- Numerical Chromosomal Aberrations.

Numerical Chromosomal Aberrations:

Aneuoploidy

A chromosome profile with fewer or greater than the normal diploid number where the total is not a multiple of 23.

n  If an extra chromosome is present (presence of three copies of the chromosome) : trisomy for that particular chromosome e.g. trisomy 21, trisomy 18, trisomy 13.

Trisomies are the most common numerical chromosomal anomalies found in humans.

Most autosomal aneuploidies are fatal in utero.

Three are survivable to term: Trisomy 13, 18 and 21.

Children with trisomy 21 (Down’s syndrome) are believed to have the most favorable outcome, as chromosome 21 has fewer genes than the other autosomes (it is short and has a low gene density)

Mechanism:  Non disjunction (Failure of the two chromosomes of one pair to disjoin).

n  If a chromosome is missing: monosomy for that chromosome e.g. Turnersyndrome (monosomy X chromosome).

Mechanism:

ü  Non-dysjunction.

ü  Anaphase lag; failure of the chromosome to move quickly to be incorporated in the daughter cell, so it will be lost. 

- Genetic Counseling.

Genetic Counseling

Definition: A process of communication and education which deals with estimating the risk of developing and/or transmitting a genetic disorder.

Goals of Genetic Counseling:

The consultand الذى يطلب الاستشارة should be provided with information and support which enables him to understand:

1.     The medical diagnosis and its consequences as: prognosis and possible treatment.

2.     Mode of inheritance of the disorder and the risk of developing or transmitting it.

3.     To make their own decisions about choices or options available for managing a particular disease and those for dealing with genetic testing and reproduction and the following risks.:

ü  Recurrence risk in future children

ü  Recurrence risk in near relatives

ü  Recurrence risk in children of unaffected brothers & sisters

A primary goal of genetic counselling is to provide information to allow for greater autonomy and choice in reproductive decisions and other areas of personal life. Avoiding additional cases of genetic disease in a family may be a consequence of genetic counselling but is not the primary aim.

Indications

1.     Maternal age > 35 years

2.     Known or suspected hereditary condition in the family

3.     Hx of child with birth defect or MR

4.     Hx of recurrent abortion

5.     Exposure to known or suspected teratogens

6.     consanguinity

 

Prevention of Genetic Disorders

Prevention is by 4 ways:

1. Genetic councelling (click here).

2. Carrier detection.

3. Prenatal diagnosis.

4.Neonatal screening.