Chromosomal aberrations (structural disorders)

Chromosomal aberrations (structural disorders)

| |  Clinical Cytogenetics

 (1)    (0)    (0)

1. Translocations - transfer portion from one chromosome to another or to a different location of the same chromosome.

Outcomes - death, congenital malformations, a high risk of birth of sick children. For example, a merger of 2 chromosomes in one (Down syndrome) - 21 chromosome with the 14th or 15th chromosome.

2. Inversion - at break of chromosomes  in two places, freed portion unfolds at 180% and getting back to its original location.

Outcomes - spontaneous abortions, multiple congenital malformations, minor malformations, mental retardation, without anomalies.

3. Deletion - the disappearance of a torn portion of chromosomes. In each chromosome there are a long and short arm. Short shoulder indicated by a small letter "p", the long arm - "q". The lack of any arm of chromosome denoted by the corresponding latin letters and then is put the sign "-" and the digit standing before the letter indicates the sequence number of abnormal chromosomes.

  • Lejeune Syndrome (cat-cry Syndrome)

Karyotype 46 XX or XY, 5p -. Frequency - 1˸ 40 000 - 50 000 live births.


- Low birth weight,
- High-pitched, plaintive cry by an infant (reminiscent "cat's meowing")
- Mental retardation
- Microcephaly, ptosis, low location and deformation of auricles, the skin folds in front of the ear, hypertelorism, palpebral, moon face; broad nasal root;
- Small larynx and epiglottis;
- Micrognathia or retrognathia;
- Muscular hypotonia;
- Birth defects, hernias, the discrepancy recti;
- Flatfoot, "monkey-fold";
- Congenital heart defect.

Such signs as "cat crying", muscular hypotonia, moon face, in most cases completely disappear with age. But the majority of children die at an early age.

  • Prader-Willi syndrome (males) and Angelman syndrome (in women)

Karyotype 46 XX or XY, 15p -.


- Muscular hypotonia;
- Hypogonadism;
- Obesity;
- Craniofacial anomalies with microcephaly;
- Tapering extremities;
- Mental retardation;
- High-arc-shaped sky caries;
- Hypoplasia of the auricles;
- Scoliosis;
- Syndactylism;
- Transverse palmar crease;
- Incoordination, convulsions;
- Diabetes;
- Simian creases.

4. Duplication - doubling of chromosomes. Tandem duplication - the emergence of a neighboring shoulder extra chromosome from centromeres chromosomes. mechanism aberration:

- Due to an increase of a segment of the chromosome;

- As a result of unbalanced translocations.

  • Syndrome 9p +

Karyotype 46 XX or XY 9p + In terms of frequency of occurrence ranked 2nd after Down syndrome.

Clinical and morphological features

- Prenatal moderate hypoplasia, growth retardation;
- Microcephaly, palpebral;
- Mental retardation;
- Hyperplasia, 3 and 4 phalanxes of fingers;
- Malformations of internal organs (heart and kidney).

Prediction of life - a favorable, in the absence of pathology of the internal organs.

  • The syndrome of fragile chromosome (Syndrome Fra, Martin-Bell) - one of the most common (after Down's syndrome) forms of mental retardation.

Population frequency 1˸2000 - 1˸5000
Sick Boy in 2-3 times more than girls

Diagnostic features

- Moderate or profound mental retardation;
- Large protruding ears, protruding forehead, a massive chin;
- Increasing the size of the testicles;

Intellectual defects

- The lack of contact with others people;
- Motor disinhibition syndrome;
- Obsessive motion (creaking teeth, rocking, etc.);
- Speech - agrammatism, echolalia, neologisms;
- Aggressive behavior (desire to do anything out of spite, to hit, bite, etc.);
- Lack of desire to please, to achieve praise, approval;
- Autism, psychological isolation;
- The lack of criticism in the behavior.

There are also an obesity, gynecomastia, hypospadias, soft extendible skin, weakness ligamentous apparatus of the knee and ankle joints, mitral valve prolapse.

 (1)    (0)    (0)

Leave a Comment