This is a prospective, observational study examining the impact of highly effective cystic fibrosis transmembrane conductance regulator (CFTR) modulators on chronic rhinosinusitis (CRS) and olfactory dysfunction (OD) in young children with cystic fibrosis (YCwCF). This study involves two groups: children 2-8 years old, inclusive at initial visit, receiving highly effective modulator therapy (HEMT), and a control group of children 2-8 years old, inclusive at initial visit, not receiving HEMT. Outcomes will include sinus magnetic resonance imaging (MRI) scans, olfactory tests, and quality of life surveys obtained over a two-year period.

This multi-center, prospective, observational study investigates the effects of highly effective modulator therapy (HEMT) on chronic rhinosinusitis (CRS) and olfactory dysfunction (OD) in young children with cystic fibrosis (YCwCF). The study spans two years and includes two distinct groups of children with cystic fibrosis: children ≤ 8 years old receiving HEMT and a control group of children ≤ 8 not receiving HEMT. The study aims to assess the efficacy of HEMT in improving sinus health and olfactory capabilities in this young demographic.

Key assessments include magnetic resonance imaging (MRI) sinus opacification, olfactory bulb volume measured via MRI, objective olfactory testing, and various quality (QOL) surveys. This investigation seeks to characterize the severity of CRS and OD in YCwCF, and to elucidate if early initiation of HEMT improves CRS and OD .

In the HEMT group, participants will have a pre-HEMT assessment followed by 1-year and 2-year post-HEMT evaluations. In the control/non-HEMT group, participants will undergo parallel assessments at baseline, 1-year, and 2-year intervals to track the natural progression of CRS and OD without HEMT.

Inclusion Criteria:

HEMT Group:

• Children with documentation of a CF diagnosis
• Age 2-8 years old at first study visit
• CFTR mutation consistent with FDA labeled indication of highly effective modulator therapy (ivacaftor or elexacaftor/tezacaftor/ivacaftor)
• Clinician intent to prescribe ivacaftor or ETI so that enrollment is before start of HEMT

Non-HEMT/Control Group:

• Children with documentation of a CF diagnosis
• Age 2-8 years at first study visit
• Ineligible for highly effective modulator therapy (ivacaftor or elexacaftor/tezacaftor/ivacaftor) based on CFTR mutation or clinical decision not to initiate HEMT if eligible

Exclusion Criteria:

For Both Groups:

• Use of an investigational drug within 28 days prior to the first study visit
• Use of ivacaftor or elexacaftor/tezacaftor/ivacaftor within the 180 days prior to and including the first study visit
• Use of chronic oral corticosteroids within the 28 days prior to and including the first study visit.
• Sinus surgery within 180 days prior to the first study visit

Participants for this study will be enrolled into one of two groups. The first group (HEMT Group) will enroll children between 2-8 years of age who have a clinical intent to initiate HEMT, which is defined as ivacaftor or elexacaftor/tezacaftor/ivacaftor based on underlying CFTR mutation status. The second group (non-HEMT Group) will consist of children under the age of 8 without intent to clinically initiate HEMT. Children for both groups will be identified and recruited from cystic fibrosis clinics.

Participant data will be securely stored using REDCap software.