This iron build-up can lead to some serious conditions including INAD
(also known as Seitelberger disease) and NBIA (also known as
Hallervorden-Spatz syndrome). With NIAD the symptoms start by age two
and worsen over time. Children may lose head control and the ability to
sit, crawl or walk, as well as deteriorating vision and speech. The
disease usually kills the victim between the ages of 5 and 10.
NBIA manifests itself in between the teen years and adulthood and
involves involuntary muscle contractions, rigidity and spasms in the
limbs, face and torso, as well as confusion, disorientation, seizures,
stupor and dementia. The rapid determination is punctuated by stable
periods lasting one to two months, with a rate of progression
correlating with the patient's age.
The gene PLA2G6 is thought to encode an enzyme that breaks down lipids
involved in the reconstruction of a cell's membrane following damage by
light and other toxins. But when mutated, the gene can trigger the iron
buildup.
According to Susan, the direct outcome of this work will help families
determine their chances of passing the disorders to their children. She
added, "There are families who literally are waiting to have this test.
They've been waiting for years. To have the option of bringing a child
into this world you know won't have to suffer like this is extraordinary
for a parent who's been through this. Some of them have had multiple
children with the disease."
Both Susan and Shawn Westaway, Ph.D, co-author of study, worked with the
University Of Birmingham School Of Medicine (UK), collecting DNA samples
from 30 to 40 families affected by the diseases and narrowed the search
for the suspect gene to a 100-gene block of DNA on chromosome 22. This
is the second smallest chromosome in humans that contains only 500 to
800 genes.
They continued to narrow their search. The team looked for genes in the
region whose function was suggestive of the symptoms and parts of the
body affected by the diseases. Again the search narrowed to just 75
genes. Finally they found “mutations in PLA2G6 in a large kindred with
multiple generations of affected individuals, and in three other smaller
families”, according to Westaway. The research has led to the
identification of 44 different changes in the gene which will lead to
disease.
The chromosomes containing the mutations are then compared to almost 200
control chromosomes not affected by the disease. "The severity of the
mutation is usually a very good clue that the gene has been found," she
said. "That evidence is confirmed by continuing to find different, but
severe, mutations in the same gene in new patients diagnosed with INAD,
which we have done."
"You just start sequencing genes and compare healthy people to people
with the disease," Hayflick said. "In people with the disease, you see
changes that are clearly disease causing."
Their research was published online June 18, in the journal Nature
Genetics.
Dan Wilson
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