Description:

Trisomy 13 is one of the most common trisomies in clinically recognized pregnancies and one of the few trisomies identified in liveborns, yet relatively little is known about the errors that lead to trisomy 13. Accordingly, we initiated studies to investigate the origin of the extra chromosome in 78 cases of trisomy 13. Our results indicate that the majority of cases (>91%) are maternal in origin and, similar to other autosomal trisomies, the extra chromosome is typically due to errors in meiosis I. Surprisingly, however, a large number of errors also occur during maternal meiosis II (∼37%), distinguishing trisomy 13 from other acrocentric and most nonacrocentric chromosomes. As with other trisomies, failure to recombine is an important contributor to nondisjunction of chromosome 13.

A significant number of fetuses with trisomy 13 are spontaneously or voluntarily lost before birth; however, very few such fetuses have been systemically autopsied. In the present study, ten trisomy 13 fetuses of 130–305 mm in crown-rump length, estimated gestational age from 108 days to 239 days, were examined following either karyotype or ultrasonographic diagnosis and voluntary termination. Mean maternal age was 35.1 years. The spectrum of anatomical features was similar to that observed in neonates or older infants with trisomy 13, namely, holoprosencephaly, cyclopia, microphthalmia, cleft palate and lip, cardiac defect, polydactyly, and cystic kidney. Kidney weights were significantly increased above normal in eight of nine fetuses. Histologically, the cortex of these kidneys showed increased mitotic activity and blastemic appearance, which extended deep into the medullary areas. The weights and histology of other organs were normal except for slight increases in spleen weight.

We have coined the term “pseudo-trisomy 13 syndrome” to designate cases of holoprosencephaly, severe facial anomalies, postaxial polydactyly, various other congenital defects, and normal chromosomes. Eleven instances are summarized. Two pairs of sibs and two other cases with consanguinity suggest autosomal recessive inheritance. Autosomal recessive inheritance is possible. Alternately, an undetected microdeletion and etiologic heterogeneity (some cases possibly representing dominant new mutations) must be considered. Further delineation is necessary. It is hoped that this paper will serve as a focus for further discussion of the problem.

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Sophia
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Global Journal of Research and Review