Nephronophthisis in two siblings

Orphan kidney diseases

Rare kidney diseases are a unique subset of renal disorders that are often termed 'orphan' as a result of a multitude of reasons: the small number of patients with the consequent lack of well-defined natural history and course of many of these diseases, limited awareness among the medical community, and finally the significant cost of developing novel therapeutics which makes many of these diseases unattractive targets for the pharmaceutical industry. Nevertheless, in the last decade the study and clinical management of rare kidney disease patients has been the focus of many investigative efforts. In recent years we have witnessed an enormous expansion in our knowledge of the genetic nature of a number of rare kidney diseases. Moreover, the investigation of the role of genetic disruption aiming at elucidating the pathogenesis of different and complex renal diseases has helped not only in understanding the disease states, but has also given us fundamental insights into a number of kidney developmental and physiological functions. This article will give an overview of orphan renal diseases with particular emphasis on monogenic kidney diseases. It will also focus on the classification of these diseases while highlighting a prominent example in each category.

Urinary concentration defects and mechanisms underlying nephronophthisis

The cystic kidney disease nephronophthisis (NPHP) is the commonest genetic cause of end-stage renal failure in young people and children. Histologically the disease is characterized by interstitial fibrosis, tubular atrophy with corticomedullary cyst development and disruption of the tubular basement membrane. Affected children present with polydipsia and polyuria, secondary to a urinary concentration defect, before these structural changes develop. Recently, molecular genetic advances have identified several genes mutated in NPHP, providing novel insights into its pathophysiology for the first time in decades. Here we review the normal physiological mechanisms of urinary concentration and explain, in the context of recent discoveries, the possible mechanisms underlying urinary concentration defects in patients with NPHP. The pattern of a ciliary and adherens junction subcellular localization of nephrocystin proteins is discussed. Recent animal models of cystic kidney disease and treatment with vasopressin V2 receptor antagonists are reviewed and a hypothesis regarding urinary concentration defects in NPHP is proposed. Understanding the cellular mechanisms underlying NPHP and other cystic kidney diseases will provide the rationale for therapeutic interventions in this disease. Early urinary concentration defects provide both a clue to clinical diagnosis of NPHP and potential therapeutic targets for pharmacological treatment of this condition.