Differences in expression of cystic fibrosis in blacks and whites
S. A. McColley, B. J. Rosenstein and G. R. Cutting
Eudowood Division of Pediatric Respiratory Sciences, Johns Hopkins University School of Medicine, Baltimore, MD.
The recent identification of the cystic fibrosis (CF) gene confirms that
genetic heterogeneity occurs in CF. A three-base-pair deletion in exon 10
resulting in a loss of the phenylalanine residue at amino acid position 508
of the gene product, termed the CF conductance regulator protein, accounts
for 70% of cases of CF in white subjects. However, this gene defect occurs
in only 37% of affected blacks. Analysis of CF genes from American blacks
has revealed a number of mutations, most of which are unique to that
population. We therefore searched for potential differences in expression
of CF between 24 black and 48 white patients with CF matched for birth date
and gender. Black patients more frequently presented with only respiratory
symptoms (38% vs 10%). Black patients had fewer hospitalizations for
pulmonary exacerbations (2 vs 6.9), a better mean forced vital capacity
(77% vs 62% of predicted), and higher chest roentgenogram scores (18.2 vs
14.4) than white patients. Complication rates were similar except for a
higher incidence of hyponatremic dehydration (21% vs 2%) and peptic ulcer
disease (13% vs 0%) in blacks. Survival time appeared to be longer in
blacks, but the difference was not statistically significant. We conclude
that phenotypic differences exist between black and white patients with CF,
which may be due to the genetic heterogeneity between these two
populations.