title: Intrachromosomal triplication 12p11.22-p12.3 and gonadal mosaicism of partial tetrasomy 12p.
abstract: Cases of tetrasomy 12p and trisomy 12p are known to be associated with specific phenotypic abnormalities well described in the literature. Here, we report on the unusual case of a partial tetrasomy 12p found in an affected patient and in a mosaic constellation in the patient's mother, who showed no phenotypic abnormality. The index patient was a 16-year-old boy with clinical features similar to the "trisomy 12p syndrome" including mental retardation, macrocephaly, a short nose with anteverted nostrils, and a broad protruding lower lip. G-banding analysis and fluorescence in situ hybridization (FISH) experiments using locus specific YAC DNA probes revealed a derivative chromosome 12 with a partial triplication of the short arm with an inverted copy, flanked by two direct copies. Chromosome analyses in parental lymphocytes showed a chromosomal mosaicism in the phenotypically normal mother, with 12% cells exhibiting the same partial tetrasomy 12p as detected in her son. The allelic pattern of short tandem repeats (STR) in the mother's blood DNA showed that a chimerism can be excluded with high probability. To our knowledge, this is the first report of intrachromosomal triplication on chromosome 12, as well as partial tetrasomy 12p mosaicism. Moreover, as a consequence of the chromosomal aberration in the son it can be concluded that a gonadal mosaicism is present in the mother.
authors.affiliation: Institute of Human Genetics, Otto von Guericke University, Magdeburg, Germany.
authors.forename: Heike
authors.initials: H
authors.lastname: Eckel
authors.forename: Rainer
authors.initials: R
authors.lastname: Wimmer
authors.forename: Marianne
authors.initials: M
authors.lastname: Volleth
authors.forename: Sibylle
authors.initials: S
authors.lastname: Jakubiczka
authors.forename: Petra
authors.initials: P
authors.lastname: Muschke
authors.forename: Peter
authors.initials: P
authors.lastname: Wieacker
mesh_terms: D000015:Abnormalities, Multiple / Q000235:genetics* / Q000473:pathology; D000293:Adolescent; D002869:Chromosome Aberrations; D002871:Chromosome Banding; D002881:Chromosomes, Human, Pair 12 / Q000235:genetics*; D019465:Craniofacial Abnormalities; D005192:Family Health; D005260:Female; D006066:Gonads / Q000378:metabolism; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D008607:Intellectual Disability / Q000473:pathology; D007621:Karyotyping; D008297:Male; D009030:Mosaicism