The tumour-specific L1 mutation in MeCP2 appeared to reduce the expression of this gene concomitant with copy number gain for the L1 mutant MeCP2 allele and, as suggested by increased L1 expression and reduced L1 5′UTR methylation, may have reduced MeCP2 function throughout the tumour mass, causing a molecular phenotype. The gene discussed is MECP2; the disease is neoplasm.