Article Sections

Introduction

Trisomy 13 (Patau syndrome) is characterized by the presence of 3 copies of chromosome 13.  It is the most severe and least common (ie, 1 in 7,000 live births) of the trisomy disorders (eg, 21, 18, 13).  It is associated with severe congenital anomalies and a high mortality rate.

Pathogenesis

Normally, homologous chromosomes separate during meiosis, resulting in 4 gametes with 1 copy of each chromosome in each gamete.  However, in meiotic nondisjunction, a pair of homologous chromosomes fails to separate, resulting in 4 gametes with 0, 1, or 2 copies of the chromosome in each gamete ( Figure 1).  If a gamete with 2 copies of the chromosome is fertilized by a gamete with 1 copy of the chromosome, then the zygote has 3 copies of the chromosome.  Maternal

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