genetic counselling

GENETIC COUNSELLING

GENES Genes are the units of heredity. They affect development and function, both

normal and abnormal.

They are of 3 types:

1.Chromosomal abnormalities

2.Mendelian diseases

3.Multifactorial disorders

CLASSIFICATION OF GENETIC DISORDERS

1.CHROMOSOMAL ABNORMALITIESA.Klinefilter syndromeB.Turners syndrome.

2.MENDELIAN DISEASESA.DominantB.RecessiveC.Sex linked diseases

3.MULTIFACTORIAL DISORDERS

A.HypertensionB.SchizophreniaC.DiabetesD.Congenital heart disease

1.HEALTH PROMOTIONAL MEASURES:

A.EUGENICS:a.Negative eugenics:

AIM:To reduce the frequency of hereditary disease and disability in the community to as low as possible

PREVENTIVE AND SOCIAL MEASURES

B.POSITIVE EUGENICS:

AIM:To improve the genetic composition of the population by encouraging carriers of desirable genotypes.

B.EUTHENICS :

Studies with mentally retarded children indicated that exposure to environmental stimulation improved their IQ.

This environmental manipulation is called euthenics.

They are of 2 types:

1.Prospective2.Retrospective

1. Prospective genetic counselling:

This allows for the true prevention of disease.

GENETIC COUNSELLING

This approach requires

Identifying heterozygous individuals for any particular defect by screening

Explaining to them the risk of their having affected children if they marry another heterozygote for the same gene.

If heterozygous marriage can be prevented or reduced,the prospects of giving birth to affected children will diminish.

EX: Sickle cell anaemia Thalassemia

2. Retrospective genetic counselling:Most genetic counselling at present is retrospective,i.e,the hereditary

disorder has already occurred within the family .

A survey carried out by the WHO showed that genetic advice was chiefly sought in connection with congenital abnormalities

Mental retardation Psychiatric illnes Inborn errors of metabolism Premarital advice

The WHO recommends the establishment of genetic counselling centres in sufficient numbers in regions where infectious disease and nutritional disorders have been brought under control

And in areas where genetic disorders have always constituted a serious public health problem.

The methods which could be suggested under retrospective genetic counselling are:

1. Contraception2. Pregnancy termination.3. Sterilization

OTHER GENETIC PREVENTIVE MEASURES

1.CONSANGUINEOUS MARRIAGES:

When blood relatives marry each other there is an increased risk in the offspring of traits controlled by recessive genes and those determined by polygenes.

EX: Albinism, Alkaptonuria, Phenylketonuria

An increased risk of premature death is also noted in such offspring.

Therefore , a lowering of consanguineous marriages would be advantageous to the health of the community.

2.LATE MARRIAGES:

Trisomy or mongolism is more frequent in children born of elderly mothers.Hence early marriage of females is better than late marriage from the point of view of preventing mongolism.

SPECIFIC PROTECTION:

Patients undergoing x-ray examination should be protected against unnecessary exposure of the gonads to radiation.

X-ray examination of the pregnant uterus to determine the twins or the lie of the foetus is to be strongly deprecated.

Rh haemolytic disease of the newborn which is a genetically determined immunological disorder is now preventable by immunization by anti D globulin.

EARLY DIAGNOSIS AND TREATMENT:

1.DETECTION OF GENETIC CARRIERS :

It is possible to identify the healthy carriers of a number of genetic disorders, especially the inborn errors of metabolism.

2.PRENATAL DIAGNOSIS:

INDICATIONS:

- Advanced maternal age- Previous child with chromosome aberration- Intrauterine growth delay- Biochemical disorders- Congenital anomaly- Screening for neural tube defects and

trisomy.

3.SCREENING OF NEWBORN INFANTS:

Screening tests for early diagnosis of :

- chromosome abnormalities- congenital dislocation of hip- congenital hypothyroidism - sickle cell disease- cystic fibrosis

Genetic counselling can have the greatest impact when individuals or couples at genetic risk are identified,

before they have developed symptoms themselves or produced their first affected child.

REFERENCE

TEXT BOOK OF PREVENTIVE AND SOCIAL MEDICINE : PARK