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Elevated serum lactate dehydrogenase isoenzymes and aspartate transaminase distinguish Albers‐Schönberg disease (Chloride Channel 7 Deficiency Osteopetrosis) among the sclerosing bone disorders

Osteopetrosis (OPT) refers to the consequences of generalized failure of skeletal resorption during growth. Most cases are explained by loss‐of‐function mutation within the genes that encode either chloride channel 7 (CLCN7) or a vacuolar proton pump subunit (TCIRG1), each compromising acid secretion by osteoclasts. Patients suffer fractures and sometimes cranial nerve entrapment and insufficient medullary space for hematopoiesis. In 1996, we reported that a high serum level of the brain isoenzyme of creatine kinase (BB‐CK), the CK of osteoclasts, characterizes OPT dueamong the sclerosing bone disorders (J Clin Endocrinol Metab. 1996;11:1438). Now, we show that elevation in serum of multiple lactate dehydrogenase (LDH) isoenzymes with aspartate transaminase (AST) distinguishes autosomal dominant OPT due to loss‐of‐function mutation in CLCN7 [Albers‐Schönberg disease (A‐SD)] among these conditions. Serum total LDH and AST levels as high as 3× and 2×, respectively, the upper limits of normal for age‐appropriate controls, were persistent and essentially concordant in A‐SD. Serum LDH was elevated in 7 of 9 children and in the 2 adults studied with A‐SD. LDH isoenzyme quantitation showed excesses of LDH‐2, ‐3, and ‐4. Neither total LDH nor AST increases were found in other forms of OPT, including bisphosphonate‐induced OPT, or in 41 children and 6 adults representing 20 additional sclerosing bone disorders. Serum TRACP‐5b and BB‐CK also were markedly elevated in A‐SD. Hence, high serum levels of several enzymes characterize A‐SD. Elevated serum LDH isoenzymes and AST indicate a disturbance (of uncertain clinical significance) within multiple extraosseous tissues when there is CLCN7 deficiency. © 2010 American Society for Bone and Mineral Research.