Followed by which subgroup of LS is of interest (e.g. MSH2 carriers, MLH1 carriers, the type of mutation (missense, nonsense etc.)female patients, any genotype/phenotype correlation etc.)and as precise a definition as possible with respect to what modification is being searched for (i.e. age of disease onset, the site of disease development, environmental triggers of disease). The gene discussed is MSH2; the disease is Leigh syndrome.