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- UPD, uniparental disomy
- cenM-FISH, centromere specific multicolour FISH
- SMC, supernumerary marker chromosome
Uniparental disomy (UPD) describes the inheritance of a pair of chromosomes from only one parent, either as both homologues (heterodisomy), as two copies of one homologue (isodisomy), or as a mixture of heterodisomic and isodisomic segments. So far, UPD of whole chromosomes has been described in different clinical cases for most of the human chromosomes, except for maternal UPD(3), (5), (11), (12), (18), and (19) and paternal UPD(3), (4), (9), (12), (17), (18), and (19).1,2 Problems associated with UPD include trisomy mosaicism, homozygosity of autosomal recessively inherited mutations, and genomic imprinting. The latter describes the epigenetic phenomenon of a parental origin dependent gene expression. Cases with complete or segmental UPD might be helpful in mapping rare autosomal recessive disorders or chromosomal regions of genomic imprinting. We report here the first case of maternal uniparental disomy 12 in a healthy girl.
Amniocentesis was performed, because of advanced maternal age, in the 19th week of gestation in a 45 year old gravida 1, para 0 woman. Cytogenetic analysis using standard procedures showed a supernumerary marker chromosome (SMC, fig 1A) in 16 of 30 metaphase spreads (karyotype 47,XX,+mar /46,XX ). The SMC was further characterised by centromere specific multicolour fluorescence in situ hybridisation (cenM-FISH)3 and, because several cases of SMC and UPD have been published,4 molecular analysis was undertaken.