Polymorphic gene for human carbonic anhydrase II: a molecular disease marker located on chromosome 8

Blessing in disguise: when head trauma solves the riddle of carbonic anhydrase II deficiency

Carbonic anhydrase II deficiency is a rare autosomal recessive disorder with a classical triad of renal tubular acidosis, intracerebral calcifications and osteopetrosis. We present a case of a 6-year and 4-months old male patient presented to our pediatric gastroenterology outpatients' clinic with parental concern of poor growth. The patient is a known case of unexplained global developmental delay, recurrent fractures and constipation since birth. As a result of the patient's hyperactivity, he hit his head with the clinic's door resulting in a cut wound. Brain computed tomography scan showed abnormal symmetrical calcifications seen in both basal ganglia, thalami and subcortical white matter associated with increased bone density of the skull and upper cervical spine reassembling osteopetrosis. The suspicion of carbonic anhydrase II deficiency was confirmed by arterial blood gases revealing a marked metabolic acidosis fulfilling the diagnostic triad. The patient was discharged on sodium bicarbonate therapy, lactulose and vitamin D3 supplements and has been followed up regularly.

Carbonic anhydrase II deficiency: report of a novel mutation

Carbonic anhydrase II (CAII) deficiency is an autosomal recessive disorder characterized by renal tubular acidosis, osteopetrosis, recurrent bone fractures, renal stones, growth failure, and mental retardation. Several cases have been reported in Saudi Arabia with homozygous mutations in CA2 consistent with a high degree of consanguinity. We report a case of carbonic anhydrase II deficiency with short stature, mixed renal tubular acidosis, recurrent bone fractures due to trivial trauma, recurrent renal stones and cerebral calcification. This patient was compound heterozygous for a novel CA2 mutation and a previously reported mutation in Arabs.

The neurology of carbonic anhydrase type II deficiency syndrome

Carbonic anhydrase type II deficiency syndrome is an uncommon autosomal recessive disease with cardinal features including osteopetrosis, renal tubular acidosis and brain calcifications. We describe the neurological, neuro-ophthalmological and neuroradiological features of 23 individuals (10 males, 13 females; ages at final examination 2-29 years) from 10 unrelated consanguineous families with carbonic anhydrase type II deficiency syndrome due to homozygous intron 2 splice site mutation (the 'Arabic mutation'). All patients had osteopetrosis, renal tubular acidosis, developmental delay, short stature and craniofacial disproportion with large cranial vault and broad forehead. Mental retardation was present in approximately two-thirds and varied from mild to severe. General neurological examinations were unremarkable except for one patient with brisk deep tendon reflexes and two with severe mental retardation and spastic quadriparesis. Globes and retinae were normal, but optic nerve involvement was present in 23/46 eyes and was variable in severity, random in occurrence and statistically correlated with degree of optic canal narrowing. Ocular motility was full except for partial ductional limitations in two individuals. Saccadic abnormalities were present in two, while half of these patients had sensory or accommodative strabismus, and seven had congenital nystagmus. These abnormalities were most commonly associated with afferent disturbances, but a minor brainstem component to this disorder remains possible. All internal auditory canals were normal in size, and no patient had clinically significant hearing loss. Neuroimaging was performed in 18 patients and repeated over as long as 10 years. Brain calcification was generally progressive and followed a distinct distribution, involving predominantly basal ganglia and thalami and grey-white matter junction in frontal regions more than posterior regions. At least one child had no brain calcification at age 9 years, indicating that brain calcification may not always be present in carbonic anhydrase type II deficiency syndrome during childhood. Variability of brain calcification, cognitive disturbance and optic nerve involvement may imply additional genetic or epigenetic influences affecting the course of the disease. However, the overall phenotype of the disorder in this group of patients was somewhat less severe than reported previously, raising the possibility that early treatment of systemic acidosis with bicarbonate may be crucial in the outcome of this uncommon autosomal recessive problem.

Loss of the apical V-ATPase a-subunit VHA-6 prevents acidification of the intestinal lumen during a rhythmic behavior in C. elegans

In Caenorhabditis elegans, oscillations of intestinal pH contribute to the rhythmic defecation behavior, but the acid-base transport mechanisms that facilitate proton movement are not well understood. Here, we demonstrate that VHA-6, an intestine-specific a-subunit of the H(+)-K(+)-ATPase complex (V-ATPase), resides in the apical membrane of the intestinal epithelial cells and is required for luminal acidification. Disruption of the vha-6 gene led to early developmental arrest; the arrest phenotype could be complemented by expression of a fluorescently labeled vha-6 transgene. To study the contribution of vha-6 to pH homeostasis in larval worms, we used a partial reduction of function through postembryonic single-generation RNA interference. We demonstrate that the inability to fully acidify the intestinal lumen coincides with a defect in pH recovery of the intestinal epithelial cells, suggesting that VHA-6 is essential for proton pumping following defecation. Moreover, intestinal dipeptide accumulation and fat storage are compromised by the loss of VHA-6, suggesting that luminal acidification promotes nutrient uptake in worms, as well as in mammals. Since acidified intracellular vesicles and autofluorescent storage granules are indistinguishable between the vha-6 mutant and controls, it is likely that the nutrient-restricted phenotype is due to a loss of plasma membrane V-ATPase activity specifically. These data establish a simple genetic model for proton pump-driven acidification. Since defecation occurs at 45-s intervals in worms, this model represents an opportunity to study acute regulation of V-ATPase activity on a short time scale and may be useful in the study of alternative treatments for acid-peptic disorders.

Effects of thyroid hormone on carbonic anhydrase I gene expression in human erythroid cells

Individuals with hyperthyroidism exhibit concentrations of carbonic anhydrase I (CAI) in red blood cells that reflect the integrated serum thyroid hormone concentration over the preceding few months. Furthermore, triiodothyronine T3, at a physiological free concentration, decreases the CAI concentration in both human erythroleukemic YN-1 cells and burst-forming unit-erythroid (BFU-E)-derived cells. In the present study, the effect of T3 on CAI mRNA levels in various human erythroleukemic cell lines (YN-1, HEL and KU-812) and BFU-E-derived cells was studied. Northern analysis of RNA extracted from erythroid cells revealed a CAI mRNA of 1.5 kilobases. T3 significantly decreased the levels of CAI mRNA in YN-1 and BFU-E-derived cells in a dose-dependent manner. Incubation of T3-stimulated cells with actinomycin D prevented the decrease in CAI mRNA levels. By contrast, T3 had no effect on either the concentrations of CAI or the levels of CAI mRNA in HEL and KU-812 cells. These results suggest that YN-1 and BFU-E-derived cells may be useful models for investigating T3 actions on CAI mRNA in human cells.

Diagnostic approaches to renal genetic disorders using DNA analysis

Recent developments in molecular genetic technology have made it possible to diagnose many genetic disorders affecting the kidney before they are clinically manifest. For a disorder to be diagnosed by DNA analysis, either the causative gene must be known and cloned, or a closely linked DNA segment must have been identified. If one of these criteria is met, the disorder may be diagnosed either by direct detection of a mutation, if it is known, or indirectly by linkage analysis of the region using closely linked genetic markers. The methodology currently employed for direct detection of mutation includes the Southern blot, which will detect large structural alterations of genes or mutations altering a restriction recognition site, or the use of allele-specific oligonucleotides, which will detect specific point mutations. Linkage analysis is performed on DNA from multiple family members of the person at risk. Polymorphic markers are "tracked" in the family to determine the allele segregating with the disease gene. These methods are now routinely applied to the diagnosis of mendelian disorders affecting the kidney. It is anticipated that progress over the next decade will extend these applications to detection of the genetic component(s) contributing to multifactorial conditions.

Induction of carbonic anhydrase I isozyme precedes the globin synthesis during erythropoiesis in K562 cells

Induction of carbonic anhydrase isozyme I (CA-I) by erythropoietin or hemin was investigated using erythroleukemia (K562) cells. Immunological estimation and purification of carbonic anhydrases showed that untreated K562 cells contained only carbonic anhydrase isozyme II(CA-II), while incubation of the cells with 2 units of erythropoietin (EP) per ml of the incubation medium or with 50 microM hemin resulted in the induction of CA-I. The purified CA-I induced in K562 cells was enzymatically and immunologically identical to that from mature erythrocytes. Flow cytometric analysis showed that incubation of K562 cells with EP as well as hemin induced CA-I at the 3rd h, while alpha-globin was detected at the 8th h. Northern blot analysis of CA-I mRNA using a cloned genomic DNA as a probe showed that mRNA of CA-I was induced by EP. These results suggest that induction of CA-I is regulated at the transcriptional level during developmental changes of erythroid cells, and that CA-I may play a physiologically important role during erythroid differentiation.

Case report 668. Carbonic anhydrase II deficiency syndrome (osteopetrosis associated with renal tubular acidosis and cerebral calcification)

A 4-month-old infant with bronchiolitis was found to have hyperdense bones on chest roentgenograms. The diagnosis of osteopetrosis was demonstrated by generalized increased radiological bone density and by a bone biopsy showing persistence of calcified cartilage. The infant also had a mixed proximal and distal renal tubular acidosis requiring as much as 12 mEq/kg per day of sodium bicarbonate. Measurement of his erythrocyte carbonic anhydrase activity revealed a deficiency of CA II. His parents showed values of CA activity that were intermediate between controls and the proband. Thus, this is a patient with the CA II deficiency syndrome; he is the youngest reported case without any family history of osteopetrosis to be diagnosed initially on the basis of his radiographic features.

The polymorphic human DNA sequence D8S8 assigned to 8q13-21.1, close to the carbonic anhydrase gene cluster, by isotopic and nonisotopic in situ hybridization and by linkage analysis

Restriction fragment length polymorphism at the D8S8 locus is explained by the occurrence of at least two alternative alleles at two separate TaqI sites; TaqI-A allele frequencies 0.73 and 0.27 and TaqI-B allele frequencies 0.94 and 0.06. The D8S8 locus has been assigned to 8q13-21.1, near to the carbonic anhydrase (CA) gene cluster, by in situ hybridization to metaphase chromosomes using both tritium and immunofluorescently labelled probes. Linkage analysis using the CEPH family DNA panel indicates a close genetic linkage between D8S8 and CA3, with a lod score of +7.80 at theta = 0.05 in males.

Mouse carbonic anhydrase III: nucleotide sequence and expression studies

A cDNA for the mouse carbonic anhydrase, CAIII, has been isolated from a lambda gt11 expression library. The cloned cDNA contains all of the coding region (777 bp) and both 5' untranslated (86-bp) and 3' untranslated (217-bp) sequences. The coding sequence shows 87% homology at the nucleotide level and 91% homology, when amino acid residues are compared, with human CAIII. Protein and mRNA analyses show that CAIII is present at low levels in cultured myoblasts and is abundant in adult skeletal muscle and in liver. The marked sex-related differences in CAIII distribution, described for rat liver, are not seen in the mouse. Restriction fragment length polymorphisms using TaqI and PstI are described which distinguish between Mus spretus and Mus musculus domesticus.

Human chromosome 8

The role of human chromosome 8 in genetic disease together with the current status of the genetic linkage map for this chromosome is reviewed. Both hereditary genetic disease attributed to mutant alleles at gene loci on chromosome 8 and neoplastic disease owing to somatic mutation, particularly chromosomal translocations, are discussed.

Human muscle carbonic anhydrase: gene structure and DNA methylation patterns in fetal and adult tissues

We report the isolation and analysis of genomic clones comprising the entire gene coding for the human muscle carbonic anhydrase, CAIII. The gene spans 10.3 kb and has a seven-exon/six-intron structure. A noncanonical TATA box, a CCAAT motif, and two CCGCCC elements are present in the sequences upstream of exon 1. Although the expression of CAIII shows strict tissue specificity, the gene exhibits a number of features normally associated with housekeeping enzymes. For example, there is 48% homology with a 25-bp consensus sequence between the TATA box and the cap site and there is a CpG-rich island spanning a 469-bp sequence near to the origin of transcription. Methylation studies suggest that some CCGG sites clustered in the CpG-rich island are undermethylated in DNA from fetal and adult muscle and in other tissues irrespective of CAIII expression. In contrast, several nonclustered CCGG sites show a methylation pattern that correlates with gene expression. However DNA from differentiated type II adult muscle fibers is undermethylated at these sites even though CAIII is not expressed.

Regional localization of carbonic anhydrase genes CA1 and CA3 on human chromosome 8

The human carbonic anhydrase isozymes represent a family of homologous proteins which are important in respiratory function, fluid secretion, and maintenance of cellular acid-base homeostasis. Using somatic cell genetic techniques we have mapped two of the CA genes (CA1 and CA3) to human chromosome 8. In situ hybridization data demonstrates that both CA1 and CA3 map to the same region (q13-q22) of chromosome 8.

Nucleotide sequence, tissue-specific expression, and chromosome location of human carbonic anhydrase III: the human CAIII gene is located on the same chromosome as the closely linked CAI and CAII genes

The carbonic anhydrases (CA) are a class of metalloenzymes that catalyze the reversible hydration of carbon dioxide. The genes for the carbonic anhydrase isozymes are members of a multigene family that are differentially expressed in a number of cell types. We have isolated a full-length representative of a CAIII mRNA transcript from an adult human muscle cDNA library, and we present the complete nucleotide sequence of this cDNA clone. RNA blots demonstrate that CAIII messages can be detected in a variety of cell types but that high-level expression is limited to human fetal and adult skeletal muscle and to rodent slow skeletal muscle and liver. In addition, we have used a panel of human-mouse cell hybrids to localize the human CAIII gene to chromosome 8. Previous reports have established the CAI and CAII isozyme genes to be closely linked on chromosome 8, and the assignment of the CAIII gene to the same chromosome raises the possibility that these genes may all be linked at a single complex locus.

Differentiation of leukemia cells to polymorphonuclear leukocytes in patients with acute nonlymphocytic leukemia

We used recombinant-DNA techniques to determine the origin of polymorphonuclear leukocytes in patients with acute nonlymphocytic leukemia, at presentation, in remission, and in relapse. Studies using X chromosome-linked DNA polymorphisms strongly suggested that leukemic blast cells in this form of leukemia can differentiate in vivo to form mature granulocytes. Common chromosomal changes seen in blast cells, such as the addition of a chromosome 8 or the loss of a chromosome 7, were found to be present in the mature granulocytes of patients with leukemia. In addition, rearrangement of the immunoglobulin heavy-chain gene was detected in the polymorphonuclear leukocytes of one patient. Finally, we have observed the persistence of a single dominant hemopoietic clone in the granulocytes of 3 of 13 patients in complete remission. These findings demonstrate that recombinant-DNA probes can detect clonal populations of granulocytes in patients with acute nonlymphocytic leukemia, and provide further evidence that in some patients leukemic blast cells differentiate to form mature cells.

Assignment of the gene determining human carbonic anhydrase, CAI, to chromosome 8

A cDNA clone complementary to the mRNA encoding the rabbit erythrocyte specific carbonic anhydrase, CAI, has been used as probe for human CAI sequences in the analysis of DNA from panels of rodent/human somatic cell hybrids. The presence of the human CAI gene in all hybrids correlates with the presence of chromosome 8. Together with published mapping data, this assignment indicates that three CA loci are situated on chromosome 8.

Carbonic anhydrase II deficiency: diagnosis and carrier detection using differential enzyme inhibition and inactivation

Carbonic anhydrase (CA) I and II are soluble isozymes that represent the major nonhemoglobin proteins in the erythrocyte. We recently identified a deficiency of CA II as the enzymatic basis for the autosomal recessive syndrome of osteopetrosis with renal tubular acidosis and cerebral calcification. Virtual absence of the CA II peak on high-performance liquid chromatography, of CA II esterase activity, and of immunoprecipitable CA II were demonstrated on extracts of red cell lysates from all patients studied. Reduced levels of CA II were found in obligate heterozygotes. Here, we present evidence that CA II in red cell lysates can be quantitated by measuring CO2 hydratase activity in the presence of inhibitors that selectively inhibit the activity of CA I to a much greater extent than that of CA II. This was done with iodide (anion binding) and bromopyruvic acid (alkylation), and the respective assays evaluated as diagnostic tools for CA II deficiency in human red cells. These techniques greatly simplify the quantitation of CA II in hemolysates and should make genetic diagnosis and counseling for the newly described inborn error of metabolism due to CA II deficiency generally available. They also allow quantitation of CA I in red cell lysates.

The gene for human muscle specific carbonic anhydrase (CAIII) is assigned to chromosome 8

A cDNA clone complementary to the mRNA encoding the human muscle specific carbonic anhydrase CAIII has been used as probe in the analysis of DNA from panels of rodent/human somatic cell hybrids. The presence of the CA III gene in all hybrids correlates with the presence of chromosome 8. This is the first assignment of the CAIII gene in any species and, together with published mapping data, indicates that all of the human CA loci are situated on chromosome 8.

Carbonic anhydrase II deficiency in 12 families with the autosomal recessive syndrome of osteopetrosis with renal tubular acidosis and cerebral calcification

Osteopetrosis with renal tubular acidosis and cerebral calcification was identified as a recessively inherited syndrome in 1972. In 1983, we reported a deficiency of carbonic anhydrase II, one of the isozymes of carbonic anhydrase, in three sisters with this disorder. We now describe our study of 18 similarly affected patients with this syndrome in 11 unrelated families of different geographic and ethnic origins. Virtual absence of the carbonic anhydrase II peak on high-performance liquid chromatography, of the esterase and carbon dioxide hydratase activities of carbonic anhydrase II, and of immunoprecipitable isozyme II was demonstrated on extracts of erythrocyte hemolysates from all patients studied. Reduced levels of isozyme II were found in obligate heterozygotes. These observations demonstrate the generality of the findings that we reported earlier in one family and provide further evidence that a deficiency of carbonic anhydrase II is the enzymatic basis for the autosomal recessive syndrome of osteopetrosis with renal tubular acidosis and cerebral calcification. We also summarize the clinical findings in these families, propose mechanisms by which a deficiency of carbonic anhydrase II could produce this metabolic disorder of bone, kidney, and brain, and discuss the clinical evidence for genetic heterogeneity in patients from different kindreds with this inborn error of metabolism.

Isolation of a cDNA clone for the human muscle specific carbonic anhydrase, CAIII

The molecular cloning of cDNA for the human muscle specific carbonic anhydrase CAIII is described. The recombinant was isolated from a human muscle cDNA library prepared in the expression vector lambda gt11, and was characterized by hybridization selection and immunoprecipitation. A comparison of insert cDNA and mRNA sizes suggests that the cDNA is full length and includes extensive untranslated sequences. Preliminary sequence data have confirmed the authenticity of this clone and Southern blotting of human and rodent DNA indicates that it will be a useful probe in the analysis of somatic cell hybrids.

DNA polymorphism in the 5' flanking region of the human carbonic anhydrase II gene on chromosome 8

A restriction-fragment-length polymorphism (RFLP) is described which is associated with the human carbonic anhydrase II gene (CA2) that codes for one of the three genetically distinct carbonic anhydrase isozymes, CA I, CA II, and CA III. The isolated DNA was cleaved with several restriction enzymes and subjected to Southern blot hybridization analysis using a DNA probe containing the 5' end of the human CA II gene. A two allele RFLP which was detected with the restriction endonuclease, Taq I, is expressed phenotypically on Southern blots as either a 5.4 kilobase (kb) fragment or as 4.0 and 1.4kb fragments. These fragments result from the presence or absence of a Taq I recognition site in the 5' flanking region approximately 1.0kb from the initiation codon of the CA II gene. Segregation analysis showed that the alleles are inherited in a Mendelian fashion, with a frequency of 50%.

Cloned cDNA for rabbit erythrocyte carbonic anhydrase I: A novel erythrocyte-specific probe to study development in erythroid tissues

Present understanding of gene expression in erythropoietic tissues is derived solely from studies of the globin genes. Of the three distinct carbonic anhydrase (carbonate dehydratase; carbonate hydro-lyase, EC 4.2.1.1) isozymes, carbonic anhydrase I is erythrocyte-specific and, in humans, is under developmental control. The appearance of carbonic anhydrase I in the erythrocyte late in fetal life follows closely the gamma- to beta-globin switch. In order to study the expression of this erythrocyte-specific nonglobin protein, we set out to isolate a cloned carbonic anhydrase I cDNA. A mixture of 17-base-long synthetic oligonucleotides was used as an in situ hybridization probe to screen a rabbit reticulocyte cDNA library. Two clones were isolated, and the complete nucleotide sequence of the clone with the largest insert was determined and shown to code for carbonic anhydrase I. This clone, designated pRCAI, is near full length and has provided the 40% of the amino acid sequence of rabbit carbonic anhydrase I, which was not known hitherto. The deduced primary structure has revealed potentially significant changes in the vicinity of the active site of the rabbit carbonic anhydrase I when compared with carbonic anhydrase I and II sequences from other species.

Chromosome maps of man and mouse II

Chromosome displays and listings are presented showing loci whose position is known in both man and mouse, in similar manner to our previous report (Dalton et al. 1981). There is now evidence for at least 27 conserved autosomal segments with two or more loci in the two species. The human and mouse chromosome maps show the location of homologous genes. The mouse map also shows the positions of translocations used in gene location and of some other genes used in linkage studies on them.