Mutations in the excision-repair cross-complementing-6 and 8 (ERCC6 and ERCC8) genes cause Cockayne syndrome type B (CSB) and type A (CSA) respectively. CSB is more common than CSA. Approximately 75% of cases of Cockayne syndrome are due to mutations in the CSB/ERCC6 gene, and most of the remaining 25% are due to mutations in the CSA/ERCC8 gene. A small number of cases are due to a deletion/duplication in either the ERCC6 or ERCC8 gene. This laboratory performs both Sanger sequencing and deletion/duplication by MLPA for both genes.