A novel expression based approach for assessing the inactivation status of human X-linked genes

We present a novel RT-PCR-based approach for determining the inactivation status of X-linked genes. Using cDNA from cloned female cell lines in which only the maternal or paternally derived X chromosome is active, we are able to demonstrate expression from only one allele in genes known to be inactivated. Following reverse transcription, amplification across a polymorphism will yield a product from a single allele if the gene of interest is inactivated, and products from both alleles in a gene escaping inactivation. We have verified this approach using the human androgen receptor and FMR1 loci which have been shown to be subjected to normal inactivation. The potential for widespread application of this approach was shown by the successful demonstration of inactivation at the MAOA and HPRT loci using intronic polymorphisms.