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

ABSTRACT: The cause of mental retardation in one-third to one-half of all affected individuals is unknown. Microscopically-detectable chromosomal abnormalities are the most frequent 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 their parents using the Affymetrix GeneChip® Mapping 100K Assay and found de novo duplications as small as 1.1 Mb in three cases, de novo deletions as small as 178 kb in eight 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 in people with mental retardation. Keywords: mental retardation, trio analysis, copy number variant, CNV, chromosome aberration, array CGH

ORGANISM(S): Homo sapiens

PROVIDER: GSE7226 | GEO | 2007/03/12

SECONDARY ACCESSION(S): PRJNA98281

REPOSITORIES: GEO

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Project description:A female patient with a partial trisomy 16q was described previously. Her clinical characteristics included obesity, severe anisomastia, moderate to severe mental retardation, dysmorphic facies, and contractions of the small joints. In this paper, we describe a more detailed analysis of the genetic anomaly in this patient. We were particularly interested in the involvement of the fat mass and obesity associated gene (FTO) in her duplication. Single nucleotide polymorphisms in FTO have recently been associated with obesity. We have precisely mapped the breakpoints of the duplication using high resolution oligonucleotide array comparative genome hybridization (CGH). We found that the duplication spans 11.45 Mb on 16q11.2 to 16q13 and it includes FTO. The increased copy number of FTO was confirmed with a qPCR on genomic DNA of the patient and healthy controls. We investigated the influence of the increased FTO copy number on FTO gene expression in immortalized lymphocytes from the using qPCR. We found no evidence of increased FTO expression in the patient. This observation could be explained by maternal imprinting. We found evidence supporting this hypothesis in a database of imprinted genes. In addition, our results generated new candidate genes for the mental retardation, dysmorphic facies, small joints contractions, small teeth, and anisomastia of the patient. We used a high density oligonucleotide microarray to delineate the borders of the duplication with high resolution. This analysis enabled us to confirm the inclusion of FTO in the duplication. This was confirmed with quantitative real-time PCR (qPCR) at the level of genomic DNA. To further investigate the role of FTO in the obese phenotype of the patient, we used qPCR to study the expression of FTO in immortalized lymphocytes of the patient. Remarkably, the increased FTO copy number in the patient’s genomic DNA did not give rise to an increased copy number of FTO mRNA molecules. We think this may be the result of maternal imprinting of the gene. The CGH results also allowed us to generate new hypotheses regarding the etiology of the other clinical problems of the patient. We propose candidate genes for her mental retardation, dysmorphic facies, joint contractures, small teeth, and anisomastia.

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

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