Renal Injury in Children with a Solitary Functioning Kidney

Abstract and Introduction

Abstract

Background. Children with a solitary functioning kidney (SFK) have an increased risk of developing hypertension, albuminuria and chronic kidney disease in later life. This renal injury is hypothesized to be caused by glomerular hyperfiltration that follows renal mass reduction in animal studies. Furthermore, children with an SFK show a high incidence of congenital anomalies of the kidney and urinary tract (CAKUT), which could further compromise renal function.
Methods. A retrospective study of renal injury markers was performed in 206 children, divided into groups based on the origin of SFK [primary (congenital) SFK (n = 116) and secondary SFK (n = 90)]. Data on ipsilateral CAKUT were stratified separately. For blood pressure, albuminuria and glomerular filtration rate, longitudinal models were additionally developed using generalized estimated equation analysis.
Results. Renal injury, defined as the presence of hypertension and/or albuminuria and/or the use of renoprotective medication, was present in 32% of all children with an SFK at a mean age of 9.5 (SD 5.6) years. Children with ipsilateral CAKUT had higher proportions of renal injury (48.3 versus 24.6%, P < 0.05). Furthermore, longitudinal models showed a decrease in glomerular filtration rate in both groups from the beginning of puberty onwards.
Conclusions. This large cohort study demonstrates that renal injury is present in children with an SFK at a young age, whereas our longitudinal models show an increased risk for chronic kidney disease in adulthood. Renal injury is even more pronounced in the presence of ipsilateral CAKUT. Therefore, we underline that clinical follow-up of all children with an SFK is needed.

Introduction

Children with a solitary functioning kidney (SFK) are at potential risk of developing hypertension, albuminuria and chronic kidney disease in later life.^[1–3] Several reports have studied the long-term outcome of children with an SFK;^[4–10] however, conclusions remain conflicting.^[11] The rationale behind these studies is the 'hyperfiltration hypothesis' described by Brenner et al. in the 1980s.^[12–14] In their groundbreaking studies using animal models, subtotal renal mass reduction resulted in hypertension, proteinuria and glomerulosclerosis due to glomerular hyperfiltration in remnant nephrons. Moreover, compensatory hypertrophy was found in the remnant kidney.^[15] All this sets a perpetuating cycle of nephron loss and, since new nephrons cannot be formed after birth, may result in chronic kidney disease. In human studies, the hyperfiltration hypothesis remains unproven, most probably due to the inability to measure single nephron glomerular filtration rate (GFR) and, more importantly, total nephron number in vivo. Nevertheless, a low nephron number is described in deceased patients with hypertension.^[16] By definition, an SFK from childhood onwards implies renal mass reduction for a longer period of time, suggesting that children with an SFK have an increased risk for developing hypertension, albuminuria and chronic kidney disease.

An SFK in childhood can be of either primary (congenital) origin (pSFK) or secondary after unilateral nephrectomy (sSFK) due to congenital anomalies of the kidney and urinary tract (CAKUT). Different anomalies underlie a pSFK. Unilateral renal agenesis (URA) involves the complete absence of developing renal tissue and a ureter in fetal life (estimated incidence 1: 500–1000 births^[17]). It is suggested that most cases diagnosed as 'URA' are actually cases of renal aplasia (i.e. abnormal renal elements that involute), which is not easily detectable on ultrasound.^[18] As these entities are not distinguishable in daily clinical practice, both agenesis and aplasia are referred to as URA. In a multicystic dysplastic kidney (MCDK), renal parenchyma shows dysplastic and cystic differentiation with a normally atretic ureter due to abnormal fetal renal development (incidence 1: 4300 births^[19]).

Unilateral nephrectomy is performed after severe loss of function due to recurrent urinary tract infection, which can occur with or without the presence of vesicoureteric reflux (VUR) or obstructive nephropathy. The latter mainly encompasses pelviureteric junction obstruction (PUJO), ureterovesical junction obstruction (UVJO) and posterior urethral valves (PUV) in boys. An sSFK can also be acquired after renal malignancy. This diagnosis often requires subsequent nephrotoxic chemotherapy.

Another factor that may contribute to the increased risk of chronic kidney disease in children with an SFK is the high incidence of associated anomalies in this population.^[20] CAKUT are the most important cause of chronic kidney disease in childhood^[21] and, due to the longer survival of these children, become increasingly important in adult life.^[22] A recent report on renal outcome in patients with CAKUT demonstrated that ~50% of children with a pSFK required dialysis at 30 years of age.^[23] In line with this, our research group showed that 50% of children with a pSFK showed signs of renal injury at the mean age of 8 years.^[24]

The KIMONO study (KIdney of MONofunctional Origin) is designed to study the development of renal injury in children with different origins of SFK. Therefore, we study the presence of hypertension, albuminuria and impaired GFR in a large cohort of children with either a pSFK or an sSFK. As the presence of ipsilateral CAKUT in an SFK may imply a more severe clinical course of renal injury, we stratified according to the presence of ipsilateral CAKUT. Finally, in order to study the clinical course of SFK and renal injury into adulthood, we developed a model for blood pressure, albuminuria and GFR related to age.

Nephrol Dial Transplant. 2011;26(5):1533-1541. © 2011 Oxford University Press

Cite this: Renal Injury in Children with a Solitary Functioning Kidney - Medscape - May 01, 2011.