July 20, 1998 Bar Harbor -- Scientists at The Jackson Laboratory are working towards identifying the gene that causes Alström Syndrome. The research is providing increased understanding of the genetic basis for the disease and may offer fundamental insights into the underlying causes of obesity, diabetes, and sensory defects in humans.
As part of the research effort, 46 living Alström individuals have been located in 10 countries, including the U.S. and Canada. Many of those individuals will be attending the Second International Alström Syndrome Gathering, sponsored by the Society for Alström Syndrome Families, July 17-21 in San Luis Obispo, Calif. The first Alström gathering was in Yarmouth, Nova Scotia, in 1995, when only nine individuals were known.
The rare inherited syndrome, first described in 1959 by Swedish physician C.H. Alström, is a disease of the young, causing progressively severe conditions such as blindness, hearing loss, kidney disease, scoliosis, obesity, heart disease, and non-insulin-dependent (type 2) diabetes. There is no known cure.
Alström syndrome is a recessive genetic disorder. Parents who carry the defective gene don't show any signs of the disease. In order for a child to be affected, he or she must inherit the defective gene in combination from both parents. This requirement for a "double dose" of the Alström gene explains why the syndrome is so rare.
Progress towards finding the molecular basis for the Alström gene at The Jackson Laboratory has been accomplished through a combination of research in the labs of Drs. Patsy M. Nishina and Jürgen Naggert and genealogical sleuthing by Jan D. Marshall, a senior professional assistant for Dr. Nishina who is a leading point of contact for Alström families and maintains an Alström Syndrome webpage at http://www.jax.org/alstrom.
Although Alström Syndrome is extremely rare, chances that a child will inherit the double dose of the gene are increased in culturally isolated populations. Marshall located an extended French Acadian family in which at least 17 members are thought to have died from Alström Syndrome. She traced the disease back 13 generations in this "kindred", connecting a common ancestor in 1650 to five living children with Alström Syndrome. The children, from four nuclear families, range in age from 8 to 14.
Because of the common ancestor, the researchers believe the five are "homozygous by descent", meaning that they inherited the same form, or allele, of the defective gene from both their mother and father. That characteristic made possible a strategy known as "homozygosity mapping" to identify the gene's location by looking for a chromosomal region that was identical among all five, and always present in two copies.
Testing performed by Senior Research Assistant Gayle Collin, a French Acadian herself, on DNA samples from the interrelated children resulted in 1996 in the successful mapping of the Alström gene to human chromosome 2. Since then, the chromosomal region, or locus, known to contain the gene has been progressively narrowed. The research has been funded in part by the National Institutes of Health and the American Diabetes Association.
The Jackson Laboratory researchers believe they may be able to identify the gene as more people with the disease -- both within the French Acadian kindred and beyond -- are located and tested. "Alström Syndrome exists worldwide," says Marshall, "and we'd like to find all of this very special international family." If the gene can be identified, the researchers plan to make an animal model to study the developmental and pathological consequences of the disease.
Dr. Nishina's research interest in Alström Syndrome goes beyond the identification of the mutation that causes the disease. The syndrome is one of several human conditions -- Bardet-Biedl syndrome is another -- that exhibit "overlapping" phenotypes of a large number of common complex diseases, suggesting the existence of shared developmental pathways.
"The Alström gene could also provide clues to the normal pathways that regulate weight and normal blood glucose levels and sight and hearing, and how those normal biological pathways function," says Dr. Nishina.
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