A genetic study found that a cluster of genes on chromosome six is the only one that plays a significant role in multiple sclerosis ( MS ).

" Our results confirm the strong role of the major histocompatibility complex genes in multiple sclerosis, and provides a definitive statement that no other region of the genome harbors a gene with a similar overall influence on multiple sclerosis genetics," said Jonathan Haines, of Vanderbilt University in Nashville.

The major histocompatibility complex ( MHC ) is a cluster of genes that play a critical role in the recognition of cells in the body as belonging to the body, i.e., not intruders such as bacteria or other pathogens.

When this system of recognition breaks down, the immune system may mistakenly launch an attack against cells, as happens in multiple sclerosis.
Researchers believe that some genetic variations in MHC genes make people more susceptible to whatever environmental causes also contribute to multiple sclerosis.

Previous studies have implicated the MHC, but also regions on other chromosomes, as harboring genes that increase multiple sclerosis risk. Haines suggests that these studies failed to include enough subjects.

Ten centimorgan microsatellite map have been the standard tool used for whole genome linkage screening since the mid 1990's and to date 11 screens employing this methodology have been published in multiple sclerosis.
However the scale and quality of the data in these studies is limited.

In order to establish a definitive linkage map researchers have typed 4506 single nucleotide polymorphism markers in a set of 730 multiplex families from Australia, Scandinavia, the United Kingdom and the United States, which together provide 945 affected relative pairs.

Highly significant linkage is observed in the region of the Major Histocompatibility Complex ( lod score 11.7 ) and suggestive linkage is identified on chromosome 17 and 5.
Ordered sub-set analysis identifies a further locus on chromosome 19.

The mean information extraction provided by the marker panel is 79.3% ( range 42.4 - 91.3% ) and the observed Mendelian inconsistencies suggests that within this data set the genotyping error rate is just 0.002%.

Source: American Neurological Association, 2005


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