Abstract
Background and Aims
2, 8 dihydroxyadenine (DHA) deposition is a less known etiology of crystal-induced nephropathy, caused by a deficiency in a purine salvage enzyme, the adenine phosphoribosyl transferase (APRT). DHA is an insoluble molecule in urine leading to crystal formation, tubular obstruction or stone formation. The disease manifests as a history of urolithiasis, chronic kidney disease and even loss of renal allograft when the disease is undiagnosed in native kidneys. The cornerstone of treatment is the inhibition of xanthine dehydrogenase reducing thus the formation of 2,8-DHA and its renal excretion.
Method
A 59-year-old obese Lebanese male patient, born to a consanguineously married couple, was admitted to another hospital with desaturation, a history of progressive shortness of breath and a creatinine level of 2,8 mg/dl. He had no hypertension nor diabetes. His family history was positive for a sister with ESRD of unknown etiology. He was discharged on oxygen and continuous airway positive pressure therapy for severe obstructive sleep apnea. His renal function deteriorated leading to a creatinine level of 9.8 mg/dl three months later. There were no signs of systemic disease, no gross hematuria, no fluid overload. His blood pressure was normal. Laboratory work up showed anemia, low grade proteinuria, intermittent microscopic hematuria and negative serological and immunological workup. Kidney ultrasound showed normal size kidneys with no evidence of collecting system dilatation or urolithiasis. Due to this atypical presentation, the patient was admitted for a renal biopsy with a creatinine level of 11 mg/dl upon admission.
Results
The renal biopsy showed tubulo-interstitial nephritis associated with numerous brown-green crystals by Haematoxylin and eosin of various shapes birefringent under polarized light with the characteristic “maltese cross”. Crystals were found within tubular lumens and cytoplasm, interstitium, and macrophages. These findings were characteristic of 2,8 DHA crystals deposition in the kidney. The patient was started on 120 mg of Febuxostat with a low purine and high fluid diet. A genetic testing showed a pathogenic homozygous variant in the APRT gene which causes an amino acid change from Glycine to Aspartate at position 63. Two weeks later the patient was admitted to the ICU with pneumonia, respiratory failure, a creatinine of 9 mg/dl and severe metabolic encephalopathy. He received 4 sessions of hemodialysis followed by an improvement in his kidney function with a creatinine level down to 3.2 mg/dl a month after his discharge and he remains off dialysis until now.
Conclusion
Around 400 cases are currently recognized worldwide, emphasizing the under recognition of this autosomal recessive disease. Considering that the homozygoty causing a complete APRT deficiency should range between 1/50 000 and 1/100 000 cases, this would translate in at least 80 000 cases worldwide. The variant found in our patient has previously been described as disease causing for APRT deficiency in four cases. Reviewing the phenotype of these cases we find differences in terms of presentation and evolution, highlighting the variability in the APRT deficiency phenotype and underlining the fact that no correlation between phenotype and genotype was reported to date even for the same type of mutation. This case report shows us that the initiation of an adequate therapy is necessary even at advanced stages of the disease since it can improve our kidney outcome.
Clinical application of the 2011 IFCPC colposcope terminology
