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We report the case of an 8-year-old girl diagnosed with atypical hemolytic uremic syndrome (aHUS) with a complement factor B (CFB) gene mutation. aHUS is a disease of complement dysregulation. In approximately 50% of patients, mutations are identified in genes encoding regulators of complement-complement factor H (CFH), membrane cofactor protein or complement factor I (CFI)-or activators of complement-complement factor B (CFB) or C3. The mutation in this patient was identified in exon 12 of CFB and changes a lysine at amino acid position 533 to an arginine (c.1598A>G p.Lys533Arg). The two other mutations previously reported in CFB associated with aHUS are c.858C>G, p.F286L in exon 6 and c.967A>Gp.K323E in exon 7.

The differential diagnosis of macroscopic hematuria in patients with sickle cell disease (hgb SS), and more rarely in sickle cell trait (hgb AS), includes papillary necrosis, renal infarction, membranoproliferative glomerulonephritis associated with the hepatitis C virus, interstitial nephritis due to analgesic abuse, pyelonephritis, nephrolithiasis and, very rarely, a renal malignancy, such as renal medullary carcinoma. Acute papillary necrosis is often suspected and is frequently the cause, but further studies are mandatory if the hematuria persists. In this case, the renal ultrasound (Fig. 1) demonstrated an echogenic mass in the upper pole of the left kidney. The computed tomography (CT) scan with intravenous contrast (Fig. 2) revealed a heterogeneous mass in the same location. A tissue diagnosis was required to confirm the diagnosis, and the patient underwent unilateral nephrectomy. Figure 3 shows the gross pathology of the tumor found in the upper pole of the left kidney. The pathologic diagnosis was renal cell carcinoma, papillary cell type, collecting-duct sub-type. Figure 4 shows the microscopic pathology. Our patient had no evidence of metastases and appears to be completely well after 6 months of follow-up.

An 11-year-old African American boy with sickle cell trait (hemoglobin AS) was admitted for evaluation of intermittent painless gross hematuria for 3 months. Initially, the hematuria occurred once every 2 weeks, but it had increased in frequency to two to three times per week. He denied colicky abdominal pain, urinary frequency, or urgency. There was no history of recent trauma. He had never had a urinary tract infection. He was taking no medications and had no recent history of exposure to high altitude. The family history and his review of systems were otherwise unremarkable. Physical examination revealed: weight, 60 kg (>97%); height, 155 cm (95%); temperature, 98°F; heart rate, 87/min; respirations, 18/min; blood pressure, 116/68 mmHg. In general, the patient appeared healthy and not in acute distress. He had no pallor. The abdomen was soft, with mild tenderness in the right upper quadrant. The remainder of the examination was normal. Admission laboratory testing revealed: white blood cell count, 6760/mm; hemoglobin, 12.3 g/dL; hematocrit, 37.7%; mean corpuscular volume, 73.9 fL; platelet count, 390,000/ mm; sodium, 135 mmol/L; potassium, 4.2 mmol/L; chloride, 105 mmol/L; bicarbonate, 21 mmol/L; blood urinary nitrogen, 10 mg/dL; creatinine, 0.54 mg/dL; glucose 107 mg/dL; calcium, 9.5mg/dL; total protein, 7.1 g/dL; albumin, 4.4 g/dL; uric acid, 4 mg/dL; Creactive protein, 1.4 mg/dL (normal); C3 complement, 78 mg/dL (normal); ratio of urinary calcium to creatinine, 0.05 (normal