Buccal swab as a reliable predictor for X inactivation ratio in inaccessible tissues

Abstract

BackgroundAs a result of the epigenetic phenomenon of X chromosome inactivation (XCI) every woman is a mosaic of cells with either an inactive paternal X chromosome or an inactive maternal X chromosome. The ratio between inactive paternal and maternal X chromosomes is different for every female individual, and can influence an X-encoded trait or disease. A multitude of X linked conditions is known, and for many of them it is recognised that the phenotype in affected female carriers of the causative mutation is modulated by the XCI ratio. To predict disease severity an XCI ratio is usually determined in peripheral blood samples. However, the correlation between XCI ratios in peripheral blood and disease affected tissues, that are often inaccessible, is poorly understood. Here, we tested several tissues obtained from autopsies of 12 female individuals for patch size and XCI ratio.MethodsXCI ratios were analysed using methyl-sensitive PCR-based assays for the AR, PCSK1N and SLITRK4 loci. XCI patch size was analysed by testing the XCI ratio of tissue samples with decreasing size.ResultsXCI patch size was analysed for liver, muscle, ovary and brain samples and was found too small to confound testing for XCI ratio in these tissues. XCI ratios were determined in the easily accessible tissues, blood, buccal epithelium and hair follicle, and compared with ratios in several inaccessible tissues.ConclusionsBuccal epithelium is preferable over peripheral blood for predicting XCI ratios of inaccessible tissues. Ovary is the only inaccessible tissue showing a poor correlation to blood and buccal epithelium, but has a good correlation to hair follicle instead.

Molecular characterization of Spanish patients with MECP2 duplication syndrome

“…For P16, we obtained different data from the two different tissues, that is, blood lymphocytes and fibroblasts. Previous evidence has suggested that different XCI patterns depend on the tissue type . Furthermore, P16 was suspected to be mosaic, thanks to her FISH data.…”

“…Previous evidence has suggested that different XCI patterns depend on the tissue type. 25 Furthermore, P16 was suspected to be mosaic, thanks to her FISH data. This fact, along with skewed XCI in some of her tissues may explain her mild phenotype.…”

De novo mosaic MECP2 mutation in a female with Rett syndrome

“…As brain is not an easily accessible tissue, a buccal swab would be a feasible alternative in order to get a closer estimation of the possible level of mosaicism in the brain. The utility of this approach has been demonstrated in testing for various psychiatric disorders using expression and XCI studies which have shown correlating results in buccal and brain tissue cells . Despite the high potential value of buccal swab analysis, we were unable to obtain a sample, as the family was not available for further testing.…”

“…The utility of this approach has been demonstrated in testing for various psychiatric disorders using expression and XCI studies which have shown correlating results in buccal and brain tissue cells. 19,20 Despite the high potential value of buccal swab analysis, we were unable to obtain a sample, as the family was not available for further testing.…”

Developmental regulation of X-chromosome inactivation

“…When no secondary skewing due to cell selection is prevalent, blood or buccal swab samples can be used to relatively accurately predict the skewing ratio in many tissues of the individual [140,141]. Thereby they can provide diagnostic information for the prevalence of active X--linked disease alleles also for inaccessible tissues like the brain.…”