X chromosome inactivation does not define the development of premature ovarian failure in fragile X premutation carriers.
Since only 20% of female fragile X premutation carriers develop premature ovarian failure (POF, i.e., amenorrhea before age of 40 years), and since X chromosome inactivation (XCI) determines the phenotypic severity of full mutation women, we reasoned that the development of POF in fragile X premutation carriers could be due to skewed XCI (XCI ratio >80:20). To determine inactivation ratios and activities of the premutations, inactivation patterns were assessed in peripheral blood samples from 101 fragile X premutation carriers (mean age 47.1 years, range 12-72) through analysis of the AR and FMR1 loci, respectively. In addition, AR inactivation patterns were assessed in peripheral blood samples from 25 women with idiopathic POF (mean age 31.7 years, range 19-48). We addressed the association between age and skewed XCI because older women are prone to XCI skewness. The median XCI ratios were 68% for premutation carriers with POF (N = 37), 67% for premutation carriers without POF (N = 64) and 61% for women with idiopathic POF (N = 25). The incidence of skewing was similar in all groups, that is, 7 of 37 (18.9%) in premutation carriers with POF, 11 of 64 (17.2%) in premutation carriers without POF, and 3 of 25 (12%) in women with idiopathic POF. There was good concordance between inactivation ratios at the two loci tested in 62 premutation carriers (intraclass correlation coefficient = 0.86; P < 0.01). No age-specific skewing was observed. Skewed XCI and activity of the premutation are not associated with POF in fragile X premutation carriers.
Spath
Marian A
MA
Department of Obstetrics and Gynecology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands. m.spath@obgyn.umcn.nl
Nillesen
Willy N
WN
Smits
Arie P T
AP
Feuth
Ton B
TB
Braat
Didi D M
DD
van Kessel
Ad Geurts
AG
Yntema
Helger G
HG
D000328:Adult; D000367:Age Factors; D041321:Chromosomes, Human, X; D015331:Cohort Studies; D005260:Female; D051860:Fragile X Messenger Ribonucleoprotein 1 / Q000235:genetics; D005600:Fragile X Syndrome / Q000235:genetics*; D006579:Heterozygote; D006801:Humans; D015994:Incidence; D007621:Karyotyping; D008875:Middle Aged; D010641:Phenotype; D016649:Primary Ovarian Insufficiency / Q000235:genetics*; D049951:X Chromosome Inactivation
D051860:Fragile X Messenger Ribonucleoprotein 1