Respiratory chain defects may present only with hypoglycemia.

Area of Science:

• Biochemistry
• Pediatric Endocrinology
• Genetics

Background:

• Hypoglycemia can stem from oxidative phosphorylation deficiency, often linked to liver failure.
• However, impaired glucose metabolism in respiratory chain defects can occur with normal liver function, a mechanism poorly understood.

Observation:

• Three unrelated children presented with hypoglycemia as the primary symptom of oxidative phosphorylation deficiency, notably without liver dysfunction.
• Specific complex deficiencies (III and IV) were identified, manifesting as prolonged fasting hypoglycemia.
• Metabolic investigations revealed impaired gluconeogenesis and fatty acid oxidation in two patients, while the third showed complex IV deficiency with potential growth hormone insufficiency and impaired glycogen metabolism.

Findings:

• Oxidative phosphorylation deficiency, specifically complex III and IV defects, can cause hypoglycemia in children independent of liver failure.
• Impaired gluconeogenesis, fatty acid oxidation, and glycogen metabolism are key metabolic disturbances observed.
• Growth hormone insufficiency may also contribute to hypoglycemia in certain complex deficiencies.

Implications:

• Respiratory chain defects should be considered in the differential diagnosis of unexplained hypoglycemia in children.
• Reduced cofactors resulting from oxidative phosphorylation deficiency may underlie hypoglycemia.
• This highlights the critical role of mitochondrial function in maintaining glucose homeostasis.