Key Point

Patients with adult-onset CF can be distinguished from those with CF diagnosed in childhood based on clinical, demographic, and genetic characteristics.

DENVER—In the past, patients with adult-onset cystic fibrosis (CF) who survived to old age were considered curiosities. However, such patients are no longer quite so rare, a recent study by investigators at the Cystic Fibrosis Center of the National Jewish Medical and Research Center in Denver has suggested. The study also confirmed that patients diagnosed as adults are distinctly different from long-term CF survivors diagnosed in childhood, regarding lung function, sputum microbiology, genotype, and several other characteristics.¹

Among 334 patients treated at the University of Colorado adult CF clinic during an eight-year period, the investigators identified 59 who were older than 40 at the time of their last contact with the clinic. Sufficient data were available for 55 of these patients, who were divided into early- and late-diagnosis groups (n = 28 and n = 27, respectively). The median age at CF diagnosis was 2 years in the former group and 48.8 years in the latter group.

“To put this information into perspective, a similar analysis was performed using the 2003 CFF [Cystic Fibrosis Foundation] registry database of 23,105 individuals followed at US CF centers,” the investigators related. “When the subset of 1,160 individuals who were older than age 40 was analyzed, the median age at diagnosis was 13 years.”

FEV₁ was about 40% of the predicted value in the early-diagnosis group and about 60% in the late-diagnosis group. The two groups’ median sweat chloride values were about 110 and 90 mmol, respectively; however, the difference did not quite achieve significance. Sweat chloride is loosely correlated with the presence of missense mutations, the investigators explained.

GENETIC DIFFERENCES FOUND

Ten patients in the early-diagnosis group were homozygous for delta F508, the gene mutation that is most often responsible for CF. Furthermore, every patient in that group with a known mutation had a least one delta F508 allele.

In contrast, 19 patients in the late-diagnosis group had at least one delta F508 allele, but only one was homozygous for the mutation. “The CFF registry population is 50.6% delta F508 homozygote, and 88% of the population have at least one copy of delta F508,” noted the investigators.

Sputum analysis showed that Pseudomonas aeruginosa was present in about 90% of the early-diagnosis group, 63% of the late-diagnosis group, and 70% of the patients in the CFF registry who were older than 40. The presence of mucoid P aeruginosa in the three groups occurred at rates of approximately 80%, 45%, and 55%, respectively. Also, there was a greater likelihood of testing positive for nontuberculous mycobacteria in the late-diagnosis group, and the patients in that group were more likely to be female and to have normal pancreatic function.

—Timothy Begany

Reference
1. Rodman DM, Polis JM, Heltshe SL, et al. Late diagnosis defines a unique population of long-term survivors of cystic fibrosis. Am J Respir Crit Care Med. 2005;171:621-626.

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