Genetic modifiers play a substantial role in diabetes complicating cystic fibrosis.
BACKGROUND
Insulin-requiring diabetes affects 7-15% of teens and young adults, and more than 25% of older adults with cystic fibrosis (CF). Pancreatic exocrine disease caused by CF transmembrane conductance regulator (CFTR) dysfunction underlies the high rate of diabetes in CF patients; however, only a subset develops this complication, indicating that other factors are necessary.


OBJECTIVE
Our objective was to estimate the relative contribution of genetic and nongenetic modifiers to the development of diabetes in CF.


METHODS
This was a twin and sibling study involving 1366 individuals at 109 centers in the CF Twin and Sibling Study, from which were derived 68 monozygous twin pairs, 23 dizygous twin pairs, and 588 sibling pairs, all with CF.


METHODS
Chronic, insulin-requiring diabetes in the setting of CF, as established using longitudinal clinical and biochemical data, was studied.


RESULTS
About 9% of this predominantly pediatric population (mean age = 15.8 yr) had diabetes. Key independent risk factors identified by regression modeling included having a twin or sibling with CF and diabetes, increasing age, pancreatic exocrine insufficiency or two mutations causing severe CFTR dysfunction, decreased lung function or decreased body mass index, and longer duration of glucocorticoid treatment. The concordance rate for diabetes was substantially higher in monozygous twins (0.73) than in dizygous twins and siblings with CF (0.18; P = 0.002). Heritability was estimated as near one (95% confidence interval 0.42-1.0).


CONCLUSIONS
Diabetes is a frequent complication of CF that is associated with worse outcomes. Although a nongenetic factor (steroid treatment) contributes to risk, genetic modifiers (i.e. genes other than CFTR) are the primary cause of diabetes in CF.
Blackman
Scott M
SM
Division of Pediatric Endocrinology, McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
Hsu
Stephanie
S
Vanscoy
Lori L
LL
Collaco
J Michael
JM
Ritter
Sarah E
SE
Naughton
Kathleen
K
Cutting
Garry R
GR
D000293:Adolescent; D003550:Cystic Fibrosis / Q000150:complications* / Q000235:genetics*; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics*; D004247:DNA / Q000235:genetics / Q000302:isolation & purification; D003922:Diabetes Mellitus, Type 1 / Q000188:drug therapy / Q000209:etiology* / Q000235:genetics*; D005260:Female; D005951:Glucose Tolerance Test; D006801:Humans; D006943:Hyperglycemia / Q000453:epidemiology; D007004:Hypoglycemic Agents / Q000627:therapeutic use; D007328:Insulin / Q000627:therapeutic use; D008297:Male; D016017:Odds Ratio; D035781:Siblings; D014429:Twins, Dizygotic / Q000235:genetics; D014430:Twins, Monozygotic / Q000235:genetics; D055815:Young Adult
D007004:Hypoglycemic Agents; D007328:Insulin; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D004247:DNA