Developmental delay of phospholipid incorporation into the pulmonary surfactant is the most commonly recognized cause of respiratory distress among newborn infants However, studies of twins, gender, genetic linkage, and targeted gene ablation have strongly suggested that genetic regulation of the pulmonary surfactant contributes significantly to respiratory distress in infancy. We have described the first clinical syndrome of inherited pulmonary surfactant deficiency due to a specific mutation (l2lins2) in the surfactant protein B gene that causes respiratory distress immediately after birth and is lethal within the first 6 months of life. The contributions of mutations in the surfactant protein B gene to respiratory distress syndrome in infancy have not been assessed. Because extrapolation from small patient groups may exaggerate or underestimate frequency estimates of rare recessive genes due to ethnic stratification, environmental selection, or genotype-phenotype heterogeneity, we propose to test the hypothesis that mutations in the surfactant protein B gene contribute significantly to genetic risk of respiratory distress in infancy by using high throughput mutation detection systems to screen large, defined populations for the 121ins2 and other mutations. Specifically, we propose descriptive and case-control population-based studies for clinically significant mutations in the surfactant protein B gene and estimation of the frequency of the 121ins2 mutation in ethnically and geographically distinct populations. To identify mutations and assess mutation frequency, we will use denaturing high performance liquid chromatography separation of duplexed amplicons from DNA extracted from 20,000 blood spots from infants in a single, annual Missouri birth cohort and automated sequencing of heteroduplexes. To determine the clinical phenotype of infants with identified mutations, we will use identifiers from the Missouri birth-death certificate database linked to each blood spot to retrieve individual medical records for chart review. To determine whether identified mutations result in lower surfactant protein B concentrations in tracheal effluent, we will perform a case-control study of approximately 1800 infants from metropolitan St. Louis with clinically significant respiratory distress syndrome. Finally, we will estimate ethnic frequency of the 121ins2 mutation using molecular amplification and restriction enzyme digestion of DNA extracted from blood spots of infants in an Asian population (Seoul, South Korea), a Black and White African population (Cape Town, South Africa), a western European population (Oslo, Norway), and compare these to an admixed American population (Missouri). These studies will lead to clinically useful methods with which to evaluate genetic risk for respiratory distress and, potentially, genetic risk for longer term respiratory morbidity of childhood, and more rational design of treatment for both lethal and non-lethal respiratory distress in infancy.
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