Bradford L. Therrell

Congenital adrenal hyperplasia due to 21-hydroxylase deficiency: Newborn screening and its relationship to the diagnosis and treatment of the disorder

Abstract Congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency can be detected by newborn screening. The screening alone in 29 programs from 13 countries resulted in the diagnosis of CAH in 1 2 of affected newborns and expedited the diagnosis in 1 3 of affected newborns clinically suspected to have CAH. The benefits of newborn screening for CAH were prevention of severe adrenal crisis, its sequela, incorrect male sex assignment of severely virilized female newborns, and progressive signs of androgen excess. Screening revealed a higher incidence of CAH worldwide (1:15000 live births) compared with the case survey incidence (1:32000 live births) The false-positive rate (usually found in low birth weight and premature infants) was acceptably low (0.01–0.5%) except for three programs (0.7–2.5%). The false-negative rate of CAH screening was negligible. Prenatal diagnosis of CAH is possible by HLA typing or 21-hydroxylase B gene analysis of cultured fetal cells from chorionic villus biopsy sampling in the first trimester and from amniotic cells or hormonal analysis of amniotic fluid in the second trimester. Prenatal treatment of CAH is possible via maternal dexamethasone therapy beginning early pregnancy. However, efficacy and side effects of maternal dexamethasone therapy require further investigation.

Hemoglobin Tarrant: alpha126(H9) Asp leads to Asn. A new hemoglobin variant in the alpha1beta1 contact region showing high oxygen affinity and reduced cooperativity.

Abstract Hemoglobin (Hb) Tarrant was detected by its electrophoretic mobility on cellulose acetate (pH 8.4) and citrate agar (pH 6.2). On cellulose acetate it moved as a band between hemoglobins F and S, and on citrate agar as a band at hemoglobin S. The test for solubility in 2 M phosphate buffer with Na2S2O4 was negative. The new variant has a substitution of asparagine for aspartic acid in position 126 of the α-chain, one of the sites involved in the α1β1 contact. Furthermore, in deoxyhemoglobin aspartic acid 126 of each α chain also forms a non-covalent electrostatic salt bridge with arginine 141 of the corresponding α chain (Perutz, M. F. and Ten Eyck, L. F. (1972) Cold Spring Harbor Symp. Quant. Biol. 36, 295–310 and Perutz, M. F. (1970) Nature 228, 726–739). As a consequence of this substitution in hemoglobin Tarrant, the deoxy conformation or T state is destabilized because these two bridges cannot be formed. This condition is reflected in high oxygen affinity and low cooperativity.

Monoclonal antibody immunoassay for the identification of hemoglobin variants in neonatal screening

Abstract Background: Four monoclonal antibody assay kits (HemoCard) for the identification of hemoglobins A, S, C and E were evaluated. Current methods used to screen newborns for hemoglobin variants are based on charge separation techniques. Unlike the charge separation methods, these kits require no instrumentation. The suitability of HemoCard for the confirmation of results from charge separation screening methods was examined. Methods: Neonatal filter paper blood samples, previously analyzed in several newborn screening labs, were reanalyzed using the various HemoCard kits. These samples included homozygotes and heterozygotes for hemoglobins A, S, C and E. Also, over 20 rare variants were used to test the specificity of the HemoCard assays. Other evaluations included tests for detection limit, sample concentration, reproducibility and temperature. Sample stability was also examined. Results: All results (n = 2305) from the filter paper blood samples were correctly confirmed by HemoCard. Differentiation of heterozygotes and homozygotes for hemoglobin A was possible by use of HemoCard A, except in samples containing hemoglobin E. None of the rare hemoglobin variants tested interfered with the HemoCard S, C and E assays. These kits gave a positive result when the variant concentration was at least 1.5% of the total hemoglobin present. The HemoCard assays detected various hemoglobins over a wide range of concentrations. All of the assay kits gave positive results on the 15 replicates of all samples tested for reproducibility. There was no effect of temperature in the range of 4–37°C. All samples tested for room temperature stability continued to exhibit the same results for at least 6 months. Conclusions: The monoclonal antibody conjugates used in the HemoCard assays were specific for the targeted variants. Since the HemoCard A monoclonal antibody is directed to the β6 epitope, it also binds to hemoglobin variants that have intact β6 epitopes which include Hb E. The HemoCard assays were found to be extremely beneficial in confirming the absence and presence of Hb S, C and E in neonatal blood spot samples.

Computerized newborn screening in Texas-a multiple microcomputer approach

The Texas Department of Health expanded its newborn screening program to include four disorders in February of 1980. Because of the large volume of specimens being processed (approximately 2500 daily), it was essential that laboratory aspects of this program be computerized. Currently, both laboratory and follow-up activities are linked by computer. The modular, microcomputer approach employed has provided the necessary capabilities to ensure accurate and efficient tracking of newborns from specimen submission through diagnosis and treatment. Continual program evaluations are also possible through statistical tabulations of various types of data collected and maintained in the system.

Hemoglobin Cubujuqui (α141 ARG-SER): Functional Consequences of the Alteration of the C-Terminus of the αChain of Hemoglobin

Hemoglobin Cubujuqui (1) was detected in several members of a Mexican-American family. Structural analysis of this hemoglobin indicated that the carboxyl terminal arginine at position 141 in the α chain had been replaced by serine. This residue is critical not only in stabilizing the deoxy or T conformation by electrostatic interactions, but it is also involved in the Bohr effect through its linkage with Val lα of the opposite a chain in the tetramer. The variant exhibits high affinity for oxygen that is associated with destabilization of the deoxy conformation, and reduced cooperativlty. The pH and the chloride sensitivity of the variant are also reduced, as compared to Hb A.