[Diagnostic strategy for mitochondrial diseases].

OBJECTIVE

The variability of both phenotypic and genotypic expression in mitochondrial diseases makes clinical diagnosis difficult, which is essential to establish therapy, aid in genetic counselling or for performing prenatal diagnosis. We have therefore proposed a strategy to help determine correct diagnosis of these alterations, in an attempt to rationalize the number of tests and, whenever possible, avoid tissue biopsy and minimize the size of the biopsy when indicated.

DEVELOPMENT

Based on mitochondrial metabolism and molecular bases, as well as their alterations, a preliminary metabolic examination is carried out including at least one study of cytoplasmatic (lactate/pyruvate) and mitochondrial oxide reduction (hydroxibutirate/acetoacetate) in basal conditions or, if required, following glucose overload or an effort test. Metabolic study, in addition to clinical exploration, are the screening tests used to determine the need for tissue biopsy in which biochemical (pyruvate dehydrogenase, free and total carnitine, beta oxidation enzymes and respiratory chain complexes), genetic (mitochondrial DNA or nuclear alterations) and histologic tests are carried out to confirm diagnosis.

CONCLUSIONS

a) Metabolic exploration may discard mitochondrial disease and many cases, avoid the use of an invasive procedure such as tissue biopsy. b) Biochemical study of tissue biopsy is the only useful key in the confirming of the diagnosis when no mitochondrial and/or nuclear DNA are observed.