Modification of 15q11-q13 DNA methylation imprints in unique Angelman and Prader-Willi patients.

The clearest example of genomic imprinting in humans comes from studies of the Angelman (AS) and Prader-Willi (PWS) syndromes. Although these are clinically distinct disorders, both typically result from a loss of the same chromosomal region, 15q11-q13. AS usually results from either a maternal deletion of this region, or paternal uniparental disomy (UPD; both chromosomes 15 inherited from the father). PWS results from paternal deletion of 15q11-q13 or maternal UPD of chromosome 15. We have recently described a parent-specific DNA methylation imprint in a gene at the D15S9 locus (new gene symbol, ZNF127), within the 15q11-q13 region, that identifies AS and PWS patients with either a deletion or UPD. Here we describe an AS sibship and three PWS patients in which chromosome 15 rearrangements alter the methylation state at ZNF127, even though this locus is not directly involved in the rearrangement. Parent-specific DNA methylation imprints are also altered at ZNF127 and D15S63 (another locus with a parent-specific methylation imprint) in an AS sibship which have no detectable deletion or UPD of chromosome 15. These unique patients may provide insight into the imprinting process that occurs in proximal chromosome 15 in humans.