Mental Retardation Developmental Delay Research Articles

Detection of genomic copy number variations in patients with unexplained mental retardation/developmental delay by low coverage whole-genome sequencing

To detect genomic copy number variations (CNVs) among 145 children with unexplained mental retardation/developmental delay (MR/DD) by using low-depth whole-genome copy number variation sequencing (CNV-seq). Peripheral blood samples were collected from the patients and subjected to DNA extraction and CNV-seq. The results were analyzed by a combination of bioinformatic tools. Forty-nine patients were found to carry a total of 67 CNVs with an average size of 5.27 Mb. Among these, 22 patients were assessed to carry MR/DD-related CNVs involving 21 syndromes. This gave a diagnostic rate of 15.17%(22/145) for CNVs associated with unexplained MR/DD. The corresponding regions of the 22 MR/DD-related CNVs in the human genome covered 174 MR/DD-related pathogenic genes, which have mapped to 18 sections on 10 chromosomes. Genomic CNVs-related microdeletions/duplications account for a significant proportion of unexplained MR/DD, for which CNV-seq can provide an accurate diagnosis.

Analysis of copy number variations in 66 children with unexplained mental retardation/developmental delay using chromosomal microarrays

To investigate clinically relevant copy number variations (CNV) in patients with unexplained mental retardation/developmental delay (MR/DD) through chromosomal microarray analysis (CMA). Sixty-six patients with unexplained MR/DD were analyzed with CMA. All identified CNVs were verified with database of genomic variations (DGV), DECIPHER, ISCA and the literature. Nineteen clinically relevant CNVs were detected among the 16 individuals. The diagnostic yield for the MR/DD patients was 24.2%. The most common abnormality was Phelan-McDermid syndrome (3/16, 18.8%), which was followed by Prader-Willi syndrome/Angelman syndrome (2/16, 12.5%) and Wolf-Hirschhorn syndrome (2/16, 12.5%). CNVs are one of the most common causes for unexplained MR/DD. CMA can improve the detection rate of CNVs and confer genetic testing with greater sensitivity in elucidating the diagnosis for unexplained MR/DD.

Identification of Chromosome Abnormalities in Subtelomeric Regions Using Multiplex Ligation Dependent Probe Amplification (MLPA) Technique in 100 Iranian Patients With Idiopathic Mental Retardation

BackgroundMental retardation/Developmental delay (MR/DD) is present in 1 - 3% of the general population (1, 2). MR is defined as a significant impairment of both cognitive (IQ < 70) and social adaptive functions, with onset before 18 years of age.ObjectivesThe purpose was to determine the results of subtelomeric screening by the Multiplex Ligation Dependent Probe Amplification (MLPA) Technique in 100 selected patients with idiopathic mental retardation (IMR) in Iran.Materials and MethodsA number of 100 patients with IMR, normal karyotypes and negative fragile-X and metabolic tests were screened for subtelomeric abnormalities using MLPA technique.ResultsNine of 100 patients showed subtelomeric abnormalities with at least one of the two MLPA kits. Deletion in a single region was found in 3 patients, and in two different subtelomeric regions in 1 patient. Duplication was only single and was present in 2 patients. Three patients were found to have both a deletion and duplication.MLPA testing in the parental samples of 7 patients which was accessible showed that 4 patients were de novo, 2 patients had inherited from a clinically normal mother, and one had inherited from a clinically normal father. Screening with the two MLPA kits (SALSA P036 and SALSA P070) proved abnormality in only five of the 9 patients.ConclusionsSo, the prevalence rate of abnormal subtelomeres using MLPA technique in patients with idiopathic MR in our study was 5 - 9%, the higher limit referring to the positive results of one of the two MLPA kits, and the lower limit representing the results of positive double-checking with the two MLPA kits.

7q36 deletion and 9p22 duplication: effects of a double imbalance

The etiology of mental retardation/developmental delay (MRDD) remains a challenge to geneticists and clinicians and can be correlated to environmental and genetic factors. Chromosomal aberrations are common causes of moderate to severe mental retardation and may represent 10% of these occurrences. Here we report the case of a boy with development delay, hypoplasia of corpus callosum, microcephaly, muscular hypotonia, and facial dysmorphisms. A deletion of 7q36.1 → 36.3 and duplication of 9p22.3 → 23 was detected as a result of an unbalanced translocation of paternal origin. Breakpoint delimitation was achieved with array comparative genomic hybridization assay. Additional multiplex ligation dependent probe amplification (MLPA) analyzes confirmed one copy loss of 7q36.3 region and one copy gain of 9p24.3 region. Patient resultant phenotype is consistent with the already described findings for both 7q deletion and 9p duplication syndromes.

A Cytogenetic Study of Children with Developmental Delay Mental Retardation

The presented study was carried out to identify the chromosomal abnormalities in children with mental retardation and associated anomalies, registered at Kasturba Hospital, Manipal and in and around clinics during 2005-2009. Four hundred and twenty children were subjected to clinical and G-banded cytogenetic evaluation. Of these, 245 children reported as autosomal trisomy and variants who were initially diagnosed for Down syndrome, 14 had structural abnormalities, who were mentally retarted with associated congenital anomalies. The rest were found to have normal chromosomal karyotypes although they were diagnosed with developmental delay and associated malformations. In conclusion, the study suggests that G-banded karyotyping is a routine clinical test for Mental retardation (MR) patients with or without congenital anomalies, albeit molecular karyotyping needs to be applied for detection of submicroscopic chromosome alterations.

A Cytogenetic Study of Children with Developmental Delay Mental Retardation

A Cytogenetic Study of Children with Developmental Delay Mental Retardation

Diagnosis and fine localization of deletion region in Wolf- Hirschhorn syndrome patients

Background Wolf-Hirschhorn syndrome (WHS) results from the partial deletion of 4p. This study aimed to identify and finemap the chromosome deletion regions of Chinese children with Wolf-Hirschhorn syndrome among the developmental delay/mental retardation (DD/MR) patients. Methods We analyzed the relationship of phenotype and genotype. Inclusion criteria were: moderate to severe DD/MR, no definite perinatal brain injury, and no trauma, toxication, hypoxia, infection of central nervous system; routine karyotyping was normal, no evidence of typical inherited metabolic disorder or specific neurodegenerative disorders from cranial neuro-imaging and blood/urinary metabolic diseases screening; no mutation of FMR1 in male patients, no typical clinical manifestation of Rett syndrome in female patients. Multiplex ligation-dependent probe amplification (MLPA) and Affymetrix genome-wide human SNP array 6.0 assays were applied to accurately define the exact size of subtelomeric aberration region of four WHS patients. Results All four WHS patients presented with severe DD, hypotonia and microcephaly, failure to thrive, 3/4 patients with typical facial features and seizures, 2/4 patients with congenital heart defects and cleft lip/palate, 1/4 patients with other malformations. The length of the deletions ranged from 3.3 Mb to 9.8 Mb. Two of four patients had “classic” WHS, 1/4 patients had “mild”-to-“classic” WHS, and 1/4 patients had “mild” WHS. Conclusions WHS patients in China appear to be consistent with those previously reported. The prevalence of signs and symptoms, distribution of cases between “mild” and “classic” WHS, and the correlation between length of deletion and severity of disease of these patients were all similar to those of the patients from other populations.

Submicroscopic subtelomeric aberrations in Chinese patients with unexplained developmental delay/mental retardation

BackgroundSubtelomeric imbalance is widely accepted as related to developmental delay/mental retardation (DD/MR). Fine mapping of aberrations in gene-enriched subtelomeric regions provides essential clues for localizing critical regions, and provides a strategy for identifying new candidate genes. To date, no large-scale study has been conducted on subtelomeric aberrations in DD/MR patients in mainland China.MethodsThis study included 451 Chinese children with moderate to severe clinically unexplained DD/MR. The subtelomere-MLPA (multiplex ligation dependent probe amplification) and Affymetrix human SNP array 6.0 were used to determine the subtelomeric copy number variations. The exact size and the breakpoint of each identified aberration were well defined.ResultsThe submicroscopic subtelomeric aberrations were identified in 23 patients, with a detection rate of 5.1%. 16 patients had simple deletions, 2 had simple duplications and 5 with both deletions and duplications. The deletions involved 14 different subtelomeric regions (1p, 2p, 4p, 6p, 7p, 7q, 8p, 9p, 10p, 11q, 14q, 15q, 16p and 22q), and duplications involved 7 subtelomeric regions (3q, 4p, 6q, 7p, 8p, 12p and 22q). Of all the subtelomeric aberrations found in Chinese subjects, the most common was 4p16.3 deletion. The sizes of the deletions varied from 0.6 Mb to 12 Mb, with 5-143 genes inside. Duplicated regions were 0.26 Mb to 11 Mb, with 6-202 genes inside. In this study, four deleted subtelomeric regions and one duplicated region were smaller than any other previously reported, specifically the deletions in 11q25, 8p23.3, 7q36.3, 14q32.33, and the duplication in 22q13. Candidate genes inside each region were proposed.ConclusionsSubmicroscopic subtelomeric aberrations were detected in 5.1% of Chinese children with clinically unexplained DD/MR. Four deleted subtelomeric regions and one duplicated region found in this study were smaller than any previously reported, which will be helpful for further defining the candidate dosage sensitive gene associated with DD/MR.

The prevalence of PTEN mutations in a clinical pediatric cohort with autism spectrum disorders, developmental delay, and macrocephaly

PurposeTo define the prevalence of PTEN mutations in a clinical cohort of pediatric subjects with autism spectrum disorders (ASDs), developmental delay/mental retardation (DD/MR), and/or macrocephaly and to assess genotype–phenotype correlations. MethodsMedical records of patients who had clinical PTEN gene sequencing ordered through our institution between January 1, 2005 and December 31, 2007 were abstracted to confirm genetic test results and medical diagnoses. Phenotypic information related to the diagnoses, prenatal history, early developmental milestones, physical characteristics, and family history for those with a confirmed PTEN mutation was also recorded. ResultsOne hundred fourteen patients were tested during this time period for indications of ASDs (N = 60), DD/MR (N = 49), or macrocephaly only (N = 5). Eleven mutations were identified: five in patients with ASDs and six in those with DD/MR, resulting in a prevalence of 8.3% and 12.2% in these respective clinical populations. All individuals with a PTEN mutation had significant macrocephaly (>2.0 SD) ConclusionsThese data illustrate that PTEN gene sequencing has a high diagnostic yield when performed in a selected population of individuals with ASDs or DD/MR and macrocephaly. Germline mutations in PTEN are an important, identifiable etiology among these patients.

Increased Risk of Adverse Neurological Development for Late Preterm Infants

To assess the risks of moderate prematurity for cerebral palsy (CP), developmental delay/mental retardation (DD/MR), and seizure disorders in early childhood. Retrospective cohort study using hospitalization and outpatient databases from the Northern California Kaiser Permanente Medical Care Program. Data covered 141 321 children > or =30 weeks born between Jan 1, 2000, and June 30, 2004, with follow-up through June 30, 2005. Presence of CP, DD/MR, and seizures was based on International Classification of Diseases, Ninth Revision codes identified in the encounter data. Separate Cox proportional hazard models were used for each of the outcomes, with crude and adjusted hazard ratios calculated for each gestational age group. Decreasing gestational age was associated with increased incidence of CP and DD/MR, even for those born at 34 to 36 weeks gestation. Children born late preterm were >3 times as likely (hazard ratio, 3.39; 95% CI, 2.54-4.52) as children born at term to be diagnosed with CP. A modest association with DD/MR was found for children born at 34 to 36 weeks (hazard ratio, 1.25; 95% CI, 1.01-1.54), but not for children in whom seizures were diagnosed. Prematurity is associated with long-term neurodevelopmental consequences, with risks increasing as gestation decreases, even in infants born at 34 to 36 weeks.

Application of metaphase HR‐CGH and targeted chromosomal microarray analyses to genomic characterization of 116 patients with mental retardation and dysmorphic features

Recent advances in molecular cytogenetics enable identification of small chromosomal aberrations that are undetectable by routine chromosome banding in 5-20% of patients with mental retardation/developmental delay (MR/DD) and dysmorphism. The aim of this study was to compare the clinical usefulness of two molecular cytogenetic techniques, metaphase high-resolution comparative genomic hybridization (HR-CGH) and targeted array CGH, also known as Chromosomal Microarray Analysis (CMA). A total of 116 patients with unexplained mild to severe MR and other features suggestive of a chromosomal abnormality with apparently normal or balanced karyotypes were analyzed using HR-CGH (43 patients) and/or CMA (91 patients). Metaphase HR-CGH detected seven interstitial deletions (16.3%). Rare deletions of chromosomes 16 (16p11.2p12.1) and 8 (8q21.11q21.2) were identified. Targeted CMA revealed copy-number changes in 19 of 91 patients (20.8%), among which 11 (11.8%) were clinically relevant, 6 (6.5%) were interpreted as polymorphic variants and 2 (2.1%) were of uncertain significance. The changes varied in size from 0.5 to 12.9 Mb. In summary, our results show that metaphase HR-CGH and array CGH techniques have become important components in cytogenetic diagnostics, particularly for detecting cryptic constitutional chromosome imbalances in patients with MR, in whom the underlying genetic defect is unknown. Additionally, application of both methods together increased the detection rates of genomic imbalances in the tested groups.

Frequency of truly cryptic subtelomere abnormalities – a study of 534 patients and literature review

Frequency of truly cryptic subtelomere abnormalities - a study of 534 patients and literature review. Unbalanced subtelomere chromosome rearrangements are a significant cause of mental retardation with approximately 5% of over 3000 affected individuals tested worldwide having a chromosome rearrangement of this type. Many of these abnormalities are detectable using routine karyotyping at the 550 band level and therefore are not considered to be cryptic. The frequency of truly cryptic subtelomere abnormality should be less than 5% but has not been established. In this study, we defined 'cryptic abnormality' as one not detectable at the 550 band level on routine karyotyping. Using this as one of the selection criteria, we have studied 534 individuals with mental retardation/ developmental delay (MR/DD) and referred for subtelomere study by clinical geneticists. We have identified seven cases with cryptic subtelomere abnormalities. The clinical features of the seven abnormal cases are summarized. Literature review identified five publications on the identification of subtelomere abnormalities which used similar recruitment criteria: (a) normal karyotype at the 550 band level and (b) subjects were selected for subtelomere studies. Combining the data from these studies with those of the current study, 1154 patients were tested and 30 subtelomere abnormalities were identified. We estimate the frequency of truly cryptic subtelomere abnormality to be approximately 2.6% (30/1154) in children with MR/DD who are referred for subtelomere study.

Neuroimaging studies in the evaluation of developmental delay/mental retardation.

The employment of neuroimaging studies in the evaluation of individuals with developmental delay/mental retardation (DD/MR) is still highly debated. The Consensus Conference of the American College of Medical Genetics has suggested that "neuroimaging appears to have an especially important role in patients with microcephaly or macrocephaly, seizures, loss of psychomotor skills and neurologic signs," whereas the value of neuroimaging investigations "in the normocephalic patient without focal neurological signs is unclear" [Curry et al., 1997]. However, recent literature reports show how the latest neuroimaging techniques (in vivo proton magnetic resonance spectroscopy [H-MRS]) may prove to be useful in the diagnostic process of those individuals with DD/MR and no neurological signs/symptoms. The use of these techniques can, in addition, help in monitoring treatment in distinct metabolic disorders. This review will focus on the usefulness of neuroimaging studies in some of the newer metabolic disorders. This paper will also cover those recognizable patterns of human malformation where neuroimaging findings seem to be relevant both toward diagnosis and management, and add to our understanding of the related behavior phenotype. The essential role of magnetic resonance imaging (MRI) on the progress in the diagnostic recognition of malformations of cerebral cortical development is stressed.