Some people feel no pain – this is known as congenital analgesia. Though this might sound like an advantage, people with this condition may not know when they are injured or have an internal problem such as appendicitis.It can also lead to bullying and psychological problems. Congenital analgesia can be caused by a mutation in SCN9A, and this gene is also linked with lack of sense of smell (congenital anosmia).

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