ALS, or amyotrophic lateral sclerosis, is a progressive neurodegenerative disease that affects nerve cells in the brain and spinal cord. It causes loss of muscle control, eventually leading to paralysis and death. ALS is not considered a hereditary disease, but research suggests there may be genetic factors that predispose someone to developing it. This article will explore what ALS is, its causes and risk factors, and whether you can be born with it.
What is ALS?
ALS is a motor neuron disease that progressively damages the nerve cells that control voluntary muscle movement. Motor neurons extend from the brain and spinal cord to muscles throughout the body. As these neurons degenerate and die, the brain loses its ability to initiate and control muscle movement. Early symptoms of ALS often include muscle weakness, twitching, and cramping. Eventually all voluntary movement can be lost as muscles waste away. Other functions like breathing, swallowing, and speaking can also be impaired as the disease spreads. While ALS leads to severe disability, it does not impair sensory function, bowel and bladder control, or sexual function. Most cases of ALS occur sporadically with no clear risk factors. About 5-10% of cases are familial ALS (FALS) and caused by inherited genetic mutations. The lifespan for an ALS patient averages 2-5 years from time of diagnosis, often due to respiratory failure. Currently there is no cure, but treatment focuses on managing symptoms to improve quality of life.
Causes and Risk Factors
The exact causes of ALS are not fully understood, though research points to a combination of genetic and environmental factors.
Genetic Factors
About 5-10% of ALS cases are inherited. Mutations in over 25 genes have been linked to familial ALS, including:
- SOD1 – encodes the enzyme superoxide dismutase 1
- C9orf72 – involved in cellular trafficking and transport
- TARDBP – encodes the TDP-43 protein
- FUS – encodes the FUS protein
These mutations cause motor neurons to dysfunction and die prematurely. Offspring of an affected parent have a 50% chance of inheriting the mutation. However, ALS symptoms may not manifest until mid-life, making it appear sporadic.
Environmental Factors
For sporadic ALS cases with no family history, researchers believe environmental exposures may trigger disease onset. Proposed risk factors include:
- Heavy metals like lead, mercury, and selenium
- Pesticides and herbicides
- Smoke from cigarettes, wood, or chemicals
- Trauma or injury
- Viruses such as HIV, HTLV, or West Nile
- Strenuous physical activity
These may cause increased oxidative stress, inflammation, and damage to motor neurons. Military veterans have a higher ALS risk, possibly due to chemical exposures, trauma, or intense physical activity.
Are You Born with ALS?
ALS is not considered a disease that you are directly born with. While some genetic mutations that lead to familial ALS are present from birth, disease symptoms typically don’t appear until adulthood. There are several reasons ALS is not evident at birth:
Age of Onset
The average age of ALS onset is 55-65 years old. Juvenile ALS can rarely occur in people under age 25, but this represents less than 5% of cases. The delayed onset indicates environmental and lifestyle factors later in life influence disease development.
Incomplete Penetrance
People born with ALS-linked mutations do not always develop the disease. Estimates of penetrance vary widely – as low as 50% for some genotypes. Other genetic and environmental factors may determine if the disease ultimately manifests.
New Mutations
Not all familial ALS is inherited. Around 10% of genetic cases arise from de novo mutations that occurred spontaneously rather than being passed down from a parent. These mutations are present at birth but not through hereditary transmission.
No Apparent Symptoms
There are no distinguishing signs or symptoms of ALS present at birth. Babies with genetic mutations develop normally with no impaired motor function. Weakness and paralysis do not emerge until adulthood when neurodegeneration begins.
Is Genetic Testing Available?
Genetic testing for ALS is available but not routinely performed. Testing may be considered in the following situations:
- Someone with a confirmed family history of ALS
- Onset of ALS symptoms before age 50
- Presence of risk factors like frontotemporal dementia
- Unusual presentation, like slow disease progression
Testing panels search for mutations in known ALS-related genes. A genetic counselor can help interpret results. Early genetic testing gives the opportunity to make lifestyle changes and plan for the future. It also informs relatives of potential inherited risks. However, a negative result does not rule out developing sporadic ALS later.
Key Points
- ALS causes progressive paralysis due to the death of motor neurons.
- About 5-10% of cases are inherited due to genetic mutations.
- Symptoms typically begin in adulthood around ages 55-65.
- Genetic mutations for familial ALS are present at birth but don’t directly cause the disease.
- Environmental triggers and aging later in life drive disease onset and progression.
- Genetic testing is available but not routinely performed.
Conclusion
In summary, ALS is not a disease you are directly born with. While some familial cases stem from inherited genetic mutations, these do not completely determine the onset and progression of ALS. Environmental exposures and aging during adulthood significantly contribute to neurodegeneration. Most cases of ALS occur sporadically in people with no family history. Genetic testing can identify mutations that increase risk, but absence of mutations does not rule out developing ALS later in life. Ongoing research aims to unravel more genetic contributors and environmental triggers to better understand this complex disease. For now, the origins of ALS cannot be boiled down solely to hereditary factors present at birth.