Nephronophthisis,an autosomal recessive cystic kidney disease, is the most frequent monogeniccause of renal failure in childhood. There are four forms of nephronophthisiscaused by mutations in four different genes. Clinically, there is astatistically different age at onset at end-stage renal disease: terminal renalfailure develops at median ages of 13 years, 1 year, 19 years, and 11-34 yearsin NPHP1, NPHP2, NPHP3, and NPHP4 respectively. Hallmarks of familialnephronophthisis are tubular basement membrane disruption, interstitiallymphohistiocytic cell infiltration, and development of cysts at thecorticomedullary border of the kidneys. The histology in later stages of NPHalways merges into a chronic sclerosing tubulointerstitial nephropathy, whichis found in chronic renal failure of all origins.
Inone study, individuals with infantile nephronophthisis (NPHP2) presented withinthe first months of life with severe renal failure and acidosis, which could beassociated with hypertension and/or polyuria and/or severe cholestatic liverdisease. A renal biopsy, performed in all patients, showed similar featurescharacterized by a diffuse chronic tubulointerstitial nephritis andparticularly by the presence of microcystic dilatation of proximal tubules andBowman space. Progression of the renal disease was extremely rapid and patientscan reach end-stage renal failure before the age of 2 years (11 to 22 months).
Inanother study, phenotypic presentation ranged from a Potter-like syndrome tohyperechogenic kidneys, renal insufficiency, hypertension, and hyperkalemia.Affected individuals showed rapid deterioration of kidney function, leading toend-stage renal failure within 3 years. The manifestations range from prenatalfetal oliguria and oligohydramnios resulting in postnatal respiratory failure anddeath to postnatal onset of disease later than 30 months of age. None of thepostnatally diagnosed patients had a history of either oligohydramnios orneonatal respiratory symptoms. All affected individuals developed anemia,hyperkalemic metabolic acidosis, and increased serum creatine. None of theaffected subjects had polyuria, polydypsia, or associated ocular or hepaticcomplications.
Thespecific clinical features of this disease are its early onset and rapidprogression to end-stage renal failure. Pathologically, it differs fromlater-onset nephronophthisis by the absence of medullary cysts and thickenedtubular basement membranes and by the presence of cortical microcysts. NPHP2 iscaused by mutations in the INVS gene(also known as NPHP2) (9q31). Theprotein product of the INVS gene,inversion, has been shown to interact with that of the NPHP1 gene, nephrocystin.
Click here for the OMIM summary on this condition.
This test is indicated for:
- Confirmation of a clinical/biochemical diagnosis of infantile nephronophthisis in individuals who have tested negative for sequence analysis
- Carrier testing in adults with a family history of infantile nephronophthisis who have tested negative for sequence analysis
Isolation using the Perkin Elmer™Chemagen™ Chemagen™ Automated Extraction method or Qiagen™ Puregene kit for DNA extraction is recommended.
Infants and Young Children (<2 years of age): 2-3 ml
Children > 2 years of age to 10 years old: 3-5 ml
Older Children & Adults: 5-10 ml
Autopsy: 2-3 ml unclotted cord or cardiac blood
Submit copies of diagnostic biochemical test results with the sample, if appropriate. Contact the laboratory if further information is needed.
Sequence analysis is required before deletion/duplication analysis by targeted CGH array. If sequencing is performed outside of EGL Genetics, please submit a copy of the sequencing report with the test requisition.
- Sequencing analysis of the INVS gene is available and is required before deletion/duplication analysis.
- Custom diagnostic mutation analysis is available to family members if mutations are identified by targeted mutation testing or sequencing analysis.
- Prenataltesting is available to couples who are confirmed carriers ofmutations. Please contact the laboratory genetic counselor to discussappropriate testing prior to collecting a prenatal specimen.