The importance of liver biopsy in the investigation of possible mitochondrial respiratory chain disease.

The diagnosis of mitochondrial respiratory chain deficiency is usually made by analysis of mitochondrial respiratory chain activity in muscle biopsy. We describe 4 patients in whom the diagnosis was based on mitochondrial respiratory chain deficiency in liver alone. In 3 patients, liver complex IV activity was deficient, and the 4th patient had liver complex I deficiency (relative to citrate synthase and complex II activity). The enzyme activities in skeletal muscle biopsies from these patients were normal or equivocal. The age at presentation and the neurological symptoms differed from one patient to another. All 3 patients with complex IV deficiency had non-specific white matter changes on brain MRI. None of the patients had clinical or biochemical evidence of liver disease. These findings illustrate the wide variety of presentations associated with liver mitochondrial respiratory chain deficiency. They also demonstrate the importance of mitochondrial respiratory chain enzyme analysis in liver, in addition to muscle, even in cases where the primary clinical deficit is neurological and there is no liver disease.