A large deletion spanning XG and GYG2 constitutes a genetic basis of the Xgnull phenotype, underlying anti-Xga production.

We identified a large deletion on the X chromosome, resulting in a true, tissue-wide Xgnull phenotype. This deletion was found in 10 of 11 anti-Xga makers from which DNA could be amplified. One sample remained unexplained, indicating further heterogeneity to be explored.