Renal Agenesis
A rare, congenital renal tract malformation characterized by the complete absence of development of one or both kidneys (unilateral or bilateral renal agenesis respectively), accompanied by absent ureter(s).
Epidemiology
The birth prevalence of unilateral renal agenesis (RA) is estimated at around 1/2,000. Fetal prevalence of bilateral renal agenesis in Europe has been estimated at 1/8,500.
Clinical description
Most patients with unilateral RA are asymptomatic early in life if the other kidney is fully functional in which case the condition is commonly detected as an incidental finding later in life. However, hypertension, proteinuria and renal failure may develop in the long run (20-50% of cases at the age of 30). Unilateral RA is occasionally associated with additional urogenital tract anomalies on the same side (e.g. seminal vesicle hypoplasia and absence of the vas deferens), cardiac anomalies (such as atrial or ventricular septal defects) and/or gastrointestinal anomalies (such as anal atresia). Bilateral RA is characterized by complete absence of kidney development, absent ureters and subsequent absence of fetal renal function resulting in Potter sequence with pulmonary hypoplasia related to oligohydramnios, which left untreated is fatal shortly after birth.
Etiology
Renal agenesis results from a developmental 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). A few cases of bilateral renal agenesis have been found to be caused by mutations in the RET, FGF20 (8p22) or ITGA8 (10p13) genes. Maternal diabetes mellitus or use of specific drugs during pregnancy may also causerenal agenesis.
Diagnostic methods
Diagnosis is based on ultrasonography, showing an empty renal fossa and no ectopic kidney. Additional radiological examinations like MRI (magnetic resonance imaging) and/or DMSA (dimercaptosuccinic acid) scintigraphy may confirm the diagnosis. The contra-lateral kidney may be compensatory hypertrophied.
Differential diagnosis
Differential diagnoses of an empty renal fossa include kidney ectopia and involution of multi-cystic dysplastic kidneys (MCDK).
Antenatal diagnosis
Prenatal diagnosis may be made by prenatal ultrasonography.
Genetic counseling
In familial cases, unilateral RA is typically inherited in an autosomal dominant manner with incomplete penetrance. Bilateral RA is inherited autosomal recessively.
Management and treatment
Clinical management of unilateral renal agenesis with fully functioning contra-lateral kidney included routine evaluations of blood-pressure and screening for proteinuria as individuals with RA have an elevated risk of chronic kidney disease.
Prognosis
The prognosis of RA with fully functioning contra-lateral kidney is generally good. Without intensive care, bilateral RA is fatal shortly after birth.