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## What Causes ALS?
For most people, the exact cause is unknown.
Approximately **90% of ALS cases are sporadic**, meaning there is no obvious family history. Around 10% are familial and linked to inherited genetic variants. ([NINDS][3])
Scientists have identified multiple genes associated with ALS, including:
* C9orf72
* SOD1
* FUS
* TARDBP
Research continues into how genetics, cellular processes, and environmental factors contribute to the disease.
## How Is ALS Diagnosed?
There is no single simple blood test that confirms ALS.
Diagnosis generally involves:
* Detailed neurological examination
* Medical history
* Electromyography (EMG)
* Nerve-conduction studies
* Blood tests
* Imaging when appropriate
* Other testing to exclude similar conditions
ALS can be difficult to diagnose early because several neurological and muscular diseases can mimic its symptoms. ([Mayo Clinic][2])
## Conditions That Can Mimic ALS
Progressive weakness, twitching, or speech problems can occur with many conditions other than ALS.
