Final answer:
Identifying the cause of nervous system disorders can be challenging due to unknown genetic factors, absence of obvious brain defects, and variation in symptoms among patients.
Step-by-step explanation:
When it comes to identifying the cause of many nervous system disorders, it can be difficult due to various factors.
Firstly, the genes associated with these disorders are often not known, which makes it challenging to pinpoint the exact genetic causes.
Secondly, there might not be obvious defects in brain structure, making it harder to identify any anatomical abnormalities directly linked to the disorders.
Lastly, the onset and display of symptoms can vary greatly between patients, making it difficult to identify a single cause that applies to everyone.