Prenatal diagnosis of complete ring chromosome 22 without phenotypical abnormalities

Abstract

A healthy 34-year-old, para 1, Taiwanese woman presented for genetic amniocentesis at 18 weeks of gestation due to advanced maternal age. Her previous medical history was unremarkable except for a cesarean delivery following prolonged labor with a failed induction. Prenatal ultrasonography did not detect any structural abnormalities, except for borderline ventriculomegaly (Fig. 1). The karyotype of amniotic fluid cell culture was identified as 46,XY,r(22)(p13q13) (Fig. 2), which was further confirmed by cord blood sampling. Following detailed consultation and nondirective genetic counseling with physicians, the patient and her husband chose to terminate the pregnancy via hysterotomy. The procedure was performed uneventfully at 21 weeks of gestation. A dead male fetus weighing 520 g was delivered from breech presentation without any significant phenotypical abnormalities (Fig. 3) and no structural anomalies were found in an autopsy. Fetal skin and umbilical cord cultures were used to confirm the initial karyotype report postdelivery. Ring chromosome 22 [r(22)] is a rare cytogenetic abnormality first identified by Weleber et al in 1968 [1]. Since that initial report, more than 60 cases have been described in medical literature. Ring chromosomes usually occur when a terminal break in both arms of the chromosome and the broken ends fuse together, or one broken chromosome end joins with the opposite telomeric region. This condition results in the loss of genetic material. Alternatively, ring chromosomes can be formed by the fusion of subtelomeric sequences or telomere-telomere fusion with no deletion, resulting in complete ring chromosomes. Ring chromosomes often lead to developmental anomalies but are