The Mayo Clinic team reviewed the records of 81 patients with characteristic clinical MELAS or with a positive genetic test for MELAS but without all the clinical criteria, with a mean follow-up of 5.8 years:
- 42 had MELAS, including 13 with a “late” onset, i.e. where the first neurological vascular pseudo-episode occurred after the age of 40;
- 30 presented less severe forms such as myopathy, MIDD (Maternally Inherited Diabetes and Deafness) syndrome, isolated deafness, mitochondrial encephalopathy without pseudo-episode of vascular deficiency;
- 9 were asymptomatic.
- Compared with others, patients with MELAS had a lower body mass index and tended to have higher serum heteroplasmy, particularly those with onset before the age of 40;
- people with MELAS had more frequent epileptic seizures and a shorter lifespan, although those with a late onset lived longer (62 years vs. 30 years on average);
- people with MELAS before the age of 40 had more neurological signs than those with a late onset, who were more likely to have diabetes or nephropathy, or even multi-system involvement, than those with MELAS starting before the age of 40;
- conductive deafness was the most frequent first sign in the less severe forms.
