Molecular basis of reduced or absent expression of decay-accelerating factor in Cromer blood group phenotypes

The human erythrocyte blood group system Cromer consists of high- incidence and low-incidence antigens that reside on decay-accelerating factor (DAF; CD55), a glycosyl-phosphatidylinositol-anchored membrane protein that regulates complement activation on cell surfaces. In the Cromer phenotypes Dr(a-) and Inab there is reduced or absent expression of DAF, respectively. This study investigated the molecular basis of the reduced DAF expression by polymerase chain reaction amplification of genomic DNA and RNA/cDNA obtained from Epstein-Barr virus- transformed lymphoblastoid cell lines. Sequence analysis of the Inab propositus showed a single nucleotide substitution in exon 2 of the DAF gene and at the corresponding position in the cDNA, G314-->A resulting in Trp53-->Stop. This truncation near the amino terminus explains the complete absence of surface DAF in the Inab phenotype. A similar analysis was performed for two Dr(a-) individuals, including KZ, who was previously reported to be Inab phenotype but is now shown by immunochemical and serologic methods to be Dr(a-) phenotype. A single nucleotide change was found in exon 5 of the DAF gene, C649-->T resulting in Ser165-->Leu, which we had previously shown to lead to loss of the Dra epitope. However, two species of cDNA were found, one encoding full-length DAF with the single amino acid change and the more abundant species having a 44-nucleotide deletion. The 44 nucleotide deletion includes the single polymorphic site, which creates a cryptic branch point in the Dr(a-) allele that leads to use of a downstream cryptic acceptor splice site. This shifts the reading frame and leads to a premature stop codon that precludes membrane anchoring. Thus, the single point mutation in the Dr(a-) phenotype results in a novel use of alternative splicing and provides a molecular explanation for both the antigenicity and the reduced DAF expression seen in this phenotype.     

Adrenoleukodystrophy: correlating MR imaging with CT

The effect on the brain of the sex-linked recessive form of adrenoleukodystrophy was studied in 40 boys, 4-18 years old. All underwent computed tomography (CT) scanning; six underwent magnetic resonance (MR) imaging. MR showed a high sensitivity in demonstrating white matter disease. Auditory pathway disease was characterized as involvement of the lateral lemniscus and medial geniculate body, and visual pathway disease was characterized by lateral geniculate body, Meyer loop, and optic radiation involvement. Contrast-enhanced CT still proved to have a greater capacity (at this time) to show the active, advancing form of the disease and concomitant calcifications. This large CT series also demonstrated the broad and variable expressions of adrenoleukodystrophy, which allowed the unification of previously described atypical forms of the disease.     

Minimal-exposure transfusion and the committed donor

Autologous blood (collected preoperatively or salvaged intraoperatively) is the safest blood available for transfusion, but its use is not always feasible. It may be possible to decrease a patient's exposure to homologous donors. Pediatric cardiac surgery patients frequently are unable to donate autologous blood preoperatively. Since 1984, attempts have been made to provide parental apheresis platelets and intraoperative blood salvage to such patients to decrease their donor exposure. Further decreases in donor exposure have been the object of a program of collecting from one committed donor all the blood a patient is anticipated to need. This article reviews the experience with 50 pediatric cardiac surgery patients on such a program, in whom the mean decrease in homologous-donor exposure was 57 percent (range, 12-93%). Thirteen of these patients received only homologous blood products from one committed donor, for a mean decrease in homologous-donor exposure of 80 percent (range, 50-93%). A comparison of 12 of these 13 recipients with a matched control group showed no significant difference in red cell transfusion practice but a significant difference in the number of homologous-donor exposures per m2 of body surface area (BSA) (mean donor exposures/m2 of BSA: patients = 1.5, controls = 10.5). The use of one committed donor and autologous blood can provide a minimal-exposure transfusion.     

Combined factor V-VIII deficiency: a case report with studies of factor V and VIII activation by thrombin

A new case of combined factor V-VIII deficiency is reported with in vitro studies of factors V and VIII activation by thrombin. The normal activation of factors V and VIII demonstrated in the patient's plasma and the equivalent levels of factor VIII coagulant activity and coagulant antigen support the hypothesis that a quantitative rather than qualitative defect in factors V and VIII is present in this disorder.     

Increased detection of intracranial metastases with intravenous Gd-DTPA

Three patients with intracranial metastases were studied with magnetic resonance imaging at 1.5 T before and after intravenous administration of 0.1 mmol/kg gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA). Axial pre- and postcontrast images demonstrated a total of six and 38 metastases, respectively. Of the 35 lesions detected only after administration of contrast material, all were less than 10 mm, and none had evidence of surrounding edema. Lesion conspicuity was comparable on postcontrast mixed (T1, proton density, and T2) images and T1-weighted images, indicating the feasibility of effectively screening for metastases with a single postcontrast spin-echo sequence providing mixed and T2-weighted images. Sagittal and coronal images depicted temporal lobe lesions not seen on axial images. No discomfort, side effects, or complications resulted from the contrast medium. The detection of additional lesions with Gd-DTPA increased the radiologic suspicion of metastatic disease, revealed locations more favorable for biopsy, prompted the search for a primary tumor, and modified therapeutic objectives and methods.