Children taking CFTR modulators may grow taller by age 18

Use of therapy may help bridge gap in adult height, study suggests

Margarida Maia, PhD avatar

by Margarida Maia, PhD |

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Taking CFTR modulators as a child may make boys and girls with cystic fibrosis (CF) grow about a third of an inch taller by the time they turn 18, according to a large study of data from the CF Foundation patient registry.

Researchers also observed that being taller than average at age 2 meant growing faster, and at a younger age, for boys. A greater height at that age also was linked to being taller as adults, regardless of whether the patients were boys or girls.

“The timing of puberty is similar between those with CF and the general population, but … final adult height is significantly lower in those with CF,” the researchers noted.

“CFTR modulators may help bridge this gap in height, although more research is needed,” the team wrote.

The study, “Factors associated with pubertal growth outcomes in cystic fibrosis: Early Growth and Puberty in CF,” was published in the Journal of Cystic Fibrosis.

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Greater height at age 2 linked to faster growth in puberty

It is thought that CF may cause delays in puberty, in part due to difficulty maintaining a healthy weight or not getting the right nutrition.

The introduction of CFTR modulators — a treatment taken by mouth to ease signs and symptoms of CF — has brought better lung function and improved nutritional status and quality of life for people with CF. Indeed, the researchers noted that “CFTR modulators have rapidly changed the CF landscape.”

However, there is scant evidence on the impact of CFTR modulators on puberty among adolescent patients.

“It is unclear to what degree puberty is affected in the new era of CF care or the role of early nutritional status,” the researchers wrote.

To know more, a team of researchers in the U.S. traced a link between early growth trajectories and physical changes during the teenage years. Their goal was to evaluate how CFTR modulators may affect puberty.

The study included 9,186 young adults with a diagnosis of CF who were enrolled in the CF Foundation patient registry — a database used to study treatments and outcomes, and to design clinical trials in cystic fibrosis.

The patients ranged in age from 18 to 21. About two-thirds (68%) were prescribed CFTR modulators, but they started them after puberty, at an average age of 21.6.

The mean age at peak height velocity — the time when children and teenagers grow the fastest — was 13.7 years for boys and 11.9 years for girls. Being diagnosed at 3-6 months old versus a younger age was linked to a later growth spurt.

During this growth spurt, boys grew 8.4 centimeters (cm), or about 3.3 inches, per year, whereas girls grew slightly slower, at 7 cm (about 2.8 inches) per year. Getting nutrition through a tube in the stomach or small intestine, or intravenously (through the veins) was linked to slower growth.

About 15% of both boys and girls started taking CFTR modulators before turning 18. A small proportion were started on Kalydeco (ivacaftor) or Trikafta (elexacaftor, tezacaftor, and ivacaftor) as a child.

Children who received treatment with CFTR modulators were taller by the time they were adults by 0.92 cm (about 0.36 inches) if they were boys, and by 1.02 cm (about 0.4 inches) if they were girls.

CFTR modulator therapy shows the potential to improve pubertal growth outcomes, but further research is necessary.


Moreover, boys with CF who were taller than average at the age of 2 reached peak height velocity at a younger age and grew faster during the growth spurt. Children also were taller by the time they were adults, regardless of whether they were boys or girls.

“CF care guidelines emphasize the importance of weight gain to optimize health outcomes,” the researchers wrote. However, in this study, weight or body mass index — known as BMI, it’s a ratio of weight to height — were not linked to growth outcomes during puberty.

Rather, “early height … may be associated with pubertal growth outcomes,” the researchers concluded.

“CFTR modulator therapy shows the potential to improve pubertal growth outcomes, but further research is necessary,” they wrote.