A high rate (20%-30%) of parental consanguinity in cytochrome-oxidase deficiency.

By studying a large series of 157 patients, we found that complex I (33%), complex IV (28%), and complex I+IV (28%) deficiencies were the most common causes of respiratory chain (RC) defects in childhood. Truncal hypotonia (36%), antenatal (20%) and postnatal (31%) growth retardation, cardiomyopathy (24%), encephalopathy (20%), and liver failure (20%) were the main clinical features in our series. No correlation between the type of RC defect and the clinical presentation was noted, but complex I and complex I+IV deficiencies were significantly more frequent in cases of cardiomyopathy (P<.01) and hepatic failure (P<.05), respectively. The sex ratio (male/female) in our entire series was mostly balanced but was skewed toward males being affected with complex I deficiency (sex ratio R=1.68). Interestingly, a high rate of parental consanguinity was observed in complex IV (20%) and complex I+IV (28%) deficiencies. When parental consanguinity was related to geographic origin, an even higher rate of inbreeding was observed in North African families (76%, P<.01). This study gives strong support to the view that an autosomal recessive mode of inheritance is involved in most cases of mitochondrial disorders in childhood, a feature that is particularly relevant to genetic counseling for this devastating condition.