Kidney and heart tissues were found to not have a COX deficiency.French Canadian Leigh syndrome has similar symptoms to other types of Leigh syndrome. The age of onset is, on average, 5 months and the median age of death is 1 year and 7 months. Children with the disease are developmentally delayed, have mildly dysmorphic facial features, including hypoplasia of the midface and wide nasal bridge, chronic metabolic acidosis, and hypotonia (decreased muscular strength). Other symptoms include tachypnea (unusually quick breathing rate), poor sucking ability, hypoglycemia (low blood sugar), and tremors. Severe, sudden metabolic acidosis is a common cause of mortality.Estimates of the rate of genetic carriers in the Saguenay-Lac-Saint-Jean region range from 1 in 23 to 1 in 28; the number of children born with the disease has been estimated at 1 in 2063 to 1 in 2473 live births. Genealogic studies suggest that the responsible mutation was introduced to the region by early European settlers. Pathophysiology
The characteristic symptoms of Leigh syndrome are at least partially caused by bilateral, focal lesions in the brainstem, basal ganglia, cerebellum, and other regions of the brain. The lesions take on different forms, including areas of demyelination, spongiosis, gliosis, necrosis, and capillary proliferation. Demyelination is the loss of the myelin sheath around the axons of neurons, inhibiting their ability to communicate with other neurons. The brain stem is involved in maintaining basic life functions such as breathing, swallowing, and circulation; the basal ganglia and cerebellum control movement and balance.
This means that two copies of the mutated gene are required to cause the disease, so two unaffected parents, each of whom carries one mutant allele, can have an affected child if that child inherits the mutant allele from both parents.75 to 80 percent of Leigh syndrome is caused by mutations in nuclear DNA; mutations affecting the function or assembly of the fourth complex involved in oxidative phosphorylation, cytochrome c oxidase (COX), cause most cases of Leigh disease. Mutations in a gene called SURF1 (surfeit1) are the most common cause of this subtype of Leigh syndrome. The protein that SURF1 codes for is terminated early and therefore cannot perform its function, shepherding the subunits of COX together into a functional protein complex. This results in a deficit of COX protein, reducing the amount of energy produced by mitochondria. SURF1 is located on the long arm of chromosome 9. Another nuclear DNA mutation that causes Leigh syndrome affects another protein complex in the mitochondria, pyruvate dehydrogenase, which is an enzyme in the Link reaction pathway. Some types of SURF1 mutations cause a subtype of Leigh syndrome that has a particularly late onset but similarly variable clinical course.Other nuclear genes associated with Leigh syndrome are located on chromosome 2 (BCS1L and NDUFA10); chromosome 5 (SDHA, NDUFS4, NDUFAF2, and NDUFA2); chromosome 8 (NDUFAF6), chromosome 10 (COX15); chromosome 11 (NDUFS3, NDUFS8, and FOXRED1); chromosome 12 (NDUFA9 and NDUFA12); and chromosome 19 (NDUFS7). Many of these genes affect the first oxidative phosphorylation complex.