Carbonic anhydrase II deficiency syndrome: recessive osteopetrosis with renal tubular acidosis and cerebral calcification.

Four new Saudi Arabian cases of the carbonic anhydrase II deficiency syndrome from two families are described. This autosomal recessive syndrome includes osteopetrosis with renal tubular acidosis and cerebral calcification. Additional features are mental retardation, growth failure, typical facial appearance, and abnormal teeth. Two patients showed evidence of restrictive lung disease, a finding not previously described. One of the patients reported represents the first neonate reported to be affected with this syndrome. Intrauterine growth was normal, but metabolic acidosis was already evident in the neonatal period. Radiographic evidence of osteopetrosis was probably absent at birth but appeared during the late neonatal period. Carbonic anhydrase II deficiency was demonstrated in erythrocyte hemolysates from the older two siblings of this neonate, and a 50% normal level of carbonic anhydrase II was demonstrated in the erythrocyte hemolysate from their father.

Evaluation of carbonic anhydrase isozymes in disorders involving osteopetrosis and/or renal tubular acidosis.

Carbonic anhydrase II (CA II) deficiency in man is an autosomal recessive disorder manifest by osteopetrosis, renal tubular acidosis, and cerebral calcification. Other features include growth failure and mental retardation. Complications of the osteopetrosis include frequent bone fractures, cranial nerve compression symptoms, and dental malocclusion. The anemia and leukopenia seen in the recessive, lethal infantile form of osteopetrosis are not seen in CA II deficient patients. The renal tubular acidosis usually includes both proximal and distal components. Symptoms of metabolic acidosis respond to therapy, but no specific treatment is available for the osteopetrosis or cerebral calcification. We review here the role of carbonic anhydrases in bone resorption and renal acidification, and discuss clinical features and laboratory findings which distinguish CA II deficiency from other disorders producing osteopetrosis, renal tubular acidosis, or brain calcification. Methods to evaluate patients with pure proximal renal tubular acidosis for deficiency of CA IV are also discussed.

Purification and characterization of human salivary carbonic anhydrase.

A novel carbonic anhydrase was purified from human saliva with inhibitor affinity chromatography followed by ion-exchange chromatography. The molecular weight was determined to be 42,000 on sodium dodecyl sulfate polyacrylamide gel electrophoresis, indicating that the human salivary enzyme is larger than the cytosolic isoenzymes CA I, CA II, and CA III (Mr 29,000) from human tissue sources. Each molecule of the salivary enzyme had two N-linked oligosaccharide chains which were cleaved by endo-beta-N-acetylglucosaminidase F but not by endo-beta-N-acetylglucosaminidase H, indicating that the oligosaccharides are complex type. The isoelectric point was determined to be 6.4, but significant charge heterogeneity was found in different preparations. The human salivary isozyme has lower specific activity than the rat salivary isozyme and the human red blood cell isozyme II in the CO2 hydratase reaction. The inhibitory properties of the salivary isozyme resemble those of CA II with iodide, sulfanilamide, and bromopyruvic acid, but the salivary enzyme is less sensitive to acetazolamide and methazolamide than CA II. Antiserum raised in a rabbit against the salivary enzyme cross-reacted with CA II from human erythrocytes, indicating that human salivary carbonic anhydrase and CA II must share at least one antigenic site. CA I and CA III did not crossreact with this antiserum. The amount of salivary carbonic anhydrase in the saliva of the CA II-deficient patients was greatly reduced, indicating that the CA II deficiency mutation directly or indirectly affects the expression of the salivary carbonic anhydrase isozyme. From these results we conclude that the salivary carbonic anhydrase is immunologically and genetically related to CA II, but that it is a novel and distinct isozyme which we tentatively designate CA VI.

Enveloped virus acquires membrane defect when passaged in fibroblasts from I-cell disease patients.

Sindbis virus obtained after passage on human fibroblasts from patients with I-cell disease (mucolipidosis II) and called I-cell virus differed from Sindbis virus obtained from chick fibroblasts or from normal human fibroblasts in two ways: (1) The I-cell virus was extremely unstable to freezing and thawing, (2) The I-cell virus showed greatly exaggerated sensitivity to inactivation by Triton X-100. Sindbis virus from fibroblasts from two patients with mucolipidosis III, a milder form of I-cell disease, showed similar, though milder, freeze-sensitivity. When freeze-sensitive I-cell virus was passaged once in mouse L-cells or normal human fibroblasts, the virus was no longer abnormal. The viral glycoproteins of I-cell virus were not distinguishable from viral glycoproteins of controls by sodium dodecyl sulfate gel electrophoresis. Gel filtration of the glycopeptides suggested small differences in two of the four glycopeptides. These findings indicate that Sindbis virus is phenotypically altered when grown on I-cell fibroblasts. These alterations must be attributed to viral envelope components derived from the host plasma membrane (membrane lipids) or to alterations in viral envelope glycoproteins. In either case, the alterations appear related to the genetic defect in I-cell fibroblasts. From these results it is clear that enveloped viruses can be useful to demonstrate and to analyze membrane defects in certain human diseases. The phenotypically altered viruses may, in turn, provide probes for studying the functional relationships of virus membrane components.

Secretory carbonic anhydrase isoenzyme (CA VI) in human serum.

Carbonic anhydrase VI (CA VI) is a secretory isoenzyme that, by analogy to alpha-amylase, is produced in the salivary glands and delivered into saliva. To determine whether CA VI is transferred into the circulation and is detectable in human serum, we collected blood samples from four healthy subjects at 3-h intervals throughout a 24-h period and measured concentrations of CA VI by a specific time-resolved immunofluorometric assay. All serum samples contained CA VI, the concentrations being approximately 22 times lower in serum than in the corresponding saliva samples. The presence of CA VI in serum was confirmed by Western blotting, which under reducing conditions identified a 42-kDa polypeptide band corresponding to the monomeric CA VI. The described time-resolved immunofluorometric assay for CA VI might be useful to identify or exclude diseases of the salivary glands in the differential diagnosis of patients whose serum amylase concentrations are increased.

An oculocerebrofacial syndrome.

A syndrome of mental retardation, microcephaly, a mongoloid slant to the palpebral fissures, microcornea, strabismus, myopia, optic atrophy, high-arched palate, preauricular skin tags and small mandible is described in four (including one set of twins) of seven sibs born to unaffected, nonconsanguineous parents of German ancestry. An autosomal recessive mode of inheritance seems most likely.