Partial lyonisation of steroid sulphatase gene in single hair roots.

Steroid sulphatase (STS) activity was measured in single hair roots from 9 patients with X-linked ichthyosis, 7 obligate heterozygotes, 12 male controls and 12 female controls. STS activity was deficient (less than 0.3 pmol dehydroepiandrosterone (DHEA) in 5 h per hair root) in the patients as compared to male controls (4.6 +/- 1.8 pmol DHEA in 5 h per hair root). All single hair roots from obligate heterozygotes showed STS activity (3.0 +/- 0.9 pmol DHEA in 5 h per hair root). Female controls had a significantly higher STS activity (6.0 +/- 1.8 pmol DHEA in 5 h per hair root) than male controls (p less than 0.05) and heterozygotes (p less than 0.001). Both the female-male sex ratio of control STS activity (1.3) and the absence of STS-deficient hair roots in heterozygotes confirm previous evidence for incomplete lyonisation of the X-linked steroid sulphatase gene.