Cystic fibrosis (CF) is the most common lethal autosomal recessive disease in the United States, occurring in 2000 to 4000 newborns.1 It is caused by one of the more than 2000 mutations of the CF transmembrane conductance regulator (CFTR). Although most of its morbidity and mortality stems from pulmonary decline, it was first recognized in 1938 as a cause of severe failure to thrive in infants due to characteristic pancreatic insufficiency. Decades later, we are starting to understand the full implication of the effects CFTR mutations on the entirety of the gastrointestinal (GI) system (Table 1).
The CFTR transports chloride and bicarbonate across the apical surface of epithelial cells in the respiratory and GI tracts. Mutations are classified as I to VI, with I to III being the most severe. Mutations result in abnormal structure, synthesis, and/or function of the CFTR protein.
Newborn screening detects trypsinogen, a protein released from the pancreas during the process of its destruction in utero. However, there are false negative results or cases where the specimen is unacceptable, or not received, and there is no appropriate follow-up. As 60% of infants are born with pancreatic insufficiency and another 30% will develop insufficiency in the next 3 years, and as GI, pancreatic, and hepatic manifestations are the most common initial manifestations of CF, before pulmonary manifestations become apparent, clinicians should have a low threshold for obtaining additional testing if CF is suspected.1
Achieving optimal growth in early life correlates with fewer pulmonary exacerbations and fewer hospitalizations.2 Infants with CF should be seen monthly to monitor proper growth and then every 3 months for routine care.3 Patients with suboptimal growth should be seen more frequently.
Children with CF require 110% to 200% of normal caloric intake to achieve normal growth.4 In general, the goal body mass index (BMI) is the 50th percentile for age, or the 50th percentile weight-for-length in children aged younger than 2 years. In instances where BMI offers a poor reflection of nutritional status, such as hepatomegaly or ascites, mid-arm circumference serves as an alternative measure. Attainment of nutritional goals involves adequate caloric intake, supplementation with fat-soluble vitamins (A, D, E, K), and pancreatic enzyme replacement therapy (PERT) under the guidance of a CF-trained nutritionist.
In addition to BMI, stunted height must be screened for, as height also correlates with lung function.5 There are multiple causes of stunting in CF (Table 2). A chronic inflammatory state makes insulin-like growth factor 1 (IGF1) less responsive to growth hormone. In addition, CF-related diabetes (CFRD), a unique form of diabetes specific to CF, can lead to growth failure.
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