DNA testing for fragile X syndrome in schools for learning difficulties

Fragile X syndrome is the most common inherited cause of mental retardation. Early diagnosis is important not only for appropriate management of individuals but also to identify carriers who are unaware of their high risk of having an affected child. The disorder is associated with a cytogenetically visible fragile site (FRAXA) at Xq27.3, caused by amplification of a (CGG)n repeat sequence within the gene at this locus designated FMR1. Clinical and molecular studies have been undertaken to screen for fragile X syndrome in 154 children with moderate and severe learning difficulties of previously unknown origin. Southern blot analysis of peripheral blood showed the characteristic abnormally large (CGG)n repeat sequence associated with fragile X syndrome in four of the 154 children. The findings were confirmed by cytogenetic observation of the fragile site and by further molecular studies. The families of the affected children were offered genetic counselling and DNA tests to determine their carrier status. These findings show that there are still unrecognised cases of fragile X syndrome. Given the difficulty of making a clinical diagnosis and the implications for families when the diagnosis is missed, screening in high risk populations may be justified. The issues involved in screening all children in special schools for fragile X syndrome are discussed.     

Institutional screening for the fragile X syndrome

Cytogenetic screening of mentally retarded patients for the fragile X (fra[X]) chromosome is helpful in identifying individuals who could benefit from genetic counseling and treatment. Previous studies have demonstrated a prevalence of the fra(X) syndrome as high as 6% in institutionalized retarded males. The physical and behavioral predictors of positive findings from cytogenetic testing have not been clarified, since many features of the fra(X) syndrome are found in other retarded populations. We performed physical and cytogenetic examinations on 440 patients at the Wheat Ridge (Colo) Regional Center. Twenty-eight (6.3%) demonstrated abnormal karyotypes. Seventeen of these were autosomal abnormalities or sex chromosome aneuploidies and 11 demonstrated the fra(X) chromosome (seven males, four females). In males, the physical features that were predictive of the fra(X) syndrome included the combination of ear lengths of 7.0 cm or greater, macroorchidism of 30 mL or greater, and the presence of hand calluses or lesions secondary to hand biting. The fra(X) chromosome was not seen in spastic quadriplegic patients. All seven males with the fra(X) syndrome were detected among the 141 ambulatory males who resided in the highest functioning units at this institution.     

发根脆性X智力低下蛋白检测法诊断脆性X综合征

目的：至今已有多种筛查和诊断脆性X综合征(fragile X syndrome,FXS)的方法,以PCR法和Southern印迹方法应用最广,然而每种方法均存在各自的局限性。该研究探讨发根脆性X智力低下蛋白（fragile X mental retardation protein,FMRP）检测在诊断或筛查FXS中的可靠性,以建立一种快速、简便、价廉且可靠的诊断FXS的方法。方法：采用发根FMRP免疫组化的检测方法对80例健康儿童、40例不明原因智力低下儿童、已确诊FXS家系成员12例进行检查; 用7-deza-dGTP PCR 法进行对照,探讨其对诊断FXS的应用价值。结果：在80例健康儿童中,发根FMRP的表达率均在80%以上。40例不明原因智力低下患儿中,2例确诊为FXS患儿的发根FMRP表达率分别为10%和0,另38例非FXS患者发根FMRP的表达率均在80%以上。在FXS家系调查中,确诊的2例FXS患者的发根FMRP表达率均为0。结论：发根FMRP检测诊断FXS具有快速、简便、价廉、可靠等特点,值得进一步推广应用。［中国当代儿科杂志,2009,11（10）：817-820］     

Screening for fragile X syndrome in handicapped boys]

From a group of 201 mentally retarded boys 149 were clinically and somatometrically examined. Chromosomal analysis for detection of a fra(X)-syndrome was undertaken, when more than 3 of the chosen examination parameters were suspicious or when anamnestic clues for X-chromosomally linked mental retardation were present. 89 boys fulfilled above requirements, 14 of these had a fra(X)-syndrome (15.7%). The following symptoms were found with outstanding frequency: hyperactivity, hypotonic muscles, enlargement of testes, increased length of hands, retarded development of speech, dermatoglyphic abnormalities. If more than 3 of these findings occur, a chromosomal analysis for exclusion of a fra(X)-syndrome should be performed.     

Health supervision for children with fragile X syndrome

Fragile X syndrome (an FMR1-related disorder) is the most commonly inherited form of mental retardation. Early physical recognition is difficult, so boys with developmental delay should be strongly considered for molecular testing. The characteristic adult phenotype usually does not develop until the second decade of life. Girls can also be affected with developmental delay. Because multiple family members can be affected with mental retardation and other conditions (premature ovarian failure and tremor/ataxia), family history information is of critical importance for the diagnosis and management of affected patients and their families. This report summarizes issues for fragile X syndrome regarding clinical diagnosis, laboratory diagnosis, genetic counseling, related health problems, behavior management, and age-related health supervision guidelines. The diagnosis of fragile X syndrome not only involves the affected children but also potentially has significant health consequences for multiple generations in each family.     

GABAA受体与脆性X综合征

脆性X综合征(fragile X syndrome,FXS)是引起先天性智力低下的常见疾病,GABAA受体是哺乳动物中枢神经系统内最主要的抑制性神经递质受体,与焦虑、抑郁、癫癎、睡眠、认知等相关.多项研究证明GABA能神经系统特别是GABAA受体的变化与FXS的遗传表型有关.GABAA受体某些亚基的表达变化是FXS患者神经行为学改变的原因之一,可为FXS的治疗提供一个新的方向.     

Molecular pathogenesis of fragile X syndrome

The fragile X syndrome is an X-linked genetic disorder; manifesting primarily as intellectual disability. The disease is caused by the absence of functional FMRP, a protein encoded by the FMR1 gene. The expansion of trinucleotide repeats within the first exon of the gene contributes to most cases of the syndrome. This review summarizes the present knowledge of the relationship between the molecular defect in the FMR1 gene and the clinical phenotype associated with disease.     

GABAA受体与脆性X综合征

脆性X综合征(fragile X syndrome,FXS)是引起先天性智力低下的常见疾病,GABAA受体是哺乳动物中枢神经系统内最主要的抑制性神经递质受体,与焦虑、抑郁、癫癎、睡眠、认知等相关.多项研究证明GABA能神经系统特别是GABAA受体的变化与FXS的遗传表型有关.GABAA受体某些亚基的表达变化是FXS患者神经行为学改变的原因之一,可为FXS的治疗提供一个新的方向.     

Recurrent otitis media in the fragile X syndrome

Thirty prepubertal boys with fragile X syndrome (fra[X]) were evaluated retrospectively to document the incidence of recurrent otitis media by physician records. The number of documented otitis media infections in the first five years of life was statistically more than those of the normal male siblings and of unrelated, cytogenetically normal controls. Nineteen (63%) of the 30 boys with fra(X) experienced six or more otitis infections. Of the 30 boys with fra(X), 13 (43%) were treated with polyethylene tubes or prophylactic antibiotics for persistent middle ear effusion. Males with fra(X) are at high risk for recurrent ear disease, which may exacerbate the cognitive, language, and behavior problems that exist in this syndrome.     

The Prader-Willi phenotype of fragile X syndrome

The Prader-Willi phenotype (PWP) of fragile X syndrome (FXS) is associated with obesity and hyperphagia similar to Prader-Willi syndrome (PWS), but without cytogenetic or methylation abnormalities at 15q11-13. Thirteen cases of PWP and FXS are reported here that were identified by obesity and hyperphagia. Delayed puberty was seen in 5 of 9 cases who had entered puberty, a small penis or testicles in seven of 13 cases, and infant hypotonia and/or a poor suck in seven of 13 cases. Autism spectrum disorder occurred in 10 of 13 cases, and autism was diagnosed in seven of 13 cases. We investigated cytoplasmic interacting FMR1 protein (CYFIP) expression, which is a protein that interacts with FMR1 protein (FMRP) because the gene for CYFIP is located at 15q11-13. CYFIP mRNA levels were significantly reduced in our patients with the PWP and FXS compared to individuals without FXS (p < .001) and also individuals with FXS without PWP (p = .03).     

Nasopharyngeal carcinoma in a boy with fragile X syndrome

The authors report on what they believe to be the first case of nasopharyngeal carcinoma in a patient with fragile X syndrome. In the literature, a few cases of fragile X syndrome associated with malignancies are described. Although this association seems more than coincidental, the molecular correlation between this syndrome and cancer is yet unclear.     

Understanding the biological underpinnings of fragile X syndrome

PURPOSE OF REVIEW: The purpose of this review is to present the latest findings on fragile X syndrome and to put them into perspective. Fragile X syndrome is a relatively common form of inherited mental retardation, caused by loss of function of the FMR1 gene on the long arm of the X chromosome. The molecular mechanisms underlying the syndrome are complex and continue to surprise researchers more than 12 years after the cloning of the gene. RECENT FINDINGS: We will specifically discuss the various aspects of the clinical phenotype, reassessed with the employment of functional imaging and electrophysiological techniques. The unexpected finding of a pathologic phenotype in premutation carriers is highlighted, as it represents a new and distinct condition with a different presentation in males and females. The third section deals briefly with the various functions of the FMRP protein, an RNA-binding protein interacting with multiple RNA molecules as well as proteins. It is important to realize that FMRP is probably changing partners several times, depending on its localization, on posttranslational modifications and on the available interacting proteins. In the following section, we present in short recent discoveries on the defective neuronal circuits in the fragile X syndrome. Most of these new data were made available by the study of animal models, mostly the Fmr1 knockout mouse, but also Drosophila. SUMMARY: We briefly discuss the alternative options for treating fragile X syndrome. Presently, a neuropharmacological approach acting on either critical receptors or aimed at reactivating the silenced FMR1 gene appears promising.     

Temperament and vagal tone in boys with fragile X syndrome

Physiological hyperarousal, an elevated state of physiological arousal and poor modulation, has been postulated to be a significant source of behavior problems in children with fragile X syndrome (FXS). Temperament has been associated with behavior problems and may also reflect biological reactivity. Young boys with FXS display poorly modulated and low levels of vagal tone (Roberts, Dev Psychobiol 2001;39:107-123) and high activity, poor attention, low adaptability, poor persistence, and low intensity when compared with a reference sample of typically developing (Hatton, Dev Med Child Neurol 1991;41:625-632). In this study, we integrated physiological indices of vagal tone with temperament ratings and compared a sample of 29 young boys with FXS to 31 typically developing boys matched on chronological age and ethnicity. Boys with FXS were more active, less adaptable, and less persistent than the comparison group. Boys with FXS also showed lower baseline levels and less suppression of vagal tone in response to changing task demands. A relationship between baseline vagal tone and persistence was shown across both groups. However, group differences in temperament dimensions did not appear to be mediated or moderated by vagal tone.     

Discovering fragile X syndrome: family experiences and perceptions

We used surveys from 274 families who had at least 1 child with fragile X syndrome (FXS) to determine their experiences in discovering FXS, factors associated with the timeliness of discovery, and the perceived consequences of obtaining this information. For families of male children who were born in the last decade, someone first became concerned about the child's development at an average age of 13 months. Professional confirmation of a developmental delay did not occur until an average age of 21 months, and a FXS diagnosis occurred at an average age of nearly 32 months. Families reported several barriers to discovering FXS and frustration with the process. Many families had additional children with FXS without knowing reproductive risk. A range of perceived benefits and challenges associated with the discovery were reported. We conclude that selected pediatric practices could promote earlier identification but in only a limited way and predict that disorders such as FXS will continue to challenge current criteria for determining viable candidate disorders for newborn screening.     

Girls with fragile X syndrome: physical and neurocognitive status and outcome.

The fragile X syndrome, a common X-linked form of mental retardation and autism, affects females as well as males. Previous work has shown that approximately 35% of heterozygotes (women who carry the fragile X gene) demonstrate cognitive impairment. Thirty-two girls, 18 years or younger, who demonstrate the fragile X chromosome were evaluated and compared with 19 sisters who do not demonstrate the fragile X chromosome. Evaluations included a physical examination, behavioral assessment, and intelligence testing. Significant differences (in intellectual, behavioral, and physical features) were seen between the two groups. Twenty-five percent of fragile X-positive girls had an IQ in the mentally retarded range (IQ less than 70) and 28% had an IQ in the borderline range (70 to 84). Prominent ears, shyness, and poor eye contact were significant findings in fragile X-positive girls compared with fragile X-negative girls. Thirty-one percent of the fragile X-positive girls had significant attentional difficulties and most of these girls were successfully treated with stimulant medication. The majority of fragile X-positive girls in this study demonstrated significant behavioral and developmental problems which required identification and appropriate treatment. Pediatricians and health care providers should be aware of the frequency and manner with which fragile X affects females in order to initiate cytogenetic studies and treatment when indicated.     

Developmental and behavioural disturbances in 13 boys with fragile X syndrome

Developmental and behavioural aspects were studied in 13 boys aged 2.6–12.5 years from three families with the fragile X syndrome.The following observations were made. (1) Moderate to severe retardation was present in all boys; non-verbal IQs ranged between 25 and 67 (mean 46±14); IQ and age were negatively correlated (P<0.01). (2) Language development was grossly delayed in all boys: most had severe articulation problems. (3) Imitative and symbolic play (e.g. doll play) were strikingly retarded as compared to abstract play (e.g. block design). (4) Autistic features such as no use of eye contact, stereotyped movements and echolalia were found in 9/13 boys; the same number showed aggressive behaviour. (5) General activity was reduced during the 1st year of life; most boys became very hyperactive during the second year; and short attention span and increased distractability were observed in all. (6) Motor development was mildly delayed; all boys were clumsy and moderately hypotonic.The fragile X syndrome ought to be considered in retarded boys with a dissociated developmental pattern, in particular a striking delay in language and play development, and autistic features.