Novel methylation markers of the dysexecutive-psychiatric phenotype in FMR1 premutation women

Abstract

Objective: To examine the epigenetic basis of psychiatric symptoms and dysexecutive impairments in FMR1 premutation (PM: 55 to 199 CGG repeats) women.Methods: A total of 35 FMR1 PM women aged between 22 and 55 years and 35 age-and IQmatched women controls (CGG ,45) participated in this study. All participants completed a range of executive function tests and self-reported symptoms of psychiatric disorders. The molecular measures included DNA methylation of the FMR1 CpG island in blood, presented as FMR1 activation ratio (AR), and 9 CpG sites located at the FMR1 exon1/intron 1 boundary, CGG size, and FMR1 mRNA levels. Results:We show that FMR1 intron 1 methylation levels could be used to dichotomize PM women into greater and lower risk categories (p 5 0.006 to 0.037; odds ratio 5 14-24.8), with only FMR1 intron 1 methylation, and to a lesser extent AR, being significantly correlated with the likelihood of probable dysexecutive or psychiatric symptoms (p , 0.05). Furthermore, the significant relationships between methylation and social anxiety were found to be mediated by executive function performance, but only in PM women. FMR1 exon 1 methylation, CGG size, and FMR1 mRNA could not predict probable dysexecutive/psychiatric disorders in PM women.Conclusions: This is the first study supporting presence of specific epigenetic etiology associated with increased risk of developing comorbid dysexecutive and social anxiety symptoms in PM women. These findings could have implications for early intervention and risk estimate recommendations aimed at improving the outcomes for PM women and their families. Neurology ® 2015;84:1631-1638 GLOSSARY 5-hmC 5 5-hydroxymethylacytosine; ADHD-PI 5 attention-deficit/hyperactivity disorder-predominantly inattentive; AR 5 FMR1 activation ratio; DASS 5 Depression Anxiety Stress Scale; ELVF 5 Excluded Letter Verbal Fluency; FM 5 full mutation; FMR1 5 fragile X mental retardation 1 gene; FMRP 5 fragile X mental retardation protein; FREE 5 fragile X-related epigenetic element; FXS 5 fragile X syndrome; GEE 5 generalized estimating equation; IQR 5 interquartile range; LNS 5 Letter-Number Sequencing; OR 5 odds ratio; PM 5 premutation; ROC 5 receiver operating characteristic.The common premutation (PM) CGG expansion (55-199 repeats) in the 59 UTR of the fragile X mental retardation 1 (FMR1) gene (;1 in 450 males and ;1 in 150 females) 1 leads to a number of late-onset disorders 2 and high rates of dysexecutive and psychiatric symptoms, all with incomplete penetrance. 3 The RNA gain-of-function toxicity 4 and deficient FMR1 protein (FMRP) translation 5 are primary molecular features of PM-related disorders and are directly related to the CGG size. However, their effects on the phenotype are diluted in PM females through methylation-related silencing as part of X-inactivation.

Trajectory and Predictors of Depression and Anxiety Disorders in Mothers With the FMR1 Premutation

“…Both our study and others (1; 20; 27; 29) note the subtlety of the relationships between mid-level CGG repeats and psychiatric symptoms that are challenging to detect given the relatively small samples of women with larger premutation alleles and a failure to intentionally examine non-linear effects in the presence of linear effects. The lack of replication of these findings in some studies may be due, in part, to these factors as many conduct simple correlations or exclusively linear analyses which obscure detection of non-linear effects and preclude detecting a potential relationship between mid-range repeats and psychiatric symptomology (33; 34). …”

“…Alternatively, undiscovered genetic or epigenetic factors and mediating cognitive or environmental factors are rival hypotheses given evidence of differential sensitivity to stressful life events in relation to depressive and anxious symptomology in women with midsize CGG repeats (21) and recent discoveries of novel methylation markers associated with anxiety mediated by executive functioning in women with the premutation (33) Progressive mRNA toxicity is an associated putative explanatory mechanism with recognition of the cumulative effects of stress and the presence of protective factors as contributory factors (34). …”

Epigenetics of fragile X syndrome and fragile X‐related disorders

“…This seems to be the case in relation to the clinical and radiological features of FXTAS; 33,34 however, in contrast, there is no evidence for a relationship between skewed X-inactivation and fragile X-associated primary ovarian insufficiency. 35 Interestingly, in premutation females, FREE2 methylation, which is sensitive to X-inactivation changes, has been found to be correlated both with poorer performance on tasks of executive function 36 and with increased grey matter volume of cortical structures that have known roles in executive function, such as frontal and parietal gyri. 37…”

Advanced technologies for the molecular diagnosis of fragile X syndrome

“…These regions, located within the FMR1 promoter (FREE1) and within exon1/intron1 (FREE2) are methylated in FXS but unmethylated in typical developing controls or in those carrying small-expanded alleles. The methylation status of these regions associates with the methylation in the FMR1 promoter region in subjects with FXS, with FMRP expression (76), and with an increased risk for clinical involvement in premutation carriers including comorbid dysexecutive and social anxiety symptoms, verbal impairment and working memory in premutation women (78–80). As the other bisulfite based approach, the MALDI-TOF MS possesses the limitation that females with a full mutation or carriers cannot be easily distinguished from normal females.…”