Congenital Anosmia – The Inability To Smell And Its Influence On A Person’s Life

Congenital anosmia is the inability to smell at birth. There are a variety of factors that may causethis congenital anomaly. These include isolated anomalies with no familial history, associations with specific genetic disorders as well as genetic mutations. Scant research has been done on the disorder as well as ways to test for the disorder. A few studies have been performed on mice to restore protein IF88 which caused the mice to gain weight and showed an increase in olfactory neurons. This increase in the neurons caused them to increase in firing with strong smells. Losing the sense of smell does not cause a decrease in lifespan but it does cause problems with the quality of life to include problems with heating homes, food safety and personal hygiene.

Congenital Anosmia is a little known condition affecting the olfactory sense in those with this disorder. There has not been much research in the field of anosmia; therefore, there is also not much in the way of treatment for those afflicted with it. The way in which congenital anosmia affects our sense of smell is not truly known, it could be the mutation of genetics or abnormal anatomy or a mixture of both. The quality of life, as well as the safety of those with anosmia, is important to address for the sufferer.Disorders of smell are classified as “-osmias”. Congenital anosmia is the inability to smell anything from birth for an entire lifetime. Historically speaking, disorders of taste and smell have been difficult to diagnose as well as treat due to the little research that has been put forth until recently. The University of Pennsylvania has created a standardized test called the UPSIT which can be used to detect the presence of olfactory disorders as well as those who may be malingering. This is the most widely used test because “it is reported to have the highest reliability of any olfactory test”. The ability to smell is linked to our olfactory cranial nerve or cranial nerve I. Odor molecules travel into our nasal passages and diffuse into our mucus. Beneath the mucus lining our nasal passages is a specialized epithelium called olfactory epithelium. Specialized cells called olfactory receptor neurons catch the odor molecules. They are then sent to the olfactory bulbs and those bulbs send the information off to two different locations to be processed by the brain. However, with congenital anosmia this does not occur.

Congenital anosmia usually occurs in one of two ways. It can either be paired with a genetic disorder, such as Kallman’s Syndrome, or isolated, meaning with no other symptoms, diseases or disorders. There are no studies or concrete data stating what the cause is for isolated congenital anosmia. From a few of the studies that were reviewed it seems that the cause could be in part genetic and/or abnormal development of the olfactory system (Genetic and rare diseases information center). There have been a few genes linked to familial or genetic isolated congenital anosmia and they are PROK2 or PROKR2, and CNGA2. These genes appear to be autosomal dominant with reduced penetrance meaning that not everyone that inherits the mutated gene are affected by the mutation (Genetic and rare diseases information center).A study was completed on a large Iranian family with five affected and five unaffected members with a stop-gain mutation of gene CNGA2. The affected individuals were hemizygotes for the gene and the unaffected individuals were either heterozygous or homozygous for the reference allele. Smell tests were conducted on all individuals in the study and it was found that the five unaffected individuals may have some degree of hyposmia from the mutated gene, but they still fall within the normal range.

Sailani, et al also referenced another study that found two brothers with anosmia and both had a variant of the CNGA2 gene. Throughout this study the authors also frequently referenced another study done on congenitally anosmic mice. One of the references to that study suggested that the mutation to the CNGA2 gene affected the olfactory signaling pathway. The mutation in this gene caused the mice to lack the essential CNG channel subunits that are essential for olfactory neurons to create an action potential that leads to a perception of smell. This study, in conjunction with the study of the Iranian family, strongly suggests that the CNGA2 gene mutation plays a role in familial cases of congenital anosmia. (

The depth of the olfactory sulcus is another indicator for isolated congenital anosmia. During a study 106 individuals were asked to have MRI images done. With these images the depth of the olfactory sulcus was measured. It was found that the individuals with isolated congenital anosmia had a sulcus depth less than or equal to 8mm. This led to the conclusion that if the olfactory sulcus depth was less than or equal to 8mm then it could indicate isolated congenital anosmia.

The most obvious sign of congenital anosmia is the lack of smell. A person with congenital anosmia is born without a sense of smell as opposed to losing the ability because of an incident or an illness in their lifetime. In 2016, the statistics were 1 in 10,000 people had congenital anosmia. The two subgroups are: isolated congenital anosmia, those with a lack of smell as their only symptom, and those with congenital anosmia caused by a specific genetic disorder. The most prevalent research to date states that congenital anosmia is most likely a secondary symptom to someone who has the primary condition of congenital insensitivity to pain. Congenital insensitivity to pain is considered a form of peripheral neuropathy because it affects the peripheral nervous system, which connects the brain and spinal cord to muscles and to cells that detect sensations such as touch, smell, and pain. It is part of a group known as hereditary sensory and autonomic neuropathies and inherited in an autosomal recessive pattern. The common belief is 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. The consensus about anosmia is that there is little known about it, and there is not a great push for further research.

Equally interesting is the link between a lack of smell and the ability to taste. The anosmics declare they can taste fine, while those whose olfactory centers operate normally, state that that is impossible. 75% of taste is based on smell. The two sides have agreed that “flavor” is different from “taste”. Flavor is the depth, the complexities of food, acquired from the inhalation in the back of the throat when eating. It combines the smell of air in your mouth with the taste of the food on your tongue. It is the ‘icing on the cake’ so to speak. The taste of food is merely there for the tongue to experience, and because structurally there is nothing wrong with an anosmic's tongue, they believe they can taste just fine. If you ask an anosmic if they can taste like a normal person who can smell, they will inevitably answer “yes” because they have nothing to compare it to.There is no cure or treatment for congenital anosmia disease. Fortunately, there is research being done to find a cure. Inability to smell has been undervalued for so long that research for anosmia cures is quite limited. Congenital anosmia is a rare disease that few know about and are less much aware of how this affects anosmics lives.

The inability to smell endangers one's life. People that suffer from congenital anosmia have never perceived a sense of smell. Therefore, they do not know how to relate to the environment as well as others. Eating is not as satisfying for congenital anosmics as is it for everyone else. Consequently, their consumption declines, sometimes leading to other health issues. A nearby fire may be perceived by the nose well before the eye sees it. This sense is the first to alert. Hence, one acts upon the circumstance, many times saving one's life. Another important effect of congenital anosmia is the inability to smell when food is spoiled. The connection of sense of smell and taste is so strong that sometimes anosmics eat spoiled food without knowing. This alone can send them to the hospital and it may even cause death. Annette Heist, a registered nurse that suffered from congenital anosmia, wrote an article explaining how the disease has affected her life. In this article she mentions how she benefited from her family’s sense of smell. Smell feedback was given to her by her family so that she could be alerted to personal hygiene or personal safety factors she should be made aware of. She trusted that if there was a fire her family would warn her. Heist feared the day she had to leave home for college since no one would be available to help her with a sense of smell. Heist also wrote about how the inability to smell affected her memory. She noticed how her sister remembered things in more detail than she did. When one smells something, the olfactory signal enters and triggers a response in the limbic system where emotions take place. This takes someone to think about it therefore, laying down a more vivid memory. Heist acknowledges in this article how finding a cure for congenital anosmia is years away because of the rarity of this disease.

Few studies have been done on congenital anosmia. Among these studies, there is one promising study done on mice through gene therapy. This study, done by the University of Michigan, consists of the following: The mice used in this study have a cilia dysfunction through a genetic defect that affects a protein called IFT88. Loss of cilia results in the inability to smell because the receptors that bind odorants are on the cilia. Researchers did a three-day treatment that involved inserting IFT88 normal genes into the mice cells through a common cold virus loaded with normal DNA sequence. In 14 days after the given treatment, researchers found that mice had gained weight significantly and the neuron cells involved in smelling were firing appropriately when exposed to a strong smell. This proved that the absence sense of smell can be restored. More research is still required before these methods can be used in human treatment. There are different cilia-related genetic causes of anosmia, for example there is the lack of cilia as well as cilia dysfunction.

Living with congenital anosmia can be both frustrating and frightening. With the proper knowledge, help, and planning it is possible to not succumb to some of the dangers that this ailment carries. Research is increasing in the causes and ways to help restore the sense of smell in those living with anosmia. In the near future, those living with anosmia may have the ability to live a life full of smells and experience the full spectrum of life, much like their counterparts who do possess the gift of smell.