Ankylosing spondylitis is caused by the inflammation of the spine and the sacroiliac joints. The sacroiliac joints are placed at low back region where the sacrum (the bone just over the tailbone) meets the iliac bones (bones on the sides of upper buttocks). The severe inflammation in these areas causes spondylitis and results in increased pain and stiffness. Gradually, this disorder can result in the total fusion of the vertebrae. Such a process is referred to as ankylosis. Ankylosing spondylitis makes the spine immobile.
Ankylosing spondylitis is a systemic rheumatic disease and shares many of the features of other arthritic types such as psoriatic arthritis, reactive arthritis etc. Compared to females, males are more prone to Ankylosing spondylitis. Though it can occur to people of all age groups, those who are in their twenties and thirties are under increased threat. The true cause of the spine inflammation is yet to be found out. The observations made by scientists in this regard have helped in making certain conclusions.
In majority of cases, ankylosing spondylitis is genetically inherited. Almost ninety percent of the affected people are born with the HLA-B27 gene. This finding has led the researchers to concentrate on the connection between this gene and the disease. However, it has been concluded that HLA-B27 gene is not the cause of ankylosing spondylitis. But this gene enhances the tendency to develop the disorder in the presence of certain other factors such as environmental.
It has been found that the risk of developing this disorder also is related to heredity. People with HLA-B27-positive relatives are six times more prone to be affected by ankylosing spondylitis than others who do not have the gene in them.
Recent researches in this regard have brought to light two more genes that are related with this disease. Named as ARTS1 and IL23R, these genes are found to influence the immune system. The relation between the disease and the two genes are being explored.