In a recent article, Amacker et a1 [1986] reported two cases with "prune belly" anomaly (PBA) in association with Down syndrome. To the best of our knowledge, these two cases plus a third reported by Curry et a1 219841 are the only reports of a congenital obstructive uropathy association with Down syndrome. Amacker et a1 [ 19861 suggested three hypotheses to explain the low frequency of chromosome abnormalities described in association with PBA: 1) incidental association of PBA and chromosomal abnormalities due to two independent and rare events in one pregnancy; 2) early fetal losses with PBA caused by Down syndrome; and 3) bias of ascertainment against chromosomal studies in fetuses/newborns where one diagnosis has already been made.
In British Columbia (BC), live-birth incidence rates have been determined for both Down syndrome [Trimble and Baird, 19781 and PBA [Baird and MacDonald, 19811 using the population-based Health Surveillance Registry (the "Registry"). We think that if there is causal relationship between Down syndrome and PBA, it would have become apparent for several reasons. Firstly, since 1964, there has been virtually complete ascertainment by the Registry of all live births with either Down syndrome and/or PBA. Over 60 sources register cases in this province, and these include physician's notices of birth, hospital discharge diagnoses on all children under the age of 7, vital registrations of death, medical genetics clinics, and provincial cytogenetic laboratories. The Registry records all congenital malformations per individual. Secondly, prenatal diagnostic services for the entire province are centralized through the Department of Medical genetics, and information is therefore available on the outcome of all pregnancies monitored. All women having prenatal diagnosis in BC undergo ultrasonography and have cytogenetic studies.
In BC, the live-born incidence rate for Down syndrome is 11685 [Trimble and Baird, 19781; and for PBA, 1/29,231 [Baird and MacDonald, 19811. Using Registry data, 16 out of 18 infants with PBA, identified among 526,166 consecutive live births, had additional congenital malformations [Baird and MacDonald, 19811, but none had Down syndrome. Most of the additional malformations in infants with PBA were