Letter to the Editor

Potential usefulness of coenzyme Q10 in the treatment of idiopathic dilated cardiomyopathy in children

Plasma coenzyme Q10 (CoQ10) response to oral ingestion of various CoQ10 formulations was examined. Both total plasma CoQ10 and net increase over baseline CoQ10 concentrations show a gradual increase with increasing doses of CoQ10. Plasma CoQ10 concentrations plateau at a dose of 2400 mg using one specific chewable tablet formulation. The efficiency of absorption decreases as the dose increases. About 95% of circulating CoQ10 occurs as ubiquinol, with no appreciable change in the ratio following CoQ10 ingestion. Higher plasma CoQ10 concentrations are necessary to facilitate uptake by peripheral tissues and also the brain. Solubilized formulations of CoQ10 (both ubiquinone and ubiquinol) have superior bioavailability as evidenced by their enhanced plasma CoQ10 responses.

Controlled studies of coenzyme Q₁₀ dosing and tolerance have been reported in adults, but not in pediatric patients. This study compares low- and high-dose coenzyme Q₁₀ (LiQ-NOL syrup) absorption and tolerance in children with Down syndrome. After a 1-month low-dose (1.0 mg/kg/day) run-in period, all participants received high-dose coenzyme Q₁₀ (10.0 mg/kg/day) for two additional months (in randomized sequence as one daily dose or split into two daily doses). Chemistry profiles and complete blood counts were determined just before and at the study completion. Plasma coenzyme Q₁₀ concentrations were determined initially and at each study visit. Parents reported adverse events and study drug evaluations using standardized forms. Most of the 16 children who completed this study tolerated high-dose coenzyme Q₁₀ well. Uncooperative behavior resulted in premature withdrawal of two participants, and may have been treatment-related. Pre- and posttreatment laboratory test changes were considered to be clinically nonsignificant. Study results indicate that high-dose coenzyme Q₁₀ (10 mg/kg/day) is well-absorbed and well-tolerated by most children with Down syndrome, and appears to provide plasma concentrations which are comparable to previous adult studies administering much higher coenzyme Q₁₀ dosages.

The prognosis of patients with idiopathic dilated cardiomyopathy (DCM) is poor. Most patients die while waiting for cardiac transplantation because of the small number of donors in Taiwan. The purpose of this study was to review our experience with pediatric patients diagnosed with idiopathic DCM and attempt to discover prognostic factors.

Eighteen patients with idiopathic DCM presenting between 1990 and 2004 were identified. They were classified into 2 groups according to outcome: group 1 comprised 13 patients who died; group 2 comprised 5 who survived. Clinical findings and laboratory investigations were compared between the 2 groups.

The age at initial diagnosis for the 18 patients (11 males, 7 females) ranged from fetus to 13 years (median, 3 months). The follow-up period ranged from 12 days to 44 months (median, 7 months) in group 1, and from 1 to 48 months (median, 39 months) in group 2. Of the 18 patients, 13 (72%) died: 11 died from severe heart failure while waiting for cardiac transplantation. The cumulative survival rate was 50% at 1 year and 28% at 4 years. The presence of arrhythmia and low left ventricular ejection fraction were predictive of a poor outcome.

The diagnosis of idiopathic DCM in children is associated with a generally poor prognosis. The lack of available donors results in significant mortality for pediatric patients awaiting transplantation. Advocating organ donation to increase the size of the organ donor pool is needed to significantly reduce the mortality rate in such patients.

Pediatric cardiomyopathy (PCM) represents a group of rare and heterogeneous disorders that often results in death. While there is a large body of literature on adult cardiomyopathy, all of the information is not necessarily relevant to children with PCM. About 40% of children who present with symptomatic cardiomyopathy are reported to receive a heart transplant or die within the first two years of life. In spite of some of the advances in the management of PCM, the data shows that the time to transplantation or death has not improved during the past 35 years.

Coenzyme Q10 is a vitamin-like nutrient that has a fundamental role in mitochondrial function, especially as it relates to the production of energy (ATP) and also as an antioxidant. Based upon the biochemical rationale and a large body of data on patients with adult cardiomyopathy, heart failure, and mitochondrial diseases with heart involvement, a role for coenzyme Q10 therapy in PCM patients is indicated, and preliminary results are promising. Additional studies on the potential usefulness of coenzyme Q10 supplementation as an adjunct to conventional therapy in PCM, particularly in children with dilated cardiomyopathy, are therefore warranted.