Chromosomal aberrations (structural disorders)

Chromosomal aberrations (structural disorders)

| |  Clinical Cytogenetics

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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.

Clinical

- 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 -.

Clinic

- 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.

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