pentasomies

Pentasomies are a type of chromosomal abnormality characterized by the presence of an extra chromosome in a set. Typically, chromosomes are found in pairs, meaning humans have 23 pairs, or 46 chromosomes in total. A trisomy, for example, involves having three copies of a particular chromosome instead of the usual two. A pentasomy, however, is a more extreme condition where there are five copies of a specific chromosome. This means that instead of the normal diploid number of two sets of chromosomes, an individual with a pentasomy would have four extra chromosomes for one specific pair, resulting in five copies of that chromosome.

Pentasomies are exceedingly rare and are often incompatible with life. They are typically lethal during embryonic development, leading to spontaneous abortion. If a pregnancy with a pentasomy does progress, the resulting infant will usually have severe, multiple congenital anomalies and a very poor prognosis. The extra genetic material causes a significant disruption in development. For instance, pentasomies affecting sex chromosomes have been observed in some cases, but even these often lead to severe developmental issues and can be lethal. Autosomal pentasomies, involving non-sex chromosomes, are even more rarely seen and are almost universally fatal. The genetic imbalance created by having five copies of a chromosome is too great for normal cellular function and organismal development.