- Clinical science
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.
Chromosomal aberrations: deviation from the normal chromosome constellation
- ; (e.g., aneuploidy, polyploidy)
- ; (e.g., deletion, translocation)
- Triploidy: : presence of three sets of chromosomes
- Trisomy: : presence of triplicate instead of duplicate number of a particular chromosome or part of a chromosome
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
Autosomal chromosomal aberrations
- ( )
- ( )
Gonosomal chromosomal aberrations
- Karyotype: ♀: 47 XX+13; ♂: 47 XY+13
- Frequency: ∼ 1:10,000 children
- Microcephaly, holoprosencephaly
- Cleft lip and palate; , “punched-out” scalp lesions, low-set malformed ears, bulbous nose, small chin
- Microphthalmia, possibly , ocular hypotelorism
- Polydactyly, primarily hexadactyly, flexed fingers
- Congenital heart defects (particularly ventricular septal defect, patent ductus arteriosis)
- Rocker-bottom feet
- Visceral and genital anomalies, especially of the kidneys and ureter
- Capillary hemangioma
Diagnostics: See .
- Usually detected during first trimester screening with combined ultrasound and maternal serum testing (↓↓ PAPP-A, ↑ nuchal translucency)
- Prognosis: Only 5% of infants survive past 6 months of age.
- Karyotype: ♀: 47 XX+18; ♂: 47 XY+18
- Frequency: ∼ 1:6,000 children
- Gender: ♀ > ♂
- Prominent occiput, microcephaly
- Low-set ears (malformed auricle), micrognathia, cleft lip and palate, high palate, broad nose
- Clenched fists, with flexion contracture of the fingers
- Rocker-bottom feet; : convex deformity of the plantar side of the foot; , with a vertical talus, and prominent calcaneus
- Congenital heart defects (particularly VSD, ASD, tetralogy of Fallot)
- Malformations of internal organs: diaphragmatic hernia, ureter, and kidneys (horseshoe kidneys)
- Diagnosis See .
- Prognosis: Only 5–10% of patients survive past 12 months of age.
- See .