Imprinting in human disease with special reference to transient neonatal diabetes and Beckwith-Wiedemann syndrome.

There are at least 6 well-studied imprinting domains on human autosomes. Each domain is under the regulatory control of an 'imprinting centre' that harbours a differentially methylated region. A number of molecular mechanisms result in differential silencing of some genes within these domains and gene expression is tightly regulated in normal individuals. However, this makes them vulnerable to naturally occurring genetic and epigenetic aberrations. Nine recognisable developmental syndromes have been described due to abnormalities within these 6 domains: transient neonatal diabetes (TND; at 6q24); Beckwith- Wiedemann syndrome (BWS) and Silver-Russell syndrome (at 11p15.5; 2 imprinted domains); maternal and paternal uniparental disomy syndromes (at 14q32); Angelman and Prader-Willi syndromes (at 15q11-13), and pseudohypoparathyroidism type 1b (at 20q12-13). Furthermore, it is now recognised that involvement at multiple domains can occur simultaneously and result in what has been described as the hypomethylation syndrome. TND and BWS are discussed in more detail as examples of imprinting disorders.