Gene dosage effect for human triosephosphate isomerase and glyceraldehyde-3-phosphate dehydrogenase in partial trisomy 12p13 and trisomy 18p.

An 8-year-old girl with profound mental retardation and a neurologic syndrome associated with morphologic abnormalities was found to have a supernumerary small submetacentric chromosome. Several members of her family carried a balanced translocation t(12;18)(p12;q11), and the child's karyotype could be explained by 3:1 maternal segregation (tertiary trisomy). The proband was trisomic for 12p13 and 18p. A gene dosage effect was demonstrated for triosephosphate isomerase and glyceraldehyde-3-phosphate in erythrocytes and leukocytes allowing us to assign the corresponding loci to the tip of the chromosome 12 short arm.