Imprinted genes differ from most gene pairs in that only one gene of the pair is expressed determined by the parent they originate from. Many have been shown to play an important role in fetal growth and neurodevelopment. Most imprinted genes are found in clusters and expression is controlled by imprinting centres that contain differentially methylated regions. Monoallelic expression makes imprinted genes particularly vulnerable to naturally occurring genetic rearrangements and epigenetic alterations. At least eight disorders known to be due to imprinting errors are now well recognised; Prader Willi syndrome (15q1113), Angelman syndrome (15q1113), Transient Neonatal Diabetes (6q24), Beckwith Wiedemann syndrome (11p15.5), Silver Russell syndrome (11p15.5 and UPD7 -locus not known), Maternal and Paternal UPD 14 (14q32) and Pseudohypoparathyroidism Type 1B (20q13). There are some overlapping clinical features particularly aberrant growth, abnormal glycaemic control and developmental delay.
Transient neonatal diabetes (TND) is due to imprinting aberrations at 6q24 involving ZAC over-expression. Patients present in the neonatal period with diabetes and low birth weight and require insulin for an average period of 3 months. Non diabetic features such as macroglossia and umbilical hernia have been underemphasised. The TND cases share overlap with other imprinting disorders particularly Beckwith Wiedemann syndrome. Recently the clinical overlap has been proven molecularly and generalised partial hypomethylation of several imprinted loci has been identified. There is accumulating evidence that imprinted genes are part of an imprinted gene network. It is likely that more human imprinting disorders will be recognised as testing for epigenetic mutations becomes more widespread.
03 - 07 May 2008
European Society of Endocrinology