Isolated and syndromic forms of congenital anosmia

Abstract

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.

PROKR2 and PROK2 mutations cause isolated congenital anosmia without gonadotropic deficiency

“…The most common form is acquired anosmia related to trauma or upper respiratory tract infection (2). An association with neurodegenerative disorders has been reported (2).…”

“…The most common form is acquired anosmia related to trauma or upper respiratory tract infection (2). An association with neurodegenerative disorders has been reported (2). A small minority of patients with anosmia are classified as having congenital anosmia (CA), defined as absent recall of olfactory sensations since birth in the absence of any disease known to cause anosmia.…”

“…ICA may be due to developmental abnormalities such as olfactory bulb agenesis. It may also occur in the absence of developmental defect, possibly as a result of deficient intracellular signaling in the olfactory receptor pathway (2,3,4).…”

Making Sense of the Chemical Senses

“…Behavioural studies investigating taste sensitivity in congenital olfactory im paired subjects are scarce, given the low prevalence of the condition, which affects only 0.05% of the general population (Karstensen and Tommerup, 2011). Hasan et al (2007) found similar electrogustometric thresholds in patients with congenital anosmia due to Kallman syndrome and healthy normosmic subjects, although this negative result could easily be attributed to their low samples size of only four subjects per group.…”

Isolated Congenital Anosmia and CNGA2 Mutation

“…Isolated congenital anosmia (OMIM 107200) is a rare condition where patients have no recollection of ever being able to smell 1 . Unlike syndromic forms of anosmia, ICA patients have no additional symptoms, and no other underlying disease-causing condition can be identified 1 .…”