X-linked Leigh syndrome
Leigh syndrome can also be caused by deficiency of the pyruvate dehydrogenase complex (PDHC), most commonly involving a PDHC subunit which is encoded by an X-linked gene (OMIM 308930). The neurological features of Leigh syndrome caused by PDHC deficiency are indistinguishable from other forms. However, non-neurological features (other than lactic acidosis) are not seen in PDHC deficiency.X-linked recessive Leigh syndrome affects male children far more often than female children because they only have one copy of the X chromosome. Female children would need two copies of the faulty gene to be affected by X-linked Leigh syndrome. French Canadian Leigh syndrome
The type of Leigh syndrome found at a much higher rate in the Saguenay-Lac-Saint-Jean region of Quebec is caused by a mutation in the LRPPRC gene, located on the small (p) arm of chromosome 2. Both compound heterozygosity and homozygous mutations have been observed in French Canadian Leigh syndrome. This subtype of the disease was first described in 1993 in 34 children from the region, all of whom had a severe deficiency in cytochrome c oxidase (COX), the fourth complex in the mitochondrial electron transport chain. Though the subunits of the protein found in affected cells were functional, they were not properly assembled. The deficiency was found to be almost complete in brain and liver tissues and substantial (approximately 50% of normal enzyme activity) in fibroblasts (connective tissue cells) and skeletal muscle.
When hyperbilirubinemia is not treated with phototherapy, the bilirubin can accumulate in the basal ganglia and cause lesions similar to those seen in Leigh syndrome. This is not common since the advent of phototherapy. Treatment
Succinic acid has been studied, and shown effective for both Leigh syndrome, and MELAS syndrome. A high-fat, low-carbohydrate diet may be followed if a gene on the X chromosome is implicated in an individuals Leigh syndrome. Thiamine (vitamin B1) may be given if pyruvate dehydrogenase deficiency is known or suspected. The symptoms of lactic acidosis are treated by supplementing the diet with sodium bicarbonate (baking soda) or sodium citrate, but these substances do not treat the cause of Leigh syndrome. Dichloroacetate may also be effective in treating Leigh syndrome-associated lactic acidosis; research is ongoing on this substance. Coenzyme Q10 supplements have been seen to improve symptoms in some cases.Clinical trials of the drug EPI-743 for Leigh syndrome are ongoing.In 2016, John Zhang and his team at New Hope Fertility Center in New York, USA, performed a spindle transfer mitochondrial donation technique on a mother in Mexico who was at risk of producing a baby with Leigh disease. A healthy boy was born on 6 April 2016. However, it is not yet certain if the technique is completely reliable and safe. Prognosis
Different genetic causes and types of Leigh syndrome have different prognoses, though all are poor. The most severe forms of the disease, caused by a full deficiency in one of the affected proteins, cause death at a few years of age.