Trisomy 17p10-p12 resulting from a supernumerary marker chromosome derivedfrom chromosome 17: molecular analysis and delineation of the phenotype

We report a 5-year-old boy with a small de novo marker chromosome derived f rom the proximal short arm of chromosome 17. His clinical features include hypotonia, global developmental delay, oval face with large nose and promin ent ears, and ligamentous laxity of the fingers Magnetic resonance imaging of the brain demonstrated mildly delayed myelination. G-band chromosome ana lysis revealed mosaicism for a small marker chromosome in 85% of the periph eral blood cells analyzed. Fluorescence in situ hybridization and microsate llite polymorphism studies showed that the der(17) was of maternal origin a nd included genetic material from the 17p10-p12 region but did not contain the PMP22 gene. One breakpoint mapped within the centromere the second brea kpoint mapped adjacent to the Charcot-Marie-Tooth disease type 1A proximal low-copy repeat (CMT1A-REP). We compare the clinical characteristics of our patient with those previously reported to have a duplication involving the proximal short arm region of chromosome 17 to further delineate the phenot ype of trisomy 17p10-p12.