A Boy with Steroid-Resistant Nephrotic Syndrome and Cortical Blindness

Introduction: Renal involvement in primary mitochondrial disorders may be a dominant or non-dominant feature. Primary mitochondrial disorders should be considered in the etiology of steroid-resistant nephrotic syndrome due to focal segmental glomerulosclerosis. The aim of this study is to describe the prominent extra-neurologic phenotype including steroid-resistant nephrotic syndrome associated with focal segmental glomerulosclerosis characterized by abnormal mitochondria in podocytes, cortical blindness and pancreatitis in a Chinese boy with primary mitochondrial disease. Case Description: A 5-year-old previously healthy Han ethnicity boy experienced loss of vision after fever and proteinuria 3.5 months before admission to our hospital. Proteinuria did not improve after 5 weeks of prednisolone at 10 mg thrice daily (2mg/kg/d). His personal history indicated he was very prone to fatigue and motor coordination was not good. His past medical history was negative for systemic illness, rash or joint pain. Family history was not remarkable for renal disease. Physical examination showed edema in face and both legs, and less muscle volume of lower extremities. Laboratory findings revealed hypoalbuminaemia (24 g/L), significant proteinuria (2.98 g/24h), normal renal function, and increased level of serum lactate (three times). The serum level of C3 and C4 was normal. The anti-nuclear antibody, anti-DNA antibody, anti-neutrophil cytoplasm antibodies, and anti-hepatitis B virus were all negative. Brain MRI (three times) indicated bilateral parietal occipital lesions and cerebellar atrophy. Visual evoked potentials were absent bilaterally. Renal biopsy revealed focal segmental glomerulosclerosis (collapsing variant). Electron microscope examination revealed mitochondrial abnormality in the renal tissue. Mitochondrial DNA (mtDNA) screening using peripheral blood and urine specimens for common point mutations was negative. Four and a half months after the onset of disease, he was diagnosed with acute pancreatitis with acute peritonitis. Discussion: The multi-organ impairments of our young patient associated with elevated serum lactate levels and prominent abnormal mitochondria in the podocytes indicated a mitochondrial disease. Screening for the blood lactate level should be included in initial workup for clinically presumed unknown causes of proteinuria or nephrotic syndrome.