far. However, their mutation loads in all 4 tissue samples were higher than those in the corresponding samples from the proband. Follow-up of this family over time is necessary to understand the relationship between the heteroplasmic mutation loads in the 4 different samples and the clinical manifestations of MIDD/MELAS.