• Clinical science

Chromosomal aberrations


Structural and numerical chromosomal aberrations may affect either the autosomes or gonosomes and are a common cause of spontaneous abortions. Autosomal aberrations that are frequently observed are trisomy 13 (Patau syndrome), trisomy 18 (Edwards syndrome), and the most common and widely recognized chromosomal aberration, trisomy 21 (Down syndrome). These conditions have an extra copy of the chromosome to which their name refer. The risk of autosomal aberrations increases with maternal age. Characteristic features include facial and skeletal malformations, which are usually recognizable at birth. The conditions are further associated with congenital heart defects and malformations of other internal organs. Turner syndrome and Klinefelter syndrome are gonosomal aberrations in which individuals have a missing X chromosome or an additional X chromosome, respectively. These conditions are primarily characterized by impaired development of secondary sexual characteristics and infertility secondary to gonadal dysgenesis. The diagnosis for all chromosomal aberrations is confirmed via karyotyping.

General information



  • Chromosomal aberrations are the most common cause of spontaneous abortions (accounting for 60% of cases).
    • Approx. 50% of anomalies are trisomies.
    • Approx. 20% of anomalies are triploidies.

Overview of viable numerical chromosomal aberrations


Trisomy 13 (Patau syndrome)

To remember that Patau syndrome is caused by trisomy 13, think of the age of Puberty onset (13).

To remember the most common features of this syndrome, think of the 7 Ps of Patau syndrome: holoProsencephaly, cleft liP and Palate, Polydactyly, Pump disease (congenital heart disease), Polycystic kidney disease, cutis aPlasia.


Trisomy 18 (Edwards syndrome)

To remember the most important features of Edwards syndrome, think “PRINCE Edward turned 18:Prominent occiput, Rocker-bottom feet, Intellectual disability, Nondisjunction (in meiosis), Clenched fists, low-set Ears, and chromosome 18.


Down syndrome (trisomy 21)

See article on Down syndrome.