Trisomy 13-15.

Abstract

In April 1960, Patau and others described a characteristic pattern of numerous anomalies associated with a trisomy in the 13–15 group (also known as D1 trisomy) (13). Although there have been over thirty published examples of trisomy 13–15, only brief mention of the disorder has been made in the radiological literature (1). After review of the radiographic features in our eight cases of trisomy 13–15, we felt that the pattern of radiologic abnormalities was diagnostic and could be differentiated from trisomy 18, cri du chat syndrome, and mongolism. Karyotype Patients with trisomy 13–15 have a basic number of 47 chromosomes with an extra chromosome in the medium-sized group (D, 13–15) that has the centromere toward one end (acrocentric) (2, 7) (Fig. 1). Trisomy 13–15 is generally thought to result from maternal nondisjunction (3, 6, 10). The similar clinical pattern of this trisomy suggests that the same genes on the same chromosomes are present in triplicate (5). Embryology The extra chromosome in the 13–15 group is associated with abnormalities of the embryonic developmental events that occur at five to six weeks gestation (11). For example, at five weeks gestation limb buds develop ossification centers in the mesenchyme, and septation of the heart and midline craniofacial development begins. The auricles develop during the following week. The reason for the association of the embryonic changes with the presence of an extra 13–15 chromosome has not yet been established but has been the subject of considerable investigation. Clinical Features As with the other autosomal abnormalities, both the average paternal (36.4 years) and maternal (34.3 years) age is advanced (5). However, pregnancy and delivery are normal in most patients (16). Although early reports of this autosomal disorder involved only females, recent studies show that this was probably due to the small numbers in the series (17) and males are certainly affected. Infants with trisomy 13–15 are usually grossly malformed at birth and die before the age of four months (the oldest reported case being three and one-half years) (17). Listed below are the many physical abnormalities which have been reported in association with an extra chromosome in the 13–15 group with the incidence of the abnormalities most often found in our 8 cases. Every patient with trisomy 13–15 will not have all the clinical features enumerated above. It is the association of several abnormalities in a patient that makes the presence of a triplicate chromosome at the 13–15 position likely. Radiographic Findings One can predict the radiographic findings from an understanding of embryonic abnormalities and clinical features. A review of our series of 8 cases of trisomy 13–15 and those reported in the literature (14, 18) revealed a broad spectrum of radiographic abnormalities. The incidence of the most common and therefore most diagnostic features in our experience is listed below.