47,XX,UPD(7)mat,+r(7)pat/46G,XX,UPD(7)mat mosaicism in a girl with Silver-Russell syndrome (SRS): possible exclusion of the putative SRS gene from a 7p13-q11 region

Maternal uniparental disomy for chromosome 7 (UPD7) may present with a char acteristic phenotype reminiscent of Silver-Russell syndrome (SRS). Previous studies have suggested that approximately 10% of SRS patients have materna l UPD7. We describe a girl with a mos47,XX,+mar/46,XX karyotype associated with the features of SRS. Chromosome painting using a chromosome 7 specific probe pool showed that the small marker was a ring chromosome 7 (r(7)). PC R based microsatellite marker analysis of the patient detected only one mat ernal allele at each of 16 telomeric loci examined on chromosome 7, but sho wed both paternal and maternal alleles at four centromeric loci. Considerin g her mosaic karyotype composed of diploid cells and cells with partial tri somy for 7p13-q11, the allele types obtained at the telomeric loci may refl ect the transmission of one maternal allele in duplicate, that is, maternal UPD7 (complete isodisomy or homodisomy 7), whereas those at the centromeri c loci were consistent with biparental contribution to the trisomic region. It is most likely that the patient originated in a 46,XX,r(7) zygote, foll owed by duplication of the maternally derived whole chromosome 7 in an earl y mitosis, and subsequent loss of the paternally derived ring chromosome 7 in a subset of somatic cells. The cell with 46,XX,r(7) did not survive ther eafter because of the monosomy for most of chromosome 7. If the putative SR S gene is imprinted, it can be ruled out from the 7p11-q11 region, because biparental alleles contribute to the region in our patient.