RESUMEN
In this report we present a method to determine sex chromosomal aneuploidies by duplex polymerase chain reaction with sufficient precision to distinguish between one, two and more copies of X and Y sequences. We 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 relative gene dosage for the X-, and Y-specific AMXY sequences in the DNA sample under consideration. We have evaluated this method in normal males and females and in patients with known sex chromosomal aneuploidies and have found it to be a reliable and quick tool for detection of numerical sex chromosomal abnormalities.