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Renal agenesis, unilateral
Unilateral renal agenesis (URA) is a form of renal agenesis (see this term) characterized by the complete absence of development of one kidney accompanied by an absent ureter.
- Synonym(s): -
- Prevalence: Unknown
- Inheritance: Autosomal dominant
- Age of onset: All ages, Antenatal
- ICD-10: Q60.0
- OMIM: 617805
- UMLS: C0266294
- MeSH: -
- GARD: -
- MedDRA: 10053624
The annual incidence of URA is estimated at around 1/2,000. The male to female ratio is around 1.2:1. Approximately 56% of URA occurs on the left side.
The disease is usually clinically silent and is commonly detected as a chance observation. URA can present during routine fetal ultrasound with an empty renal fossa, during renal ultrasound for the evaluation of a urinary tract infection, or in adults who present with hypertension. Most patients are asymptomatic if the other kidney is fully functional. However, hypertension, proteinuria and renal failure may develop in the long run (20-50% of cases at the age of 30), which may be based on glomerular hyperfiltration. Renal agenesis is occasionally associated with genital tract anomalies on the same side (e.g. seminal vesicle hypoplasia and absence of the vas deferens). Other organs may show anomalies as well (up to 44%), mainly cardiac (such as atrial or ventricular septal defects) and gastrointestinal (such as anal atresia).
Renal agenesis results from a development failure of the ureteric bud and the metanephric mesenchyme. Unilateral renal agenesis can be caused by mutations in many genes, such as RET (10q11.2), BMP4 (14q22-q23), FRAS1 (4q21.21), FREM1 (9p22.3 ) or UPK3A (22q13.31), PAX2 (10q24.31), HNF1B (17q12), DSTYK (1q32). Unilateral renal agenesis can occur as part of multi-organ syndromes, several of which have defined genetic bases, including Kallmann syndrome, branchio-oto-renal syndrome, diGeorge syndrome, Fraser syndrome, MURCS association, Poland syndrome, renal cysts and diabetes syndrome, and Williams-Beuren syndrome (see these terms). Maternal diabetes mellitus or use of specific drugs during pregnancy can also result in RA.
Prenatal suspicion of URA is confirmed by postnatal ultrasound showing an empty renal fossa, followed by renography to confirm the presence of a solitary functioning kidney. The size of the solitary functioning kidney is increased in the majority of patients. A voiding cystourethrogram should be considered in order to detect vesicoureteral reflux (VUR).
Differential diagnoses include extreme unilateral renal dysplasia (i.e. renal aplasia), involuted multicystic dysplastic kidney (see these terms), and renal ectopia.
Ultrasonographic screening can detect renal agenesis from midway through gestation. However, antenatal diagnosis can be complicated when the fetal adrenal gland occupies the empty renal bed as it can mimic a kidney.
In most familial cases, URA is inherited in an autosomal dominant manner with incomplete penetrance. When a genetic cause is known, families may benefit from genetic counseling. Patients' offspring, parents and sibs have an increased risk of having a renal anomaly as well, with risks of 12, 4 and 2% respectively.
Management and treatment
Due to an increased risk of hypertension and/or proteinuria, individuals with URA deserve long-term follow-up. Information on renal function (blood pressure, an estimate of the glomerular filtration rate and proteinuria) should be obtained to evaluate the function of the remaining solitary functioning kidney.
The risk of renal failure in childhood is minimal, however patients may develop hypertension, proteinuria and renal failure. URA can occur with dysplasia or hypoplasia of the solitary functioning kidney (renal dysplasia and renal hypoplasia; see these terms), which makes the prognosis more serious.