Genetics of Insulin and Incretins in Cystic Fibrosis

CFRD is associated with worse nutritional status, greater pulmonary function decline, and
increased mortality, highlighting its relevance in CF and arises primarily from compromised
insulin secretion--traditionally considered a by-product of pancreatic exocrine tissue damage
and fibrosis. Recent developments in the field of diabetes are propelling a re-examination of
this basic explanation. Genome-wide association studies have associated genetic variants in
TCF7L2, a transcription factor implicated in enteroendocrine function, with increased
susceptibility to T2DM and CFRD.

The Objectives of this study are to perform targeted sequencing of TCF7L2 and other
GWAS-associated T2DM genes in the pediatric and adult CF populations and then to compare
insulin secretory capacity, β-cell sensitivity to glucose, and incretin secretion in
non-diabetic CF subjects with high and low-risk alleles.

Phase 1 will include 350 subjects (Children age>= 2 years, adolescents, and adults) for
TCF7L2 genotype and ten other GWAS-implicated T2DM genes. The distribution of TCF7L2 and
other GWAS-implicated T2 DM genes across the spectrum of glucose abnormalities will be
described. Phase 1 requires a single blood sample and review of medical records.

Phase 2 will include a subset of 30 non-diabetic children (age >8) and adults who will have
insulin and incretin secretion studies performed to look at how the body secretes insulin and
other hormones in relation to having or not having these "diabetes" genes. These studies
include Glucose Potentiated Arginine Tests (GPA, which measures β-cell secretory capacity and
sensitivity to glucose) and Mixed Meal Tolerance Test (MMTT, which measures incretin and
insulin secretion).

FIRST PHASE OF STUDY:

Inclusion Criteria

1. Subjects age >2y

2. Diagnosis of Cystic Fibrosis

3. For subjects< 18 years, parental/guardian permission (informed consent) and if
appropriate, child assent

Exclusion Criteria 1. Established diagnosis of non-CFRD (cystic fibrosis related diabetes)
(e.g T1DM)

SECOND PHASE OF STUDY:

Inclusion Criteria

1. Subjects age >8y

2. Diagnosis of Cystic Fibrosis

3. pancreatic insufficient

4. negative urine pregnancy test at enrollment

5. TCF7L2 rs7903146 genotype of T/T or C/C

6. For subjects< 18 years, parental/guardian permission (informed consent) from both
parents and if appropriate, child assent

Exclusion Criteria

1. Established diagnosis of non-CF diabetes (i.e. T1DM) or CFRD

2. History of clinically symptomatic pancreatitis within last year

3. Prior lung or liver transplant

4. Severe CF liver disease, as defined by presence of portal hypertension

5. Fundoplication-related dumping syndrome

6. Medical co-morbidities that are not CF-related or are unstable per the Investigator
opinion (i.e. history of bleeding disorders, immunodeficiency)

7. Acute illness or changes in therapy (including antibiotics) within 6 weeks prior to
study procedures

8. Treatment with oral or intravenous corticosteroids within 6 weeks of study

9. Hemoglobin <10 g/dL, within 90 days of Day 1 or at Screening

10. Abnormal renal function, within 90 days of Day 1 or at Screening; defined as
creatinine >2x upper limit of normal (ULN) or potassium > 5.5 milliequivalent per
liter {mEq/L} on non-hemolyzed specimen

11. Weight< 26 kg (limit for blood draw is 5 mL/kg/day; GPA requires 130 mL)

12. Inability to perform study specific procedures (MMTT, GPA)

13. Parents/guardians or subjects who, in study team opinion, may be non-compliant with
study procedure

14. Pregnant or lactating females.