Epigenetic effects

Epigenetic effects are inherited molecular changes that do not
alter DNA sequence. These can affect the expression of genes
or the function of the protein product. Epigenetic effects
include DNA methylation and alteration of chromatin
configuration or protein conformation. Methylation of
controlling elements silences gene expression as a normal
event during development. Abnormalities of methylation may
result in genetic disease. In fragile X syndrome, methylation of
the promotor occurs when there is a large CGG expansion,
inactivating the gene and causing the clinical phenotype.
Methylation is also involved in the imprinting of certain genes,
where abnormalities lead to disorders such as Angelman and
Prader–Willi syndromes.