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More information about genetics
Genes are the instructions that tell our bodies how to grow and
function. There are genes for eye color, and hair color and a gene
that tells the body how to break down isoleucine. In each child
there are two copies of each gene, one from the mother and one from
the father. Most of the time genes work correctly. Sometimes, by
chance, a gene is changed from its original form. A random change
in a gene that causes the gene not to work correctly is called a
genetic mutation.
In
2-MBADD, there is a genetic mutation that changes how isoleucine is
broken down by the body. Some of the Hmong babies who have 2-MBADD
had a blood test to see what the mutation was in the gene. That
test showed that Hmong children with 2-MBADD have a different
mutation in their gene than the children who have a severe form of
2-MBADD and who are not Hmong.
Mutations are passed on from parent to child. This happens in the
same way other characteristics are inherited or passed down from
parent to child. It is no one's fault that your child has 2-MBADD.
Genetic conditions such as 2-MBADD are usually quite rare. In Hmong
families in Wisconsin, 2-MBADD seems to be fairly common compared to
other genetic conditions. Approximately 1 in every 225 Hmong babies
born in Wisconsin has 2-MBADD.
The
mutation that causes 2-MBADD is inherited in a pattern called
“autosomal recessive” inheritance. The gene with the mutation that
causes 2-MBADD is called the non-working gene. In autosomal
recessive inheritance, one copy of the non-working gene is inherited
from each of the parents. So the baby has two non-working genes and
that's why the baby has 2-MBADD. The parents do not have 2-MBADD
because they have one gene that is working in addition to the
non-working gene. Therefore, each parent is called a “carrier”.
About 1 in 10 Hmong are carriers for 2-MBADD.
The
chance that two parents who are carriers for 2-MBADD will have a
child with 2-MBADD is one in four, or 25%. The chance that these
parents will have a child who is a carrier for 2-MBADD is one in
two, or 50%. There is also a one in four, or 25% chance that these
parents will have a child who is not a carrier and does not have
2-MBADD.
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