Comparison of the clinical manifestations of cystic fibrosis in black and white patients

No large-scale studies of the incidence or disease severity of cystic fibrosis (CF) in black patients have been reported to date. In this study, the CF Foundation National Patient Registry was used to establish new incidence figures and to compare the clinical status of U.S. black (n = 601) and white patients (n = 17,755) with CE Results indicate that the incidence of CF is approximately 1 in 3,200 white and 1 in 15,000 black live births in the United States. Black patients with CF are currently, and were at diagnosis, younger and have poorer nutritional status and pulmonary function than white patients with CF. Fewer have meconium ileus, but more have distal intestinal obstruction syndrome. To control for genotype, each black deltaF508 homozygote (n = 47) was compared with four age- and sex-matched white deltaF508 homozygotes. Only the difference in nutritional status remained. The deltaF508 mutation is associated with higher levels of meconium ileus than other genotypes, independent of race. In conclusion, the clinical manifestations of CF are similar in black and white patients except for poorer nutritional status in black patients, which appears to be independent of age and genotype.

Possible association of the allele status of the CS.7/HhaI polymorphism 5' of the CFTR gene with postnatal female survival

Cystic fibrosis (CF) patients show a high degree of linkage disequilibrium between the CF transmembrane conductance regulator (CFTR) gene and polymorphisms 5' of that gene. To determine whether the region 5' of CFTR contains biologically important sequences, the allele frequencies of six CFTR-linked polymorphisms (metH/MspI, XV-2c/TaqI, CS.7/HhaI, KM19/PstI, MP6d9/MspI, J44/XbaI) were determined in 417 randomly selected elderly individuals (over 75 years of age) from the Czech population. The elderly individuals were considered "escapees" of strong selective pressures that had operated during their lifetime, prior to the introduction of modern health care since 1950. The pooled allele frequencies of the analyzed marker polymorphisms in the elderly did not significantly differ from published data. However, when analyzed by ex, the allele frequencies of markers CS.7/HhaI and KM19/PstI differed significantly (P < 0.05) between elderly females and males. The allele frequencies of the six polymorphisms were then determined in 646 newborns and 345 young adults of reproductive age; these individuals were selected in a similar manner and drawn from the same population. In these control groups, the studied marker polymorphisms exhibited no statistically significant differences between sexes and/or between individuals of the same sex, only between different age groups. A gradual relative increase in the frequency of allele "2" of marker CS.7/HhaI was observed from newborn females to elderly women, the overall difference in allele frequencies of this marker polymorphism between newborn females and elderly women reaching statistical significance (P < 0.05). Interestingly, allele "2" is the major constituent of the extended "B-haplotype", which is in strong linkage disequilibrium with common CF alleles. Taken together, our data suggest that the region spanning markers CS.7 and KM19 is associated with a genetic factor that influences postnatal female survival, providing a possible mechanism for increasing the frequency of particular mutations in the adjacent CFTR gene.

Identification of common cystic fibrosis mutations in African-Americans with cystic fibrosis increases the detection rate to 75%

Cystic fibrosis (CF)--an autosomal recessive disorder caused by mutations in CF transmembrane conductance regulator (CFTR) and characterized by abnormal chloride conduction across epithelial membranes, leading to chronic lung and exocrine pancreatic disease--is less common in African-Americans than in Caucasians. No large-scale studies of mutation identification and screening in African-American CF patients have been reported, to date. In this study, the entire coding and flanking intronic sequence of the CFTR gene was analyzed by denaturing gradient-gel electrophoresis and sequencing in an index group of 82 African-American CF chromosomes to identify mutations. One novel mutation, 3120+1G-->A, occurred with a frequency of 12.3% and was also detected in a native African patient. To establish frequencies, an additional group of 66 African-American CF chromosomes were screened for mutations identified in two or more African-American patients. Screening for 16 "common Caucasian" mutations identified 52% of CF alleles in African-Americans, while screening for 8 "common African" mutations accounted for an additional 23%. The combined detection rate of 75% was comparable to the sensitivity of mutation analysis in Caucasian CF patients. These results indicate that African-Americans have their own set of "common" CF mutations that originate from the native African population. Inclusion of these "common" mutations substantially improves CF mutation detection rates in African-Americans.

False-positive results of genetic testing in cystic fibrosis

We describe a patient in whom newborn immunoreactive trypsin screening and mutation analysis suggested a diagnosis of cystic fibrosis; however, the clinical course and sweat test results were not consistent with the diagnosis. Direct sequencing of the patient's genomic DNA showed compound heterozygosity for delta F508 and F508C, a polymorphism not associated with clinical disease.

Cystic fibrosis transmembrane conductance regulator (CFTR) gene mutations in allergic bronchopulmonary aspergillosis

The etiology of allergic bronchopulmonary aspergillosis (ABPA) is not well understood. A clinical phenotype resembling the pulmonary disease seen in cystic fibrosis (CF) patients can occur in some individuals with ABPA. Reports of familial occurrence of ABPA and increased incidence in CF patients suggest a possible genetic basis for the disease. To test this possibility, the entire coding region of the cystic fibrosis transmembrane regulator (CFTR) gene was analyzed in 11 individuals who met strict criteria for the diagnosis of ABPA and had normal sweat electrolytes (< or = 40 mmol/liter). One patient carried two CF mutations (deltaF508/R347H), and five were found to carry one CF mutation (four deltaF508; one R117H). The frequency of the deltaF508 mutation in patients with ABPA was significantly higher than in 53 Caucasian patients with chronic bronchitis (P < .0003) and the general population (P < .003). These results suggest that CFTR plays an etiologic role in a subset of ABPA patients.

Association of anophthalmia and esophageal atresia

We report on a boy and a girl with bilateral anophthalmia and proximal esophageal atresia. In addition to vestigial optic nerves and chiasma, MRI studies showed other central nervous system abnormalities; one had ectopic tissue in the hypothalamic region, and the other hand generalized ventriculomegaly associated with atrophy. Two other cases, both males, have been reported with anophthalmia and esophageal atresia as their only malformations. These 4 cases are reviewed in light of recent advances in the understanding of ocular embryogenesis and of the midbrain as a development field. Concurrence of these defects appears to be non-random.

Regulation of cystic fibrosis transmembrane conductance regulator (CFTR) gene transcription and alternative RNA splicing in a model of developing intestinal epithelium

Transcriptional and post-transcriptional regulation of CFTR (cystic fibrosis transmembrane conductance regulator) gene expression was studied in HT29 cells. It is known that the abundance of CFTR mRNA increases during differentiation of pluripotent HT29-18 cells and is maintained at high levels in the stably differentiated HT29-18-C1 subclone. Nuclear run-on assays suggest that increased transcription of the CFTR gene explains the increased abundance of total CFTR mRNA in differentiated HT29 cells. The increased transcription cannot be ascribed to cell cycle-dependent expression of the CFTR gene or to changes in CFTR gene copy number between subcloned cells. Similar to native tissue cells, differentiated HT29 cells contain low copy numbers of CFTR transcripts (1-5/cell), and a portion of the CFTR transcripts are alternatively spliced to remove exon 9 (and make 9-mRNA). During differentiation of HT29-18 cells, the absolute amount of full-length CFTR mRNA increases 8-fold, whereas the amount of 9- mRNA increases 18-fold. The fraction of 9- mRNA in the CFTR mRNA pool is increased in differentiated HT29 cells. The results show that gene transcription regulates the abundance of CFTR transcripts and that regulatory control of alternative RNA splicing may also be a cellular mechanism to modulate CFTR function.

Cystic fibrosis patients bearing both the common missense mutation Gly----Asp at codon 551 and the delta F508 mutation are clinically indistinguishable from delta F508 homozygotes, except for decreased risk of meconium ileus

The glycine-to-aspartic acid missense mutation at codon 551 (G551D), which is within the first nucleotide-binding fold of the cystic fibrosis transmembrane conductance regulator (CFTR), is the third most common cystic fibrosis (CF) mutation, with a worldwide frequency of 3.1% among CF chromosomes. Regions with a high frequency correspond to areas with large populations of Celtic descent. To determine whether G551D confers a different phenotype than does delta F508, the most common CF mutation, we studied 79 compound heterozygotes for G551D/delta F508, from nine centers in Europe and North America. Each subject was matched, by age and sex, with a delta F508 homozygote from the same center. A retrospective cohort analysis was performed on the following outcome parameters: age at diagnosis, sweat chloride, meconium ileus at birth, height, weight, weight for height, FVC, FEV1, chest X-ray score, pseudomonas colonization, pancreatic sufficiency, and Shwachman clinical score. There was less meconium ileus among the G551D/delta F508 compound heterozygotes (relative risk 0.33; 95% confidence interval .13-.86), as well as a trend toward later age at diagnosis of pancreatic insufficiency. No statistically significant difference was found between the groups for any other parameter. These results suggest that the CF genotype can be a predictor of pancreatic and intestinal phenotype. Prenatal counseling for the two genotype groups should differ only with respect to probability of meconium ileus. Clinical outcome (after survival of meconium ileus) for G551D/delta F508 compound heterozygotes and delta F508 homozygotes is indistinguishable; therefore, prognostic counseling should not differ.

Dextromethorphan and high-dose benzoate therapy for nonketotic hyperglycinemia in an infant

To test the hypothesis that nonketotic hyperglycinemia causes overstimulation of the excitatory N-methyl-D-aspartate receptor by allosteric glycine activation, and that reduction of glycine and blocking of the cation channel coupled to the receptor would be beneficial, we administered benzoate and dextromethorphan, a blocker of the N-methyl-D-aspartate channel to an infant with nonketotic hyperglycinemia. Therapy with benzoate, 500 mg/kg per day, was started on day 5, and the dosage was increased to 750 mg/kg per day on day 8, with prompt normalization of the neurologic and electroencephalographic findings. The glycine concentrations in both plasma and cerebrospinal fluid were substantially reduced. Dextromethorphan was added to the regimen on day 12. The electroencephalogram remained normal until the infant was 8 months of age, when diffuse slowing became apparent. Serial brain magnetic resonance imaging showed delayed myelination. At 12 months of age, physical examination findings and growth were normal except for hypotonia. The developmental quotient was approximately 60, and the child was free of seizures. This outcome, although not ideal, is better than that typical for nonketotic hyperglycinemia. Our results suggest that trials with additional patients and other N-methyl-D-aspartate cation channel blockers are warranted.

CFTR protein expression in primary and cultured epithelia

The gene responsible for the lethal disorder cystic fibrosis encodes a 1480-amino acid glycoprotein, CFTR. Using polyclonal antibodies directed against separate phosphorylation sites in the pre-nucleotide-binding fold (exon 9) and the R domain (exon 13), we have identified a 165-kDa protein in Xenopus laevis oocytes injected with recombinant CFTR cRNA transcribed from the full-length CFTR plasmid pBQ4.7. A protein of the same mobility was also detected with Western blotting techniques in whole cell extracts of cells that express CFTR mRNA (T84, FHTE, HT-29), including biopsied human nasal and bronchial tissue. Immunodetectable 165-kDa protein was concentrated in the apical membrane fraction of ileal villus tissue. We also report that the 165-kDa protein levels can be modulated pharmacologically, and these levels are appropriately correlated with second-messenger-regulated Cl- efflux. Thus, native or recombinant CFTR can be recognized by these anti-CFTR peptide polyclonal antibodies.

Severe deficiency of cystic fibrosis transmembrane conductance regulator messenger RNA carrying nonsense mutations R553X and W1316X in respiratory epithelial cells of patients with cystic fibrosis

Cystic fibrosis (CF) is the most common, lethal inherited disorder in the Caucasian population. We have recently reported two African-American patients with nonsense mutations in each CF gene and severe pancreatic disease, but mild pulmonary disease. In order to examine the effect of these nonsense mutations on CF gene expression, bronchial and nasal epithelial cells were obtained from one of these patients (no. 246), a compound heterozygote for nonsense mutations R553X and W1316X; a healthy normal individual; a patient (no. 528) homozygous for the common CF mutation (delta F508); and a CF patient (no. 272) who carries the R553X mutation and a missense mutation, S549N. When mRNA from bronchial cells of the normal individual, the delta F508 homozygote, and the S549N/R553X compound heterozygote was reverse transcribed and amplified by polymerase chain reaction using primers derived from the CF gene, DNA fragments of the predicted size were observed. However, patient no. 246 with nonsense mutations in each CF gene has no detectable cystic fibrosis transmembrane conductance regulator (CFTR) messenger RNA, and therefore should have severely diminished, and possibly absent, CFTR protein. Furthermore, less than 2% of the CFTR transcripts in nasal epithelial cells from patient no. 272 (S549N/R553X) were derived from the gene with the nonsense mutation. We conclude that severe reduction in CFTR mRNA causes CF, but can have different consequences in the lung and pancreas.

Marfan syndrome caused by a recurrent de novo missense mutation in the fibrillin gene

Marfan syndrome is an inherited disorder of connective tissue manifested in the ocular, skeletal and cardiovascular systems. It is inherited as an autosomal dominant with high penetrance, but has great clinical variability. Linkage studies have mapped the Marfan locus to chromosome 15q15-21.3. There have been no reports of genetic heterogeneity in the syndrome. Following the identification of fibrillin (a glycoprotein component of the extracellular microfibril), immunohistopathological quantification of the protein in skin and fibroblast culture, and examination of fibrillin synthesis, extracellular transport, and incorporation into the extracellular matrix (D. M. Milewicz, R.E.P., E. S. Crawford and P. H. Byers, manuscript in preparation) have demonstrated abnormalities of fibrillin metabolism in most patients. A portion of the complementary DNA encoding fibrillin has been cloned and mapped by in situ hybridization to chromosome 15. Here we report that the fibrillin gene is linked to the Marfan phenotype (theta = 0.00; logarithm of the odds (lod) = 3.9) and describe a de novo missense mutation in the fibrillin gene in two patients with sporadic disease. We thus implicate fibrillin as the protein defective in patients with the Marfan syndrome.

The Marfan syndrome locus: confirmation of assignment to chromosome 15 and identification of tightly linked markers at 15q15-q21.3

The Marfan syndrome is a common autosomal dominant disorder of connective tissue. Despite many years of intensive investigation, the primary genetic defect has not yet been identified. Reverse genetic methods, targeted at mapping this disease gene, have resulted in an initial report of linkage of the genetic locus for the Marfan phenotype in Finnish families to two polymorphic markers on chromosome 15. We have investigated four large multiplex American families with classic Marfan syndrome using standard genetic linkage methods. Our data confirm the assignment of the Marfan syndrome gene to chromosome 15, but establish a more centromeric location (defined by markers D15S25 and D15S1) as the most probable site for the genetic defect (lod score = 12.1, theta = 0.00). These data should facilitate identification and characterization of the Marfan syndrome gene and, in selected families, have immediate application to diagnosis of equivocal cases or prenatal counseling.