US scientists have identified a gene that may increase the risk of an early onset of stroke. They analysed the genomes of 14 Amish people affected by stroke and found a mutation in the SAMHD1 gene was associated with this brain condition.
The study was conducted at the DDC Clinic for Special Needs Children in Ohio and was led by the clinic's Medical Director, Dr Heng Wang. The participants all suffered from cerebral vasculopathy - a disease of the blood vessels in the brain - which led to early stroke, but the severity of brain damage after the stroke varied widely. Some showed severe developmental disability, while others did not. Each person also showed signs of an immune system disorder.
The gene mutation was identified using a technique called genome-wide homozygosity mapping. This technique is used for studying recessive genetic disorders - where two copies of the mutation must be inherited together before the disease manifests. It involves comparing the genomes of distantly-related people to find stretches of DNA that are identical.
The assumption is that affected individuals who share a common ancestor are likely to have inherited the exact same mutation from their parents. Shared regions of the genome between those affected are therefore highly likely to contain the culprit gene.
The Old Order Amish are unique participants in homozygosity mapping studies because a tradition of marrying within the community has led to a genetically similar population, with most Amish having descended from a small founder population. As a result, the incidence of genetic diseases in the Amish population is higher than normal.
The homozygosity mapping identified a region on chromosome 20 that was identical in the 14 Amish participants. The researchers sequenced each gene located within this region and found a mutation in the SAMHD1 gene. The mutation leads to the production of an abnormal protein in which a large section has been deleted. The exact function of SAMHD1 is currently unknown, but Dr Wang and colleagues believe it must play a role in maintaining the blood vessels in the brain.
'The function of SAMHD1 remains unclear, but the inflammatory (blood vessel abnormalities) of the brain found in the patients with SAMHD1 mutation indicate its important roles in (the regulation of the immune system) and cerebral (blood vessel maintenance)', said Dr Wang.
As this mutation was identified in a genetically isolated community, further work is needed to see if it is present in other populations.
The research was published online this week in the Proceedings of the National Academy of Sciences.