# Associations Between Nasal Receptors and Olfactory Dysfunction and Dysgeusia in Coronavirus Disease 2019 (COVID-19)

## TL;DR

This study investigates whether nasal receptor expression levels are linked to olfactory dysfunction and taste changes in COVID-19 patients.

## Contribution

The study provides empirical evidence that baseline receptor expression alone does not directly cause sensory impairments in COVID-19.

## Key findings

- No statistically significant associations were found between receptor expression levels and olfactory dysfunction or dysgeusia.
- Higher ACE2 and furin expression showed a nonsignificant trend toward increased sensory alterations.
- Intermediate NRP1 levels were associated with lower disease severity.

## Abstract

Background/Objectives: Olfactory dysfunction and dysgeusia are common neurosensory manifestations of Coronavirus Disease 2019 (COVID-19), affecting approximately 60% of patients. These symptoms have been mechanistically linked to receptors involved in Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) cell entry, including angiotensin-converting enzyme 2 (ACE2), transmembrane protease serine 2 (TMPRSS2), furin, and neuropilin-1 (NRP1), which are highly expressed in the olfactory epithelium. Nevertheless, clinical evidence supporting a direct association between receptor expression and sensory impairment remains inconsistent. Methods: We conducted a multicenter, observational, cross-sectional study including 104 adults with polymerase chain reaction–confirmed SARS-CoV-2 infection during the first and second pandemic waves. Approximately 75 days after diagnosis, nasal and/or pharyngeal samples were obtained to quantify gene expression levels of ACE2, TMPRSS2, furin, and NRP1 using quantitative polymerase chain reaction. Olfactory dysfunction and dysgeusia were recorded as dichotomous variables. Logistic regression analyses were performed with adjustment for age, sex, and race, considering receptor expression as continuous variables and as tertiles. Missing data were addressed using multiple imputation methods. Results: Olfactory dysfunction was reported by 37.5% of participants, and dysgeusia by 36.5%. No statistically significant associations were observed between baseline expression levels of ACE2, TMPRSS2, furin, or NRP1 and the presence of olfactory dysfunction or dysgeusia in either adjusted continuous or categorical models. Although these associations did not reach statistical significance, higher ACE2 and furin expression showed a nonsignificant trend toward an increased probability of sensory alterations, whereas intermediate NRP1 levels were associated with lower disease severity. Conclusions: COVID-19-related olfactory dysfunction and dysgeusia do not appear to be directly determined by isolated baseline expression of SARS-CoV-2 entry receptors. These findings support a multifactorial and dynamic pathophysiological model involving temporal receptor regulation, inflammatory processes, and host-related factors, highlighting the need for longitudinal and interventional studies.