Fragile X syndrome

Fragile X syndrome is the most common form of inherited mental retardation. It is seen in people of all nationalities and in all areas of the world. Fragile X syndrome can be a devastating condition, as many boys are severely retarded and require multiple services. Treatment involves behaviour management techniques, appropriate school placement, community support for the family, and careful medical follow-up often including psychopharmacology. The genetics of fragile X syndrome is now understood, prenatal testing is available, and the disorder is preventable through appropriate genetic counselling. This review focuses on the neurobiology of fragile X syndrome, its clinical features and treatment.     

Fragile X syndrome

Fragile X syndrome is the most common inherited condition causing mental retardation in males. Females with the full mutation expansion can have milder signs of the disorder. Families with members who have been diagnosed with fragile X syndrome face concerns about the health of their newborn infant, decisions regarding family planning, and questions about the possibility that other family members could have this disorder. Neonatal nurses participate in assessment, health care management, counseling, and referral of the families regarding this syndrome.     

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.     

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.     

Screening for fragile X syndrome: results from a school for mentally retarded children

Fragile X syndrome is the most common inherited form of familial mental retardation. The purpose of this study was to identify yet unrecognized fragile X individuals and to estimate the frequency of both the FRAXA and FRAXE forms of the disease in a population of mentally retarded children attending a special school in Croatia. The results are reported of molecular screening of 114 children with mild to severe mental retardation. Three individuals (2.6%) with the FRAXA form of the fragile X syndrome and one boy (0.9%) with FRAXE mental retardation were detected; a total of four newly diagnosed fragile X families were identified. Closer clinical examination revealed that behavioural and speech disturbances were clearly present among all fragile X cases (both FRAXA and FRAXE), indicating that these features could be additional diagnostic criteria for the preselection of individuals at risk.

Conclusion: Fragile X screening among mentally retarded children attending a special school should be highly encouraged to reveal the cause of mental retardation and to detect yet unrecognized fragile X individuals. The frequency of fragile X syndrome in a such population in Croatia was found to correlate with similar results from previous studies. However, since at the time of diagnosis all affected families had a second or even a third child born, earlier diagnosis should be considered to provide greater benefit to fragile X families.     

Unbalanced X; autosome translocation

Unbalanced X; autosome translocation can result in multiple congenital abnormalities/mental retardation syndrome due to chromosomal imbalance. Here is described a patient with developmental delay, microcephaly, agenesis of corpus callosum spasticity, seizures and dysmorphism as a result of meiotic malsegregation of balanced X; autosome translocation in mother. Present case signifies the importance of chromosomal analysis in a patient with developmental delay/ mental retardation and discuss lyonization in cases with X; autosome translocation.     

Fragile X syndrome

The fragile X syndrome is the most common inherited form of mental retardation known. Its phenotype includes large or prominent ears, macroorchidism, and characteristic behavioral problems. It has attracted the interest of cytogeneticists and molecular biologists because of its characteristic fragile site on the X chromosome. It has puzzled geneticists because of its unusual inheritance pattern involving nonpenetrant males. This syndrome has also spearheaded an appreciation of cytogenetic abnormalities in the etiology of all degrees of developmental delay.     

The fragile X syndrome (Martin-Bell syndrome). Clinical and cytogenetic findings in 16 prepubertal boys and in 4 of their 5 families

Clinical and cytogenetic findings from 16 prepubertal males with the fragile X syndrome (X-linked mental retardation with postpubertal macro-orchidism and fragile site at Xq27/8, or Martin-Bell syndrome) and from their families are reported. During the first postnatal years, protruding, large ears, full periorbital tissue, and thick septum and alae nasi were the most characteristic phenotypic findings, while after approximately 6 years of age a longish face with full lips and prominent maxilla and mandible became more distinct. It was estimated that a clinical suspicion of the fragile X syndrome could be made in most of the 16 boys from phenotypic findings in combination with the characteristic developmental profile described in our previous paper. The marker X chromosome was demonstrated in each of the 16 patients; the incidence of fra(X)-positive cells did not correlate with either age or the degree of mental retardation. 13 boys stemmed from 2 families, the other 3 were sporadic cases. In one family with 11 affected boys, the gene was transmitted by 4 brothers, grandfathers to the probands, who were intellectually normal; three of them did not show the clinical picture of the fragile X syndrome and did not express the marker. All mentally subnormal heterozygote females and one half of daughters of heterozygotes revealed the marker, but this was present only in a minority of non-retarded adult heterozygotes. In contrast to the overall incidence of about 1/4 to 1/3 mentally retarded heterozygotes, all 15 daughters of the four normal obligatory hemizygous brothers were of normal intelligence.     

New X linked mental retardation syndrome

IntroductionResearching inherited mental retardation, from a diagnostic and aetiological point of view, is a great challenge. A particular type of mental retardation is the one linked to the X chromosome which is classified under syndromic and non-syndromic types, according to the presence or absence of a specific physical, neurological or metabolic pattern associated with mental retardation.Patients and methodFive generations of a family have been studied with eight males suffering from mental retardation. Six of these males were clinically tested using anthropometric indicators and genetic tests: high resolution karyotypes, fragile X research, linkage and MID1 and PQBP1 gene studies.ResultsAlong with mental retardation, the clinical study showed a pattern of microcephaly, micrognathia, osteoarticular and genital anomalies, short stature and other less frequent malformations. The linkage study mapped the possible causal gene of this mental retardation syndrome and multiple congenital abnormalities in the Xp11.23-q21.32 segment, with a LOD score of 2. As far as we know, a medical profile, similar to the one these patients have, linked to this X segment has not been described.ConclusionsWe suspect that this family has a “new syndrome” of mental retardation and multiple congenital anomalies linked to the X chromosome.     

Fragile X syndrome among children with mental retardation

Prospective screening for fragile X syndrome was carried out among 1,111 patients with mental retardation who attended the Genetic clinic. Using defined clinical criteria, 55 patients were selected for cytogenetic studies to detect folate sensitive fragile sites. Twenty patients were diagnosed to have the fragile X syndrome. The prevalence of fragile X (A) syndrome was 18 per 1,000 patients of both sexes with mental retardation, 2.8% among male patients with mental retardation, and 5.8% among subjects with nonspecific mental retardation.     

Fragile X syndrome

Fragile X syndrome is one of the most intriguing genetic conditions now being studied. As the most common inherited form of mental retardation, it has an incidence of approximately 1 in 1000 male infants and boys. Because the cytogenetic diagnosis has only recently been available, many affected boys and female carriers have not yet been identified. This article reviews the characteristic, clinical features of fragile X syndrome and discusses treatment and intervention.     

Fragile X syndrome: recognition in young children

In recent years, a number of articles have appeared in the literature concerning the fragile X syndrome; however, in few cases was the diagnosis of the syndrome in young children discussed. A review of 20 children younger than 7 1/2 years of age who had the fragile X syndrome seen at the Cincinnati Center of Developmental Disorders was undertaken in an attempt to establish guidelines that would aid the practicing physician in determining which children should have a chromosomal analysis. All children were developmentally delayed; 95% had speech delays. Short attention span with hyperactivity, temper tantrums, mouthing of objects persisting at an age beyond when it would be expected, autistic behaviors, and poor gross motor coordination were seen in 50% or more of the children. Mental retardation was present in the family history of 65%, and 90% had a family history of at least one of the following: mental retardation, learning disabilities, or hyperactivity. The most common physical findings were long and/or wide and/or protruding ears, prominent jaw and/or long face, high arched palate, and a flattened nasal bridge. The fragile X syndrome can be recognized by noting key aspects of the behavioral and family histories as well as the physical findings.     

Learning disabilities and attentional problems in boys with the fragile X syndrome

The fragile X syndrome is a relatively common form of mental retardation that tends to affect boys more severely than girls. The syndrome is associated with a fragile site at q27 on the X chromosome and with physical features including large or prominent ears and macro-orchidism. Four boys had physical and cytogenetic features of the fragile X syndrome. However, the IQ scores of these patients extended into the normal range. All four patients demonstrated similar learning difficulties that included hyperactivity, visuomotor incoordination, language deficits, and academic delays in mathematics. The fragile X syndrome should be considered in the differential diagnosis of learning disabled children.     

The child with developmental delay: An approach to etiology

OBJECTIVE:

To describe an approach to history, physical examination and investigation for the developmentally delayed child.

METHODS:

A review of electronic databases from 1997 to 2001 was done searching for articles relating to the approach to or investigations of children with developmental delay. Five studies, including a review of a consensus conference on evaluation of mental retardation, were chosen because of their general approaches to developmental delay and/or mental retardation, or specific evaluations of a particular laboratory investigation.

CONCLUSIONS:

A diagnosis or cause of mental retardation can be identified in 20% to 60% of cases. Evaluation of the developmentally delayed child should include a detailed history and physical examination, taking special care to record a three-generation pedigree, as well as to look for dysmorphic features. If no other cause is apparent, routine investigations should include a chromosome study and fragile X studies. Further investigations are warranted depending on the clinical features.     

Two patients with Kabuki syndrome presenting with endocrine problems

A 4 year-old boy with mental retardation and seizures presented to the pediatric endocrinology clinic because of a history of hypoglycemia; a 16 month-old girl with developmental delay presented with bilateral breast tissue enlargement; in both, a diagnosis of Kabuki syndrome was made because of typical facial features, neurodevelopmental delay and other stigmata consistent with Kabuki syndrome. Kabuki syndrome is a mental retardation-malformation syndrome affecting multiple organ systems with a broad spectrum of abnormalities. The facial features of the syndrome are specific and independent of ethnic origin. In addition to presenting with endocrine problems, the patients reported here exhibit some novel findings such as congenital alopecia areata and hyperpigmented skin lesion. The diagnosis of Kabuki syndrome should be considered in patients with hypoglycemia or premature thelarche when associated with developmental delay and a peculiar facies.     

Fragile X syndrome

Fragile X syndrome is the most common familial form of mental retardation. This X-linked disorder affects one in every 1000 males and one in every 2000 females. The female carrier rate in the general population is estimated to be 1/600. A fragile site at the distal long arm of the X chromosome (Xq 27.3) is the hallmark cytogenetic feature of the syndrome. Clinical features include physical as well as cognitive and neuropsychological deficits. Although fragile X syndrome follows an X-linked pattern of inherltance (which explains the predominance of affected males), females can also beaffected,Many inconsistencies exist between the genetic inheritance pattern of fragile X and traditional Mendelian inheritance tenets of most X-linked diseases. Due to recent molecular advances, our understanding of the perplexing genetic issues surrounding fragile X syndrome has grown and diagnostic techniques have become both reliable and readily available.     

Family experiences and factors associated with the diagnosis of fragile X syndrome

The authors interviewed 41 mothers of young boys with fragile X syndrome to determine the process by which they learned their child had fragile X syndrome. The average family had concerns about the child's development at 9 months of age. Developmental delay was determined at an average age of 24 months, and fragile X syndrome was diagnosed at a mean age of 35 months. Considerable variability was found in age of first concern, determination of delay, and diagnosis of fragile X syndrome. Three child variables (severity of delay, autistic behavior, temperament style) and four family variables (mother's age, mother's education, sibling status, social support) did not account for this variability, although birth year did (children born more recently were somewhat more likely to be identified earlier). Families often encountered physicians who initially discounted concerns or said that it was too early to determine whether a problem did indeed exist. Given current knowledge and practice, improving the early identification (under 3 years of age) of children with fragile X syndrome is likely to remain difficult if based solely on behavioral and clinical observations.     

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.     

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.     

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］