Ankyrin-1 mutations are a major cause of dominant and recessive hereditary spherocytosis.

Hereditary spherocytosis (HS) is the most common inherited haemolytic anaemia in Northern Europeans. The primary molecular defects reside in the red blood cell (RBC) membrane, particularly in proteins that link the membrane skeleton to the overlying lipid bilayer and its integral membrane constituents. Ankyrin-1 is the predominant linker molecule. It attaches spectrin, the major skeletal protein, to the cytoplasmic domain of band 3, the RBC anion exchanger. Two-thirds of patients with HS have combined spectrin and ankyrin-1 deficiency; deficiency of band 3 occurs in about 15 to 20% (ref.1). These data suggest that ankyrin-1 or band 3 defects may be common in HS. To test this we screened all 42 coding exons plus the 5' untranslated/promoter region of ankyrin-1 and the 19 coding exons of band 3 in 46 HS families. Twelve ankyrin-1 mutations and five band 3 mutations were identified. Missense mutations and a mutation in the putative ankyrin-1 promoter were common in recessive HS. In contrast, ankyrin-1 and band 3 frameshift and nonsense null mutations prevailed in dominant HS. Increased accumulation of the normal protein product partially compensated for the ankyrin-1 or band 3 defects in some of these null mutations. Our findings indicate that ankyrin-1 mutations are a major cause of dominant and recessive HS (approximately 35 to 65%), that band 3 mutations are less common (approximately 15 to 25%), and that the severity of HS is modified by factors other than the primary gene defect.

Refinement of the hereditary xerocytosis locus on chromosome 16q in a large Canadian kindred.

The hereditary stomatocytoses are a group of heterogeneous conditions associated with chronic red cell hemolysis for which the causative genetic mutations are not known. We investigated 137 members of a large Canadian kindred with phenotypic findings consistent with hereditary xerocytosis, one of the most common stomatocytosis syndromes. The objectives of this study were to characterize the clinical hallmarks of the hemolytic process, and to define the chromosomal region carrying the disease locus. The mode of inheritance was autosomal dominant. Affected family members had a well-compensated hemolysis, associated with an elevated MCHC, decreased osmotic fragility, decreased haptoglobin, and indirect hyperbilirubinemia. Cholelithiasis and progressive iron loading were common, despite normal hemoglobin levels. Quantitative erythrocyte morphologic evaluation revealed increased schistocytes, target cells, reticulocytes, and eccentrocytes in affected individuals; stomatocytes were not increased. Genetic linkage analysis confirmed the localization of the disease phenotype to chromosome 16q, and refined the candidate region to 16q24.2-16qter, a 2.4 million base pair interval containing 51 known or predicted genes.

Spectrin Rouen (beta 220-218), a novel shortened beta-chain variant in a kindred with hereditary elliptocytosis. Characterization of the molecular defect as exon skipping due to a splice site mutation.

The molecular defect responsible for the shortened beta-spectrin chain variant, spectrin Rouen, was identified by analysis of cDNA and genomic DNA of affected individuals after amplification by the polymerase chain reaction. Peripheral blood reticulocyte RNA was transcribed into cDNA and amplified using primers corresponding to the 3' end of beta-spectrin cDNA. Agarose gel electrophoresis of cDNA amplification products from affected individuals revealed the expected band of 391 bp as well as a shortened band of 341 bp. Nucleotide sequencing of the shortened cDNA amplification product revealed that the sequences corresponding to the penultimate exon of the beta-spectrin gene (exon Y) were absent. This result was confirmed by hybridization of a Southern blot of amplification products with a labeled probe specific for exon Y. Nucleotide sequencing of the proband's amplified genomic DNA corresponding to this region of the beta-spectrin gene revealed a mutation in the 5' donor consensus splice site of the intron downstream of the Y exon, TGG/GTGAGT to TGG/GTTAGT, in one allele. We postulate that this mutation leads to the splicing out or skipping of exon Y, thus producing a shortened beta-spectrin chain. To our knowledge, this is the first documented example of exon skipping as the cause of a shortened beta-spectrin chain in a case of hereditary elliptocytosis. The exon skip results in the loss of the 17 amino acids of exon Y and creates a frameshift with the synthesis of 33 novel amino acids prior to premature chain termination 14 residues upstream of the normal carboxy terminus of the beta-spectrin chain, giving a mutant beta-spectrin chain that is 31 amino acids shorter than the normal chain.

A common type of the spectrin alpha I 46-50a-kD peptide abnormality in hereditary elliptocytosis and pyropoikilocytosis is associated with a mutation distant from the proteolytic cleavage site. Evidence for the functional importance of the triple helical model of spectrin.

We studied nine individuals from five unrelated families with alpha I/46-50a hereditary elliptocytosis (HE) or hereditary pyropoikilocytosis (HPP), including one of the original HHP probands first reported by Zarkowsky and colleagues (1975. Br. J. Haematol. 29:537-543). Biochemical analysis of erythrocyte membrane proteins from these patients revealed, as a common abnormality, the presence of the alpha I/46-50a peptide after limited tryptic digestion of spectrin. The polymerase chain reaction was utilized to study the structure of the DNA encoding the alpha I domain of spectrin in the affected individuals. The DNA sequence of the alpha-spectrin gene encoding the region of the alpha-spectrin chain surrounding the abnormal proteolytic cleavage site was normal. We identified a point mutation causing the replacement of a highly conserved leucine residue by proline at position 207 in the alpha-spectrin chain, a site 51 residues to the amino-terminal side of the abnormal proteolytic cleavage site. Analysis of the proposed triple helical model of spectrin repeats reveals that the mutation occurs in helix 2 at a position directly opposite the abnormal proteolytic cleavage site in helix 3, making this the first report of a mutation occurring in helix 2 of a repeat in the alpha I domain of spectrin. These results add to the molecular heterogeneity of mutations associated with HE/HPP and provide further support for the proposed triple helical model of spectrin. Disruption of this proposed alpha-helical structure by helix-breaking proline substitutions may result in a functionally defective spectrin chain.

Mutation of a highly conserved residue of betaI spectrin associated with fatal and near-fatal neonatal hemolytic anemia.

We studied an infant with severe nonimmune hemolytic anemia and hydrops fetalis at birth. His neonatal course was marked by ongoing hemolysis of undetermined etiology requiring repeated erythrocyte transfusions. He has remained transfusion-dependent for more than 2 yr. A previous sibling born with hemolytic anemia and hydrops fetalis died on the second day of life. Peripheral blood smears from the parents revealed rare elliptocytes. Examination of their erythrocyte membranes revealed abnormal mechanical stability as well as structural and functional abnormalities in spectrin. Genetic studies revealed that the proband and his deceased sister were homozygous for a mutation of betaIsigma1 spectrin, L2025R, in a region of spectrin that is critical for normal function. The importance of leucine in this position of the proposed triple helical model of spectrin repeats is highlighted by its evolutionary conservation in all beta spectrins from Drosophila to humans. Molecular modeling demonstrated the disruption of hydrophobic interactions in the interior of the triple helix critical for spectrin function caused by the replacement of the hydrophobic, uncharged leucine by a hydrophilic, positively charged arginine. This mutation must also be expressed in the betaIsigma2 spectrin found in muscle, yet pathologic and immunohistochemical examination of skeletal muscle from the deceased sibling was unremarkable.

A nonsense mutation in the erythrocyte band 3 gene associated with decreased mRNA accumulation in a kindred with dominant hereditary spherocytosis.

We studied a French kindred with typical hereditary spherocytosis (HS). Studies of erythrocytes and erythrocyte membranes from HS individuals revealed abnormal erythrocyte membrane mechanical stability as well as 15-20% deficiency of band 3, the anion transporter. Anion transport studies of red cells from two affected individuals revealed decreased sulfate flux. Nucleotide sequence of cDNA encoding the distal third of the cytoplasmic domain and the entire transmembrane domain of band 3 obtained by RT-PCR of reticulocyte RNA of an affected family member was normal. Sequence analysis of genomic DNA from an HS individual identified a nonsense mutation of the band 3 gene, Q330X, near the end of the band 3 cytoplasmic domain. This mutation was present in genomic DNA of all HS family members and absent in DNA of unaffected family members. Using an RT-PCR-based assay, a marked quantitative decrease in accumulation of the mutant band 3 RNA was detected. Thus the codon 330 nonsense mutation is responsible for the decreased accumulation of mutant band 3 RNA and the deficiency of band 3 protein in this kindred. These results have important implications for the role of band 3 defects in the membrane pathobiology of HS as well as for the techniques used in detection of HS mutations.

Recurrent fatal hydrops fetalis associated with a nucleotide substitution in the erythrocyte beta-spectrin gene.

We studied a kindred in which four third-trimester fetal losses occurred, associated with severe Coombs-negative hemolytic anemia and hydrops fetalis. Postmortem examination of two infants revealed extensive extramedullary erythropoiesis. Studies of erythrocytes and erythrocyte membranes from the parents revealed abnormal erythrocyte membrane mechanical stability as well as structural and functional abnormalities in spectrin, the principal structural protein of the erythrocyte membrane. Genetic studies identified a point mutation of the beta-spectrin gene, S2019P, in a region of beta spectrin that is critical for normal spectrin function. Both parents and two living children were heterozygous for this mutation; three infants dying of hydrops fetalis were homozygous for this mutation. In an in vitro assay using recombinant peptides, the mutant beta-spectrin peptide demonstrated a significant abnormality in its ability to interact with alpha spectrin. This is the first description of a molecular defect of the erythrocyte membrane associated with hydrops fetalis.

Substitution of the human beta-spectrin promoter for the human agamma-globin promoter prevents silencing of a linked human beta-globin gene in transgenic mice.

During development, changes occur in both the sites of erythropoiesis and the globin genes expressed at each developmental stage. Previous work has shown that high-level expression of human beta-like globin genes in transgenic mice requires the presence of the locus control region (LCR). Models of hemoglobin switching propose that the LCR and/or stage-specific elements interact with globin gene sequences to activate specific genes in erythroid cells. To test these models, we generated transgenic mice which contain the human Agamma-globin gene linked to a 576-bp fragment containing the human beta-spectrin promoter. In these mice, the beta-spectrin Agamma-globin (betasp/Agamma) transgene was expressed at high levels in erythroid cells throughout development. Transgenic mice containing a 40-kb cosmid construct with the micro-LCR, betasp/Agamma-, psibeta-, delta-, and beta-globin genes showed no developmental switching and expressed both human gamma- and beta-globin mRNAs in erythroid cells throughout development. Mice containing control cosmids with the Agamma-globin gene promoter showed developmental switching and expressed Agamma-globin mRNA in yolk sac and fetal liver erythroid cells and beta-globin mRNA in fetal liver and adult erythroid cells. Our results suggest that replacement of the gamma-globin promoter with the beta-spectrin promoter allows the expression of the beta-globin gene. We conclude that the gamma-globin promoter is necessary and sufficient to suppress the expression of the beta-globin gene in yolk sac erythroid cells.

Gene transfer to ankyrin-deficient bone marrow corrects spherocytosis in vitro.

OBJECTIVE: The goal of this study was to transfer by retroviral vector the cDNA for ankyrin to progenitors from normal bone marrow and from the nb/nb spherocytosis mutant deficient in expression of full-length ankyrin to achieve erythroid expression of functional ankyrin protein. MATERIALS AND METHODS: A minigene composed of the human ankyrin promoter, murine ankyrin cDNA, and the 3' human domain corresponding to the ankyrin 2.2 isoform was assembled in the retroviral vector, pG1. Murine erythroleukemia (MEL) cells, normal murine bone marrow cells, 3T3 fibroblasts, and nb/nb mutant bone marrow and spleen cells were transduced with the retroviral supernatant. Transduced mutant cells were induced to differentiate in liquid culture. Gene transfer was assessed by colony polymerase chain reaction (PCR) and reverse transcriptase (RT)-PCR, immunofluorescence, and Southern, Northern, and Western blot analysis. RESULTS: MEL cells, normal bone marrow progenitors, and nb/nb cells were all successfully transduced and expressed ankyrin by RT-PCR and Western blot. Transduced murine 3T3 fibroblasts and MEL cells exhibited cell membrane staining by immunofluorescence. Colony RT-PCR demonstrated dependence of expression on erythropoietin. In vitro, the transduced nb/nb cells matured to polychromatophils, whereas nontransduced nb/nb cells matured to microspherocytes. CONCLUSION: Retroviral transfer of ankyrin corrected the defect leading to formation of microspherocytes in erythroid differentiation cultures from the nb/nb mutant. The human ankyrin promoter conferred erythropoietin-dependent expression in normal and mutant erythroid progenitors, which could have implications for the gene therapy of human hemolytic anemias.

Disorders of erythrocyte volume homeostasis.

Inherited disorders of erythrocyte volume homeostasis are a heterogeneous group of rare disorders with phenotypes ranging from dehydrated to overhydrated erythrocytes. Clinical, laboratory, physiologic, and genetic heterogeneities characterize this group of disorders. A series of recent reports have provided novel insights into our understanding of the genetic bases underlying some of these disorders of red cell volume regulation. This report reviews this progress in understanding determinants that influence erythrocyte hydration and how they have yielded a better understanding of the pathways that influence cellular water and solute homeostasis.

Molecular diagnosis of hemoglobinopathies and other red blood cell disorders.

This article provides an overview of the techniques currently available for the molecular diagnosis of hemoglobinopathies and other inherited erythrocyte disorders. Advances in both clinical practice and molecular biology have permitted rapid genetic diagnosis of many of these disorders. In turn, rapid diagnosis has led to improvements in prenatal diagnosis and in early detection of at-risk individuals, permitting appropriate prenatal counseling to at-risk couples, allowing for appropriate patient education, and improving clinical outcome.

Genomic organization and chromosomal localization of the murine 2 P domain potassium channel gene Kcnk8: conservation of gene structure in 2 P domain potassium channels.

A 2 P domain potassium channel expressed in eye, lung, and stomach, Kcnk8, has recently been identified. To initiate further biochemical and genetic studies of this channel, we assembled the murine Kcnk8 cDNA sequence, characterized the genomic structure of the Kcnk8 gene, determined its chromosomal localization, and analyzed its activity in a Xenopus laevis oocyte expression system. The composite cDNA has an open reading frame of 1029 bp and encodes a protein of 343 amino acids with a predicted molecular mass of 36 kDa. Structure analyses predict 2 P domains and four potential transmembrane helices with a potential single EF-hand motif and four potential SH3-binding motifs in the COOH-terminus. Cloning of the Kcnk8 chromosomal gene revealed that it is composed of three exons distributed over 4 kb of genomic DNA. Genome database searching revealed that one of the intron/exon boundaries identified in Kcnk8 is present in other mammalian 2 P domain potassium channels genes and many C. elegans 2P domain potassium channel genes, revealing evolutionary conservation of gene structure. Using fluorescence in situ hybridization, the murine Kcnk8 gene was mapped to chromosome 19, 2B, the locus of the murine dancer phenotype, and syntenic to 11q11-11q13, the location of the human homologue. No significant currents were generated in a Xenopus laevis oocyte expression system using the composite Kcnk8 cDNA sequence, suggesting, like many potassium channels, additional channel subunits, modulator substances, or cellular chaperones are required for channel function.

Group B streptococcal bacteremia in a community teaching hospital.

Group B streptococcal bacteremia outside the perinatal setting is not commonly emphasized. This report reviews all episodes of group B streptococcal bacteremia during a four and a half year period in a large community teaching hospital. Fourteen episodes occurred in neonates, four in parturient women, and 28 in other adults. Bacteremic adults were usually elderly with an average age of 68 years. Group B streptococcal bacteremia occurred in adults with various underlying diseases, including diabetes mellitus, liver disease, peripheral vascular disease, and hematologic disease, and in those receiving long-term steroid therapy. Infections causing group B streptococcal bacteremia in adults included decubitus ulcers, pneumonia, endocarditis, cellulitis, arthritis, osteomyelitis, and meningitis. Thirteen of 28 episodes of group B streptococcal bacteremia in adults were hospital-acquired. Overall mortality in adults was 70 percent. Group B streptococcal bacteremia in adults outside of the perinatal setting is associated with significant underlying diseases and has a high mortality.

Complications of conjunctivitis caused by Pseudomonas aeruginosa in a newborn intensive care unit.

BACKGROUND: In infancy Pseudomonas aeruginosa conjunctivitis may lead to a rapidly progressive invasive eye infection. In some cases this destructive eye disease is associated with or followed by infection at other sites. We observed seven hospitalized infants with P. aeruginosa conjunctivitis who developed systemic complications of P. aeruginosa infection without evidence of invasive eye disease, prompting us to examine the characteristics of this infection and its associated systemic complications in hospitalized infants. METHODS: We reviewed retrospectively the course, treatment and outcome of infants with nonepidemic P. aeruginosa conjunctivitis in the Newborn Special Care Unit at Yale-New Haven Hospital during a 10-year period from November 1, 1986, to October 31, 1996. RESULTS: Eighteen infants with P. aeruginosa conjunctivitis had mean birth weights and gestational ages of 29.3 weeks and 1380 g, respectively. The average postnatal age at onset of P. aeruginosa conjunctivitis was 17 days. No infant had invasive eye disease. Systemic complications occurred in seven (39%) infants and included bacteremia, meningitis, brain abscess and death. Infants who developed systemic complications had lower mean birth weights (850 g vs. 1716 g, P = 0.04) and lower mean gestational ages (26.4 vs. 31.2 weeks, P = 0.02) than infants who did not. Six of seven infants weighing < 1000 g developed systemic complications; two of these infants died. CONCLUSIONS: In hospitalized infants P. aeruginosa conjunctivitis may be associated with systemic complications with or without invasive eye infection, emphasizing the need for early detection and treatment of this infection in this population.

Increasing incidence of gram-negative rod bacteremia in a newborn intensive care unit.

OBJECTIVES: To determine whether there has been an increase in the incidence or a change in the epidemiology of gram-negative rod (GNR) bacteremia in patients in a newborn special care unit. METHODS: Retrospective review of GNR bacteremia in patients hospitalized in the NBSCU at Yale-New Haven Hospital during a 10-year period. RESULTS: There were 120 isolates from 113 episodes of GNR bacteremia during the study period. The incidence of GNR bacteremia increased from a mean of 10.2 to 25.5 (P = 0.017) episodes of GNR bacteremia per 1000 admissions per year between the time periods 1988 to 1994 and 1995 to 1997, respectively, paralleling an increase in the overall incidence of bacteremia. The increase in GNR bacteremia in these two groups was not related to changes in the patient population, the number of admissions or duration of hospitalization. Stepwise multivariate analysis identified two independent variables associated with infants who had GNR bacteremia during the period 1995 to 1997 as compared with 1988 to 1994, maternal intrapartum antibiotics (odds ratio, 4.9; 95% confidence interval, 1.9 to 12.6) and the presence of a percutaneous central venous catheter (odds ratio, 4.6; 95% confidence interval, 1.8 to 11.8). CONCLUSIONS: We observed changes in clinical obstetric and neonatal care that paralleled the increase in GNR bacteremia at our institution. A prospective study is needed to elucidate the impact of these changes on the incidence of GNR bacteremia in this population.

Development of a stable retrovirus vector capable of long-term expression of gamma-globin mRNA in mouse erythrocytes.

Gene therapy for patients with hemoglobin disorders such has been hampered by the inability of retrovirus vectors to transfer globin genes and the locus control region (LCR) into hematopoietic stem cells without rearrangement. In addition, the expression from intact globin gene vectors has been variable in red blood cells as a result of position effects and retrovirus silencing. We hypothesized that by substituting the globin gene promoter for the promoter of another gene expressed in red blood cells, we could generate stable retrovirus vectors that would express globin at sufficient levels to treat hemoglobinopathies. Transgenic mice containing the human ankyrin (Ank) gene promoter fused to the human gamma-globin gene showed position-independent, copy number-dependent expression of a linked gamma-globin mRNA. We generated a "double-copy" Ank/A gamma-globin retrovirus vector that transferred two copies of the Ank/A gamma-globin gene into target cells. Stable gene transfer was observed in primary primary mouse progenitor cells and long-term repopulating hematopoietic stem cells. Expression of Ank/A gamma-globin mRNA in mature red blood cells was approximately 8% of the level of mouse alpha-globin mRNA. We conclude that this novel retrovirus vector may be valuable for treating a variety of hemoglobinopathies by gene therapy if the level of expression can be further increased.

Hematologic disorders and nonimmune hydrops fetalis.

Hematologic disorders are implicated in approximately 10% to 27% of cases of nonimmune hydrops fetalis. In almost all of these disorders, anemia leading to heart failure, edema, ascites, and anasarca is the final common denominator. The etiology of the anemia in these cases can be conveniently divided into two categories: (1) excessive erythrocyte loss by hemolysis or hemorrhage, and (2) erythrocyte underproduction. The former include intrinsic erythrocyte abnormalities such as alpha-thalassemia and glucose-6-phosphate dehydrogenase deficiency, and conditions with excessive fetal blood loss such as fetomaternal hemorrhage and twin-twin transfusion. The latter include bone marrow replacement syndromes and conditions associated with failure of erythrocyte production. The presentation, diagnosis, and management of hematologic disorders associated with nonimmune hydrops fetalis are reviewed.

Cystic hygroma in the fetus and newborn.

Cystic hygromas are developmental abnormalities of the lymphoid system that occur at sites of lymphatic-venous connection, most commonly in the posterior neck. They are frequently associated with karyotypic abnormalities, various malformation syndromes, and several teratogenic agents. The disease course of an infant with cystic hygroma is unpredictable. When diagnosed prenatally, the overall prognosis is poor. Cystic hygroma diagnosed after birth is usually associated with a good prognosis. This article reviews the embryologic, genetic, and pathologic correlates of these lymphatic system abnormalities, as well as the clinical course and outcome of the fetus and newborn with a cystic hygroma. Management strategies are reviewed, including newer nonsurgical therapies for the neonate with a cystic hygroma.

Bacteremia, meningitis, and brain abscesses in a hospitalized infant: complications of Pseudomonas aeruginosa conjunctivitis.

This report describes a preterm infant hospitalized in a neonatal intensive care unit who developed Pseudomonas aeruginosa conjunctivitis associated with bacteremia, meningitis, and multiple brain abscesses. P. aeruginosa conjunctivitis can rapidly progress to an invasive eye infection, such as corneal ulceration or endophthalmitis, leading to poor vision or blindness. Progression of this infection may lead to systemic disease. However, as illustrated in this report, P. aeruginosa conjunctivitis may be associated with the development of systemic complications such as bacteremia and meningitis in the absence of invasive eye disease. P. aeruginosa is a relatively common cause of conjunctivitis in hospitalized preterm and low birth weight infants. Given the severity of the ocular and systemic complications of Pseudomonas conjunctivitis, clinicians are reminded that prompt detection and treatment of neonatal conjunctivitis is critical.

Nutritional anemias in infancy.

Anemia in the 1st year of life should be an important warning sign to the clinician of a potential underlying nutritional deficiency. Prompt diagnosis and treatment are warranted in many cases, not only to treat the anemia but also, more important, to prevent other long-term sequelae associated with the underlying, causative deficiency. As more information about the impact of nutrition on various aspects of health is collected and newer therapies for the treatment of disease are developed, it will be important to understand and consider the role of vitamins and minerals in a light beyond the realm of nutritional anemia.