LS is estimated to affect 1 in 279 people [3], and predisposes to a range of malignancies, most notably colorectal cancer (CRC) and endometrial cancer (EC), with the cumulative risk of any cancer reaching ~75% for MLH1-variant carriers and ~85% for MSH2-variant carriers by the age of 75 years [2]. The gene discussed is MSH2; the disease is Leigh syndrome.