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PubMed1993

Mental retardation.

In children with mental retardation, development is altered so that adaptive and cognitive skills are significantly deficient. Causes of mental retardation are varied and include newborn trauma, infectious diseases, chromosomal abnormalities, metabolic disorders, and environmental toxins. In many cases, however, the cause of mental retardation remains unknown. Most affected children have mild retardation and are able to achieve economic and social independence as adults. Early identification by the pediatrician of a developmental delay is important to ensure appropriate treatment and to enable the child to develop all of his or her capabilities.

Child Development↗
PubMed1994

The genetics of mental retardation.

Individuals affected by mental retardation are a clinically and aetiologically heterogeneous group. This heterogeneity is particularly highlighted when we consider the genetics of mental retardation. Recent advances in molecular genetic techniques have enabled us to understand more about the molecular basis of several genetic syndromes associated with mental retardation. In contrast, where there is no discrete cause, the interplay of genetic and environmental influences remains poorly understood.

Humans↗
PubMed1991

Neurological assessment: adaptations for special populations with mental retardation.

The incidence of mental retardation in the United States is approximately 125,000 births per year. Recent changes in government regulations necessitate that nurses caring for mentally retarded persons perform physical appraisals. These in-depth appraisals are a new skill for many nurses caring for the retarded and the routine neurological assessment processes must be modified in order to meet the special needs and behaviors of the mentally retarded population. This article provides examples of how a functional abilities approach to the neurological appraisal process can be modified. Further, two scenarios are presented to demonstrate how neurological data can be obtained from observing an individual's activities of daily living.

Activities of Daily Living↗
PubMed1983

Influence of personal and academic experiences on formation of attitudes toward mentally retarded adults.

Attitudes toward mentally retarded adults of 135 students majoring in special education, education, and social work were studied. Educational and personal experiences having to do with mentally retarded adults were compared. Correlations were low to moderate for the personal and academic experiences of the three groups as well as with their attitudes toward mentally retarded adults. Differences in attitude could not be explained by statistically controlling any variables.

Adult↗
PubMed2003

Somatosensory cortical barrel dendritic abnormalities in a mouse model of the fragile X mental retardation syndrome.

The Fragile X mental retardation syndrome is the largest source of inherited mental retardation. The syndrome usually results from the transcriptional silencing of the fragile X mental retardation gene (FMR1). To date the most prominent reported neuronal abnormalities for the fragile X mental retardation syndrome include a higher density of long thin spines similar to those found in sensory deprived and developing tissue, suggesting a possible deficit in pruning of immature spines. Dendrites on spiny stellate cells in the inner 1/3 of the barrel wall in layer IV of the rodent somatosensory cortex have been shown to exhibit developmental pruning similar to that affecting spines. To determine if FMRP plays a role in dendritic development, these neurons were examined in two strains of adult FMRP knockout (FraX) mice. FraX mice in both strains exhibited a greater amount of septa-oriented dendritic material, a morphology consistent with pre-pruning status early in development. This observation suggests that FMRP could be necessary for normal developmentally regulated dendritic pruning.

Animals↗
PubMed2006

Diagnostic yield of various genetic approaches in patients with unexplained developmental delay or mental retardation.

The underlying cause of mental retardation remains unknown in up to 80% of patients. As chromosomal aberrations are the most common known cause of mental retardation, several new methods based on FISH, PCR, and array techniques have been developed over recent years to increase detection rate of subtle aneusomies initially of the gene rich subtelomeric regions, but nowadays also genome wide. As the reported detection rates vary widely between different reports and in order to compare the diagnostic yield of various investigations, we analyzed the diagnostic yield of conventional karyotyping, subtelomeric screening, molecular karyotyping, X-inactivation studies, and dysmorphological evaluation with targeted laboratory testing in unselected patients referred for developmental delay or mental retardation to our cytogenetic laboratory (n = 600) and to our genetic clinic (n = 570). In the cytogenetic group, 15% of patients showed a disease-related aberration, while various targeted analyses after dysmorphological investigation led to a diagnosis in about 20% in the genetic clinic group. When adding the patients with a cytogenetic aberration to the patient group seen in genetic clinic, an etiological diagnosis was established in about 40% of the combined study group. A conventional cytogenetic diagnosis was present in 16% of combined patients and a microdeletion syndrome was diagnosed in 5.3%, while subtelomeric screening revealed only 1.3% of causes. Molecular karyotyping with a 10 K SNP array in addition revealed 5% of underlying causes, but 29% of all diagnoses would have been detectable by molecular karyotyping. In those patients without a clear diagnosis, 5.6% of mothers of affected boys showed significant (>95%) skewing of X-inactivation suggesting X-linked mental retardation. The most common diagnoses with a frequency of more than 0.5% were Down syndrome (9.2%), common microdeletion 22q11.2 (2.4%), Williams-Beuren syndrome (1.3%), Fragile-X syndrome (1.2%), Cohen syndrome (0.7%), and monosomy 1p36.3 (0.6%). From our data, we suggest the following diagnostic procedure in patients with unexplained developmental delay or mental retardation: (1) Clinical/dysmorphological investigation with respective targeted analyses; (2) In the remaining patients without an etiological diagnosis, we suggest conventional karyotyping, X-inactivation screening in mothers of boys, and molecular karyotyping, if available. If molecular karyotyping is not available, subtelomeric screening should be performed.

Child, Preschool↗
PubMed1991

Recognition of affective facial expressions by children and adolescents with and without mental retardation.

Children and adolescents with mental retardation were compared with children and adolescents without mental retardation on their ability to recognize facial expressions. The groups were matched for either chronological age (CA) or mental age (MA). Children and adolescents with mental retardation recognized facial expressions less accurately than did subjects without retardation who were matched on CA. The MA-matched groups showed no differences in accuracy at the younger MA but a difference was found at the older MA. However, subjects categorized as having cultural-familial retardation did not differ from subjects without retardation matched for MA at either the younger or older MA. Results suggest that children with mental retardation are less able than children without retardation to develop emotional recognition skills by observational learning.

Adolescent↗
PubMed1993

Development of a theory of mind in individuals with mental retardation.

The ability of adolescents with mental retardation to reason about other people's mental states was examined. Subjects were asked questions about the knowledge and beliefs of characters in stories that they heard and saw enacted with props. The adolescents with mental retardation performed worse than did children without mental retardation matched for MA. The adolescents with mental retardation did better on questions requiring first-order reasoning than on those involving second-order reasoning; this pattern is similar to that found previously for children without mental retardation.

Adolescent↗
PubMed2006

C21orf5, a human candidate gene for brain abnormalities and mental retardation in Down syndrome.

Mental retardation represents the more invalidating pathological aspect of trisomy 21 and has a hard impact on public health. The dosage imbalance of chromosome 21 genes could be the cause of neurological alterations and mental retardation seen in Down syndrome. We studied C21orf5 that we have demonstrated to be overexpressed in Down syndrome tissues, as a candidate gene for trisomy 21. A new optical technology (Rachidi et al., 2000) was used to compare signal intensity and cell density in presumptive embryonic brain compartments, at their boundaries and in higher specialized brain centres during fetal lifespan. We showed a developmentally regulated transcriptional activity of C21orf5 and a regional and cellular specific distribution of gene transcripts during human embryonic and fetal development. A wide but differential expression was detected in the nervous system during embryogenesis with a relatively lower level in the forebrain than in the midbrain and hindbrain and the highest transcription intensity in the future cerebellum. This developmentally regulated expression is maintained during post-embryogenesis and evolves selectively in fetal cerebral, hippocampal and cerebellar areas. Differential and cellular specificity were detected in hippocampus with higher C21orf5 mRNA level in the pyramidal cells compared to granular cells of the dentate gyrus. The expression pattern detected in cortical and cerebellar structures correlates well to the altered cortical lamination and to the lower size of the cerebellum observed in Down syndrome patients. In addition, the patterned differential expression detected in the medial temporal-lobe system, including hippocampal formation and perirhinal cortex, working as control centres of the memory circuits and involved in cognitive processes and memory storage, also corresponds to abnormal brain regions seen in Down syndrome patients. The C21orf5 selective expression in the key brain structures for learning and memory suggests that C21orf5 overexpression could participate in mental retardation pathogenesis in Down syndrome patients.

Brain↗
PubMed1997

Myotonic dystrophy. The role of large triplet repeat length in the development of mental retardation.

OBJECTIVE: To describe mental retardation and microcephaly as initial clinical signs in myotonic dystrophy (MD) with high trinucleotide repeats. PATIENTS AND METHODS: Two patients with maternally inherited MD were examined. Southern blot analysis was performed and trinucleotide repeat expansions were related to the findings of clinical and magnetic resonance imaging investigations. RESULTS: Both patients had the large CTG trinucleotide repeat expansions often seen in congenital MD, but they lacked the typical clinical signs. Mental retardation and microcephaly were the leading features present in infancy. Muscular weakness, in contrast, developed after age 35 years. Although there was no evidence for perinatal asphyxia or sleep apnea, magnetic resonance imaging disclosed reduced brain volume and subcortical demyelination. CONCLUSIONS: Mental retardation preceding the development of muscle weakness suggests that the cerebral involvement in MD is a direct consequence of the genetic disorder and not mediated by muscle disease. Careful clinical examination of the parents for signs of MD should be considered in patients with cognitive deficits even without apparent muscular involvement.

Adult↗
PubMed1988

Depression in mentally retarded children.

Thirty-one mentally retarded emotionally disturbed children, hospitalized within a university medical school's psychiatric intensive care program, were matched on age and sex and compared to 31 children from a normal school setting on depression. Measures included the Child Depression Inventory (CDI) and the Child Behavior Profile (CBP), with children being compared on total and subfactor scores for both measures. Depression and its various subcomponents were more prevalent in the mentally retarded group. There were no significant sex or age differences. Degree of overall psychopathology and depression were highly related. The relationship between criteria for depression on the CDI and CBC were also made. Correlational data showed a strong relationship between the cut-off scores for both measures, an important finding because they were based on norms established with children of normal intelligence. These data suggest that similarities exist between depression in mentally retarded children and those without such cognitive handicaps. The relationship of depression to other forms of psychopathology in the group of 31 emotionally disturbed mentally retarded children was also examined. A wide range of disorders including schizophrenia, aggression, withdrawal, and hyperactivity were evaluated. These are the first empirical data with mentally retarded children in the United States that are aimed specifically at evaluating depression, and should be useful to the clinicians in better understanding the phenomenon.

Adolescent↗
PubMed2000

Missense mutation in PAK3, R67C, causes X-linked nonspecific mental retardation.

X-linked mental retardation is a very common condition that affects approximately 1 in 600 males. Despite recent progress, in most cases the molecular defects underlying this disorder remain unknown. Recently, a study using the candidate gene approach demonstrated the presence of mutations in PAK3 (p21-activating kinase) associated with nonspecific mental retardation. PAK3 is a member of the larger family of PAK genes. PAK proteins have been implicated as critical downstream effectors that link Rho-GTPases to the actin cytoskeleton and to MAP kinase cascades, including the c-Jun amino-terminal kinase (JNK) and p38. We screened 12 MRX pedigrees that map to a large region overlying Xq21-q24. Mutation screening of the whole coding region of the PAK3 gene was performed by using a combination of denaturing gradient gel electrophoresis and direct sequencing. We have identified a novel missense mutation in exon 2 of PAK3 gene (R67C) in MRX47. This confirms the involvement of PAK3 in MRX following the report of a nonsense mutation recently reported in MRX30. In the MRX47 family, all affected males show moderate to severe mental retardation. No seizures, statural growth deficiency, or minor facial or other abnormal physical features were observed. This mutation R67C is located in a conserved polybasic domain (AA 66-68) of the protein that is predicted to play a major role in the GTPases binding and stimulation of Pak activity.

Amino Acid Sequence↗
PubMed2004

Cryptic chromosomal rearrangement screening in 30 patients with mental retardation and dysmorphic features.

Mental retardation affects 1-3% of the general population, and the genetic causes in many cases are unknown. Cytogenetically undetected chromosomal imbalances have been indicated as an explanation. Nowadays, due to the development of molecular cytogenetic techniques, it is possible to identify cryptic rearrangements involving the ends of chromosomes. We report a screening using chromosome-specific telomere fluorescence in-situ hybridization (FISH) probes, in a group of 30 patients with a well-characterized phenotype including mental retardation, dysmorphic features, and a normal karyotype. Among them, two subtelomeric rearrangements have been detected and characterized. One of them is a de novo deletion of 1p36, which has been previously described as a new contiguous gene syndrome. The second is an unbalanced product of a cryptic translocation involving chromosomes 1 and 13, which results in a partial 1q trisomy and partial 13q monosomy. These findings highlight, the importance of searching for cryptic subtelomeric rearrangements in non-syndromic mentally retarded patients.

Adolescent↗
PubMed2006

Oligonucleotide microarray analysis of genomic imbalance in children with mental retardation.

The cause of mental retardation in one-third to one-half of all affected individuals is unknown. Microscopically detectable chromosomal abnormalities are the most frequently recognized cause, but gain or loss of chromosomal segments that are too small to be seen by conventional cytogenetic analysis has been found to be another important cause. Array-based methods offer a practical means of performing a high-resolution survey of the entire genome for submicroscopic copy-number variants. We studied 100 children with idiopathic mental retardation and normal results of standard chromosomal analysis, by use of whole-genome sampling analysis with Affymetrix GeneChip Human Mapping 100K arrays. We found de novo deletions as small as 178 kb in eight cases, de novo duplications as small as 1.1 Mb in two cases, and unsuspected mosaic trisomy 9 in another case. This technology can detect at least twice as many potentially pathogenic de novo copy-number variants as conventional cytogenetic analysis can in people with mental retardation.

Child↗
PubMed1987

Psychiatric illness among the mildly mentally retarded.

The relationship between mental retardation and psychiatric disturbance was studied by comparing the mentally retarded in the age group 20-60 years with matched controls. The mildly retarded showed a higher degree of neuroticism but did not differ significantly from persons of higher intelligence in the frequency of mental illnesses. By contrast the severely retarded showed an increased mental morbidity, mainly in the form of chronic psychoorganic syndromes, as compared with both the mildly retarded and controls.

Adjustment Disorders↗
PubMed1998

Implicit and explicit memory in individuals with mental retardation.

Students with and without mental retardation from three age groups were compared on implicit and explicit memory tasks. Consistent with previous research on intelligence-related differences in controlled and automatic processes, students without mental retardation performed better than those with mental retardation on the explicit memory task, but there was no difference between groups on the implicit memory task. For both groups implicit and explicit memory increased from age 6 to 8 to age 10 to 12, but did not significantly increase to age 15 to 17. Because implicit memory appears to be a relative strength for students with mental retardation, we suggest further exploration into broader types of implicit processes that may be useful in training situations.

Adolescent↗