UNIPARENTAL DISOMY AND GENOMIC IMPRINTING - RELEVANCE TO RARE DYSMORPHIC SYNDROMES

In uniparental disomy (UPD) both homologues of one pair of chromosomes originate from only one parent. Autosomal recessive inherited disorde rs might become homozygous in a child, although only one parent is het erozygous. Furthermore, clinical consequences are noted, if genes or c hromosomal regions are involved whose expression depend on whether the y stem from mother or father (''genomic imprinting''). Mitotic or meio tic non-disjunction with subsequent correction are assumed to be respo nsible for UPD. About 30% of cases of Prader-Willi syndrome and about 3 % of cases of Angelman syndrome are classical instances of maternal (mat) and paternal (pat) UPD 15, respectively. Mat UPD 7, pat UPD 11 ( Wiedemann-Beckwith syndrome), mat UPD 14, pat UPD 14, and mat UPD 16 d isplay a typical phenotype, demonstrated in several patients. Single c ase reports of UPD of most of the other chromosomes have been reported . Clinical consequences have been assumed in mat 2, mat 3, mat 9, pat 10, and pat 20, whereas pat 5, pat 6, pat 7, mat 10, pat 13, pat 16, m at 21, mat 22, mat X, and pat X seem not to be associated with any cli nical problems.