Nephropathic Infantile Cystinosis in an 8-year-old Girl

Abstract

Nephropathic infantile cystinosis is a rare congenital metabolic disorder with an autosomal recessive penetrance in the family, which causes the accumulation of cystine in the lysosomes of different organs of the body. The nephropathic infantile type presents in early infancy in the form of proximal renal tubular acidosis and carries a poor prognosis including renal failure requiring renal replacement therapy and blindness if left untreated. Here we report a case of nephropathic cystinosis in an 8-year-old girl who presented in her early infancy at 8 months of age and was diagnosed as distal renal tubular acidosis and started on alkali therapy. Her symptoms initially improved but she had delayed milestones of motor development, persistent polyuria, and weakness. At the presentation of 8 years, she was found to have features of rickets in both upper and lower limb and hypertensive. Her blood reports revealed a nonanion gap metabolic acidosis with hypokalemia and hypophosphatemia. She also had proteinuria and glycosuria but no hypercalciuria. Considering her clinical and biochemical features, she was sent for eye evaluation, which revealed the presence of cystine crystal in the conjunctiva, stroma of the cornea, and peripheral retina. Clinical diagnosis of cystinosis is often challenging as some cases may mimic features of distal renal tubular acidosis, so careful evaluation is necessary. Parents were counseled about the disease and genetic test and her treatment was continued with phosphate supplement along with alkali supplements. Though the genetic test is confirmatory for diagnosing nephropathic cystinosis, a complete initial evaluation including blood, urine analysis, and an ophthalmological evaluation can guide us toward early diagnosis and management.