Associated features in females with an FMR1 premutation

A variety of medical problems besides FXTAS and FXPOI have been reported to occur more frequently in premutation carriers ascertained from clinical populations, as compared to noncarrier controls. Thyroid problems were found in 17.3% of non-FXTAS female carriers (not significantly different from controls), but in 50% of women with FXTAS, which was a significantly higher frequency than in age-matched controls [10]. A study of female carriers by Rodriquez-Revenga et al. [11] also found a significant increase in thyroid disease, as did results from a large national survey of female carriers [Wheeler, A.C, Bailey D.B., Raspa M., unpublished data]. Comparison between nonclinically referred premutation carriers and non-carriers ages 18 to 50 showed an increase to 10% from 5%, but this was not statistically significant [12]. Thus, this association may be important in older women. Irrespective, these problems may include either a history of Hashimoto’s thyroiditis leading to hypothyroidism or occasionally, Graves’ disease. These problems are immune-mediated disorders (IMD) and they are one of several such problems that have been reported in female carriers [13]. Winarni et al. [13] studied 344 adult female carriers ascertained from fragile X families and found that 44.7% suffered from an IMD compared to 27.8% of controls. The odds ratio of having an IMD was significantly elevated both in females with FXTAS (OR = 5.5) and without FXTAS (OR = 2.1) from this cohort compared to controls [13].

In the study of IMD [13], autoimmune thyroid disorders were the most common problems overall (24.4%) followed by fibromyalgia in 10.2%. Both of these were significantly different compared to a limited number of controls (n = 72). However, two recent studies of FMR1 mutations among women with fibromyalgia in Spain have reported conflicting findings, with one study of 353 women finding an increased rate of FMR1 premutations, while a second study of 700 women did not find an association [14, 15]. More research is needed in this area.

Hypertension was first noted by Coffey et al. [10] in a survey of 146 premutation female carriers ascertained from fragile X families in clinic. In a large national survey of women with a premutation, 15.1% of women reported a diagnosis of hypertension, which was significantly lower than national occurrence rates [Wheeler, A.C, Bailey D.B., Raspa M., unpublished data]. Similarly, hypertension was seen in 16.4% of women without FXTAS which was not different from age-matched controls (10%). However, hypertension was seen in 61% of females with FXTAS, a significantly higher frequency than 18%, observed in age-matched controls. Hypertension may be considered an autonomic problem associated with premutation-mediated toxicity related to FXTAS.

Migraines are common among carriers and they occur in both males and females. In a single study of 315 carriers (203 females and 112 males) compared to 154 controls, a diagnosis of migraines was seen in 54.2% of female carriers, significantly different from female controls (25.3%) [16]. Smith, Seltzer, and Greenberg [17] reported that headaches (not specifically migraines) were significantly more common among premutation carrier mothers of children with FXS (26.9%) than matched controls (13.6%) who did not have children with disabilities. Of note, headaches were not significantly increased in carriers ascertained from the general population compared to controls in Seltzer et al. [7], so this may imply a relationship between migraines in families ascertained in clinic and family stress issues. Migraines can be associated with some syndromes resulting from mitochondrial dysfunction, which has been observed in cell lines from premutation carriers [18, 19]. As with the general population, the onset of migraines is typically in teenage or young adult years and migraine prevalence decreases with age [16].

Neuropathy was first reported in female premutation carriers in a series of five case reports of females with FXTAS, of whom four had signs of neuropathy on examination [20]. In a subsequent neuropathological case series [21] of eight women with the premutation with or without FXTAS, three were noted to have neuropathy. One of these women had chemotherapy with multiple neurotoxic agents, making it difficult to determine whether the neuropathy related to the premutation, and one had multiple sclerosis with likely central symptoms complicating assessment of nerve disease. One of the women, however, did have neuropathy with no obvious cause other than the premutation.

Several studies have examined neuropathic signs and symptoms in large groups of carriers relative to controls. Berry-Kravis et al. [22] found a significantly higher numerical neuropathy score based on examinations of 73 female premutation carriers relative to 32 age-matched control women, but this finding did not achieve statistical significance. The neuropathy score correlated with CGG repeat length after controlling for activation ratio, suggesting a relationship of neuropathic signs to the premutation. Neuropathy scores also correlated with the ataxia subscore on the FXTAS rating scale, suggesting that carriers beginning to have signs of FXTAS are more likely to have neuropathic signs than those without signs of FXTAS. Coffey et al. [10] studied 128 female carriers without FXTAS, 18 carriers with FXTAS and 69 controls, and found a significant rate of numbness and tingling and muscle pain in the extremities in both women with FXTAS and also in those without FXTAS compared to controls. However, neurological examination showed there was rarely sensory loss or evidence of neuropathy in women without FXTAS. Evidence of neuropathy upon examination was increased in carriers with FXTAS as compared to controls and to carriers without FXTAS. Carrier women without FXTAS also reported a history of intermittent tremor in 11%, significantly higher than the controls with 1.5% [10]. Therefore, symptoms of neurological problems by history are more common than what is documented by neurological examination, presumably because symptoms may be very intermittent early on and persistent findings only occur when the CNS changes are more significant. In Chonchaiya et al. [23], a structured questionnaire was administered to 110 female carriers who were daughters of a parent with FXTAS, 36 female carriers without a parent with FXTAS, and 43 controls. Neuropathic symptoms in the arms and legs were more frequently reported by carriers with and without parents with FXTAS than by controls. Two other studies found a significantly higher prevalence of neuropathic symptoms. Seltzer et al. [7], in a population based sample, reported that 29% of premutation carriers reported numbness (versus 13% of controls), and Smith et al. [17] found that 26.6% of premutation carrier mothers of full mutation children with FXS experienced muscle soreness (versus 16.6% of controls). Hunter et al. [12] did not find an increase in reporting of musculoskeletal symptoms by carrier women compared to controls, although they did not specifically ask about neuropathic symptoms. Based on the literature, it seems that neuropathy is clearly related to carrier status in female carriers but may not become manifest until symptoms of FXTAS also begin to emerge.

Vestibular complaints with a feeling of spinning, suddenly being unbalanced, and difficulty with ‘equilibrium’ are commonly reported complaints voiced by female premutation carriers. In Chonchaiya et al. [23] dizziness was reported more frequently by carriers with or without a parent with FXTAS than by noncarrier controls, and balance problems by carrier women with a parent with FXTAS more frequently than by carriers with no parent with FXTAS or controls. Smith et al. [17] reported significantly higher rates of dizziness in premutation carrier mothers of children with FXS (5.0%) than controls (1.3%), and this was also reported by Seltzer et al. [7] who found that dizziness and faintness were experienced by 18% of premutation carriers in a population-based sample, significantly higher than controls (4%). Recent quantitative studies using computerized dynamic posturography (CDP), a ‘gold standard’ balance assessment tool that has been shown to be highly sensitive, have shown impairments relative to control standards in a small group of female premutation carriers with the vestibular conditions of the sensory organization test and with the motor control and limits of stability test [24]. Vestibular deficits appeared to be present in carriers who did not meet clinical criteria for FXTAS, but were correlated with FXTAS motor rating scale scores and were more severe in those with FXTAS.

In addition to the symptoms reported above, Smith et al. [17] reported significantly higher rates of backache and fatigue in premutation carrier mothers of full mutation children with FXS than in controls.

Table 1 summarizes nominations for medical/health features for women with a premutation with and without a diagnosis of FXTAS.

Female premutation carriers are known to be at increased risk for Fragile X-associated Primary Ovarian Insufficiency (FXPOI). FXPOI encompasses premature ovarian failure, or cessation of menses prior to age 40, and other indicators of early ovarian aging or dysfunction [25]. On average, the age at menopause among premutation carriers is 5 years earlier than in the general population of women [5, 7, 26]. Smith et al. [17] also reported significantly higher rates of hot flashes or flushes in premutation carriers (15.4%) than controls (6.9%). CGG repeat size has been found to be associated with the risk of earlier menopause but in a non-linear manner, with the highest risk for those with mid-range repeats (approximately 70 to 100) [5, 27‐30].

Among women who are still cycling, hormonal changes associated with FXPOI are noted more often in women with the premutation compared with controls. These include decreased levels of anti-Müllerian hormone (AMH) and increased levels of follicle stimulating hormone (FSH), among others [5, 26, 29, 31‐33]. Other signs of early ovarian aging include irregular, shorter or skipped cycles and subfertility [27, 32].

The most immediate and significant consequence of POI is reduced fertility [27, 34]. Given the higher rates of early menopause, difficulty with fertility is significant for women with a premutation. Even among younger women, difficulty getting pregnant has been reported at higher than expected rates among women who are premutation carriers [27]. In a large national survey study of families affected by FX, female premutation carriers reported a significantly higher rate of use of assistive reproductive technology (for example, fertility drugs, IVF) before knowing their FMR1 status than is seen in the national occurrence rates [Wheeler, A.C, Bailey D.B., Raspa M., unpublished data]. Similar to the other symptoms of FXPOI, fertility problems appear to be most significant for women in the mid-range CGG group [27].

Despite known challenges with fertility, very little is known regarding potential obstetric or perinatal risks for FMR1 premutation carriers. One study, conducted in Finland, examined pregnancy outcomes in 63 women who were premutation carriers compared to the general obstetric population [35]. The authors of this study found a slightly higher risk for late pregnancy bleeding in the FMR1 premutation, but no other concerns related to the course or outcome of pregnancy. In a large national survey study [Wheeler, A.C, Bailey D.B., Raspa M., unpublished data] a significantly higher rate of reported preeclampsia was found in premutation carrier women than would be expected based on national occurrence rates in the United States. More research is needed to determine whether women with a premutation experience greater pregnancy or birth risks.

In general, the state of early estrogen deficiency resulting from POI leads to an increased risk for low bone density, earlier onset osteoporosis and bone fractures [36], impaired endothelial function [37], earlier onset of coronary heart disease [38], and increased cardiovascular mortality. Among premutation carriers, lower bone mineral density [39] and osteoporosis [27] is reported at a high frequency than among non-carriers, but not other estrogen deficiency related disorders.

Hypoestrogenism may have behavioral and cognitive consequences as well. Women with an earlier age at menopause are reported to have more anxiety, depression, somatization, sensitivity, hostility, and psychological distress than women with normal ovarian function [40]. Some studies have found suggestive evidence that symptoms of FXPOI may partially explain the increased vulnerability for mood disorders [41] and anxiety and depression [12].

Given the altered hormone profiles and the stress related to being a carrier of the premutation (for example, additional potential stress of having a newborn with FXS), postpartum depression would seem to be of great concern. Very few studies have specifically examined increased risks for PDD in women with a premutation. Wheeler et al. [unpublished data] found that rates of self-reported postpartum depression among women with a premutation were not higher than is found in national occurrence rates. However, among those who had experienced PPD, 41.18% experienced at least 2 episodes. In a study of 50 women with a premutation who also had children and a history of major depressive disorder, there was a significant increase in risk for PDD among women with more than one child with FXS [42]. Therefore it may be the cumulative stress of having multiple children with FXS that increases risk for PDD, rather than premutation status. More research is needed in this area.

The question of whether or not endogenous or exogenous estrogen (from replacement therapy) is related to indicators of neurocognitive deficit is unresolved (reviewed in [43]). The statistically significant association of reduced Verbal IQ and a crude measure of estrogen status among premutation carriers suggests further studies should be done [44].

Estrogen also plays a role in immune-response and inflammation and has been implicated in the onset of autoimmune disorders [45], a class of disorders reported to be elevated among women who carry the premutation carries as noted above. Lastly, estrogen has been shown to moderate the impact of chronic stress on mood and psychiatric outcomes [46] a role of particular interest given that women with the premutation often experience high levels of stress related to their role as primary caretakers of children with fragile X syndrome and older relatives with FXTAS.

Table 2 summarizes nominations for reproductive features for women with a premutation with and without probable FXPOI.

Several studies have found normal overall cognitive abilities in non-FXTAS female adult premutation carriers who underwent general intelligence tests (most commonly the Wechsler scales) [47, 52‐56]. A recent study in older female premutation carriers over age 50 also showed normal IQ scores [57]. In contrast, a few reports have documented lower verbal IQ scores among these women compared to female normal controls [44, 58] or their male counterparts [59], with CGG repeat length explaining approximately 4% of the variance of verbal IQ per linear regression [44]. Case studies have shown mixed results as well, with low [60, 61] and superior [62] IQ scores both observed in girls with the premutation. Myers and colleagues [63] examined 14 children (7 female) and found a trend towards lower performance IQ, a measure closely related to executive functioning. Arithmetic difficulties have also been reported in females with the premutation [50, 58].

Executive function involves the capacity for self-regulation of behavior and attention, and consists of multiple processes including maintaining and updating relevant information in working memory, inhibition of irrelevant information, switching task goals, and performance monitoring [64, 65]. Although executive function has been regarded as the primary cognitive domain affected in patients with FXTAS [50, 66], several studies of non-FXTAS female premutation carriers in young adulthood and midlife have reported normal scores on widely-used executive functioning tests such as the Wisconsin Card Sorting Test (WCST), Trail Making Test (TMT) and Stroop Color and Word Test [52, 54, 55, 67]. Whereas, in a study involving older female premutation carriers up to 76 years of age (mean age = 41) [47], executive function, as measured by the Behavioral Dyscontrol Scale (BDS) [68], was modulated by premutation CGG repeat length and/or FMRP level after controlling for full-scale IQ scores (FSIQ). By examining event-related brain potentials (ERPs) in older female premutation carriers, Yang et al. [57] found poorer BDS performance correlated with decreased amplitude of the frontal P300. This ERP component is thought to index selective attention and working memory updating processes, which may underlie the executive dysfunction in both males and females with FXTAS [57, 69]. Thus, executive dysfunction likely presents as a late-onset phenotype affecting non-FXTAS female premutation carriers over age 50 in addition to non-FXTAS premutation males [48, 66]. It is also worth noting that both of the two studies [47, 57] with findings of executive dysfunction have controlled for FSIQ as a covariate.

Sustained attention in a visual search task was comparable among non-FXTAS females with the premutation and various control groups [58]. A large sample of females with the premutation had more self-reported attention deficits than controls without a mutation [55]. Attention involved in enumerating 5 to 8 rectangles was shown to be modulated by both premutation CGG repeat length and age [70].

Verbal memory generally remains intact in non-FXTAS female premutation carriers [55, 57, 58, 67], but one case study reported substantially impaired verbal memory functions in a 72-year-old old woman [71]. Both immediate and delayed recall of visual memory has been shown to be affected by the premutation CGG repeat length in these carriers [47]. In a functional magnetic resonance imaging (MRI) experiment using a working memory task, carriers of both genders showed reduced frontal activation regardless of FXTAS diagnosis [72]. Interestingly, Yang et al. [57] found impairments in some measures of working memory in non-FXTAS female carriers that were not present in females with FXTAS.

As noted earlier, studies assessing global indices of verbal ability such as verbal IQ, have generally reported that premutation carriers who are not affected by FXTAS exhibit comparable abilities as matched controls or normed references (reviewed in [12]). In contrast, results from the few studies that have assessed functional language (or, the use of language in social contexts, for example, conversational ability) suggest that such language skills may be impacted among premutation carriers. Sterling et al. [73] elicited brief language samples collected from a group of nearly 200 women with the premutation and assessed samples for different types of dysfluencies, including incomplete or abandoned utterances, repetitive speech, excessive fillers (for example, um, ah, oh), and revisions to correct or modify a prior utterance. These types of dysfluencies could reflect problems with executive skills such as planning and organization, and can interfere with fluent communication. As such, they may represent clinically meaningful phenotypes. In this study, the rate and types of dysfluencies were compared between women with the premutation and women who were parents of individuals with autism, included to control for the stress of caring for a child with a disability, which the authors hypothesized could impact fluency. Analyses revealed significantly higher rates of all types of dysfluencies among the premutation carrier group (compared to the mothers of children with autism), as well as a significant association with age (increased dysfluencies with greater age). There was no association with CGG repeat length, and other molecular variables were not examined. Losh et al. [74] also reported elevated rates of subtle conversational differences among premutation carrier women, further suggesting that language may be affected in the premutation.

Table 3 summarizes nominations for cognitive features in females with a premutation with and without a diagnosis of FXTAS.

Mood disorders have been a concern in the fragile X premutation population for over two decades. Initial small studies in women failed to demonstrate meaningful difference between carriers and controls in depressive disorders [52, 75]. However, these studies were small, limited by the screening tools and by poor recall. Later, much larger research studies did demonstrate a relationship between the number of CGG repeats and the presence of depression [76] as well as the severity of depressive symptoms [77]. When comparing 93 women with the premutation screened using the strict criteria of the structured clinical interview for the DSM-IV (SCID) to a large national databank, the lifetime prevalence of major depressive disorder was 43.0% versus 31.9% [50]. Although Seltzer et al. [7] did not find evidence of elevated prevalence of depressive symptoms in a population-based sample, and Smith et al. [17] similarly did not report elevated rates of negative affect in premutation carriers than controls. Seltzer et al. [78] reported evidence of higher rates of depressive and anxiety symptoms in premutation carrier mothers of full mutation children with FXS under certain genetic and environmental conditions: mothers who experienced stressful life events in the previous year had higher rates of depression and anxiety if their CGG repeats were in the mid-range of CGG repeats. Dysthymia and bipolar disorder have generally failed to demonstrate significant levels in carriers compared to controls [79].

Because FXS is one of the most common single-gene disorders associated with autism, investigation has been undertaken to determine what risk the carrier state confers. In a screening study of individuals from families with FXS, roughly 14% of boys and 5% of girls with the premutation were found to also have an autism spectrum disorder (ASD) [80]. Even among those carriers not diagnosed with ASD, related psychological traits are more common among carriers compared to controls without the premutation. A relatively large body of research has now documented differences among parents and relatives of individuals with autism, constituting a broad autism phenotype, or, a constellation of mild behavioral features that resemble the features of autism in quality but that are more subtly expressed and not typically associated with functional impairment (reviewed in [81]). A recent study examined a broad range of pragmatic language skills as well as related behavioral features of the broad autism phenotype among women with the premutation, compared with mothers of children with autism, and mothers of typically developing children with no family history of fragile X, autism, or language impairment [74]. In this study, conversational samples from a videotaped semistructured interview were used to assess pragmatic language using the Pragmatic Rating Scale (PRS) [82]. This study replicated previous findings in the autism parent group and also showed that women with the premutation exhibited similarly elevated rates of pragmatic language problems relative to controls. Factor analysis of items on the PRS revealed that premutation carriers committed the same types of pragmatic language violations as parents of individuals with autism. Such similarities in pragmatic language profiles could suggest that the differences between these groups stem from similar underlying factors, supporting a link between FMR1 and autism-related phenotypes in carrier relatives. In support of this possibility, the study also found that premutation carriers displayed elevated rates of personality traits associated with the broad autism phenotype, rigid or inflexible traits and socially reticent dispositions. The presence of broad autism phenotype traits was associated with greater expression of autism symptoms in their children with FXS. Other studies have also found increased rates of both social aloofness [83] and a rigid perfectionism [84] among carrier women. Studies have shown that amygdala dysfunction in viewing social stimuli seen in carriers correlates with clinical findings of social deficits and both FMRP deficits and elevated FMR1 mRNA levels [85].

The largest and most recent study of life-time mood and anxiety in the premutation population was completed by Bourgeois et al. [79]. In that study, carriers both suffering and not suffering from FXTAS were compared in the prevalence of anxiety disorders to a very large age-matched national dataset. In terms of all anxiety disorders, only those suffering from FXTAS demonstrated a higher prevalence. When separated out, this was similarly true for panic disorder, post-traumatic stress disorder and specific phobia. Generalized anxiety disorder and obsessive compulsive disorder failed to demonstrate any difference between carriers and controls. Only social phobia was found to have higher levels in premutation carriers without FXTAS compared to controls. Chronic anxiety has also been associated with radiological signs on MRI; specifically, the higher the anxiety score the smaller the size of the hippocampus in women with the premutation [86].

Psychosis, given its relative rarity in the general population, has been challenging to study in premutation carriers. Initial linkage analysis failed to show a clear relationship of schizophrenia to the FMR1 gene [87]. Prevalence studies have found the overall rate of psychotic disorders to be low [83]. There have, however, been several case reports of combined psychotic illnesses and the premutation, including schizoaffective disorder [88] and a subject with combined schizophrenia and schizoid personality disorder [89]. Interestingly, as opposed to frank psychotic disorders, multiple studies have found increased prevalence of schizotypal personality traits in the carrier population [83, 90].

Attention regulation difficulties have been proposed to be a problem in people with the premutation. Notably, when compared with their control siblings, premutation carriers had significantly more issues with attention than their noncarrier siblings [91]. Inattention and impulsivity amongst FMR1 carriers can be problematic through adulthood [55], although hyperactivity was not noted to be increased in prevalence. In an analysis to examine the genetic architecture of ADHD symptoms in families with FXS, it was found that the FMR1 repeat accounts for about 5% of the variance whereas polygenes account for about 50% of the residual variance. This suggests that the premutation acts in concert with additional genetic loci to influence the severity of ADHD symptoms [92].

Sleep issues have recently been studied in carriers, and common measures such as the Pittsburgh Sleep Quality Index and the Insomnia Severity Index have shown significant pathology. These findings may be related to higher rates of Restless Legs Syndrome and sleep apnea, both of which have shown multiple-fold increases in subsets of the premutation population [93, 94]. Sleep apnea is common in older carriers with FXTAS. In a study of 229 males and 201 females with the premutation, including 118 with FXTAS and 123 controls, sleep apnea occurred in 31.4% of carriers with FXTAS, 8.6% of carriers without FXTAS and in 13.8% of controls by medical history [93]. These issues may be contributing to the development of significant fatigue, which is a common complaint of adult carriers [95].

Two hypotheses have been advanced to account for elevated psychiatric, cognitive, and somatic symptoms in premutation carriers [96]: first, that such symptoms are a primary biological feature of FMR1 CGG expansions in the premutation range, and second, that such symptoms may be exacerbated by the stress associated with parenting a child with FXS. Importantly, stress may interact with the biological vulnerabilities caused by the premutation, and thus it is important to incorporate biological markers when exploring stress effects in this population.