A mitochondrial disease, a French Canadian form of Leigh syndrome, with characteristics of chronic metabolic acidosis, hypotonia, facial dysmorphism and delayed development. It was first described in Saguenay-Lac-Saint-Jean (Quebec, Canada) in this region the prevalence of the gene mutation underlying the disorder is estimated to be 1/23 inhabitants and may be due to a founder effect. There are 3 forms of the disease corresponding to varying degrees of severity: a neonatal form, a classic form and a so-called survivor form. Survivor form describes those who have survived several episodes, cross a critical threshold and show less severe symptoms. Caused by two types of mutations in the LRPPRC gene (2p21). The disease follows a monogenic autosomal recessive pattern of inheritance.