A New Deletion Ablating NESP55 Causes Loss of Maternal Imprint of A/BGNASand Autosomal Dominant Pseudohypoparathyroidism Type Ib

This new deletion suggests that NESP55 is an additional imprinting control region that directs A/B methylation in humans. We bring arguments in support of the theory of reciprocal inhibition between the expression of NESP and AS. However, determining whether loss of methylation at the A/B differentially methylated region is a consequence of the loss of NESP expression or of the expression of AS requires additional investigations.