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Prune-Belly Syndrome
Introduction
Prune-belly syndrome (PBS), also known as Eagle-Barrett syndrome, is a triad of anomalies composed of abdominal wall flaccidity, urologic abnormalities, and bilateral cryptorchidism. The typical urologic findings are distended bladder, hydronephrosis, and renal dysplasia. A patent urachus is a common finding. In some infants, urinary obstruction may lead to oligohydramnios or anhydramnios with a resulting Potter sequence (pulmonary hypoplasia, dysmorphic facies). Concomitant cardiac, orthopedic, and gastrointestinal anomalies are frequent and are reported in approximately 75% of PBS cases.
Disorder
Definition
PBS is characterized by urologic abnormalities, dysplasia, or flaccidity of the abdominal wall musculature, and bilateral cryptorchidism (in males). The poorly developed abdominal wall results in a wrinkled appearance of the infant's abdomen, giving the syndrome its name.
Prevalence and Epidemiology
The reported incidence ranges from 1 : 29,000 to 1 : 50,000 live births with a significant male preponderance; 95% of cases occur in males. The syndrome is twice as common in blacks compared to whites. Also the incidence in twins has been reported to be four times higher than in singletons. An apparent increase in incidence of PBS in children of younger mothers has also been observed.
Etiology and Pathophysiology
Two theories exist as to the etiology of PBS. The first suggests that the sequence is initiated by an obstructive uropathy. This theory posits that a primary urinary tract obstruction leads to distention of the bladder, prohibiting formation of the anterior abdominal wall muscles and descent of the testis. The resulting oligohydramnios then results in a Potter sequence, leading to contractures and pulmonary hypoplasia. However, this theory does not fully explain the associated cardiac and gastrointestinal defects associated with PBS; furthermore, it does not explain why some urinary tract obstructions, such as posterior urethral valves, do not lead to the spectrum of findings found in PBS. Last, most infants born with PBS do not actually have a urinary tract obstruction.
The second theory focuses on embryogenesis; an aberration of mesenchymal development between the sixth and 10th weeks of gestation could lead to the spectrum of findings in PBS. A mesenchymal defect in the sixth to seventh week could explain not only the typical triad of findings, but also the commonly found orthopedic and gastrointestinal findings.
The male preponderance has suggested an X-linked recessive or perhaps a sex-influenced autosomal recessive mode of inheritance. A few case reports exist of PBS in association with a trisomy or a chromosomal deletion, but the loci of the abnormality is inconsistent across these reports. At this time, no chromosomal abnormality has been linked definitively to PBS. However, an abnormality of hepatocyte nuclear factor 1β (HNF1β), which is expressed on chromosome 17, has been demonstrated in patients with sporadic PBS. This transcription factor is found on numerous tissues in the body including mesonephric duct derivatives, renal tubules of the metanephros, and the developing prostate. Other potential genetic factors have been suggested including hypomethylation on chromosome 6q24 and 11p15 and ACTG2 mutations, which encodes for enteric actin.
The risk of recurrence of PBS is considered low ; however, considering the genetic factors/influences of PBS are not well understood, this may change as technology/genetic testing options improve.
Manifestations of Disease
Clinical Presentation
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