NEW YORK (GenomeWeb News) – Consistent with a study published last month, researchers from the US and South Africa report in Nature Genetics that more than half of the schizophrenia cases they tested involved de novo mutations not inherited from either parent. The team sequenced the exomes of 53 individuals with sporadic schizophrenia, their unaffected parents, and 22 unrelated controls using Agilent SureSelect targeted exon capture and paired-end sequencing with the Illumina HiSeq. All of the study participants were of European descent and came from South Africa's Afrikaner population. The search yielded de novo mutations in the exomes of 27 of the individuals with schizophrenia. These mutations affected 40 different genes and an exceptionally large proportion of them were non-synonymous changes.
"The fact that the mutations are all from different genes … suggests that many more mutations than we suspected may contribute to schizophrenia," senior author Maria Karayiorgou, a psychiatry researcher at Columbia University, said in a statement. "This is probably because of the complexity of the neural circuits that are affected by the disease; many genes are needed for their development and function."
In two more exome-sequencing studies in Nature Genetics, a Johns Hopkins-led group describes how it found inactivating mutations in the chromatin remodeling gene ARID2 that are especially common in individuals with a form of hepatocellular carcinoma liver cancer that's associated with hepatitis C virus infection, while a Chinese, Danish, and American research team reports on chromatin remodeling and other genes that harbor mutations in individuals with a type of bladder cancer called transitional cell carcinoma.
A Science Translational Medicine study by Canadian and German researchers suggests some of the same genes and pathways that are subject to copy number changes in autism are also prone to copy number alterations in attention deficit-hyperactivity disorder. Researchers from the Hospital for Sick Children, the University of Toronto, and elsewhere used the Affymetrix SNP 6.0 array to detect copy number variants in 248 unrelated individuals with ADHD. The CNVs identified included rare, inherited CNVs — which affected nearly eight percent of the those with ADHD but did not show up in any of the 2,357 unaffected controls — and de novo CNVs, which were present in almost two percent of those with ADHD. Among the genes affected by these CNVs were some that are have been linked to autism spectrum disorder (ASD) in past studies.
"Our results provide support for a role for rare CNVs in ADHD risk and reinforce evidence for the existence of common underlying susceptibility genes for ADHD, ASD, and other neuropsychiatric disorders," co-corresponding author Stephen Scherer, director of the Hospital for Sick Children's Centre for Applied Genomics and of the University of Toronto's McLaughlin Centre for Molecular Medicine, and co-authors wrote.
Intelligence stems from a raft of genetic variants across the genome that each make very small contributions to the trait, according to a GWAS in the early, online version of Molecular Psychiatry. An international research team genotyped 3,511 unrelated individuals from five cohorts enrolled through the Cognitive Aging Genetics in England and Scotland project using the Illumina 610-Quadv1 array. Though they didn't find any individual SNPs reaching genome-wide significance, the researchers estimated from their data that linkage disequilibrium between common SNPs in the genome explains about 40 percent of the heritability of crystallized-type intelligence, tested using assessments of acquired knowledge, and 51 percent of fluid-type intelligence, evaluated using tests of more abstract thinking.
"Our results unequivocally confirm that a substantial proportion of individual differences in human intelligence is due to genetic variation," co-corresponding author Ian Deary, a psychology, cognitive aging and epidemiology researcher at the University of Edinburgh, and co-authors wrote, "and are consistent with many genes of small effects underlying the additive genetic influences on intelligence."
Genomics In The Journals is a weekly feature pointing readers to select, recently published articles involving genomics and related research.