Original Articles
Cystic fibrosis and chromosome abnormalities associated with echogenic fetal bowel

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Abstract

Objective: To determine the prevalence of cystic fibrosis mutations and chromosome abnormalities in the fetuses of a heterogeneous population of pregnant women referred for prenatal testing for echogenic fetal bowel.

Methods: Fetal or parental samples obtained after a second-trimester sonographic finding of echogenic fetal bowel were submitted to a referral diagnostic laboratory during a 2-year period. Results of DNA testing and karyotyping on these samples were analyzed to determine the prevalence of cystic fibrosis transmembrane reductase gene mutations and chromosome abnormalities.

Results: Of 244 cases tested, two fetuses were positive for two cystic fibrosis mutations. This rate (0.8% or two of 244) is 20 times higher than the general white population rate of one per 2500. In a third case, both parents were carriers but the fetus was not tested. Nine (8%) of 113 fetuses tested had one cystic fibrosis mutation. Of 106 fetuses for whom chromosome results were available, three (2.8%) fetuses had a chromosomal abnormality: two had trisomy 21 and one had Klinefelter syndrome. A fourth fetus carried a de novo, apparently balanced, 5;12 translocation.

Conclusion: These laboratory results are representative of a broad spectrum of clinical settings and indicate a generalized increased risk associated with this sonographic finding. Therefore, when a second-trimester sonographic diagnosis of fetal echogenic bowel is made, fetal testing for both cystic fibrosis and chromosome abnormalities is warranted.

Section snippets

Materials and methods

Two hundred forty-four cases of echogenic bowel were tested for cystic fibrosis, chromosome abnormalities, or both, during a 2-year period (May 1992 to April 1994) at Genzyme Genetics, Framingham, Massachusetts. Fetal bowel is considered hyperechoic if it has echogenicity similar to or greater than the surrounding bone. The diagnosis of echogenic bowel was made by the physician submitting the sample, and cases were referred by over 100 physicians.

Blood, cheek brush, or amniotic fluid samples

Results

A total of 244 families were tested for cystic fibrosis because of a second-trimester sonographic diagnosis of fetal echogenic bowel. The ethnic background of patients tested for cystic fibrosis is shown in Table 1. The fetus was found to be a carrier of one cystic fibrosis mutation in nine of 113 cases in which fetal testing was done (8%). In five cases, one parent was found to carry a mutation and the other parent had no mutation identified; in these families the fetus was not tested. There

Discussion

We examined the prevalence of cystic fibrosis and chromosome abnormalities among 244 cases referred to a large genetics laboratory because of a sonographic indication of fetal echogenic bowel. Although our results show a lower incidence of both outcomes than previous studies,1, 2, 7 both conditions were higher than the expected background risk. The prevalence of confirmed cystic fibrosis in our study was 0.8%, or approximately one per 125, 20 times higher than the one per 2500 prevalence in the

References (10)

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Authors Sugarman and Allitto are employees of Genzyme Genetics.

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