X-linked mental retardation

A survey of the mentally retarded children with an IQ between 30 and 55 born in a 10-year period (1955-64) and now of school age was carried out in New South Wales. The number of propositi who had a similarly affected sib of the same sex was ascertained; 58 boys had a similarly affected brother(s) and 22 girls had a similarly affected sister(s). It is suggested that the excess of affected brothers represents X-linked forms of mental retardation. An estimate of prevalence rate was calculated from the brother pair excess and was found to be 0·74/1000 males. The calculated incidence of X-linked forms of mental retardation appeared to account for most of the male excess found in the survey and suggests that 1 in every 5 of the mentally retarded boys in the IQ range in this survey may be retarded on the basis of genes on the X chromosome.     

The ARX mutations: a frequent cause of X-linked mental retardation

The ARX gene mutations have been demonstrated to cause different forms of mental retardation (MR). Beside FMR1, in families with X-linked mental retardation (XLMR), the ARX dysfunction was demonstrated to be among the most frequent causes of this heterogeneous group of disorders. Nevertheless, in sporadic cases of MR, ARX mutations are extremely rare. In order to evaluate the frequency of ARX mutation in XLMR, we performed mutational analysis of ARX in 165 mentally retarded probands negative for FRAXA and belonging to families in which the condition segregates as an X-linked condition. The same recurrent mutation, an in frame 24 bp insertion (c.428-451 dup (24 bp)), was identified in five patients. In one family, the mother of two affected boys was found not to carry the mutation detected in her sons. These data suggest the presence of germline mosaicism for the mutation in the mother. Our results confirm the significant contribution of ARX mutations in the etiology of MR, especially in this group of patients selected for XLMR (3%). These data, together with those reported in the literature, imply that screening for c.428-451 dup (24 bp) mutation should be recommended in all patients with suspected XLMR.     

Non-specific X linked mental retardation.

Non-specific X linked mental retardation (MRX) is mental retardation in persons of normal physical appearance who have no recognisable features apart from a characteristic pedigree. Review of published reports shows that there is clinical variability in the degree of mental retardation within families and genetic heterogeneity, based on gene localisation, between families. We propose a classification based on genetic localisation and a set of minimal clinical features that should be recorded in the hope of identifying possible specific phenotypes.     

Novel JARID1C/SMCX mutations in patients with X-linked mental retardation

X-linked mental retardation (XLMR) is a heterogeneous disorder that affects approximately 2 in 1000 males. JARID1C/SMCX is relatively new among the known XLMR genes, and seven different mutations have been identified previously in this gene [Jensen LR et al., Am. J. Hum. Genet. 76:227-236, 2005]. Here, we report five novel JARID1C mutations in five XLMR families. The changes comprise one nonsense mutation (p.Arg332X) and four missense mutations (p.Asp87Gly; p.Phe642Leu; p.Arg750Trp; p.Tyr751Cys) affecting evolutionarily conserved amino acids. The degree of mental retardation in the affected males ranged from mild to severe, and some patients suffered from additional disorders such as epilepsy, short stature, or behavioral problems. This study brings the total number of reported JARID1C mutations to twelve. In contrast to other XLMR genes in which mutations were found only in single or very few families, JARID1C appears to be one of the more frequently mutated genes in this disorder.     

X-linked mental retardation: Renpenning revisited

Nine men with X-linked mental retardation (MR) belonging to the family originally described by Renpenning and his colleagues have been reexamined and restudied. None of these men have the fragile X chromosome, and none have macro-orchidism; their testes range in size from small to average. All but one are severely retarded; one has an IQ of 70, the mean IQ of the remainder is 30 with a range of 18 to 45. They are short in stature, have small or normal-size ears and lower jaws, and a moderate degree of microcephaly, the mean skull circumference being just below two standard deviations from the normal.     

X-linked dysmorphic syndrome with mental retardation

We present a dysmorphic syndrome in eight males of the same family (four brothers, three cousins and one uncle) that is characterised by: mental retardation, facial dysmorphia, abnormal growth of teeth, skin dimple at the lower back, clinodactyly, patella luxation, malformation of lower limbs, abnormalities of the fundus of the eye and subcortical cerebral atrophy. These physical defects do not correspond to any previously described syndrome, which suggests that it is a new syndrome. According to the model of heredity this syndrome could be due to a mutant gene situated in the X-chromosome.     

X-linked mental retardation with marfanoid habitus

Here we report on two pairs of mildly to moderately mentally retarded brothers with marfanoid habitus and similar craniofacial changes. They had a long and narrow face, small mandible, high-arched palate, and hypernasal voice, as previously reported by Lujan et al (Am J Med Genet 17:311-322, 1984) in four mentally retarded males of a large kindred. The present data suggest the existence of a specific type of X-linked mental retardation with marfanoid habitus.     

X-linked skeletal dysplasia with mental retardation

A syndrome compatible with an X-linked trait is described, affecting four male cousins in three sibships. The boys had skeletal anomalies, including short stature, ridging of the metopic suture, fusion of cervical vertebrae, thoracic hemivertebrae, scoliosis, sacral hypoplasia and short middle phalanges. In addition, they had moderate developmental retardation, and abducens palsies. Three of the four had glucose intolerance, and one was born with an imperforate anus.
Of five female obligate carriers studied, three had fusion of cervical vertebrae, three had some shortening of the middle phalanges and three had glucose intolerance.
The syndrome in this family was compared to previously reported syndromes, and the conclusion was reached that it represents a previously unreported X-linked syndrome with minor manifestations in carrier females.     

A new X-linked mental retardation syndrome

We have studied a three-generation family with 11 moderately to severely retarded males and three mildly retarded females (presumably manifesting carriers). The patients have a phenotype different from that of all other previously described types of X-linked MR (XLMR). These include short stature, macrocephaly, "coarse" facial appearance including prominent forehead and supraorbital ridges, hypertelorism, broad nasal tip with anteverted nostrils, and thick lips. All postpubertal males had macroorchidism (volume greater than 25 ml). Chromosomes were normal including fragile X analysis. X-ray findings of skull, spine, and hands were normal. The intellectually normal relatives do not resemble their affected relatives except for increased head size and testicular size. These findings suggest a new variant of XLMR different from fragile X-linked MR, the Coffin-Lowry syndrome, and other XLMR conditions.     

二代测序技术确诊一例X连锁精神发育迟滞患儿CSCD

目的对1例不明原因发育落后的患儿进行临床和遗传学分析。方法对患儿进行临床检查,提取患儿及其父母基因组DNA,用二代测序技术对患儿基因组DNA进行测序分析,并对疑似致病性突变进行患儿及其父母的Sanger测序法验证,并进行生物信息学预测。结果患儿精神发育迟滞,基因测序显示患儿GRIA3基因的第2外显子存在c.455T〉C （p.L152P）错义突变,遗传自母亲。生物信息学预测为致病性突变。结论患儿诊断为GRIA3基因突变所致X连锁精神发育迟滞。     

X chromosome inactivation and X-linked mental retardation

The expression of X-linked genes in females heterozygous for X-linked defects can be modulated by epigenetic control mechanisms that constitute the X chromosome inactivation pathway. At least four different effects have been found to influence, in females, the phenotypic expression of genes responsible for X-linked mental retardation (XLMR). First, non-random X inactivation, due either to stochastic or genetic factors, can result in tissues in which one cell type (for example, that in which the X chromosome carrying a mutant XLMR gene is active) dominates, instead of the normal mosaic cell population expected as a result of random X inactivation. Second, skewed inactivation of the normal X in individuals carrying a deletion of part of the X chromosome has been documented in a number of mentally retarded females. Third, functional disomy of X-linked genes that are expressed inappropriately due to the absence of X inactivation has been found in mentally retarded females with structurally abnormal X chromosomes that do not contain the X inactivation center. And fourth, dose-dependent overexpression of X-linked genes that normally “escape” X inactivation may account for the mental and developmental delay associated with increasing numbers of otherwise inactive X chromosomes in individuals with X chromosome aneuploidy. © 1996 Wiley-Liss, Inc.     

X-linked mental retardation associated with macro-orchidism.

Two families are described with an X-linked form of mental retardation in whom the affected males were found to have bilateral enlargement of the testes. No conclusive evidence of any endocrinological disturbance was found.     

Nomenclature guidelines for X-linked mental retardation.

Nomenclature guidelines are proposed for non-specific and for syndromal forms of X-linked mental retardation. Non-specific mental retardations (MRX) are given unique symbols for each family (MRX1, MRX2, MRX3 ...). Syndromal mental retardations (MRXS) which do not as yet have specific symbols are given unique interim symbols for each syndrome (MRXS1, MRXS2, MRXS3 ...). The prerequisite for assignment of serial MRX and MRXS gene symbols is a minimum lod score (or multipoint lod score) of +2 between the MR locus and one or more X chromosome markers. Prior approval of availability for proposed gene symbols must be obtained from the Nomenclature Committee of the Human Gene Mapping Workshops.