Congenital anosmia is a condition in which people are born with a lifelong inability to smell. It may occur as an isolated abnormality (no additional symptoms) or be associated with a specific genetic disorder (such as Kallmann syndrome or congenital insensitivity to pain). Isolated congenital anosmia is usually sporadic, although some familial cases have been reported. In most cases of isolated congenital anosmia, the genetic cause in unknown. Unfortunately, there is currently no cure or treatment for congenital anosmia.

Most cases of isolated congenital anosmia (not associated with additional symptoms) occur sporadically in people with no family history of the condition. In these people, the exact underlying cause of the condition is unknown. Scientists suspect that the condition is due to abnormal development of the olfactory system (the sensory system used for sense of smell) prior to birth. This may include abnormalities of the nasal cavity; disruptions in the pathway that carries information from the nose to the brain; or malformations of the portion of the brain that processes sense of smell.

When isolated congenital anosmia affects more than one family member, it may have a genetic component. One study found that some people affected by isolated congenital anosmia have changes (mutations) in the PROKR2 gene or PROK2 gene. These genes have previously been reported in people with Kallmann syndrome (an inherited condition associated with congenital anosmia and other symptoms). Another study found that two brothers with anosmia had a mutation in the CNGA2 gene. However, in most familial cases of isolated congenital anosmia, the cause remains unknown.

Congenital anosmia can also by associated with hereditary genetic disorders such as Kallmann syndrome and congenital insensitivity to pain. In these cases, it is inherited in the same manner as the associated condition. For example, Kallmann syndrome can be inherited in an autosomal dominant, autosomal recessive or X-linked recessive manner depending on the underlying genetic cause (it can be caused by mutations in several different genes). Congenital insensitivity to pain has an autosomal recessive pattern of inheritance.

Unfortunately, there is currently no known cure or treatment for congenital anosmia.

Studies suggest that approximately 1 in 10,000 people are affected by congenital anosmia. This includes people affected by isolated congenital anosmia (no additional symptoms) and those with congenital anosmia caused by a specific genetic disorder (such as Kallmann syndrome or congenital insensitivity to pain).