DUF1220, autism, and highly dosage-variable genes

Copy numbers. When we discuss structural genomic variants in the human genome on the Channelopathist blog, we usually refer to regions where simple deletions or duplications exert a pathogenic effect. However, there are also genes that are highly copy number variable, sometimes present at 80 copies or more. Copy numbers of a few of these genes have expanded during human evolution recently, turning these genes into potential candidate genes for human disease. A recent paper in PLOS Genetics now examines the role of DUF1220, which encodes a protein domain of the NBPF genes. This domain shows an unusually broad range of copy number variation in the human genome. Interestingly, this gene resides right next to the 1q21.1 region that is implicated in various neurodevelopmental disorders. Continue reading

Mutation intolerance – why some genes withstand mutations and others don’t

The river of genetic variants. The era of high-throughput sequencing has given us several unexpected insights into the human genome. One of these insights is the observation that mutations or variations can occur in parts of our genome without any major consequences. Every individual is a “knockout” for at least two genes in the human genome. This means that in every individual, both copies of a single gene are disrupted through mutations or small deletions or duplications. In addition, there are dozens, if not hundreds, of genes with disruptive mutations that affect only a single copy of the gene. Similar mutations in specific disease-associated genes, however, will invariably result in an early onset genetic disorder. This comparison already shows that the genes in the human genome differ with respect to the amount of disruptive genetic variation they can tolerate. A recent study in PLOS Genetics now tries to catalogue the genes in the human genome by assessing their mutation intolerance based on the genetic variation seen in large-scale exome datasets. Many genes for neurodevelopmental disorders are highly intolerant to mutations. Furthermore, some genes for monogenic epilepsies show surprising results in this assessment. Continue reading

Rare variants and olive trees

Epic dimensions. 5,000 years ago, human civilization was getting off the ground in Mesopotamia. At some point, the early human pioneers decided to use pictures as letters and human writing was invented. Ox became aleph, which became alpha, which turned into literature, which finally turned into blogging. At around the same time that the Mesopotamian people invented the direct precursor of modern day tweets and text messages, rare genetic variants started spreading through the human population. In fact, all the rare variation that we see in humans today, had probably not been present prior to the chiseling of the first human words. Continue reading

AUTS2, regulatory elements and human evolution

Recurrent themes. The era of large-scale genomics in neurodevelopmental disorders has welcomed the discovery of several genes, which predispose to a wide range of neurodevelopmental disorders. While a connection to neuronal function is obvious for a few of them, the function of other genes remains cryptic. Now, a recent paper in PLOS Genetics investigates AUTS2, a gene that is both a candidate gene for autism and a gene that has changed dramatically in recent human evolution. Continue reading