Clonality analysis using X-chromosome inactivation at the human androgen receptor gene (Humara). Evaluation of large cohorts of patients with chronic myeloproliferative diseases, secondary neutrophilia, and reactive thrombocytosis.

Chronic myeloproliferative diseases (MPDs) are not associated with consistent cytogenetic or molecular abnormalities. Demonstration of clonal cell growth by analysis of X-chromosome inactivation (XCI) patterns in females provides a promising tool for diagnosis. However, this technique can be complicated by excessive lyonization of normal cells mimicking clonal cell growth: We analyzed XCI patterns at the human androgen receptor (HUMARA) locus in 146 healthy females, 65 women with secondary neutrophilia, 31 women with reactive thrombocytosis, and 86 women with chronic MPDs. A skewed XCI pattern with greater than 75% amplification of 1 allele (allele ratio > 3:1) was found in 22 (9.1%) of 242 control subjects. The incidence of skewing was statistically significantly lower in women younger than 30 years (2/73) compared with women older than 60 years (10/53). Of 86 patients with a chronic MPD, 71 (82%) exhibited an allele ratio greater than 3:1, whereas only 10 (12%) of 86 age-matched control subjects showed a skewed XCI pattern. Although statistical evaluation of the data showed a significant difference between patients with a chronic MPD and control subjects, proof of clonality in individual, especially elderly, patients is difficult.