1. How do humans develop ALS?
Researchers believe that in most cases of amyotrophic lateral sclerosis (ALS) it is not
inherited. Researchers also think that most cases of ALS come as sporadic ALS or SALS.
It is not well understood why individuals develop this disease, but researchers believe it
may be a combination of environmental and genetic risks. About ten percent of people
with ALS have what is considered familial ALS (FALS). In such cases, more than one
person in the family has the disease and they may also have frontotemporal dementia.
People with FALS may start to experience symptoms at a younger age than someone who
has SALS. FALS is autosomal dominant. This means that the parent has a genetic
mutation that causes ALS.
The first gene found that is linked to ALS is that coding for an enzyme, copper-zinc
superoxide dismutase (SOD1). This means the parent has a fifty percent chance of passing
the disease to every child they have no matter the sex. Most of the time this disease
affects someone in the family in each generation and the family member will develop
ALS or dementia.
FALS can be present at different ages in different family members. People with
autosomal FALS have one copy of the gene with the mutation and one copy without.
Children born with FALS have a fifty percent chance of inheriting the FALS gene with
the mutation and fifty percent chance of inheriting the gene without the mutation. Parents
do not have control over which genes they pass on to their children but often feel
responsible for their children’s suffering with the ALS.
This 1 in 2, or 50% chance, comes from the fact that a parent randomly passes on only
one member of their gene pair. Even though parents often feel responsible for their
children's health, they have no control over which gene they pass on. If a child does not
inherit the gene mutation for FALS from either parent, they cannot pass it onto their
children. However, inheriting a gene for FALS does not guarantee a person will develop
ALS.
