Isolated and syndromic forms of congenital anosmia

Loss of smell (anosmia) is common in the general population and the frequency increases with age. A much smaller group have no memory of ever being able to smell and are classified as having isolated congenital anosmia (ICA). Families are rare, and tend to present in a dominant inheritance pattern. Despite a strong degree of heritability, no human disease-causing mutations have been identified. Anosmia is part of the clinical spectrum in various diseases, as seen in Kallmann syndrome, various ciliopathies and congenital insensitivity to pain. This review will focus on ICA through already published families and cases as well as syndromes where anosmia is part of the clinical disease spectrum. Furthermore, olfactory signal transduction pathway genes and animal models may shed light on potential candidate genes and pathways involved in ICA.