Mental retardation in children ages 6 to 16

Reanalysis of exome negative patients with rare disease: a pragmatic workflow for diagnostic applications

Background

Approximately two third of patients with a rare genetic disease remain undiagnosed after exome sequencing (ES). As part of our post-test counseling procedures, patients without a conclusive diagnosis are advised to recontact their referring clinician to discuss new diagnostic opportunities in due time. We performed a systematic study of genetically undiagnosed patients 5 years after their initial negative ES report to determine the efficiency of diverse reanalysis strategies.

Methods

We revisited a cohort of 150 pediatric neurology patients originally enrolled at Radboud University Medical Center, of whom 103 initially remained genetically undiagnosed. We monitored uptake of physician-initiated routine clinical and/or genetic re-evaluation (ad hoc re-evaluation) and performed systematic reanalysis, including ES-based resequencing, of all genetically undiagnosed patients (systematic re-evaluation).

Results

Ad hoc re-evaluation was initiated for 45 of 103 patients and yielded 18 diagnoses (including 1 non-genetic). Subsequent systematic re-evaluation identified another 14 diagnoses, increasing the diagnostic yield in our cohort from 31% (47/150) to 53% (79/150). New genetic diagnoses were established by reclassification of previously identified variants (10%, 3/31), reanalysis with enhanced bioinformatic pipelines (19%, 6/31), improved coverage after resequencing (29%, 9/31), and new disease-gene associations (42%, 13/31). Crucially, our systematic study also showed that 11 of the 14 further conclusive genetic diagnoses were made in patients without a genetic diagnosis that did not recontact their referring clinician.

Conclusions

We find that upon re-evaluation of undiagnosed patients, both reanalysis of existing ES data as well as resequencing strategies are needed to identify additional genetic diagnoses. Importantly, not all patients are routinely re-evaluated in clinical care, prolonging their diagnostic trajectory, unless systematic reanalysis is facilitated. We have translated our observations into considerations for systematic and ad hoc reanalysis in routine genetic care.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13073-022-01069-z.

Feasibility and Reliability of Tests Measuring Health-Related Physical Fitness in Children With Moderate to Severe Levels of Intellectual Disability

Physical fitness is an important marker for health. In this study we investigated the feasibility and reliability of health-related physical fitness tests in children with moderate to severe levels of intellectual disability. Thirty-nine children (2-18 yrs) performed tests for muscular strength and endurance, the modified 6-minute walk test (6mwt) for cardiorespiratory fitness, and body composition tests, and 30-97% of the tests were successfully completed. Short-term test-retest reliability of all tests was good (Intraclass Correlation Coefficient [ICC] > .8), long-term test-retest reliability was good for most tests (ICC > .7), but low ICCs were found for most strength tests. Measuring body composition and cardiorespiratory fitness is feasible and reliable. Measuring muscle endurance is fairly feasible and reliable.

Systematic review of field-based physical fitness tests for children and adolescents with intellectual disabilities

BACKGROUND

Testing physical fitness in children and adolescents with intellectual disabilities (ID) can be challenging. This review provides an overview on psychometric properties of field-based physical fitness tests studied in children and adolescents with ID.

METHODS

A literature search was performed in March 2014. Studies were included if they evaluated feasibility, reliability and/or validity of a field-based physical fitness test in children and adolescents with ID.

RESULTS

Twenty-six papers met the inclusion criteria and described 18 tests on body composition (4), muscular strength (4), muscular endurance (6), and cardiorespiratory fitness (4). Best results on feasibility, reliability and/or validity were found for bioelectric impedance analysis, body mass index, grip strength, arm hang and distance run/walk tests. These results were mainly found in adolescents with mild to moderate ID.

CONCLUSION

Some tests were found feasible, reliable and/or valid in subgroups of children and adolescents with ID, but not in children and adolescents with all ages and levels of ID. Further assessment is needed before wider application in all children and adolescents with ID.

Diagnostic exome sequencing in persons with severe intellectual disability

BACKGROUND

The causes of intellectual disability remain largely unknown because of extensive clinical and genetic heterogeneity.

METHODS

We evaluated patients with intellectual disability to exclude known causes of the disorder. We then sequenced the coding regions of more than 21,000 genes obtained from 100 patients with an IQ below 50 and their unaffected parents. A data-analysis procedure was developed to identify and classify de novo, autosomal recessive, and X-linked mutations. In addition, we used high-throughput resequencing to confirm new candidate genes in 765 persons with intellectual disability (a confirmation series). All mutations were evaluated by molecular geneticists and clinicians in the context of the patients' clinical presentation.

RESULTS

We identified 79 de novo mutations in 53 of 100 patients. A total of 10 de novo mutations and 3 X-linked (maternally inherited) mutations that had been previously predicted to compromise the function of known intellectual-disability genes were found in 13 patients. Potentially causative de novo mutations in novel candidate genes were detected in 22 patients. Additional de novo mutations in 3 of these candidate genes were identified in patients with similar phenotypes in the confirmation series, providing support for mutations in these genes as the cause of intellectual disability. We detected no causative autosomal recessive inherited mutations in the discovery series. Thus, the total diagnostic yield was 16%, mostly involving de novo mutations.

CONCLUSIONS

De novo mutations represent an important cause of intellectual disability; exome sequencing was used as an effective diagnostic strategy for their detection. (Funded by the European Union and others.).

Epidemiologic and clinical characteristics of 458 Tunisian patients with intellectual deficiency and a reconsidered diagnostic strategy

Intellectual Deficiency (ID) is a common neuropsychiatric disorder whose etiopathogenesis still insufficiently understood. In the last decade, several surveys, assessing epidemiologic, clinical and etiologic parameters of ID, have been performed but none of them is realized in a Tunisian population. In this retrospective survey, we propose to study these parameters, in a Tunisian cohort of 458 patients with constitutional ID, and to assess our diagnostic strategy. Data analyses, by the SPSS program, reveal a male predominance, a high level of consanguinity, an advanced mean age of patients, a rare frequentation of specialized institutions by the severely affected patients, and a high frequency of familial forms with predominance of the recessive autosomal ones. The study of clinical parameters and investigations' results shows that 72.1% of our patients present a syndromic ID. For these patients, chromosomal anomalies are rarely described, EEG anomalies were usually non-specific in patients without clinical evidence of epilepsy, and brain anomalies are common in patients with severe ID, neurological symptoms or history of seizures. Aetiology is identified in 13.1% of them whereas it is still unknown in 100% of patients with non-specific ID. This study allows us to better characterize, epidemiologically and clinically, the first large Tunisian cohort of patients with ID and to assess our diagnostic strategy in order to propose a revised one that will improve the diagnostic lead, the care chain and the preventive resources of ID.

The research on the status, rehabilitation, education, vocational development, social integration and support services related to intellectual disability in China

Intellectual disability (ID) is a prevalent form of non-progressive cognitive impairment. The objectives of this articles are: to analyze the changes of ID in China, including its definition, prevalence, rehabilitation, education, vocational development, social life and support services; to review and to compare the issues of intellectual disability in China with the international literatures and research studies and to provide useful updated information and reference data for scholars and researchers who study intellectual disability. Analyzed the data obtained from two national sample surveys on disability with respect to intellectual disability in China. The estimated prevalence of individuals with intellectual disabilities in China was 7.5‰ in 2006 nationally which was lower than the previous results obtained in the 1987 national survey. The fourth level of ID showed a downward trend, while the proportion among the population aged 60 and over with ID tended to increase. The 2006 national survey indicated that the prevalence of ID in rural areas was higher than that in urban areas. This finding was consistent with the national survey conducted in 1987. As indicated by the 2006 national survey, 29.4% cases had no known causes for the ID, the proportion tended to decrease as compared with the first survey. However, when compared to the 1987 report, the proportion of senile dementia among older people as indicated by the 2006 report was higher than before. During the past years, the prevention of ID and the quality of life of individuals with ID have improved due to the enactment and implementation of a series of national laws and regulations, however, there is more that needs to be done in the areas of education, vocational development, social integration and support services for individuals with ID in order to improve the quality of life of individuals with ID in China. The findings of this study are consistent with the research findings presented in the international literatures. ID is the conditions that deserve further study and deserve the attention of policy makers and rehabilitation professionals in China. Furthermore, with the ageing of population in China and its impact to the social security system, the in-depth study of ID and its implications has become more pertinent in China in the future.

[Psychiatric disorders and neurological comorbidity in children with intellectual disability]

INTRODUCTION

This article gives an overview of the consultant child and adolescent psychiatric services in the region of Upper Bavaria (Germany).

METHOD

The data of 257 children and adolescents with intellectual disability and psychiatric disorders were evaluated.

RESULTS

About 14% of the children with ID in special schools or day care centers, and 40% of the children with ID in residential care showed a definite psychiatric disorder. The most frequently diagnosed disorders were adjustment disorders, hyperkinetic disorders and conduct disorders, as well as emotional problems and pervasive developmental disorders. Children with severe intellectual disability had more additional somatic disorders and were more impaired in their psychosocial functions.

CONCLUSIONS

The results show the need for psychiatric services for children and adolescents with intellectual disability and psychiatric disorders. The development and implementation of integrative and interdisciplinary models is necessary to allow for adequate medical care for these patients.

Fragile x mental retardation 1 and filamin a interact genetically in Drosophila long-term memory

The last decade has witnessed the identification of single-gene defects associated with an impressive number of mental retardation syndromes. Fragile X syndrome, the most common cause of mental retardation for instance, results from disruption of the FMR1 gene. Similarly, Periventricular Nodular Heterotopia, which includes cerebral malformation, epilepsy and cognitive disabilities, derives from disruption of the Filamin A gene. While it remains unclear whether defects in common molecular pathways may underlie the cognitive dysfunction of these various syndromes, defects in cytoskeletal structure nonetheless appear to be common to several mental retardation syndromes. FMR1 is known to interact with Rac, profilin, PAK and Ras, which are associated with dendritic spine defects. In Drosophila, disruptions of the dFmr1 gene impair long-term memory (LTM), and the Filamin A homolog (cheerio) was identified in a behavioral screen for LTM mutants. Thus, we investigated the possible interaction between cheerio and dFmr1 during LTM formation in Drosophila. We show that LTM specifically is defective in dFmr1/cheerio double heterozygotes, while it is normal in single heterozygotes for either dFmr1 or cheerio. In dFmr1 mutants, Filamin (Cheerio) levels are lower than normal after spaced training. These observations support the notion that decreased actin cross-linking may underlie the persistence of long and thin dendritic spines in Fragile X patients and animal models. More generally, our results represent the first demonstration of a genetic interaction between mental retardation genes in an in vivo model system of memory formation.

CC2D2A, encoding a coiled-coil and C2 domain protein, causes autosomal-recessive mental retardation with retinitis pigmentosa

Autosomal-recessive inheritance is believed to be relatively common in mental retardation (MR), although only four genes for nonsyndromic autosomal-recessive mental retardation (ARMR) have been reported. In this study, we ascertained a consanguineous Pakistani family with ARMR in four living individuals from three branches of the family, plus an additional affected individual later identified as a phenocopy. Retinitis pigmentosa was present in affected individuals, but no other features suggestive of a syndromic form of MR were found. We used Affymetrix 500K microarrays to perform homozygosity mapping and identified a homozygous and haploidentical region of 11.2 Mb on chromosome 4p15.33-p15.2. Linkage analysis across this region produced a maximum two-point LOD score of 3.59. We sequenced genes within the critical region and identified a homozygous splice-site mutation segregating in the family, within a coiled-coil and C2 domain-containing gene, CC2D2A. This mutation leads to the skipping of exon 19, resulting in a frameshift and a truncated protein lacking the C2 domain. Conservation analysis for CC2D2A suggests a functional domain near the C terminus as well as the C2 domain. Preliminary functional studies of CC2D2A suggest a possible role in Ca(2+)-dependent signal transduction. Identifying the function of CC2D2A, and a possible common pathway with CC2D1A, in correct neuronal development and functioning may help identify possible therapeutic targets for MR.