A genetic marker of the ACKR1 gene is present in patients with Type II congenital smell loss who have type I hyposmia and hypogeusia

Genetics of congenital olfactory dysfunction: a systematic review of the literature

Olfaction, as one of our 5 senses, plays an important role in our daily lives. It is connected to proper nutrition, social interaction, and protection mechanisms. Disorders affecting this sense consequently also affect the patients' general quality of life. Because the underlying genetics of congenital olfactory disorders (COD) have not been thoroughly investigated yet, this systematic review aimed at providing information on genes that have previously been reported to be mutated in patients suffering from COD. This was achieved by systematically reviewing existing literature on 3 databases, namely PubMed, Ovid Medline, and ISI Web of Science. Genes and the type of disorder, that is, isolated and/or syndromic COD were included in this study, as were the patients' associated abnormal features, which were categorized according to the affected organ(-system). Our research yielded 82 candidate genes/chromosome loci for isolated and/or syndromic COD. Our results revealed that the majority of these are implicated in syndromic COD, a few accounted for syndromic and isolated COD, and the least underly isolated COD. Most commonly, structures of the central nervous system displayed abnormalities. This study is meant to assist clinicians in determining the type of COD and detecting potentially abnormal features in patients with confirmed genetic variations. Future research will hopefully expand this list and thereby further improve our understanding of COD.

On the mechanism of smell loss in patients with Type II congenital hyposmia

BACKGROUND

Smell function has been initiated with theophylline treatment in 63% of patients with Type II congenital smell loss. Based upon a systematic evaluation of the protein components of nasal mucus we have demonstrated that interactions among four chemical moieties in nasal mucus may play significant roles in this initiation. Prior to treatment three of these moieties, cAMP, cGMP and sonic hedgehog (Shh), were significantly decreased in concentration whereas one of these moieties, TNFalpha, was increased in concentration. The mechanism(s) responsible for initiation of smell function in these patients, not immediately apparent, may depend upon understanding interactions among these moieties.

METHODS

Measurements of cAMP, cGMP, Shh and TNFalpha in nasal mucus by specific spectrophotometric immunoassays before and after treatment with theophylline.

RESULTS

Before theophylline treatment cAMP, cGMP and Shh in nasal mucus, which act as growth factors to support olfactory receptor function, were significantly decreased below normal levels whereas TNFalpha which acts as a "death factor" to inhibit olfactory receptor function was significantly increased above normal. After theophylline treatment cAMP, cGMP and Shh increased significantly whereas TNFalpha decreased significantly.

CONCLUSIONS

These results indicate that there are specific biochemical changes associated with smell loss in patients with Type II congenital smell loss and that correction of these biochemical changes are associated with initiation of smell function in these patients. Understanding these relationships play an important role in understanding receptor action in smell function.

Initiation of smell function in patients with congenital hyposmia

BACKGROUND

Patients with congenital smell loss (hyposmia) are born without a sense of smell. They comprise two types. Type I patients have genetic abnormalities manifested by brain, gonadal and other somatic abnormalities. Type II patients have neither a family history of smell loss nor any somatic abnormalities. No systematic attempts to initiate smell function in Type II patients have been reported.

METHODS

Smell function was measured in 19 Type II congenital smell loss patients by both subjective responses and by olfactometry using measurements of detection and recognition thresholds, magnitude estimation and hedonics in response to four odors (pyridine, nitrobenzene, thiophene and amyl acetate) before and after treatment with oral theophylline, 200-800mg daily for periods of 2-36months with evaluation of smell function and serum theophylline measured at intervals of 2-6months.

RESULTS

In 12 of the 19 Type II patients (63%) smell function was initiated for the first time and was quantitated by both subjective responses and by olfactometry. Initiation of smell function occurred after treatment with 200-800mg of oral theophylline for periods of 2-19months.

INTERPRETATION

This is the first systematic demonstration of initiation of smell in patients who were born without smell function. Oral theophylline presumably acts to increase both olfactory receptor growth, development and perpetuation and brain plasticity which enables them to recognize olfactory signals with initiation of olfactory function.