2004-02-17-16 Mosaic tetrasomy 21 © Malkomes www.thefetus.net/
Mosaic tetrasomy 21
Paulo Malkomes MD
Unimed Hospital,Capivari,Sao Paulo ,Brazil
Tetrasomy 21can be diagnosed by amniocentesis performed for maternal age or because of the discovery of abnormalities in the ultrasound scans. The mosaic tetrasomy can be diagnosed by FISH(2).FISH can discriminate of the isochromosome 21q (or mosaic tetrasomy 21) from the isochromosome 12q (or mosaic tetrasomy 12q) whose cells are otherwise very similar on standard karyotypic photographs. Tetrasomy 12q is more frequent than tetrasomy 21q. The distal half of the long arm of 21q (21q22) is critical and it is very probable that some features of Down Syndrome may also result from 21q duplications.
Partial tetrasomy involving the long arm of chromosome 21 can shows mental retardation, cranio-facial dysmorphism, hernia, genital abnormalities and foot and hand deformities (1). Some of the major features include:
Head and neck: flat occiput, high and broad forehead, retrognatia and full cheeks.
Eyes: Downslating palpebral fissures, hypertelorism and prominent supraorbital ridges.
Nose: short nose with flat bridge and epicantal folds.
Mouth and oral structures: large downturned mouth, thin lips and highly arched palate.
Neck: short neck with excess of nuchal skin
Abdomen: umbilical hernia.
Hand and foot: short hands with stubby fingers, short feet, overlapping fingers and clinodactyly.
Skin: hypotricoses and hypoplastic nails.
Nervous system: mild ventricular dilation.
Urogenital system: small penis and cryptorchidism.
(1)Us National Library of Medicine (Mosaic Tetrasomy 21 in male child) http://www.nlm.nih.gov/mesh/jablonski/syndromes/syndrome205.html
(2) Nagarshet NP, Mootabar H.- Prenatal diagnosis of mosaic tetrasomy 21q confirmed by FISH in Clin. Genet. 1997 Apr,51(4):260-3 (3)Shapiro BL – The Down syndrome critical region.in J Neural Transm Suppl. 1999;57:41-60