Scientists show extra copies of a gene carry extra risk

Feb 04, 2009

Is more of a good thing better? A gene known as LIS1 is crucial for ensuring the proper placement of neurons in the developing brain. When an LIS1 gene is missing, brains fail to develop the characteristic folds; babies with lissencephaly or 'smooth brain' are born severely mentally retarded. But new research by Prof. Orly Reiner of the Institute's Molecular Genetics Department, which recently appeared in Nature Genetics, shows that having extra LIS1 genes can cause problems as well.

Reiner was the first to discover LIS1's tie to lissencephaly, in 1993. Their latest study shows that it works by helping to determine polarity in the cell - how the various organelles are arranged inside the cell as well as where it connects to neighboring cells. Neurons alter their polarity several times during development, especially when they take on an elongated shape and migrate to new locations in the brain.

But what if, rather than too little, the body has too much LIS1? One of the surprises to come out of the recent spate of post-human-genome research is the number of genes that can be repeated or deleted in an individual's genome. Most extra copies of genes may be no more harmful than a computer backup disk, but scientists have been finding that some repeats can cause disease.

Research associate Dr. Tamar Sapir and lab technician Talia Levy, working in Reiner's lab, developed a mouse model in which additional LIS1 protein was produced in the brain. The scientists found that the brains of these mice were a bit smaller than average. On closer inspection, they discovered a range of subtle changes in cell polarity and movement: Nuclei within the proliferating zone tended to move faster, but with less control; rates of cell death were higher; and various factors in the cell became more disordered.

Reiner then asked whether their findings might apply to humans. Together with Jim Lupski and Drs. Weimin Bi and Oleg A. Shchelochkov of Baylor College of Medicine in Houston, Texas, they searched through blood samples using a technique that matches a patient's DNA with control DNA to identify additions or deletions in its sequence. They identified seven individuals with extra copies of either LIS1 or adjacent genes that are also involved in brain development. All suffered developmental abnormalities. Two of the patients - children with a second LIS1 gene - had previously been diagnosed with failure to thrive and delayed development, and were found to have small brain sizes. A third, who had three copies of the gene, was mentally retarded and suffered from bone deformation as well.

Reiner: 'Several brain diseases, including schizophrenia, epilepsy and autism, have been linked to faulty neuron migration, and recent research has hinted that some of these may involve variations in gene number. Our study is the first to demonstrate the effects of the duplication of a single gene in a mouse model and tie it to a new 'copy number variation' human disease.'

For the scientific paper, please see: www.nature.com/ng/journal/v41/n2/pdf/ng.302.pdf

Source: Weizmann Institute of Science

Explore further: Project pinpoints 12 new genetic causes of developmental disorders

add to favorites email to friend print save as pdf

Related Stories

Seeing color traced back to genetic mutations

May 21, 2012

From the inside of our heads, it feels as if colors are intrinsic aspects of the outside world and our eyes are beautifully designed to see them. But we humans are merely sampling the possible ways of sensing the spectrum ...

Rett syndrome mobilizes jumping genes in the brain

Nov 17, 2010

With few exceptions, jumping genes-restless bits of DNA that can move freely about the genome-are forced to stay put. In patients with Rett syndrome, however, a mutation in the MeCP2 gene mobilizes so-called ...

Overactive FTO gene does cause overeating and obesity

Nov 15, 2010

(PhysOrg.com) -- Scientists have gained strong confirmation of the direct connection between the FTO gene and obesity, obtaining the first direct evidence that overactivity of the gene leads to overeating ...

Recommended for you

Obese British man in court fight for surgery

Jul 11, 2011

A British man weighing 22 stone (139 kilograms, 306 pounds) launched a court appeal Monday against a decision to refuse him state-funded obesity surgery because he is not fat enough.

2008 crisis spurred rise in suicides in Europe

Jul 08, 2011

The financial crisis that began to hit Europe in mid-2008 reversed a steady, years-long fall in suicides among people of working age, according to a letter published on Friday by The Lancet.

New food labels dished up to keep Europe healthy

Jul 06, 2011

A groundbreaking deal on compulsory new food labels Wednesday is set to give Europeans clear information on the nutritional and energy content of products, as well as country of origin.

Overweight men have poorer sperm count

Jul 04, 2011

Overweight or obese men, like their female counterparts, have a lower chance of becoming a parent, according to a comparison of sperm quality presented at a European fertility meeting Monday.

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.