Single Peroxisomal Enzyme and Transporter Deficiencies in Human Diseases and Mouse Models

Abstract

Peroxisomal single enzyme and transporter deficiencies are inherited human diseases caused by the absence of individual enzymatic activities exerted in peroxisomes. These deficiencies either cause an abnormal accumulation of substances normally degraded in peroxisomes or the lack of biomolecules that require peroxisomal function for their synthesis. Consequently, the symptoms observed in diverse tissues of affected patients can be interpreted as consequences of metabolic intoxications or deficiencies in essential biomolecules. Thus, these detrimental effects should add-up to a very severe pathology upon concomitant inactivation of all peroxisomal functions, which is actually observed in patients suffering from peroxisome biogenesis disorders. Interestingly, only a subset of peroxisomal enzymes has been associated with single enzyme and transporter deficiencies and the inactivation of enzymes participating in the same metabolic pathway sometimes presents with drastically different phenotypical outcomes. Moreover, a remarkable spectrum of clinical pictures has been observed in human patients suffering from the same single enzyme deficiency. The utilization of mice lacking specifically one gene encoding for a peroxisomal enzyme (knockout-mice) allows the reduction of the broad spectrum of pathologies observed in human patients, because these mice are genetically very similar and live under standardized housing conditions. Thereby, these mice can serve as valuable tools to confirm biochemical outcomes of enzyme inactivation, to attribute specific phenotypic aberrations to the absence of an individual enzyme, and to test the contribution of exogenously added compounds to the development of certain symptoms.