Preventing transmission of maternally inherited mitochondrial DNA diseases

#### Summary points #### Methods We used our personal archive of references, Medline searches, and consultation with other experts in the field to produce this review. It is derived from 22 years of research and 11 years of genetic counselling in mitochondrial DNA diseases. Maternally inherited mutations of mitochondrial DNA can be asymptomatic or cause illnesses such as developmental regression, deafness, blindness, neuropathy, diabetes, cardiomyopathy, and liver failure. Families who have lost a child from a mitochondrial DNA disease (fig 1⇓) often seek genetic counselling before trying to conceive again. They may also need support from their general practitioner when deciding between treatments that could increase their chances of having a healthy baby, but some doctors have limited knowledge of current genetic advances. In February 2008, an important step towards nuclear transfer in humans was reported.1 The nucleus of a fertilised human egg was transplanted into an enucleated recipient egg (oocyte) from an unrelated donor, resulting in an embryo with “three genetic parents.” In future, this technique might help to prevent transmission of maternally inherited mitochondrial DNA diseases, a range of potentially devastating illnesses caused by defects in mitochondrial function. Meanwhile, other in vitro fertilisation related interventions have recently become available that should be offered more widely. Here, we explain why the management of mitochondrial DNA diseases has lagged behind the genetics …