A girl with a mutation of the ciliary gene CC2D2A presenting with FSGS and nephronophthisis

Mutations in the ciliary gene TTC21B, NPHP4, and CRB2 cause familial focal and segmental glomerulosclerosis (FSGS). We report a girl with a mutation of the ciliary gene CC2D2A presenting with FSGS and nephronophthisis. The patient had mental retardation, postaxial polydactyly, and ataxic breathing, and was diagnosed as having compound heterozygous CC2D2A missense mutations at age 5. Retrospectively, azotemia at 1 year and proteinuria at 5 years were recorded but not investigated. At age 6, she was referred to the pediatric nephrology service because of hypertension, pretibial pitting edema, heavy proteinuria, and hematuria. eGFR was 66 ml/min/1.73 m², total protein 5.3 g/dl, albumin 2.4 g/dl, and cholesterol 317 mg/dl. Ultrasonography showed normal-sized kidneys with a cyst in the right. Losartan was started. On renal biopsy, 8 out of 24 glomeruli were globally sclerosed, and three showed segmental sclerosis and/or hyalinosis with no immune deposits. Mild tubular dilatation, tubular atrophy, and interstitial fibrosis were observed. On electron microscopy, glomeruli showed focal foot process effacement with no electron dense deposits. Since losartan did not exert an obvious effect, treatment with prednisolone was tried. Urine protein decreased from 6.6 to 3.7 g/gCr. Prednisolone was discontinued after 10 days, however, because she developed duodenal ulcer perforation that necessitated omentoplasty. Subsequently, she was treated with losartan only. Her renal function deteriorated and peritoneal dialysis was initiated 8 months later. FSGS in this patient could be primary glomerular associated with CC2D2A mutation, rather than the consequences of tubulointerstitial fibrosis.