Growth Retardation in the Course of Fanconi Syndrome Caused by the 4977-bp Mitochondrial DNA Deletion: A Case Report

Fanconi syndrome is one of the primary renal manifestations of mitochondrial cytopathies caused by mitochondrial DNA (mtDNA) mutation. The common 4977-bp mtDNA deletion has been reported to be associated with aging and diseases involving multiple extrarenal organs. Cases of Fanconi syndrome caused by the 4977-bp deletion were rarely reported previously. Here, we report a 6-year-old girl with growth retardation in the course of Fanconi syndrome. She had mild ptosis and pigmented retinopathy. Abnormal biochemical findings included low-molecular-weight proteinuria, normoglycemic glycosuria, increased urine phosphorus excretion, metabolic acidosis, and hypophosphatemia. Growth records showed that her body weight and height were normal in the first year and failed to thrive after the age of three. Using a highly sensitive mtDNA analysis methodology, she was identified to possess the common 4977-bp mtDNA deletion. The mutation rate was 84.7% in the urine exfoliated cells, 78.67% in the oral mucosal cells, and 23.99% in the blood sample. After three months of oral coenzyme Q10 and levocarnitine treatment in combination with standard electrolyte supplement, her condition was improved. This is a report of growth retardation as the initial major clinical presentation of Fanconi syndrome caused by the deletion of the 4977-bp fragment. Renal tubular abnormality without any other extrarenal dysfunction may be an initial clinical sign of mitochondrial disorders. Moreover, considering the heterogeneity of the phenotypes associated with mtDNA mutations, the risk of developing Kearns–Sayre syndrome (KSS) with age in this patient should be noted because she had ptosis, retinal involvement, and changes in the brain and skeletal muscle.