cystic fibrosis

Cystic fibrosis is an autosomal recessive inherited disorder.
It is the most commonly inherited disorder among Caucasian Americans.
The disorder results in the production of abnormally thick mucus causing:
- Progressive lung disease
- Pancreatic insufficiency
- Dysfunction in gastrointestinal and genitourinary systems

In the United States (2022):
- Approximately 40,000 children and adults have cystic fibrosis.
- About 1,000 new diagnoses per year.

The cause of cystic fibrosis is linked to the CF gene on chromosome 7.
This gene encodes a membrane-associated protein known as the cystic fibrosis transmembrane conductance regulator (CFTR).
Mutations of the CFTR gene lead to various dysfunctions; the most common mutation is delta F508, caused by the deletion of three DNA base pairs.

The CFTR protein is responsible for transporting:
- Sugar peptides
- Inorganic phosphate
- Chloride ions
- Metal cations across epithelial membranes.
Mutations in CFTR cause insufficient chloride transport, leading to an altered balance of salt and water across epithelial membranes.
Symptoms predominantly manifest as thick, viscous mucus, which is the hallmark of cystic fibrosis.
Diagnosis:
- Positive sweat test indicating abnormal chloride levels in sweat.

Thick mucus accumulates in the lungs, leading to:
- Persistent cough
- Recurrent lung infections
Many patients may require lung transplants, such as bilateral lung or heart-lung transplants.
Respiratory failure is a primary cause of death among cystic fibrosis patients.

The disease leads to clogging of glands in the pancreas, resulting in cyst formation.
Pancreatic enzymes crucial for digesting food do not reach the small intestine, leading to chronic malabsorption.
Patients can meet calorie intake but may not meet nutrient needs due to malabsorption.

Due to inadequate digestive enzymes:
- Steatorrhea occurs, which is stool with excessive fat content.
- Fat-soluble vitamin deficiencies (Vitamins A, D, E, K).
- Low calorie absorption contributes to poor growth and low BMI.
Development of cystic fibrosis related diabetes (CFRD) results from pancreatic damage affecting insulin production.
Electrolyte imbalances due to inadequate salt reabsorption by sweat glands.
- Salt residue observed on skin with a deficit in the body.
Risk of osteoporosis and osteopenia due to poor vitamin D status, corticosteroid use, and low body mass.
Long-term complications can include cirrhosis and portal hypertension.

Life expectancy has improved significantly over decades:
- 1950s: Average life expectancy was under age 5; most individuals did not reach elementary school.
- 2017: Life expectancy around upper 30s has improved due to pancreatic enzyme development and respiratory interventions.

Assessment of dietary needs and counseling.
Monitoring:
- Pancreatic enzyme and vitamin supplementation.
Addressing nutritional concerns such as underweight, short stature in children/adolescents, and high energy needs.
Pancreatic enzyme replacement therapy:
- Taken with meals to assist in nutrient digestion.
- Example enzyme contains:
- Lipase for fats
- Amylase for carbohydrates
- Protease for proteins
- Enteric-coated to prevent degradation by stomach acid.
- Dosing based on body weight, meal composition, and malabsorption symptoms.

Increased calorie needs due to lung disease and malabsorption:
- Start at 130-150% of RDA for age, adjusting to meet weight goals.
Protein Intake:
- 15-20% of total caloric intake.
Carbohydrate Management:
- No restrictions unless managing cystic fibrosis related diabetes — use carbohydrate counting instead.
- Meal planning helps distribute carbohydrate intake.
Fat Requirements:
- Often increased to 35-45% of total calories due to malabsorption.
- MCT oil can be used as it requires less digestion.
- Emphasis on omega-3 fatty acids to reduce inflammation.

Patients commonly require supplementation of fat-soluble vitamins (A, D, E, K) due to malabsorption:
- Annual lab tests conducted to monitor adequacy and adjust supplementation.
Electrolyte status monitored and individualized based on lab values; some may need increased salt intake.
Encourage nutrient-dense foods and frequent meals/snacks.
Supplemental enteral nutrition may be indicated for patients who cannot meet needs through oral intake:
- Nocturnal feedings preferred to avoid interference with daytime eating.
- Standard polymeric formula typically tolerated.

Genetic modulators introduced in 2012 restore CFTR protein function.
The most successful modulator therapy came in 2019, showing improvements in lung function and weight in patients.
Example case study of a 39-year-old female with severe CF:
- Initially had a BMI of 19 and required multiple nutritional support strategies.
- After starting the new therapy, she increased her body weight by 30% in under a year, showcasing the impact of the medication.

As treatments improve, some patients transition from high-calorie diets (4,000 cal/day) to lower calorie, heart-healthy diets to prevent obesity.
Patient education on hunger cues and normal portion sizes becomes vital to manage chronic disease risk.
Not all patients respond to the new therapies; about 10% do not respond to the ETI modulator therapy and may still face nutritional challenges.

Advances in medical nutrition therapy will increasingly address the needs of a growing cystic fibrosis population, with dietitians expected to provide care across the lifespan.