European Journal of Human Genetics (2009) 17, 406–416 & 2009 Macmillan Publishers Limited All rights reserved 1018-4813/09 $32.00 www.nature.com/ejhg PRACTICAL GENETICS In association with Nephronophthisis Nephronophthisis (NPHP) is an autosomal recessive kidney disorder characterized by chronic tubulointerstitial nephritis and leading to end-stage renal failure. NPHP as a renal entity is often part of a multisystem disorder and has been associated with many syndromes including Joubert syndrome (and related disorders) and Senior–Loken syndrome. Recent molecular genetic advances have allowed identification of several genes underlying NPHP. Most of these genes express their protein products, named nephrocystins, in primary cilial/basal body structures. Some nephrocystins are part of adherens junction and focal adhesion kinase protein complexes. This shared localization suggests that common pathogenic mechanisms within the kidney underlie this disease. Functional studies implicate nephrocystins in planar cell polarity pathways, which may be crucial for renal development and maintenance of tubular architecture. In brief End-stage renal failure (ESRF) typically occurs during early teenage years, with the exception of the rare Nephronophthisis (NPHP) is an autosomal recessive infantile forms, where there is ESRF before 5 years of kidney disease leading to end-stage renal failure in age. children and young adults. Molecular genetics now may allow easy detection of Key histological findings in the kidney are tubulointer- the most common mutations (involving NPHP1 and stitial fibrosis, tubular dilatation and cyst formation and accounting for 25% of all cases). tubular atrophy. NPHP is a ‘ciliopathy’ as evidence to date implicates the NPHP is often a feature of a multisystem disease that may primary renal cilium and basal body apparatus in the include retinal dystrophy (Senior–Loken Syndrome) and pathogenesis of NPHP. cerebello-ocular-renal syndromes (Joubert syndrome Patients need regular monitoring of renal and liver and related diseases (JSRD)). function, eye examinations and preparation for renal NPHP may present with an early decrease in urinary transplantation, which is the treatment of choice for concentration the renal failure that invariably ensues. Introduction failure, usually within the first 3 decades of life.1 Nephro- Nephronophthisis (NPHP) is an autosomal recessively nophthisis literally means ‘disappearance of nephrons’. inherited renal disorder, which leads to progressive renal Typical ultrasound features include normal or reduced renal size, loss of corticomedullary differentiation and 1,2 1 ,1,2 Roslyn J Simms , Lorraine Eley and John A Sayer* corticomedullary cysts (Figure 1). Renal biopsy findings 1Institute of Human Genetics, International Centre for Life, Newcastle include tubular atrophy, interstitial fibrosis and tubular University, Central Parkway, Newcastle upon Tyne, UK; 2Renal Services, basement membrane defects, including abrupt transition The Freeman Hospital, Newcastle Hospitals NHS Foundation Trust, between thickening and attenuation or disintegration.2,3 Newcastle upon Tyne, UK A rare form of NPHP may lead to end-stage renal failure European Journal of Human Genetics (2009) 17, 406–416; doi:10.1038/ (ESRF) within 5 years of age and is termed infantile NPHP.4 ejhg.2008.238; published online 10 December 2008 This differs from typical NPHP in that there is moderate Keywords: primary cilia; collecting duct; planar-cell polarity; urine renal enlargement, histological changes that include concentrating defect; tubulointerstitial nephritis cortical microcysts, cystic dilatation of Bowman’s spaces *Correspondence: Dr JA Sayer, Institute of Human Genetics, International and lack of tubular basement membrane disruption. Centre for Life, Newcastle University, Central Parkway, Newcastle upon Tyne NE1 3BZ, UK. Tel þ 44 191 2418608; Fax þ 44 191 2418666; NPHP is often part of a spectrum of multisystem disease E-mail: [email protected] and may not be detected unless appropriate investigations Received 23 July 2008; revised 4 November 2008; accepted 13 November on relevant systems are performed. These disease associa- 2008; published online 10 December 2008 tions form a very heterogeneous group (Table 1). The most Nephronophthisis RJ Simms et al 407 Table 1 Syndromes which may exhibit nephronophthisis or are associated with mutations in NPHP genes Syndrome Key features Joubert syndrome and Cerebellar vermis aplasia/ related disorders hypoplasia Cogan syndrome Oculomotor apraxia Senior–Loken syndrome Retinitis pigmentosa Meckel–Gruber syndrome Occipital meningoencephalocoele, cystic kidneys and postaxial polydactyly RHYNS syndrome Retinitis pigmentosa, hypopituitarism, nephronophthisis, skeletal dysplasia Boichis syndrome Liver fibrosis, biliary duct proliferation Mainzer–Saldino syndrome Cone-shaped epiphyses Figure 1 Ultrasound scan features of nephronophthisis. Renal or conorenal syndrome ultrasound scan demonstrating corticomedullary cysts, some of which Jeune syndrome or Short ribs are arrowed. asphyxiating thoracic dystrophy syndrome Sensenbrenner syndrome or Skeletal dysplasia cranioectodermal dysplasia commonly associated syndrome is retinal dystrophy and Ellis van Creveld Ectodermal dysplasia retinal degeneration leading to blindness (Senior–Loken Alstrom Retinal dystrophy, hearing syndrome).1 Other associations include Joubert syndrome impairment, obesity, type 2 5 diabetes mellitus and related diseases (JSRD, reviewed in reference ), which Arima syndrome Cerebro-oculo-hepato-renal often involves a cerebellar, retinal and renal phenotype syndrome referred to as CORS (cerebello-oculo-renal syndrome). Apart from these, a whole variety of syndromes have been reported in association with NPHP (Table 1). 4. Renal biopsy – interstitial fibrosis, tubular atrophy, NPHP has been reported worldwide, yet the incidence absence of tubular basement membrane irregularity, varies. A Canadian study reported an incidence of 1 in renal cortical microcysts 50 000 live births,6 whereas the incidence in the United 5. Associated extrarenal features peculiar to infantile NPHP States of America was estimated to be 9 per 8.3 million.7 A include hypertension, situs inversus, ventricular septal more recent European study reported an incidence of defect. NPHP as 1 in 61 800 live births.8 However, as NPHP may 9 present in adults with late enuresis and renal failure, these NPHP figures may be an underestimate. 1. Median onset of ESRF 12 years (may be beyond 25 years)9 2. Polyuria and polydipsia (and salt wasting) in early childhood (4–6 years of age) Clinical overview 3. Urinary concentration defect (o400 mosm/kg in early Core diagnostic criteria morning urine) that is not responsive to desmopressin NPHP is genetically and clinically heterogeneous. Tradi- 4. Growth retardation (secondary to salt wasting, dehydra- tionally, NPHP has been subdivided into infantile, juvenile tion and renal insufficiency) and adolescent forms, based on the age of onset of renal 5. Absence of (or minimal) haematuria and proteinuria failure. It remains useful to distinguish the much rarer 6. Renal USS – renal cortical hyperechogenicity, loss of infantile NPHP from the more typical (non-infantile) forms corticomedullary differentiation, corticomedullary of NPHP, to allow a targeted approach to diagnosis and cysts11 molecular testing (Figure 2). 7. Renal biopsy – microscopy typically shows interstitial nephritis, tubular atrophy and tubular dilatations. Infantile NPHP Typically there is both thickening and attenuation of 1. Early onset ESRF (less than 5 years of age) the tubular basement membranes. 2. Possible antenatal presentation with fetal oliguria and 8. The clinical diagnosis of NPHP may be made (or looked oligohydramnios10 for) following detection of an associated extrarenal 3. Renal USS – normal sized or enlarged kidneys disorder (see below and Table 2). European Journal of Human Genetics Nephronophthisis RJ Simms et al 408 Figure 2 Diagnostic algorithm for NPHP. Where there is clinical or radiological suspicion of NPHP, the NPHP1 gene should be screened first if onset of end-stage renal failure is greater than 5 years of age. NPHP1 mutations account for B25% of cases of NPHP. Infantile NPHP is rare (o1% of cases) but should be suspected, and the known genes screened, if there are clinical and radiological features suggestive of NPHP and age of end-stage renal failure is less than 5 years of age. If no mutations are found additional NPHP genes should be screened depending on phenotype and a differential diagnosis of MCKD, ARPKD and BBS should be considered. Nephronophthisis and disease associations forms present initially with night blindness, which pro- Many disorders have been described in which NPHP is a gresses to visual loss by the age of 10 years. Diagnosis is clinical feature. Such multisystem features and pleiotropy made by performing an electroretinogram, which may are typical of ‘ciliopathies’ such as NPHP. Extrarenal show abnormalities before the physical signs of retinitis manifestations are seen in 10–20% of cases of NPHP.12 pigmentosa and visual loss. Molecular mechanisms of blindness are secondary to photoreceptor cell defects Senior–Loken syndrome (reviewed in reference13). Here retinal dysplasia and degeneration (also known as tapetoretinal degeneration or retinitis pigmentosa) may Joubert syndrome and related disorders lead to early and severe visual loss (within 2 years of age), Joubert syndrome and related disorders