Expansion of the fragile X CGG repeat in females with premutation or intermediate alleles

Fragile X analysis of 1112 prenatal samples from 1991 to 2010

OBJECTIVE

To determine risks of expansion for normal, intermediate, and premutation FMR1 CGG repeats.

METHODS

PCR was used to compare the FMR1 alleles in prenatal (chorionic villi and amniocytes) and parental samples collected from 1991 to 2010. Prenatal diagnoses were confirmed by Southern analysis.

RESULTS

Fragile X analysis of 1112 pregnancies identified 558 normal, 106 intermediate, 216 premutation, and 232 full mutation fetuses. Of 509 maternal, intermediate, and premutation alleles, 350 (68.7%) were unstable on transmission with expansions ranging from one repeat to the full mutation. The smallest premutation alleles expanding to the full mutation were in mothers with 65 and 66 repeats. Transmissions from women with or without a family history of fragile X suggested greater instability in women from families that included full mutation expansions.

CONCLUSIONS

The maternal transmissions of alleles with 55 to 59 CGG repeats summarized here indicate that the risk for expansion to full mutation is substantially less than previous estimates for this size category. Most premutation alleles with no family history of fragile X exhibited less instability than those with a history of fragile X. Thus, lower risk estimates for full mutation expansion may be appropriate for women newly identified as premutation carriers through routine screening.

Increased frequency of occult fragile X-associated primary ovarian insufficiency in infertile women with evidence of impaired ovarian function

BACKGROUND

The FMR1 premutation is associated with overt primary ovarian insufficiency (POI). However, its prevalence in women with occult POI (i.e. menstrual cycles, but impaired ovarian response) has not been examined. We hypothesized that both the FMR1 premutation and intermediate allele is more frequent in infertile women with occult POI than in controls, and that a repeat length cutoff might predict occult POI.

METHODS

All subjects were menstruating women <42 years old and with no family history of unexplained mental retardation, autism or fragile X syndrome. Cases had occult POI defined by elevated FSH or poor response to gonadotrophin therapy (n = 535). Control subjects (n = 521) had infertility from other causes or were oocyte donors. Prevalence of the FMR1 premutation and intermediate alleles was examined and allele length was compared between controls and women with occult POI.

RESULTS

The frequency of the premutation (7/535 versus 1/521; P< 0.05) and intermediate alleles (17/535 versus 7/521; P< 0.05) was higher in women with occult POI than in controls. The allele with the greatest number of CGG repeats was longer in women with occult POI compared with controls (32.7 ± 7.1 versus 31.6 ± 4.3; P < 0.01). A receiver operating characteristic curve examining repeat length as a test for occult POI had an area of 0.56 ± 0.02 (P < 0.01). A repeat cutoff of 45 had a specificity of 98%, but a sensitivity of only 5% to identify occult POI. The positive predictive value was only 21% for a fertility population that has ∼ 22% of its patients with occult POI.

CONCLUSIONS

The data suggest that FMR1 premutations and intermediate alleles are increased in women with occult POI. Thus, FMR1 testing should be performed in these women as some will have fragileX-associated POI. Although the FMR1 repeat lengths were longer in women with occult POI, the data do not support the use of a repeat length cutoff to predict occult POI.

Genetic risk in autism: new associations and clinical testing

INTRODUCTION

Autism spectrum disorder (ASD) is prevalent in ∼ 1% of the population worldwide. It is also understood, through twin studies, that ASD has a heritability of 70 - 90%. Molecular genetic studies have presented some genetic risk factors associated with ASD that have potential implications in its diagnosis and genetic testing.

AREAS COVERED

In this selective review, the author refers to previous systematic reviews that consecutively cited all the published papers on ASD at that time. The article presents the replicated genetic risk factors for ASD and the clinical relevance of these findings focusing on rare copy number variations and single gene mutations. The author provides the reader with a deeper insight into the complexity of ASD genetics and its implications for diagnostic genetic testing in ASD. The author also provides the reader with an algorithm for clinical genetic testing in individuals who are clinically diagnosed with ASD.

EXPERT OPINION

Despite the high heritability of ASD and several replicated genetic risk factors, there is no clinical genetic test available that covers most genetic risk factors. Also, validity analyses on most available genetic testing procedures have not been performed so far. The variable risk genotypes, as well as related strongly variable phenotypes, have to be taken into account by genetic counseling.

Genome instability and epigenetic modification--heritable responses to environmental stress?

As sessile organisms, plants need to continuously adjust their responses to external stimuli to cope with changing growth conditions. Since the seed dispersal range is often rather limited, exposure of progeny to the growth conditions of parents is very probable. The plasticity of plant phenotypes cannot be simply explained by genetic changes such as point mutations, deletions, insertions and gross chromosomal rearrangements. Since many environmental stresses persist for only one or several plant generations, other mechanisms of adaptation must exist. The heritability of reversible epigenetic modifications that regulate gene expression without changing DNA sequence makes them an attractive alternative mechanism. In this review, we discuss recent advances in understanding how changes in genome stability and epigenetically mediated changes in gene expression could contribute to plant adaptation. We provide examples of environmentally induced transgenerational epigenetic effects that include the appearance of new phenotypes in successive generations of stressed plants. We also describe several cases in which exposure to stress leads to nonrandom heritable but reversible changes in stress tolerance in the progeny of stressed plants.

Lifetime prevalence of mood and anxiety disorders in fragile X premutation carriers

OBJECTIVE

The authors studied the lifetime prevalence of DSM-IV-TR psychiatric disorders in a population of adults with the fragile X premutation.

METHOD

The Structured Clinical Interview for DSM-IV was conducted, from 2007-2008, in 85 individuals with the fragile X premutation, 47 with the fragile X-associated tremor/ataxia syndrome (FXTAS; 33 male, 14 female; mean age = 66 years) and 38 without FXTAS (16 male, 22 female; mean age = 52 years). Lifetime prevalence for mood and anxiety disorders among carriers with and without FXTAS was compared to available age-specific population estimates from the National Comorbidity Survey Replication (NCS-R).

RESULTS

Among participants with FXTAS, 30 (65%) met lifetime DSM-IV-TR criteria for a mood disorder; 24 (52%) met lifetime DSM-IV-TR criteria for an anxiety disorder. Among the non-FXTAS participants, there were 15 instances of lifetime mood disorder (42%) and 18 of lifetime anxiety disorder (47%). When compared to age-specific NCS-R data, the lifetime prevalences of any mood disorder (P < .0001), major depressive disorder (P < .0001), any anxiety disorder (P < .0001), panic disorder (P = .006), specific phobia (P = .0003), and posttraumatic stress disorder (P = .004) were significantly higher in participants with FXTAS. The lifetime rates of social phobia in individuals with the premutation without FXTAS were significantly higher than NCS-R data (P = .001).

CONCLUSIONS

This sample of carriers of the fragile X premutation had a notably high lifetime risk of mood and anxiety disorders. Mood and anxiety disorders may be part of the clinical phenotype of the fragile X premutation conditions, especially in carriers with FXTAS. Clinicians encountering these patients are advised to consider FXTAS as a neuropsychiatric syndrome as well as a neurologic disorder.

Chromosomal abnormalities in women with premature ovarian failure

Premature ovarian failure is a complex disorder that results in the early loss of ovarian function; however this disease must be separated from early menopause because these patients can sporadically ovulate and in literature are described pregnancies. The aetiology and the patho-physiology of premature ovarian failure are still matter of debate, but is commonly accepted that genetic factors play an important role. This review is aimed to present an overview of known inherited factor implied in the pathogenesis of this disorder to help physician in the counselling of affected pregnant women.

Communication of genetic risk information to daughters in families with fragile X syndrome: the parent's perspective

Parental approaches to communicating information about genetic disorders to their children may be an important determinant in how the children manage stress as well as their adjustment and adaptation to that information. We explored communication patterns through structured interviews with 46 parents of daughters who learned about their genetic risk status as minors. Three different levels of knowledge about fragile X syndrome were explored: 1) informing that it has been diagnosed in the family and is an inherited disorder, 2) informing about the possibility of a daughter being a carrier, and 3) if testing had been done, informing the daughter of her actual carrier status. Additionally, parental perceptions of their daughter's understanding of the information were explored along with frequency of discussions. We found that communication about genetic risk was initiated by the parents. Five disclosure patterns were identified with variations in style, content, and frequency of communication related to the information that was being disclosed. Aspects of resilient communication were present for all levels of disclosure; however, as the information became more personally relevant for the daughter such as disclosure about the possibility of "being a carrier" for fragile X syndrome and there was uncertainty regarding potential outcomes, the conversations included fewer resilient characteristics. Uncertainty about what and how to present information may negatively affect a parent's ability to include elements of resilient communication when disclosing genetic risk information.

Primary ovarian insufficiency

Primary ovarian insufficiency is a subclass of ovarian dysfunction in which the cause is within the ovary. In most cases, an unknown mechanism leads to premature exhaustion of the resting pool of primordial follicles. Primary ovarian insufficiency might also result from genetic defects, chemotherapy, radiotherapy, or surgery. The main symptom is absence of regular menstrual cycles, and the diagnosis is confirmed by detection of raised follicle-stimulating hormone and declined oestradiol concentrations in the serum, suggesting a primary ovarian defect. The disorder usually leads to sterility, and has a large effect on reproductive health when it arises at a young age. Fertility-preservation options can be offered to some patients with cancer and those at risk of early menopause, such as those with familial cases of primary ovarian insufficiency. Long-term deprivation of oestrogen has serious implications for female health in general; and for bone density, cardiovascular and neurological systems, wellbeing, and sexual health in particular.

AGG interruptions in (CGG)(n) DNA repeat tracts modulate the structure and thermodynamics of non-B conformations in vitro

The trinucleotide repeat sequence CGG/CCG is known to expand in the human genome. This expansion is the primary pathogenic signature of fragile X syndrome, which is the most common form of inherited mental retardation. It has been proposed that formation of non-B conformations by the repetitive sequence contributes to the expansion mechanism. It is also known that the CGG/CCG repeat sequence of healthy individuals, which is not prone to expansion, contains AGG/CCT interruptions every 8-11 CGG/CCG repeats. Using DNA containing 19 or 39 CGG repeats, we have found that both the position and number of interruptions modulate the non-B conformation adopted by the repeat sequence. Analysis by chemical probes revealed larger loops and the presence of bulges for sequences containing interruptions. Additionally, using optical analysis and calorimetry, the effect of these structural changes on the thermodynamic stability of the conformation has been quantified. Notably, changing even one nucleotide, as occurs when CGG is replaced with an AGG interruption, causes a measurable decrease in the stability of the conformation adopted by the repeat sequence. These results provide insight into the role interruptions may play in preventing expansion in vivo and also contribute to our understanding of the relationship between non-B conformations and trinucleotide repeat expansion.

Intermediate sized CGG repeats are not a common cause of idiopathic premature ovarian failure

BACKGROUND

It is recognized that FMR1 premutation expansions are associated with premature ovarian failure (POF), but the role of smaller repeats at the boundary of premutation and normal is less clear.

METHODS

We have therefore investigated the incidence of these intermediate sized FMR1 CGG repeats (35-58 repeats) in a series of 366 women ascertained because of menopause before the age of 40.

RESULTS

We found no significant difference in the incidence of intermediates in cases compared with controls. Thus, we were unable to replicate previous studies showing a positive association, despite a significantly larger sample size.

CONCLUSIONS

We therefore conclude that intermediate sized FMR1 CGG repeat alleles should not be considered a high-risk factor for POF based on current evidence.

Fragile X carrier screening and FMR1 allele distribution in the Japanese population

Fragile X syndrome (FXS), which is the most common form of familial mental retardation, is caused by the expansion of the CGG repeat in the FMR1 gene on the X chromosome. Previous studies have suggested that as compared to other populations, Japanese have a lower prevalence of FXS. In addition, in the normal population, there are no carriers who have the premutation allele. We analyzed a total of 946 normal Japanese (576 males and 370 females) and attempted to estimate the frequency of the FMR1 allele. Within this population, we found that 1,155 alleles were in the normal range (less than 40 CGG repeats) and had a modal number of 27 repeats (35.75%). No carriers with premutations (55-200 CGG repeats) were observed in this normal population. We also identified six intermediate-sized alleles (40-54 CGG repeats), with a reported incidence of 1 in 103 males and 1 in 324 females. However, this allele frequency was different from that previously reported for the Japanese population. Since data from previous studies has suggested that FXS might possibly be associated with the genetic mechanism of autism, we also analyzed the length of the CGG repeats in 109 autistic patients. In all cases the CGG repeat numbers were within the normal range (16-36 repeats) and no individuals presented with expanded premutation or intermediate alleles. This finding indicates that the length of the CGG repeat within the FMR1 is unlikely to be responsible for autism in Japanese.

Methylation of novel markers of fragile X alleles is inversely correlated with FMRP expression and FMR1 activation ratio

The fragile X syndrome (FXS) is caused by silencing of the fragile X mental retardation gene (FMR1) and the absence of its product, fragile X mental retardation protein (FMRP), resulting from CpG island methylation associated with large CGG repeat expansions (more than 200) termed full mutation (FM). We have identified a number of novel epigenetic markers for FXS using matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS), naming the most informative fragile X-related epigenetic element 1 (FREE1) and 2 (FREE2). Methylation of both regions was correlated with that of the FMR1 CpG island detected using Southern blot (FREE1 R = 0.97; P < 0.00001, n = 23 and FREE2 R = 0.93; P < 0.00001, n = 23) and negatively correlated with lymphocyte expression of FMRP (FREE1 R = -0.62; P = 0.01, n = 15 and FREE2 R = -0.55; P = 0.03, n = 15) in blood of partially methylated 'high functioning' FM males. In blood of FM carrier females, methylation of both markers was inversely correlated with the FMR1 activation ratio (FREE1 R = -0.93; P < 0.0001, n = 12 and FREE2 R = -0.95; P < 0.0001, n = 9). In a sample set of 49 controls, 18 grey zone (GZ 40-54 repeats), 22 premutation (PM 55-170 repeats) and 22 (affected) FXS subjects, the FREE1 methylation pattern was consistent between blood and chorionic villi as a marker of methylated FM alleles and could be used to differentiate FXS males and females from controls, as well as from carriers of GZ/PM alleles, but not between GZ and PM alleles and controls. Considering its high-throughput and specificity for pathogenic FM alleles, low cost and minimal DNA requirements, FREE MALDI-TOF MS offers a unique tool in FXS diagnostics and newborn population screening.

Molecular analysis of Fragile X syndrome

The gene responsible for Fragile X syndrome, fragile X mental retardation-1 (FMR1), contains an unstable sequence of CGG trinucleotide repeats in its promoter region. Expansions of >200 trinucleotide repeats are considered full mutations and typically lead to abnormal methylation of the region resulting in loss of FMR1 expression. Males with loss of FMR1 protein are expected to be affected by Fragile X syndrome while females may or may not clinically manifest features of the condition. The protocols in this unit outline the complementary use of polymerase chain reaction (PCR) and methylation-sensitive Southern blot hybridization to accurately measure trinucleotide repeat size and methylation status. These protocols are also used to evaluate CGG repeat size in two adult-onset conditions known for their association with FMR1 premutation alleles, Fragile X Tremor/Ataxia (FXTAS) syndrome and Premature Ovarian Failure (POF).

Methyl-CpG-binding PCR of bloodspots for confirmation of fragile X syndrome in males

This study demonstrates that methyl-CpG-binding PCR (MB-PCR) is a rapid and simple method for detecting fragile X syndrome (FXS) in males, which is performed by verifying the methylation status of the FMR1 promoter in bloodspots. Proteins containing methyl-CpG-binding (MB) domains can be freeze-stored and used as stocks, and the entire test requires only a few hours. The minimum amount of DNA required for the test is 0.5 ng. At this amount, detection sensitivity is not hampered, even mixing with excess unmethylated alleles up to 320 folds. We examined bloodspots from 100 males, including 24 with FXS, in a blinded manner. The results revealed that the ability of MB-PCR to detect FMR1 promoter methylation was the same as that of Southern blot hybridization. Since individuals with 2 or more X chromosomes generally have methylated FMR1 alleles, MB-PCR cannot be used to detect FXS in females.

Translation of the FMR1 mRNA is not influenced by AGG interruptions

The fragile X mental retardation 1 (FMR1) gene contains a CGG-repeat element within its 5′ untranslated region (5′UTR) which, for alleles with more than ∼40 repeats, increasingly affects both transcription (up-regulation) and translation (inhibition) of the repeat-containing RNA with increasing CGG-repeat length. Translational inhibition is thought to be due to impaired ribosomal scanning through the CGG-repeat region, which is postulated to form highly stable secondary/tertiary structure. One striking difference between alleles in the premutation range (55–200 CGG repeats) and those in the normal range (<∼40 repeats) is the reduced number/absence of ‘expansion stabilizing’ AGG interruptions in the larger alleles. Such interruptions, which generally occur every 9–11 repeats in normal alleles, are thought to disrupt the extended CGG-repeat hairpin structure, thus facilitating translational initiation. To test this hypothesis, we have measured the translational efficiency of CGG-repeat mRNAs with 0–2 AGG interruptions, both in vitro (rabbit reticulocyte lysates) and in cell culture (HEK-293 cells). We demonstrate that the AGG interruptions have no detectable influence on translational efficiency in either a cell-free system or cell culture, indicating that any AGG-repeat-induced alterations in secondary/tertiary structure, if present, do not involve the rate-limiting step(s) in translational initiation.

The FMR1 gene and fragile X-associated tremor/ataxia syndrome

The CGG-repeat present in the 5'UTR of the FMR1 gene is unstable upon transmission to the next generation. The repeat is up to 55 CGGs long in the normal population. In fragile X patients, a repeat length exceeding 200 CGGs (full mutation: FM) generally leads to methylation of the repeat and the promoter region, which is accompanied by silencing of the FMR1 gene. The gene product FMRP is involved in regulation of transport and translation of certain mRNA in the dendrite, thereby affecting synaptic plasticity. This is central to learning and memory processes. The absence of FMRP seen in FM is the cause of the mental retardation seen in fragile X patients. The premutation (PM) is defined as 55-200 CGGs. Female PM carriers are at risk of developing primary ovarian insufficiency. Recently it was discovered that elderly PM carriers might develop a progressive neurodegenerative disorder called fragile X-associated tremor/ataxia syndrome. Although arising from the mutations in the same gene, distinct mechanisms lead to fragile X syndrome (absence of FMRP) and FXTAS (toxic RNA gain of function). The pathogenic mechanisms thought to underlie these disorders are discussed, with a specific emphasis on FXTAS. This review gives insight on the implications of all possible repeat length categories seen in fragile X families.

Fragiles-X Syndrom

Fragiles-X Syndrom, eine X-chromosomal vererbte neuronale Entwicklungsstörung, betrifft Knaben und Mädchen. Phänotypisch charakteristisch sind intellektuelle Defizite, somatische Merkmale und Verhaltensauffälligkeiten. Pathophysiologisch liegt der Verlust des Proteins FMRP („fragile X mental retardation protein“) zugrunde, in dessen Folge es zum Untergang von Synapsen mit metabotropen Glutamatrezeptoren kommt. Das Gen FMR1 („fragile X mental retardation 1“) enthält in der 5’-nichttranslatierten Genregion eine CGG-Wiederholungssequenz (CGG-Repeat). Bei fast allen Patienten mit Fragilem-X Syndrom liegt ein vollmutiertes, meist inaktives FMR1 mit >200 CGG-Repeats vor. Vollmutationen entstehen bei der Oogonienvermehrung im fetalen Ovar von Trägerinnen eines mitotisch instabilen Prämutationsallels (59–200 Repeats). Die Prämutation führt nicht zu Symptomen des Fragilen-X Syndroms, ist aber ein Risikofaktor für vorzeitige Ovarialinsuffienz und/oder fragiles X-assoziiertes Tremor/Ataxie Syndrom. Die Diagnostik beider Syndrome erfordert eine genetische Untersuchung zur Bestimmung der FMR1-CGG-Repeats. Die vorgeburtliche Diagnostik kann von allen Frauen mit prä- oder vollmutiertem Gen beansprucht werden.

Expansion of an FMR1 grey-zone allele to a full mutation in two generations

Fragile X Syndrome is caused by the expansion of an unstable CGG-repeat tract in the 5'-UTR of the FMR1 gene, which generally results in transcriptional silencing and consequent absence of the FMR1 protein. To date, the smallest premutation allele reported to expand to a full mutation allele in a single generation is 59 CGG repeats. Here, we report a single-generation expansion to a full mutation allele (male with approximately 538 CCG repeats) from a mother who is a carrier of a premutation allele of 56 CGG repeats. Furthermore, the maternal grandfather was a carrier of a gray (or intermediate)-zone allele (45 to 54 repeats) of 52 CGG repeats. Thus, in this family, a gray-zone allele expanded to the full mutation range in two generations. Interestingly, the two AGG interruptions present in the grandfather's allele were absent in the mother's premutation allele. These observations underscore the need to consider carriers of alleles of greater than 55 CGG repeats as being at risk for transmission of a full mutation allele in a single generation, and those with even smaller alleles in the gray zone as being at risk of having grandchildren with full mutation alleles.

A review of fragile X premutation disorders: expanding the psychiatric perspective

CONTEXT

Fragile X premutation conditions are associated with a significant degree of psychopathology and thus are of interest to the psychiatrist. Remarkable advances at the molecular level have enhanced our understanding of fragile X premutation disorders.

OBJECTIVE

The authors review the genetic, molecular, neuroimaging, and clinical (systemic, neurologic, and psychiatric) manifestations of the premutation carrier state (55-200 CGG repeats) of the fragile X mental retardation 1 (FMR1) gene.

DATA SOURCES

The search for the psychiatric clinical manifestations of fragile X-associated conditions was accomplished by PubMed for clinical papers published between 1970 and 2008 with the following search terms: Fragile X syndrome, depression, psychosis, anxiety, and dementia.

STUDY SELECTION

Articles addressing psychiatric symptoms in premutation carriers based on review of the abstracts were reviewed. As the majority of the literature on this topic is based on case reports and small case series, these were included in the database.

RESULTS

Reported clinical manifestations of psychiatric illness in premutation carriers include an apparently significant rate of cognitive, mood, anxiety, and other psychiatric disorders. Fragile X premutation-associated conditions are part of the clinical differential diagnosis of several psychiatric syndromes, particularly in pedigrees with known fragile X syndrome cases.

CONCLUSIONS

Fragile X-associated psychiatric manifestations serve as a useful model for a molecular genesis of neuropsychiatric illness. Because of the multigenerational expression of fragile X-associated neuropsychiatric illness, there is a prominent role for genetic testing and genetic counseling of patients and their relatives. Genetic testing is confirmatory of the FMR1 premutation and is an essential component of the clinical evaluation. Psychopharmacologic and psychotherapeutic treatment of fragile X-associated psychiatric illnesses may improve patient function and assist in adaptation to the burden of a genetic neuropsychiatric illness.

The effect of CGG repeat number on ovarian response among fragile X premutation carriers undergoing preimplantation genetic diagnosis

OBJECTIVE

To assess ovarian response among carriers of FMR1 premutation who undergo preimplantation genetic diagnosis (PGD).

DESIGN

Retrospective study.

SETTING

Academic IVF unit.

PATIENT(S)

Of 18 carriers of FMR1 premutation referred to PGD, eight had <100 CGG repeats and ten had >or=100 CGG repeats.

INTERVENTION(S)

Controlled ovarian stimulation (COH) and PGD.

MAIN OUTCOME MEASURE(S)

Correlation between the number of CGG repeats and the level of E2 at day of hCG administration, number of retrieved oocytes, number of two-pronuclear (2PN) zygotes, and dose of recombinant FSH.

RESULT(S)

There was a positive correlation between CGG repeats and the level of E2 at day of hCG administration, number of retrieved oocytes, and number of 2PN zygotes. There was a negative correlation between number of CGG repeats and the total dose of gonadotropins. The E2 level and the number of retrieved oocytes and 2PN zygotes were significantly higher and the dose of gonadotropins significantly lower for premutation patients with >or=100 CGG repeats compared with <100 CGG repeats.

CONCLUSION(S)

There is a positive correlation between E2 level, retrieved oocytes, 2PN zygotes, and number of CGG repeats. Premutation carriers with <100 CGG repeats suffer from impaired ovarian response and decreased fertilization rate.

Molecular diagnosis of Fragile X syndrome

Fragile X syndrome, the most prevalent inherited cause of mental retardation, is related to hyperexpansion of a polymorphic CGG repeat of the FMR1 gene. Expansion of 55-200 repeats are called premutations and characterize carriers who usually have no mental impairment. The disease causing full mutations exceed 200 CGG repeats, are hypermethylated and lead to transcriptional silencing of the gene and absence of the Fragile X mental retardation protein (FMRP). Diagnostic approaches involve molecular and immunocytochemical techniques. Southern blot, which allows mutations to be detected and methylation status to be determined in a single test, remains the procedure of choice for most laboratories. Modifications of PCR methods, including methylation specific PCR, are also proposed but their implementation is still in question because of inherent difficulties to amplify CGG repeats, distinguish between mosaic patterns and interpret results in female individuals. The FMRP antibody test is also suitable for large population screening and elucidation of Fragile X syndrome cases with no CGG expansion, but it is not widely applied. In search for novel diagnostic approaches, use of PCR as a first prescreening test followed by Southern blot is considered the most reliable procedure.

Language Development in Individuals with Fragile X Syndrome

Fragile X syndrome (FXS) is the leading inherited cause of intellectual disability. The syndrome is caused by a single gene mutation on the X chromosome. Although individual differences are large, most individuals with FXS display weaknesses across all language and literacy domains compared to peers of the same chronological age with typical cognitive and language development. Expressive, receptive, and pragmatic language abilities as well as literacy skills are similar to those of younger, typically developing peers at similar cognitive and language developmental levels, although there are areas in which impairments exceed developmental-level expectations. One area of special impairment is the higher occurrence of repetition in the language of individuals with FXS compared to developmentally matched peers. In this paper, we review the behavioral, language, and literacy characteristics of individuals with FXS and discuss potential clinical implications.

FMR1: a gene with three faces

The FMR1 gene is involved in three different syndromes, the fragile X syndrome (FXS), premature ovarian insufficiency (POI) and the fragile X-associated tremor/ataxia syndrome (FXTAS) at older age. Fragile X syndrome is caused by an expansion of a CGG repeat above 200 units in the FMR1 gene resulting in the absence of the FMR1 mRNA and protein. The FMR1 protein is proposed to act as a regulator of mRNA transport and of translation of target mRNAs at the synapse. FXS is seen as a loss of function disorder. POI and FXTAS are found in individuals with an expanded repeat between 50 and 200 CGGs and are associated with increased FMR1 mRNA levels. The presence of elevated FMR1 mRNA in FXTAS suggests that FXTAS may represent a toxic RNA gain-of-function effect. The molecular basis of POI is yet unknown. The role of the FMR1 gene in these disorders is discussed.

Fragile X syndrome detection in newborns-pilot study

PURPOSE

Fragile X syndrome is the most common form of hereditary intellectual disability. Detection of the fragile X phenotype in the prepubertal period is very difficult, and early detection might assist in early developmental intervention and reproductive counseling. A pilot study was conducted to establish the feasibility of newborn screening for fragile X syndrome.

METHODS

A prospective study was done contacting mothers postdelivery in two hospitals in upstate South Carolina from 2005 to 2006. With their permission, blood samples were obtained from the male infants via heelstick and analyzed.

RESULTS

A total of 1,459 newborns were tested, and 5 abnormal results were obtained. The results included one sex chromosome aneuploidy (47, XXY), two premutations, and two full mutations.

CONCLUSIONS

Our study establishes the potential feasibility of such a screening process. However, more complete studies assessing a larger population and risk-benefit analyses are necessary before any universal application of this test. Our detection rate for fragile X syndrome (1:730) was inexplicably greater than anticipated but likely represents a chance occurrence among the small number of infants tested.

Intermediate and premutation FMR1 alleles in women with occult primary ovarian insufficiency

OBJECTIVE

To compare the prevalence of intermediate and premutation FMR1 alleles in women with occult primary ovarian insufficiency (oPOI) and in controls.

DESIGN

Observational study.

SETTING

Division of Infertility and Service of Genetic Medicine, Geneva University Hospitals.

PATIENT(S)

The study group consisted of 27 infertile women with oPOI referred by infertility specialists for FMR1 testing in 2005-6 because of unexplained poor response to controlled ovarian hyperstimulation or altered hormonal profiles. The control group consisted of 32 women undergoing genetic testing for conditions unrelated to mental retardation or ovarian function. The DNA samples were anonymized.

INTERVENTION(S)

In the study group, data were collected concerning reproductive/family history, hormonal markers, possible fertility treatment outcomes, and results of karyotype and FMR1 testing. In the control group, FMR1 gene testing was done. The only clinical data available in controls were sex and indication for genetic testing.

MAIN OUTCOME MEASURE(S)

Distribution of FMR1 alleles.

RESULT(S)

Six (22%) of 27 women with oPOI had FMR1 alleles of >40 repeats (intermediate to premutation range), compared with one (3%) of 32 controls.

CONCLUSION(S)

These results suggest that women with oPOI might be at risk of carrying alleles in the intermediate and premutation range.

Fragile X-associated primary ovarian insufficiency: evidence for additional genetic contributions to severity

The fragile X mental retardation gene (FMR1) contains a CGG repeat sequence in its 5' untranslated region that can become unstable and expand in length from generation to generation. Alleles with expanded repeats in the range of approximately 55-199, termed premutation alleles, are associated with an increased risk for fragile-X-associated primary ovarian insufficiency (FXPOI). However, not all women who carry the premutation develop FXPOI. To determine if additional genes could explain variability in onset and severity, we used a random-effects Cox proportional hazards model to analyze age at menopause on 680 women from 225 families who have a history of fragile X syndrome and 321 women from 219 families from the general population. We tested for the presence of a residual additive genetic effect after adjustment for FMR1 repeat length, race, smoking, body mass index, and method of ascertainment. Results showed significant familial aggregation of age at menopause with an estimated additive genetic variance of 0.55-0.96 depending on the parameterization of FMR1 repeat size and definition of age at menopause (P-values ranging between 0.0002 and 0.0027). This is the first study to analyze familial aggregation of FXPOI. This result is important for proper counseling of women who carry FMR1 premutation alleles and for guidance of future studies to identify additional genes that influence ovarian insufficiency.

Methylation-specific multiplex ligation-dependent probe amplification enables a rapid and reliable distinction between male FMR1 premutation and full-mutation alleles

Fragile X syndrome is the most common cause of inherited mental retardation and the second most common cause of mental impairment after trisomy 21. It occurs because of a failure to express the fragile X mental retardation protein. The most common molecular basis for the disease is the abnormal expansion of the number of CGG repeats in the fragile X mental retardation 1 gene (FMR1). Based on the number of repeats, it is possible to distinguish four types of alleles: normal (5 to 44 repeats), intermediate (45 to 54), premutation (55 to 200), and full mutation (>200). Today, the diagnosis of fragile X syndrome is performed through a combination of PCR to identify fewer than 100 repeats and of Southern blot analysis to identify longer alleles and the methylation status of the FMR1 promoter. We have developed a methylation-specific multiplex ligation-dependent probe amplification assay to analyze male fragile X syndrome cases with long repeat tracts that are not amplifiable by PCR. This inexpensive, rapid and robust technique provides not only a clear distinction between male pre- and full-mutation FMR1 alleles, but also permits the identification of genomic deletions, a less frequent cause of fragile X syndrome.

Reproductive health of adolescent girls who carry the FMR1 premutation: expected phenotype based on current knowledge of fragile x-associated primary ovarian insufficiency

The fragile X mental retardation 1 (FMR1) gene, located on the X chromosome, is characterized by a dynamic CGG repeat expansion in the 5' untranslated region. It has long been known that female carriers of the FMR1 premutation allele (55-199 CGG) are at risk for passing the FMR1 full mutation (> or =200 repeats) to their offspring, which results in a common form of mental retardation known as fragile X syndrome. The FMR1 premutation allele, however, also places female carriers at significantly increased risk for prematurely diminished ovarian function, which we refer to as fragile X-associated primary ovarian insufficiency (FXPOI). Although of particular concern for younger women, to date, studies of FXPOI have been restricted to women > or =18 years of age and have not specifically addressed ovarian reserve and menstrual cycle characteristics among adolescent carriers. We discuss the expected reproductive phenotype among FMR1 premutation carriers during adolescence, the associated health considerations based on our current understanding of FXPOI, and the directions for future studies.

The Italian External Quality Assessment scheme for fragile x syndrome: the results of a 5-year survey

The Italian External Quality Assessment scheme for fragile X syndrome started in 2001 as an activity funded by the National Health System and coordinated by the National Institute of Public Health. The aim of this work is to present the data of 5 years (2001--2004 and 2006) of survey. The External Quality Assessment scheme was designed to cover the following points: (a) genotyping and (b) interpretation and reporting of results. Overall, the scheme covered about 65% of all Italian public laboratories. The average reporting of results was 91.6%, with an overall success rate of 76%. The rate of diagnostic errors observed was on average 5%. Inaccuracy in sizing of CGG repeats of normal and premutated alleles was reported. During the survey the proportion of laboratories using a Southern blotting, polymerase chain reaction, and ABI sizing kit in combination rose from 36.8% to 70.6%. The reports from laboratories showed incompleteness and considerable variations in expected outcomes. For this reason, in 2004 a model for written reports was introduced. In conclusion, these data underscore the need to participate in External Quality Assessment schemes as an educational resource to ensure quality in molecular genetic testing.

Molecular analysis of fragile X syndrome

The gene responsible for fragile X syndrome, fragile X mental retardation-1 (FMR1), contains an unstable repeat sequence of (CGG)(n). Additionally, an upstream promoter region of the gene--a CpG island--is abnormally methylated in most affected individuals. Amplification of CGG repeats and abnormal methylation show a correlation with affected status. The first basic and alternate protocols in this unit outline the use of the polymerase chain reaction (PCR) to rapidly detect the size of the repeat amplification. The second basic protocol describes the assessment of fragile X syndrome by direct Southern blot hybridization of genomic DNA digested with a pair of restriction enzymes, one of which is methylation-sensitive. Extent of amplification and level of methylation can be simultaneously detected. A combination of the two techniques can be used to characterize the genotypes of individual members in identified fragile X families.

A girl with fragile X premutation from sperm donation

We present a girl with the fragile X premutation who obtained the premutation allele from donated sperm. Our patient has clinical characteristics of fragile X syndrome including emotional problems and neuropsychological difficulties presenting as learning disabilities. She is also at high risk for premature ovarian failure and low risk for the fragile X-associated tremor ataxia (FXTAS). We suggest fragile X DNA screening in gamete donor candidates to decrease the chance of fragile X involvement in their offspring.

Investigation of phenotypes associated with mood and anxiety among male and female fragile X premutation carriers

The fragile X disorder spectrum, due to a CGG expansion in FMR1, includes fragile X syndrome (>200 repeats) and the premutation-associated disorders of ovarian insufficiency and tremor/ataxia syndrome (approximately 55-199 repeats). Altered neurobehavioral profiles including variation of phenotypes associated with mood and anxiety may be expected among younger premutation carriers given this spectrum of disorders. However, previous studies have produced conflicting findings, providing the motivation to examine these phenotypes further. We investigated measures of mood and anxiety in 119 males and 446 females age 18-50 ascertained from families with a history of fragile X syndrome and from the general population. Scores were analyzed using a linear model with repeat length as the main predictor, adjusting for potential confounders. Repeat length was not associated with anxiety, but was marginally associated with depression and negative affect in males and negative affect only in females. These results suggest that premutation carriers may be at risk for emotional morbidity; however, phenotypic differences were subtle and of small effect size.

Fragile X syndrome in Korea: a case series and a review of the literature

The purposes of this study were to present DNA analysis findings of our case series of fragile X syndrome (FXS) based on methylation-specific polymerase chain reaction (MS-PCR), PCR, and Southern blotting alongside developmental characteristics including psychological profiles and to review the literature on FXS in Korea. The reports of 65 children (male:female, 52:13; age, 6.12+/-4.00 yrs) referred for the diagnosis of FXS over a 26-months period were retrospectively reviewed for the identification of full mutation or premutation of fragile X mental retardation 1 (FMR1). Among the 65 children, there were 4 boys with full mutation, and one boy showed premutation of FMR1, yielding a 6.15% positive rate of FXS. All 4 children with full mutation showed significant developmental delay, cognitive dysfunction, and varying degrees of autistic behaviors. The boys with premutation showed also moderate mental retardation, severe drooling, and behavioral problems as severe as the boys with full mutation. Thirteen articles on FXS in Korea have been published since 1993, and they were reviewed. The positive rate of FXS was in the range of 0.77-8.51%, depending on the study groups and the method of diagnosis. Finally, the population-based prevalence study on FXS in Korea is required in the near future.

Prevalence and instability of fragile X alleles: implications for offering fragile X prenatal diagnosis

OBJECTIVE

To document fragile X allele frequencies in a national referral population and evaluate CGG repeat expansion in mother-offspring transmissions.

METHODS

Fragile X DNA analysis by Southern blot and polymerase chain reaction was completed for 14,675 women, aged 18 years or older, and 238 mother-offspring pairs between January 1999 and June 2004. Carrier frequencies were compared between groups referred for different clinical indications. Direct comparison of the FMR1 gene CGG repeat size in mother-offspring pairs determined intermediate and premutation allele stability.

RESULTS

Intermediate fragile X alleles (45-54 CGG repeats) occurred in 257 (1 in 57). The combined total number of patients with a premutation (55-200 CGG repeats) or full mutation (more than 200 CGG repeats) numbered 208 (1 in 71). One in 3.5 women with a family history of fragile X and 1 in 10 with premature ovarian failure had a FMR1 mutation. This compared with 1 in 86 for those with a family history of mental retardation and 1 in 257 for women with no known risk factors for fragile X. Among 238 mother-offspring pairings, the smallest allele to expand to a full mutation in one generation contained 60 CGG repeats. Although 6.6% (4 of 60) of intermediate repeat alleles did expand, none jumped to a clinically significant full mutation-sized allele.

CONCLUSION

Based on these data and other published literature, offering invasive prenatal diagnosis for fragile X syndrome is not indicated for women with intermediate alleles. Invasive prenatal diagnosis is warranted for those women with a fragile X allele containing 55 or more CGG repeats.

Fragile X-associated tremor/ataxia syndrome: clinical features, genetics, and testing guidelines

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a neurodegenerative disorder with core features of action tremor and cerebellar gait ataxia. Frequent associated findings include parkinsonism, executive function deficits and dementia, neuropathy, and dysautonomia. Magnetic Resonance Imaging studies in FXTAS demonstrate increased T2 signal intensity in the middle cerebellar peduncles (MCP sign) in the majority of patients. Similar signal alterations are seen in deep and subependymal cerebral white matter, as is general cortical and subcortical atrophy. The major neuropathological feature of FXTAS is the presence of intranuclear, neuronal, and astrocytic, inclusions in broad distribution throughout the brain and brainstem. FXTAS is caused by moderate expansions (55-200 repeats; premutation range) of a CGG trinucleotide in the fragile X mental retardation 1 (FMR1) gene, the same gene which causes fragile X syndrome when in the full mutation range (200 or greater CGG repeats). The pathogenic mechanism is related to overexpression and toxicity of the FMR1 mRNA per se. Although only recently discovered, and hence currently under-diagnosed, FXTAS is likely to be one of the most common single-gene disorders leading to neurodegeneration in males. In this report, we review information available on the clinical, radiological, and pathological features, and prevalence and management of FXTAS. We also provide guidelines for the practitioner to assist with identifying appropriate patients for DNA testing for FXTAS, as well as recommendations for genetic counseling once a diagnosis of FXTAS is made.