After birth, galactose-1-phosphate uridyltransferase (GALT) activity in the infant's blood is measured. GALT is regulated by a protein encoded on chromosome<unk> , so irregular levels of GALT activity may indicate an underlying chromosomal abnormality. Abnormal results are followed by analysis of blood, skin, and inner cheek cells, typically via fluorescence in situ hybridization, which allows genetic counsellors to physically view the chromosomal composition of the cells. Analysis of more than one tissue type is necessary in order to determine if the tetrasomy is present in its mosaic form. If<unk>  is confirmed, chromosomal analysis of additional tissue types may be performed in order to estimate the ratio of affected cells in the body.
Tetrasomy 9p
Tetrasomy 18p
Monosomy 9p
Distal trisomy 10q
Partial monosomy 13q
2q37 monosomy
Small supernumerary marker chromosome
Xp11.2 duplication