Nephronophthisis 1

A number sign (#) is used with this entry because nephronophthisis-1 (NPHP1) is caused by homozygous or compound heterozygous mutation in or deletion of the gene encoding nephrocystin (607100) on chromosome 2q13.

Description

Nephronophthisis is an autosomal recessive cystic kidney disease that leads to renal failure in childhood or adolescence. It is the most frequent genetic cause of renal failure in children. NPHP may be combined with extrarenal manifestations, such as liver fibrosis, situs inversus, or cardiac malformations. When nephronophthisis is combined with retinitis pigmentosa, the disorder is known as Senior-Loken syndrome (SLSN1; 266900); when it is combined with cerebellar vermis hypoplasia, the disorder is known as Joubert syndrome (JBTS1; 213300); and when it is combined with multiple developmental and neurologic abnormalities, the disorder is often known as Meckel-Gruber syndrome (MKS1; 249000). Because most NPHP gene products localize to the cilium or its associated structures, nephronophthisis and the related syndromes have been termed 'ciliopathies' (summary by Hoff et al., 2013).

Clinical features of familial juvenile nephronophthisis include anemia, polyuria, polydipsia, isosthenuria, and death in uremia. Simms et al. (2009) provided a detailed review of nephronophthisis, including a discussion of clinical features and molecular genetics.

Genetic Heterogeneity of Nephronophthisis

NPHP2 (602088) is caused by mutation in the INVS gene (243305) on chromosome 9q31; NPHP3 (604387) is caused by mutation in the NPHP3 gene (608002) on chromosome 3q22; NPHP4 (606966) is caused by mutation in the NPHP4 gene (607215) on chromosome 1p36; NPHP7 (611498) is caused by mutation in the GLIS2 gene (608539) on chromosome 16p13; NPHP9 (613824) is caused by mutation in the NEK8 gene (609799) on chromosome 17q11; NPHP11 (613550) is caused by mutation in the TMEM67 gene (609884) on chromosome 8q22; NPHP12 (613820) is caused by mutation in the TTC21B gene (612014) on chromosome 2q24; NPHP13 (614377) is caused by mutation in the WDR19 gene (608151) on chromosome 4p14; NPHP14 (614844) is caused by mutation in the ZNF423 gene (604557) on chromosome 16; NPHP15 (614845) is caused by mutation in the CEP164 gene (614848) on chromosome 11q; NPHP16 (615382) is caused by mutation in the ANKS6 gene (615370) on chromosome 9q22; NPHP18 (615862) is caused by mutation in the CEP83 gene (615847) on chromosome 12q22; NPHP19 (616217) is caused by mutation in the DCDC2 gene (605755) on chromosome 6p22; and NPHP20 (617271) is caused by mutation in the MAPKBP1 gene (616786) on chromosome 15q13.

Nomenclature

The disorder symbol NPHP1 was suggested to distinguish this locus from NPHL1 (nephrolithiasis, X-linked; 310468) and NPHS1 (congenital nephrosis, Finnish type; 256300) (Hildebrandt, 1997).

Clinical Features

Like several other mendelizing disorders, this one was first described by Fanconi et al. (1951). In the various reports, anemia, polyuria, polydipsia, isosthenuria, and death in uremia have been features. Hypertension and proteinuria are conspicuous in their absence. Symmetrical destruction of the kidneys involving both tubules and glomeruli (which were hyalinized) are observed. The age at death ranges from about 4 to 15 years.

Mangos et al. (1964) thought decreased urine concentrating ability might be a manifestation of heterozygotes. Herdman et al. (1967) described medullary cystic disease in 7- and 5-year-old sibs and in a 7-year-old boy whose sister had died of the disease. They were impressed with the probable identity of medullary cystic disease and familial nephronophthisis. Mongeau and Worthen (1967) came to the same conclusion, as did Strauss and Sommers (1967) who with humor commented that those who gave the name of medullary cysts of the kidney focused 'attention on the hole as the characteristic feature of the doughnut rather than on the kind of dough enclosing the hole.' Even though one form of medullary cystic disease may be the same as juvenile nephronophthisis, it is clear that a separate form of polycystic kidney, medullary type (174000), inherited as a dominant, also exists. The sibship reported by Meier and Hess (1965) had first-cousin parents and apparently independent inheritance of 2 recessive disorders, retinitis pigmentosa and nephronophthisis. (More likely this was the syndrome described in entry 266900.)

Sworn and Eisinger (1972) reported 3 affected sibs in one of whom there was biopsy demonstration of medullary cystic disease whereas in another, nephronophthisis was found at autopsy. They suggested that the morphologic findings in the kidney may be a function of age, i.e., that longer-surviving patients are more likely to show the changes of medullary cystic disease. This is the second most common cause of childhood chronic renal failure. Excessive urinary loss of sodium accounts for the rarity of hypertension. Excessive urinary loss of potassium is thought to be the 'cause' of the cystic change.

Boichis et al. (1973) described an association of nephronophthisis and congenital hepatic fibrosis in sibs. Five had demonstrated renal disease. Two died of renal failure at ages 7 and 15. A third was maintained on hemodialysis. The nosologic relation to the usual nephronophthisis on the one hand and polycystic renal disease on the other is unclear. It may be a distinct entity. Steele et al. (1980) reviewed 21 patients. In 10, there was a 'familial incidence,' consistent with autosomal recessive inheritance for the series as a whole. In 7 patients an associated and characteristic retinal degeneration dated from infancy. Renal cysts were uncommon. The authors listed 12 other designations that have been used.

In the retinal dysplasia of nephronophthisis, the classic paravenous 'bone spicule' pigmentation of retinitis pigmentosa is not seen. Pale optic nerve head and attenuated blood vessels are seen, as in other forms of chorioretinal degeneration. Cohen and Hoyer (1986) studied renal tissues from 4 patients with nephronophthisis, using immunofluorescence with antibodies to laminin, type IV collagen, and tubular basement membranes. They found constant morphologic changes affecting tubular basement membranes of all segments of the nephron, with or without cysts. These included extreme thinning and attenuation, layering, and thickening. Laminin and type IV collagen were present in normal intensity and distribution. Cohen and Hoyer (1986) compared the changes in the tubular basement membrane to the changes that occur in glomerular basement membrane in the Alport syndrome (301050). Khoury et al. (1988) described a family in which 3 of 4 sibs with congenital absence of permanent teeth (206780) were shown to have familial medullary sponge kidney; the fourth refused to be examined. Phenotypically, the autosomal dominant type of medullary cystic disease was suggested.

Hallmarks of familial nephronophthisis are tubular basement membrane disruption, interstitial lymphohistiocytic cell infiltration, and development of cysts at the corticomedullary border of the kidneys (Waldherr et al., 1982). The histology in later stages of NPH always merges into a chronic sclerosing tubulointerstitial nephropathy, which is found in chronic renal failure of all origins.

Ala-Mello et al. (1999) reviewed the clinical features of 59 nephronophthisis patients identified by a nationwide survey in Finland. The incidence was 1:61,800 live births over a 20-year period. Seventeen patients came from 4 families showing dominant inheritance and 37 from 28 apparently recessive families. Two patients were considered to have new dominant mutations; 3 sporadic patients could not be classified. About two-thirds of the recessive patients were found to be homozygous for a deletion at 2q13. The most significant difference between recessive patients with deletions, recessive patients without deletions, and dominant patients was the age at onset of disease, at the start of dialysis, and at renal transplantation, which showed a significant increase from one group to the next. These findings will help to determine the mode of inheritance in a sporadic patient without a deletion as well as the prognosis.

Inheritance

Autosomal recessive inheritance has been observed. Von Sydow and Ranstrom (1962) observed parental consanguinity.

Chamberlin et al. (1977) arrived at the following conclusion concerning the relation of juvenile nephronophthisis and medullary cystic disease: 'These diseases...very likely are a single disease entity and occur as a juvenile-onset, autosomal recessive form and as an adult-onset, autosomal dominant form.' There is an inconsistency in this sentence. In the strict genetic sense the disorders are unlikely to be the same entity if they have different modes of autosomal inheritance. There are rather abundant examples of disorders that are caused by different mutations in the same gene, some with a dominant-negative effect resulting in dominant inheritance, others with recessive inheritance due to inactivation of both alleles of the gene; see Table 15 in McKusick (1998). Actually, despite the similarity in phenotype (except for age of onset), distinctness of the autosomal recessive familial juvenile nephronophthisis and the autosomal dominant medullary cystic kidney disease (autosomal dominant nephronophthisis) is indicated by the fact that the disorders map to different chromosomal sites, 2q13 and 1q21, respectively (see later).

Mapping

By family linkage studies in 22 multiplex families (18 without and 4 with ocular abnormalities), Antignac et al. (1993) localized the mutant gene for this disorder to chromosome 2p in a region between D2S48 and D2S51. The microsatellite marker at the D2S160 locus gave a lod score of 4.78 at theta = 0.05 in 18 families with isolated NPH, whereas the same marker excluded linkage in the 4 families with associated ocular abnormalities (thus corroborating the view that Senior-Loken syndrome (266900) is a distinct entity). The markers used in mapping the locus had been shown to be tightly linked to several probes, all located on chromosome 2p and more centromeric than NMYC (164840) at 2p24.1 or APOB (107730) at 2p24; thus, the NPH1 locus can be assigned to the 2p23-cen region. However, in situ hybridization of YAC clones isolated with 2 closely linked markers led Medhioub et al. (1994) to assign the NPH1 gene to 2q13. Furthermore, based on haplotype analysis and specific recombination events, the NPH1 gene was placed between D2S293/D2S340 and D2S121, a genetic interval of about 5 to 7 cM. Hildebrandt et al. (1995) likewise concluded that the NPH1 gene is probably located in 2q13 in an interval of 6.9 cM between D2S293 and D2S363.

Medhioub et al. (1994) studied 4 NPH families in which haplotype analyses showed unequivocally that the disorder was not linked to the chromosome 2 markers, thus indicating genetic heterogeneity.

Molecular Genetics

Familial nephronophthisis that maps to chromosome 2q13 is associated with mutation in and/or deletion of the NPHP1 gene (see 607100.0001-607100.0005) (Saunier et al., 1997; Hildebrandt et al., 1997). For a complete discussion of the molecular genetics of nephronophthisis-1, see 607100.

In a worldwide cohort of 1,056 patients diagnosed with a nephronophthisis-related ciliopathy (NPHP-RC), including 447 patients with isolated nephronophthisis and 609 patients with additional extrarenal manifestations, Halbritter et al. (2013) performed a high-throughput mutation analysis of 13 genes known to cause these disorders. Biallelic mutations were found in 127 patients (12%), and heterozygous truncating mutations were found in 31 patients (2.9%). A total of 159 different mutations were found in 11 of the 13 genes, 99 of which were novel. The most common mutations occurred in the following genes: NPHP1 (23 patients), NPHP4 (22 patients), CEP290 (609237; 20 patients), NPHP3 (17 patients), and IQCB1 (610743; 16 patients).

Genetic Modifiers

Louie et al. (2010) identified a 2488C-T (arg830-to-trp; R830W) hypomorphic SNP in the WD40 repeat domain of the AHI1 gene (608894) that was associated with retinal degeneration in patients with nephronophthisis. Among 153 Italian NPHP individuals, the T allele was found at a higher frequency among those with retinal degeneration compared to those without retinal degeneration (25% compared to 1.8%, p = 5.36 x 10(-6)) and to controls, yielding a relative risk of 7.5. The findings were irrespective of the mutations causing NPHP, and suggested that variation in AHI1 may explain some of the variability in retinal phenotypes. A similar association was not observed for 155 patients with Joubert syndrome (JBTS; see, e.g., 213300).

Associations Pending Confirmation

For discussion of a possible association between NPHP-related ciliopathies and variation in the IFT81 gene, see 605489.0001 and 605489.0002.

For discussion of a possible association between nephronophthisis and variation in the INTU gene, see 610621.0005.

Animal Model

Lyon and Hulse (1971) described the mouse mutation 'kd' (kidney disease), which seems to cause a homologous disorder.

Simon et al. (1994) concluded that NPH1 is not homologous to cpk in the mouse because it appears to map to a different region of homology between 2p and mouse chromosome 12.

Jiang et al. (2009) used Nphp1-mutant mice carrying an exon 20 deletion and transgenic mice expressing EmGFP-tagged nephrocystin to demonstrate that nephrocystin was localized to the connecting cilium axoneme, where it affected the sorting mechanism and transportation efficiency of the intraflagellar transport between inner and outer segments of photoreceptors.