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Neuropsychological, neurological, and neuroanatomical profile of Williams syndrome.

The general aim of our research is to understand the brain mechanisms that underlie language and cognition. In this paper, we present a new line of investigation which attempts to forge links between a specific neurodevelopmental disorder, a specific neuropsychological profile, and abnormal brain organization. We report on a dissociation between language and cognitive functions in Williams syndrome adolescents, in contrast to age- and IQ-matched Down syndrome adolescents. The Williams syndrome individuals exhibit an unusual fractionation of higher cortical functioning, with marked cognitive deficits, but selective sparing of syntax. Differences in spatial cognitive abilities in the 2 groups are investigated, showing peaks and valleys of abilities specific to Williams syndrome individuals. These neurobehavioral profiles are explored in light of new evidence regarding neurologic and neuroanatomical differences between the 2 matched groups of adolescents. Results from these combined studies should help clarify the neural systems that mediate language and cognitive functions.

Abnormalities, Multiple↗

Isolation of a yeast artificial chromosome contig spanning the X chromosomal translocation breakpoint in a patient with Rett syndrome.

Rett syndrome is a neurodevelopmental disorder observed exclusively in females. A de novo X;3 translocation was detected in a patient (TH) with Rett syndrome. The X chromosomal breakpoint maps to Xp21.3 between the distal end of the Duchenne muscular dystrophy (DMD) gene and the DXS28 (C7) locus. To determine if this translocation caused the Rett syndrome in this patient, our efforts focused on mapping and cloning of the X chromosomal breakpoint in this patient. Toward these goals, we generated a set of radiation-reduced hybrid cell lines for the short arm of the X chromosome to use as a source for region-specific markers. Using Alu-PCR, 13 new DNA markers were isolated from a radiation-reduced hybrid, which retained both DMD and DXS28. These markers were localized within Xp21 using DNA from males with various interstitial deletions in this region. Two new markers, K23-2p and K23b-1, were found to be closer flanking markers to the X chromosomal breakpoint than DMD and DXS28. Long range restriction mapping using K23-2p and K23b-1 determined that the maximum distance between them was 800 kb. Several of the new markers were developed into sequence tagged-sites and were used to isolate yeast artificial chromosome (YAC) clones. A total of 22 YAC clones was isolated and characterized; these YACs were then developed into 3 large contigs in the Xp21.3 region. This effort resulted in the cloning of the region containing the X chromosomal translocation breakpoint of the Rett syndrome patient in a 170-kb YAC clone.

Animals↗

Angelman syndrome associated with oculocutaneous albinism due to an intragenic deletion of the P gene.

Angelman syndrome (AS) is a neurodevelopmental disorder characterized by mental retardation, speech impairment, ataxia, and happy disposition with frequent smiling. AS results from the loss of expression of a maternal imprinted gene, UBE3A, mapped within 15q11-q13 region, due to different mechanisms: maternal deletion, paternal UPD, imprinting center mutation, and UBE3A mutation. Deletion AS patients may exhibit hypopigmentation of skin, eye, and hair correlating with deletion of P gene localized in the distal part of Prader-Willi (PWS)/AS region. Our patient presented developmental delay, severe mental retardation, absence of speech, outbursts of laughter, microcephaly, ataxia, hyperactivity, seizures, white skin, no retinal pigmentation, and gold yellow hair. His parents were of African ancestry. The SNURF-SNRPN methylation analysis confirmed AS diagnosis and microsatellite studies disclosed deletion with breakpoints in BP2 and BP3. All of the 25 exons and flanking introns of the P gene of the patient, his father, and mother were investigated. The patient is hemizygous for the deleted exon 7 of the P gene derived from his father who is a carrier of the deleted allele. Our patient manifests OCA2 associated with AS due to the loss of the maternal chromosome 15 with the normal P allele, and the paternal deletion in the P gene. As various degrees of hypopigmentation are associated with PWS and AS patients, the study of the P gene in a hemizygous state could contribute to the understanding of its effect on human pigmentation during development and to disclose the presence of modifier pigmentation gene(s) in the PWS/AS region.

Albinism, Oculocutaneous↗

Rett syndrome in adolescent and adult females: clinical and molecular genetic findings.

Rett syndrome (RTT) is a neurodevelopmental disorder which is diagnosed clinically. We report on 30 adolescent and adult females with classical or atypical RTT of whom 24 have a MECP2 mutation. In these 24 females, the clinical manifestations, degree of severity, and disorder profiles are discussed as well as the genotype phenotype correlation. After X-chromosome inactivation (XCI) study in these cases, we found no correlation between skewing and milder phenotype. Three large deletions were found after additional Southern blot analysis in three classical RTT cases. We confirm that early truncating mutations in MECP2 are responsible for a more severe course of the disorder. Three disorder profiles related to the missense mutations R133C and R306C, and to deletions in the C terminal segment are described and are of interest for further clinical study on larger numbers of cases. The R133C genotype has a predominantly autistic presentation while the R306C genotype is associated with a slower disease progression. The phenotype of the "hotspot" deletions in the C terminal segment is predominantly characterized by rapid progressive neurogenic scoliosis. Older women with RTT are underdiagnosed: seven adults were first diagnosed as having RTT between 29 and 60 years of age, and confirmed on finding a MECP2 mutation. Knowledge of the clinical phenotype of RTT at an adult age is important for all involved in the care of these individuals. The involvement of the parent support group is very important in this matter.

Adolescent↗

Cognitive and adaptive behavior profiles of children with Angelman syndrome.

Angelman syndrome (AS) is a neurodevelopmental disorder caused by maternal deficiency of the UBE3A gene that encodes E6-AP ubiquitin-protein ligase. Expression of the UBE3A gene from the maternal chromosome is essential to prevent AS. AS is characterized by severe mental retardation, ataxia, and a defined behavioral pattern characterized mainly by happy/sociable disposition. This study used the Bayley Scales of Infant Development and the Vineland Adaptive Behavior Scales to examine the cognitive abilities and adaptive behavior of children (n = 20) with the four known molecular classes of AS, including patterns of strengths and weaknesses across adaptive behavior domains, and the relationship between adaptive behavior and overall cognitive abilities. Cognitive skills fell within the severe to profound range of mental deficiency. Differences in cognitive skills according to genetic subtype only partially supported previous research and suggest that there is overlap in abilities across genetic subtypes of AS. Adaptive behavior skills were also significantly delayed, with participants demonstrating a significant strength in socialization, and a weakness in motor skills. Strong, positive correlations emerge between cognitive ability scores and adaptive behaviors scores. These results provide further delineation of a cognitive/behavioral phenotype in AS.

Age Factors↗

Sensorineural hearing loss in children and adults with Williams syndrome.

Williams syndrome (WS) is a genetic neurodevelopmental disorder, most often accompanied by mild-to-moderate mental retardation. Individuals with WS show unique communication strengths and impairments that are challenging to treat in community, educational, and vocational settings. Many issues regarding characteristics of auditory sensitivity in WS remain to be resolved. Our purpose was to obtain behavioral (screening and pure-tone audiometry) and objective (distortion product otoacoustic emission-DPOAE) measures of auditory system function from a group of 27 individuals with WS, 6-48 years of age. These measures were gathered both at an international professional conference (n = 19) and in a clinic setting (n = 8). In the behavioral screening conditions, 16/19 (84%) of the individuals failed the hearing screening; and in the behavioral diagnostic hearing condition, 6/8 (75%) demonstrated sensorineural hearing loss (SNHL) and 1/8 demonstrated a hearing loss of undetermined type. In the objective DPOAE testing, 19/25 (76%) had DPOAE absolute amplitudes below the 5th percentile for ears with normal hearing [Gorga et al. (1997); Ear Hear 18(6):440-455]. We report SNHL in 14/18 (78%) of school-age children with WS. Post hoc analyses revealed a significant effect for age, suggesting a pattern of progressive hearing loss. An effect size analysis indicated a clinically meaningful difference in the hearing sensitivity between school-aged children and adults in the high frequencies (4,000 and 8,000 Hz). Similar hearing loss phenotype was observed in patients with familial nonsyndromic supravalvular aortic stenosis (SVAS), suggesting that molecular defects in the elastin gene in the pathogenesis of SNHL in WS. This study highlights the importance of early and regular hearing testing for WS patients and suggests that elastin may have a previously unappreciated function in maintaining hearing sensitivity.

Adult↗

X-chromosome inactivation patterns in females with Prader-Willi syndrome.

Prader-Willi syndrome (PWS) is a complex neurodevelopmental disorder caused by loss of paternally expressed genes from the 15q11-q13 region generally due to a paternally-derived deletion of the 15q11-q13 region or maternal disomy 15 (UPD). Maternal disomy 15 is usually caused by maternal meiosis I non-disjunction associated with advanced maternal age and after fertilization with a normal sperm leading to trisomy 15, a lethal condition unless trisomy rescue occurs with loss of the paternal chromosome 15. To further characterize the pathogenesis of maternal disomy 15 process in PWS, the status of X-chromosome inactivation was calculated to determine whether non-random skewing of X-inactivation is present indicating a small pool of early embryonic cells. We studied X-chromosome inactivation in 25 females with PWS-UPD, 35 with PWS-deletion, and 50 controls (with similar means, medians, and age ranges) using the polymorphic androgen receptor (AR) gene assay. A significant positive correlation (r = 0.5, P = 0.01) was seen between X-chromosome inactivation and age for only the UPD group. Furthermore, a significantly increased level (P = 0.02) of extreme X-inactivation skewness (>90%) was detected in our PWS-UPD group (24%) compared to controls (4%). This observation could indicate that trisomy 15 occurred at conceptus with trisomy rescue in early pregnancy leading to extreme skewness in several PWS-UPD subjects. Extreme X-inactivation skewness may also lead to additional risks for X-linked recessive disorders in PWS females with UPD and extreme X-chromosome skewness.

Adolescent↗

Energy expenditure and physical activity in Prader-Willi syndrome: comparison with obese subjects.

Prader-Willi syndrome (PWS) is a complex neurodevelopmental disorder characterized by hypotonia, suck and feeding difficulties, hypogonadism, small hands and feet, developmental delay, hyperphagia and early childhood obesity and a particular facial appearance. The obesity associated with PWS is the result of a chronic imbalance between energy intake and energy expenditure (EE) due to hyperphagia, decreased physical activity, reduced metabolic rate and an inability to vomit. EE is affected by body composition as well as exercise. Individuals with PWS have a lower lean body mass (LBM) compared with controls which may contribute to reduced basal level EE. To determine the relationship among body composition, activity levels and metabolic rates, dual energy X-ray absorptiometry (DEXA) and a whole-room respiration chamber were used to measure body composition, total EE (TEE), resting EE (REE), physical activity, and mechanical work (MW) during an 8 hr monitoring period. The chamber consisted of a live-in whole-room indirect calorimeter equipped with a force platform floor to allow simultaneous measurement of EE, physical activity, and work efficiency during spontaneous activities and standardized exercise. Participants with PWS (27 with 15q11-q13 deletion and 21 with maternal disomy 15 with an average age of 23 years) had significantly decreased TEE by 20% and reduced LBM compared to 24 obese subjects. Similarly, REE was significantly reduced by 16% in the individuals with PWS relative to the comparison subjects. Total MW performed during the 8 hr monitoring period was significantly reduced by 35% in the PWS group. The energy cost of physical activity is related to the duration, intensity and type of activity and the metabolic efficiency of the individual. After adjusting group differences in LBM by analysis of variance, TEE and REE were no longer different between the two groups. Our data indicate that there is a significant reduction of EE in individuals with PWS resulting from reduced activity but also from lower energy utilization due to reduced LBM which consists primarily of muscle.

Adolescent↗

No association between the APOE gene and autism.

Autism is a neurodevelopmental disorder characterized by stereotypic and repetitive behavior and interests, together with social and communicative deficiencies. The results of several genomic screens suggest the presence of an autism susceptibility locus on chromosome 19p13.2-q13.4. The apolipoprotein E (APOE) gene on chromosome 19 encodes for a protein, apoE, whose different isoforms (E2, E3, E4) influence neuronal growth. APOE participates in lipid transport and metabolism, repair, growth, and maintenance of axons and myelin during neuronal development. The APOE protein competes with the Reelin protein for VLDL/APOER2 receptor binding. Several studies have reported evidence for an association between autism and the Reelin gene. Based on these data we tested for association between APOE and autism using family-based association methods in a data set of 322 autism families. Three promoter, one intronic, and one 3' UTR single nucleotide polymorphisms (SNPs) in the APOE gene (-491a/t, -427c/t, -219g/t, 113c/g, and 5361c/t) as well as the APOE functional polymorphism (E2, E3, E4) were examined and failed to reveal significant evidence that autism is associated with APOE.

Apolipoproteins E↗

Lack of evidence for an association between WNT2 and RELN polymorphisms and autism.

Autism is a pervasive neurodevelopmental disorder characterized by deficits in language development and social interaction, as well as stereotypical, repetitive behaviors. The etiology of autism is largely unknown. Family and twin studies have provided compelling evidence for a strong genetic component in most idiopathic cases. Several recent candidate gene studies have suggested that alleles of WNT2 and the reelin gene (RELN), two genes involved in distinct aspects of neurodevelopment, confer greater susceptibility to autism. We screened WNT2 for DNA polymorphisms by sequencing all exons and adjacent intronic regions in 24 autistic patients, and identified not only the WNT2 variants reported previously (two common single-nucleotide polymorphisms (SNPs) in the 5' upstream region and the 3' untranslated region (UTR), respectively), but also two new SNPs in its 3' UTR. We genotyped all four WNT2 polymorphisms and a polymorphic trinucleotide repeat in the 5' UTR of RELN in 107 families with multiple autistic children, and evaluated evidence for association between these variants and autism by the transmission disequilibrium test (TDT). Our results revealed no deviation from the null hypothesis of no association. Our interpretation of these findings is that it is unlikely that DNA variations in RELN and WNT2 play a significant role in the genetic predisposition to autism.

5' Untranslated Regions↗

Linkage and association analysis at the serotonin transporter (SLC6A4) locus in a rigid-compulsive subset of autism.

Autism is a complex genetic neurodevelopmental disorder in which affected individuals display deficits in language, social relationships, and patterns of compulsive and stereotyped behaviors and rigidity. Linkage analysis in our dataset of 57 New England and 80 AGRE multiplex autism families reveals a multipoint heterogeneity LOD (HLOD) score of 2.74 at D17S1871 in 17q11.2. Analysis of phenotypic subsets shows an increased HLOD of 3.62 in families with compulsive behaviors and rigidity. The serotonin transporter locus (SLC6A4) maps nearby and is considered a functional candidate gene in autism and obsessive-compulsive disorder. We genotyped an insertion/deletion polymorphism in the promoter (5-HTTLPR), and seven single nucleotide polymorphisms (SNPs) across the 38-kb transcriptional unit. Transmission disequilibrium (TD) analysis reveals nominal association at a SNP in intron 5 (P = 0.02) as well as 5-HTTLPR (P = 0.01), corresponding to over-transmission of the short allele. TD analysis in the rigid-compulsive subset shows no evidence for association. Intermarker linkage disequilibrium was determined. All SNPs define a single haplotype block, while 5-HTTLPR lies 5' to this block. Three SNPs are sufficient to detect all common alleles (> or =5%) in this > 26-kb block. Analysis of haplotypes for these markers demonstrates no evidence for association to autism. These data indicate that a common allele within the coding region of SLC6A4 is not responsible for the observed linkage. However, the presence of heterogeneous disease variants within the block or the existence of a common disease-associated allele either upstream or downstream of this block is possible. In fact, such variants may well account for linkage to 17q11.2 in our families.

Autistic Disorder↗

Metabolic endophenotype and related genotypes are associated with oxidative stress in children with autism.

Autism is a behaviorally defined neurodevelopmental disorder usually diagnosed in early childhood that is characterized by impairment in reciprocal communication and speech, repetitive behaviors, and social withdrawal. Although both genetic and environmental factors are thought to be involved, none have been reproducibly identified. The metabolic phenotype of an individual reflects the influence of endogenous and exogenous factors on genotype. As such, it provides a window through which the interactive impact of genes and environment may be viewed and relevant susceptibility factors identified. Although abnormal methionine metabolism has been associated with other neurologic disorders, these pathways and related polymorphisms have not been evaluated in autistic children. Plasma levels of metabolites in methionine transmethylation and transsulfuration pathways were measured in 80 autistic and 73 control children. In addition, common polymorphic variants known to modulate these metabolic pathways were evaluated in 360 autistic children and 205 controls. The metabolic results indicated that plasma methionine and the ratio of S-adenosylmethionine (SAM) to S-adenosylhomocysteine (SAH), an indicator of methylation capacity, were significantly decreased in the autistic children relative to age-matched controls. In addition, plasma levels of cysteine, glutathione, and the ratio of reduced to oxidized glutathione, an indication of antioxidant capacity and redox homeostasis, were significantly decreased. Differences in allele frequency and/or significant gene-gene interactions were found for relevant genes encoding the reduced folate carrier (RFC 80G > A), transcobalamin II (TCN2 776G > C), catechol-O-methyltransferase (COMT 472G > A), methylenetetrahydrofolate reductase (MTHFR 677C > T and 1298A > C), and glutathione-S-transferase (GST M1). We propose that an increased vulnerability to oxidative stress (endogenous or environmental) may contribute to the development and clinical manifestations of autism.

Adolescent↗

Reelin gene polymorphisms in the Indian population: a possible paternal 5'UTR-CGG-repeat-allele effect on autism.

Autism is a neurodevelopmental disorder with high heritability factor and the reelin gene, which codes for an extracellular matrix protein involved with neuronal migration and lamination is being investigated as a positional and functional candidate gene for autism. It is located on chromosome 7q22 within the autism susceptible locus (AUTS1); identified in earlier genome scans and several investigations have been carried out on various ethnic groups to assess possible association and linkage of the gene with autism. However, the findings are still inconclusive. In the present study which represents the first report of such a study on the Indian population, genotyping analyses of CGG repeat polymorphism at 5'UTR, two single nucleotide polymorphisms (SNP) at exon 6 and exon 50 were performed in 73 autistic subjects, 129 parents, and 80 controls. The allelic distributions of the repeat polymorphism and exon 50 T/C SNP were quite different from earlier reports in other populations. Allelic and genotypic distribution of the markers did not show any differences between the cases and controls. While our preliminary data on family-based association studies on 58 trios showed no preferential transmission of any allele from the parents to the affected offspring, TDT and HHRR analyses revealed significant paternal transmission distortions for 10- and > or =11-repeat alleles of CGG repeat polymorphism. Thus, the present study suggests that 5'UTR of reelin gene may have a role in the susceptibility towards autism with the paternal transmission and non-transmission respectively of 10- and > or =11-repeat alleles, to the affected offspring.

5' Untranslated Regions↗

Abnormal asymmetry in language association cortex in autism.

Autism is a neurodevelopmental disorder affecting cognitive, language, and social functioning. Although language and social communication abnormalities are characteristic, prior structural imaging studies have not examined language-related cortex in autistic and control subjects. Subjects included 16 boys with autism (aged 7-11 years), with nonverbal IQ greater than 80, and 15 age- and handedness-matched controls. Magnetic resonance brain images were segmented into gray and white matter; cerebral cortex was parcellated into 48 gyral-based divisions per hemisphere. Asymmetry was assessed a priori in language-related inferior lateral frontal and posterior superior temporal regions and assessed post hoc in all regions to determine specificity of asymmetry abnormalities. Boys with autism had significant asymmetry reversal in frontal language-related cortex: 27% larger on the right in autism and 17% larger on the left in controls. Only one additional region had significant asymmetry differences on post hoc analysis: posterior temporal fusiform gyrus (more left-sided in autism), whereas adjacent fusiform gyrus and temporooccipital inferior temporal gyrus both approached significance (more right-sided in autism). These inferior temporal regions are involved in visual face processing. In boys with autism, language and social/face processing-related regions displayed abnormal asymmetry. These structural abnormalities may relate to language and social disturbances observed in autism.

Autistic Disorder↗

Olfactory biopsies demonstrate a defect in neuronal development in Rett's syndrome.

Rett's Syndrome (RTT) is a neurodevelopmental disorder resulting from mutation in the mecp2 gene that encodes methyl CpG binding protein 2, a transcriptional repressor. Because this disease primarily affects neurons, tissue is not available during active disease. We used the olfactory system as a model to investigate abnormalities in neuronal development in RTT, because olfactory receptor neurons (ORNs) are replaced throughout life by ongoing postnatal neurogenesis. Thus, even in the adult, the olfactory epithelium contains neurons at various developmental stages. We obtained biopsies of nasal epithelium containing ORNs from RTT patients and age-matched controls to study the status of the neuronal population using antibodies to stage-specific developmental markers. There were no postprocedure complications. Compared with age-matched controls, there were far fewer mature ORNs, as defined by olfactory marker protein expression, and significantly greater numbers of immature neuron-specific tubulin-positive ORNs present. In RTT biopsies, olfactory marker protein-positive neurons displayed abnormal structure. These results suggest that dysfunction of MeCP2 results in decreased survival of mature ORNs with a compensatory increase in neurogenesis, or a failure of immature neurons to mature. Our study indicates that olfactory biopsies provide a method to study neuronal developmental diseases in adults and children.

Adolescent↗

Neuroglial activation and neuroinflammation in the brain of patients with autism.

Autism is a neurodevelopmental disorder characterized by impaired communication and social interaction and may be accompanied by mental retardation and epilepsy. Its cause remains unknown, despite evidence that genetic, environmental, and immunological factors may play a role in its pathogenesis. To investigate whether immune-mediated mechanisms are involved in the pathogenesis of autism, we used immunocytochemistry, cytokine protein arrays, and enzyme-linked immunosorbent assays to study brain tissues and cerebrospinal fluid (CSF) from autistic patients and determined the magnitude of neuroglial and inflammatory reactions and their cytokine expression profiles. Brain tissues from cerebellum, midfrontal, and cingulate gyrus obtained at autopsy from 11 patients with autism were used for morphological studies. Fresh-frozen tissues available from seven patients and CSF from six living autistic patients were used for cytokine protein profiling. We demonstrate an active neuroinflammatory process in the cerebral cortex, white matter, and notably in cerebellum of autistic patients. Immunocytochemical studies showed marked activation of microglia and astroglia, and cytokine profiling indicated that macrophage chemoattractant protein (MCP)-1 and tumor growth factor-beta1, derived from neuroglia, were the most prevalent cytokines in brain tissues. CSF showed a unique proinflammatory profile of cytokines, including a marked increase in MCP-1. Our findings indicate that innate neuroimmune reactions play a pathogenic role in an undefined proportion of autistic patients, suggesting that future therapies might involve modifying neuroglial responses in the brain.

Adolescent↗

Primary progressive multiple sclerosis as a phenotype of a PLP1 gene mutation.

We report a 49-year-old woman with a history of progressive gait disturbance, white matter disease, and cerebrospinal fluid immunoglobulin abnormalities who met criteria for primary progressive multiple sclerosis and whose son died at age 10 years of an unknown congenital neurodevelopmental disorder. Sequencing of the proteolipid protein 1 gene showed a novel mutation, Leu30Arg (c.89TG), in the mother and son. Pelizaeus-Merzbacher disease is the cause of death in the son and explains the mother's adult-onset neurological disorder. This case goes against dogma that mothers of severely affected sons are asymptomatic as adults and expands the differential diagnosis of primary progressive multiple sclerosis to include proteolipid protein 1 gene mutations.

Arginine↗

Association by guilt: identification of DLX5 as a target for MeCP2 provides a molecular link between genomic imprinting and Rett syndrome.

Rett syndrome (RTT) is an X-linked dominant neurodevelopmental disorder affecting almost exclusively girls. Although mutations in methyl-CpG-binding protein (MeCP2) are known to be associated with RTT, gene expression patterns are not significantly altered in MeCP2-deficient cells. A recent study1 identified MeCP2-mediated histone modification and formation of a higher-order chromatin loop structure specifically associated with silent chromatin at the Dlx5-Dlx6 locus in normal cells, and its absence thereof in RTT patients. This altered expression of Dlx5 through loss of silent chromatin loop formation provides a molecular mechanism underlying RTT and proposes a novel role for MeCP2 in chromatin organization and imprinting.

Animals↗