Razi Journal of Medical Sciences

Physicians are families' best counsellers, and genetic counseling is one of the most important and delicate aspects of medicine. Genetic disorders are the third most common problems of mankind after infectious diseases and malnutrition.

10% of neonatal and 25% of pediatric mortalities are some how related to congenital and genetic disturbances. Genetic disorders are categorized in four major groups:

1- Cytoplasmic, such as: mitochondrial and peroxisomal diseases, which are only transmitted by the mother.

2- Single gene defect, that follow the mendelian patterns of inheritance, including, autosomal and sex-linked disorders, which are transmitted by parents ordinarily to l...­4

(recessive genes) or ~ (dominant genes) of their offsprings.

3- Polygenic or multifactorials, which are influenced by both, genetic and environmental factors. Recurrence risk is 3- 5% after recognition of index case and about three times when two individuals are detected relatives.

4- Chromosomal abnormalities, structural and numericals, or due to translocations.

They mostly occur sporadically and unless the mother, is over 34 years or carries a balanced translocation, the chance of their recurrence is not very high.

This article is concluded with the main indications for chromosomal studies.