Exome sequencing and unrelated findings in the context of complex disease research: ethical and clinical implications

Exome sequencing has identified the causes of several Mendelian diseases, although it has rarely been used in a clinical setting to diagnose the genetic cause of an idiopathic disorder in a single patient. We performed exome sequencing on a pedigree with several members affected with attention deficit/hyperactivity disorder (ADHD), in an effort to identify candidate variants predisposing to this complex disease. While we did identify some rare variants that might predispose to ADHD, we have not yet proven the causality for any of them. However, over the course of the study, one subject was discovered to have idiopathic hemolytic anemia (IHA), which was suspected to be genetic in origin. Analysis of this subject's exome readily identified two rare non-synonymous mutations in PKLR gene as the most likely cause of the IHA, although these two mutations had not been documented before in a single individual. We further confirmed the deficiency by functional biochemical testing, consistent with a diagnosis of red blood cell pyruvate kinase deficiency. Our study implies that exome and genome sequencing will certainly reveal additional rare variation causative for even well-studied classical Mendelian diseases, while also revealing variants that might play a role in complex diseases. Furthermore, our study has clinical and ethical implications for exome and genome sequencing in a research setting; how to handle unrelated findings of clinical significance, in the context of originally planned complex disease research, remains a largely uncharted area for clinicians and researchers.

Differential expression of carbonic anhydrase isoenzymes in various types of anemia

BACKGROUND

The aim of the present study was to determine the concentrations of cytosolic carbonic anhydrase (CA) isoenzymes in erythrocytes of patients with aplastic, autoimmune hemolytic, iron deficiency or beta-thalassemia anemia.

METHODS

Western blotting and CA esterase activity analysis were used to analyze cytosolic erythrocyte CA isoenzymes in 118 subjects with various types of anemia and 35 healthy controls.

RESULTS

Total CA activity and CAII concentration of anemia patients were significantly higher than that of the control subjects while CAI concentration was significantly lower in patients of autoimmune hemolytic anemia (P<0.01). Compared with controls, CAIII concentration was lower in iron deficiency anemia (P<0.01), but higher in beta-thalassemia anemia (P<0.001).

CONCLUSIONS

Carbonic anhydrase isoenzymes may contribute differently to various types of anemia. CAI may be an indicator to differentiate autoimmune hemolytic anemia from other types of anemia. CAII provides the CA activity necessary for maintaining ion transport in erythrocytes while CAIII may play an agent against oxidative damage in iron deficiency and beta-thalassemia anemia.

Ciprofloxacin-induced acute interstitial nephritis and autoimmune hemolytic anemia

Ciprofloxacin has been associated with several side effects including interstitial nephritis and hemolytic anemia. The combination of both side effects is extremely rare. In this report, we describe a case of ciprofloxacin-induced interstitial nephritis and autoimmune hemolytic anemia. Hemolytic anemia improved after stopping the drug and initiation of steroid therapy. Unfortunately, acute interstitial nephritis was irreversible and the patient developed end-stage renal disease.

Pyrimidine nucleotides impair phosphoribosylpyrophosphate (PRPP) synthetase subunit aggregation by sequestering magnesium. A mechanism for the decreased PRPP synthetase activity in hereditary erythrocyte pyrimidine 5'-nucleotidase deficiency

The activity of phosphoribosylpyrophosphate (PRPP) synthetase (ATP: D-ribose-5-phosphate pyrophosphotransferase, EC 2.7.6.1) is decreased in the erythrocyte in hereditary pyrimidine 5'-nucleotidase (P5N) deficiency. Given the increased pyrimidine nucleotide content of the P5N-deficient erythrocyte, we evaluated the effects of prototypic pyrimidine nucleotides on the activity of PRPP synthetase. In normal hemolysate a 1.0 mM combination of cytidine tri-, di- and monophosphate (CTP/CDP/CMP) inhibited PRPP synthetase activity and changed the ribose 5-phosphate (R5P) saturation curve from a hyperbola to a biphasic shape. Untreated crude hemolysate from P5N-deficient erythrocytes showed a biphasic R5P kinetic curve. Since the activity of PRPP synthetase is dependent on its state of subunit aggregation, we examined PRPP synthetase subunit aggregation using gel permeation chromatography. P5N-deficient erythrocytes had a decreased absolute amount of aggregated PRPP synthetase and almost a total loss of disaggregated PRPP synthetase. Using normal hemolysate, 1 mM CTP/CDP/CMP interfered with the ability of 1.0 mM ATP and 2.0 mM MgCl2 to promote PRPP synthetase subunit aggregation. Increasing the MgCl2 to 6.0 mM overcame the inhibitory effect of CTP/CDP/CMP. Thus, the decreased PRPP synthetase activity of the P5N-deficient erythrocyte is due, at least in part, to the ability of the accumulated pyrimidine nucleotides to sequester magnesium and to interfere with the subunit aggregation of PRPP synthetase.

Unique profile for erythrocyte membrane acetylcholinesterase in hereditary spherocytosis

Acetylcholinesterase of human erythrocytes from healthy donors and from patients with hematological disorders was analysed in a search for differential membrane parameters. Two substrates were used to estimate the exposure of acetylcholinesterase active site in the membrane: phenylacetate, a hydrophobic substrate, to determine total enzyme activity, and acetylcholine, an ionic substrate, to measure the externally reactive enzyme. The sensitivity of acetylcholinesterase to added stearic acid was also analysed. Three categories of the disorders studied were discerned: (a) The erythrocyte acetylcholinesterase profile was indistinguishable from normal control in beta-thalassemia minor and groups of patients with autoimmune hemolytic anemia or congenital dyserythropoietic anemia type II. (b) A marked decline in acetylcholinesterase with both substrates and reduced sensitivity to stearic acid were exhibited by the erythrocytes of paroxysmal nocturnal hemoglobinuria, beta-thalassemia major and other autoimmune hemolytic anemia and congenital dyserythropoietic anemia type II patients. Normal erythrocytes, either aged or pretreated to 50 degrees C, also showed similar characteristics. (c) Hereditary spherocytosis was singly differentiated by an elevated acetylcholinesterase activity with acetylthiocholine and by a vastly diminished sensitivity to stearic acid, while activity with phenylacetate was equal to control. This distinct profile may reflect the unique organization of the erythrocyte membrane in hereditary spherocytosis.

Increased erythrocyte superoxide dismutase activities in beta 0-thalassaemia/haemoglobin E and in haemoglobin H diseases

Erythrocyte superoxide dismutase activities were measured in 45 subjects, 15 each of beta 0-thalassaemia/haemoglobin (Hb) E disease, Hb H disease, and normal. The erythrocyte superoxide dismutase activities were significantly higher in the patients with beta 0-thalassaemia/Hb E and Hb H diseases than in the normal subjects. The increase of erythrocyte superoxide dismutase activities is most likely due to abnormalities specific to thalassaemic red cells rather than an increased number of younger red cells for reticulocytes and nucleated red blood cells did not affect the enzyme activity. Patients with beta 0-thalassaemia/Hb E disease with lower haemoglobin concentration had significantly higher superoxide dismutase activities. In all 45 subjects haemoglobin concentrations and superoxide dismutase activities were inversely correlated (r = -0.60 (p less than 0.001)). This indicates that the amounts of superoxide generated in the red cells may, at least partly, determine severity of red cell damage and thus severity of disease; the increased superoxide dismutase activity in thalassaemia is a response to superoxide generated in greater amounts because of accumulation of excessive globin chains and iron in the red cells. The superoxide dismutase activities in Hb H disease, an alpha-thalassaemic disease, were found to be strikingly increased, higher than in beta 0-thalassaemic disease or other conditions.

Study of a case with severe red-cell pyrimidine 5'-nucleotidase deficiency

A deficiency of erythrocyte pyrimidine 5'-nucleotidase was found in a 23-year-old male suffering from severe congenital hemolytic disease. Results from exhaustive metabolic exploration are given and compared with reticulocyte-rich blood from subjects with auto-immune hemolytic disease. Evidence is given that the 20% apparent P5N residual activity corresponds to a non-specific acid phosphatase.

[Acetylcholinesterase of erythrocytes in various blood diseases]

Appearance of low molecular components of acetylcholinesterase from erythrocyte membranes was found by gel filtration on Sephadex G-200 and polyacrylamide gel disc electrophoresis. Content of these components was distinctly increased within ghe acute period of Marchiafava-Micheli disease.

Phosphorylase activity in chronic erythremic myelosis

Phosphorylase activity was detected in the cytoplasm of erythroid precursors of 6 of 7 patients with chronic erythremic myelosis (Di Guglielmo syndrome), in proerythroblasts and megaloblasts from 3 patients with pernicious anemia and in 2 patients with severe folate deficiency in neoplastic lymphocytes from 2 patients with acute lymphoblastic leukemia, and in 1 patient with leukemic lymphosarcoma. In all of these patients, most of the erythroid precursors and/or neoplastic lymphocytes contained increased amounts of glycogen when stained with the PAS reagent. Phosphorylase activity was not detected in erythroid precursors obtained from 6 presumed normal individuals or from 3 of 7 patients with a variety of other types of anemia in which the erythroid precursors were PAS-negative. Similarly, phosphorylase activity was absent in lymphocytes obtained from presumed normal individuals. Although the mechanisms responsible for the pathogenesis of PAS positivity are unclear, it is possible that the increased phosphorylase activity found in cells that are PAS-positive may reflect a disorder in the biosynthetic pathway of glycogen.