Genome‐wide androgenetic mosaicism

Individuals with mosaic paternal uniparental disomy ( UPD ) of apparently all chromosomes have recently been described. They show a 46, XX karyotype, but with a mixture of normal biparental cells and cells entirely of paternal isodisomic origin. We describe an infant who primarily showed signs of Beckwith–Wiedemann syndrome ( BWS ), but also had other severe and eventually lethal medical problems, notably refractory hypoglycemia. We performed methylation studies for BWS , but incidentally for Angelman syndrome ( AS ) on leukocytes and in a skin FFPE sample. We also performed chromosome microarray [ CNV and single‐nucleotide polymorphism ( SNP ) array] on leukocytes. We found that the patient had hypomethylation consistent with both BWS and AS . Remarkably, this was due to mosaic paternal UPD for chromosomes 11 and 15, respectively. The SNP microarray showed mosaic paternal UPD for all chromosomes. Patients with unusual phenotypes for a typical imprinting disorder should be studied further with assays for imprinted loci on other chromosomes. Chromosomal SNP microarrays are useful in identifying patients with multiple UPDs , sometimes of the whole genome.