In this report we present a method to determine sex chromosomal aneupl
oidies by duplex polymerase chain reaction with sufficient precision t
o distinguish between one, two and more copies of X and Y sequences. W
e coamplified an autosomal gene segment (exon 33 of neurofibromatosis
type I gene on chromosome 17) as an internal standard for our sequence
of interest (AMXY) on X and Y chromosomes. By using this standard as
a reference for two gene copies we could visually estimate the relativ
e gene dosage for the X-, and Y-specific AMXY sequences in the DNA sam
ple under consideration, We have evaluated this method in normal males
and females and in patients with known sex chromosomal aneuploidies a
nd have found it to be a reliable and quick tool for detection of nume
rical sex chromosomal abnormalities.