Two different mutations in the thyroid peroxidase gene of a large inbred Amish kindred: power and limits of homozygosity mapping

Approximately 10% of newborns with congenital hypothyroidism are unable to convert iodide into organic iodine. This iodide organification defect has a prevalence of 1 in 40,000 newborns and may be caused by defects in the thyroid peroxidase enzyme (TPO), the hydrogen peroxide-generating system, the TPO substrate thyroglobulin, or inhibitors of TPO. We identified a high incidence of severe hypothyroidism due to a complete iodide organification defect in the youngest generation of five nuclear families belonging to an inbred Amish kindred. Genealogical records permitted us to trace their origin to an ancestral couple 7-8 generations back and to identify an autosomal recessive pattern of inheritance. Initial studies of homozygosity by descent using two polymorphic markers within the TPO gene showed no linkage to the phenotype. In fact, 4 of 15 affected siblings from 2 of the nuclear families were heterozygous, resulting in homozygosity values of 73% and 53% in affected and unaffected family members, respectively. A genome-wide homozygosity screen using DNA pools from affected and unaffected family members localized the defect to a locus close to the TPO gene. Linkage analysis using 4 additional polymorphic markers within the TPO gene reduced the number of homozygous unaffected siblings to zero without altering the percent homozygosity initially found in the affected. Sequencing of the TPO gene revealed 2 missense mutations, E799K and R648Q. TPO 779K was found in both alleles of the 11 affected homozygotes, both mutations were present in each of the 3 affected compound heterozygotes, and there were no TPO mutations in 1 subject with hypothyroidism of different etiology. These results demonstrate the power of the DNA pooling strategy in the localization of a defective gene and the pitfalls of linkage analysis when 2 relatively rare mutations coexist in an inbred population.     

Prevalence and prognostic significance of silent and symptomatic ischemia after coronary bypass surgery: a report from the Coronary Artery Surgery Study (CASS) randomized population

The prevalence and prognostic significance of postoperative myocardial ischemia, as detected by exercise testing, were prospectively assessed in 174 patients from the Coronary Artery Surgery Study (CASS) randomized surgical population who had exercise testing before and 6 months after coronary artery bypass graft surgery. Whereas the prevalence of symptomatic ischemia significantly decreased postoperatively (52% vs. 6%, p less than 0.001), the frequency of silent myocardial ischemia did not change (30% vs. 29%). Survival at 12 years after bypass surgery based on the 6-month postoperative exercise test results was significantly better for the 112 patients with no ischemia (80%) than for the 51 patients with silent ischemia (68%) or the 11 patients with symptomatic ischemia (45%). These data show that coronary artery bypass graft surgery diminishes the overall prevalence of symptomatic but not silent ischemia and that both silent and symptomatic ischemia adversely affect the postoperative prognosis of these patients.     

Isometric effects on treadmill exercise response in healthy young men

This study evaluated the hypothesis that the isometric stress of load carrying augments the dynamic exercise response seen on the treadmill, and estimated the magnitude of this effect on heart rate and blood pressure for several methods of carrying the same load. Thirteen healthy subjects carried 40 lb in the right hand (H), 40 lb on the back (B), 20 lb in each hand (D) and no weight (N) while walking for 3 minutes on the treadmill at a grade of 0 at 1.7 miles/ hour. A statistically significant increase in the rate of rise and peak levels of systolic blood pressure, heart rate, estimated mean blood pressure, the product of estimated mean blood pressure and heart rate and systolic blood pressure-heart rate product was shown when task H was compared with tasks B, D and N. Values for tasks D and B did not differ significantly.The effects of isometric and dynamic exercise combined were greater than those of dynamic exercise alone. An effective technique of load distribution reduced the rate of increase in blood pressure, heart rate and the peak attained during dynamic exercise, thereby suggesting a lower level of myocardial oxygen consumption for a given weight-carrying task. These results can be applied to evaluation of patients with heart disease and estimation of their exercise tolerance.     

Low frequency of p53 mutations observed in a diverse collection of primary hepatocellular carcinomas.

Recent studies of the p53 tumor suppressor locus (designated TP53) in primary hepatocellular carcinoma (PHC) have identified a high frequency of codon 249 mutations. Due to the geographic location from which the samples were obtained and the substitution observed, the mutation was suggested to be attributable to aflatoxin B1 (AFB1) exposure. To determine the generality of this phenomenon, we have examined PHC tissues from 107 geographically and ethnically diverse sources. The frequency of p53 gene mutations was evaluated by using PCR/restriction-digest methods, GC-clamp (G+C-rich sequence) denaturing gradient gel electrophoresis, and DNA sequencing. The mutation rate observed in tumors from high-AFB1-exposure regions (25%) was more than double the rate observed in low-exposure regions (12%) but lower than the 50% frequency previously reported. Codon 249 mutations occurred at a much lower frequency than previously reported (2 of 107 samples examined). These results suggest that changes in DNA encoding p53 may not represent primary oncogenic effects but instead represent genetic changes related to tumor progression. High AFB1 levels may facilitate the generation of these progressional changes, but not by inducing a specific p53 gene mutation at codon 249 as previously reported.