It has established the diagnosis in seven typical CS cases (patients # 1 to 7) with pathogenic mutations in either ERCC6(CSB) or ERCC8(CSA), and in four XP cases (patients # 10 to 13) with mutations in POLH. The technique is also reliable in cases with uncommon phenotypes (combined features or unusually mild symptoms or very rarely involved genes). The gene discussed is ERCC6; the disease is Cowden syndrome 1.