Banet et al. established that immunohistochemical analysis of p57KIP2 expression is highly correlated with genotyping results and demonstrated that CHM is almost always p57-negative, with only rare examples (0.5 %) displaying aberrant (positive) p57KIP2 expression, which is attributable to retention of the maternal copy of chromosome 11. The gene discussed is CDKN1C; the disease is choroideremia.