Genetic Disorders are very common in the areas of the world where the public is largely unaware about genetic risks having lack of genetic counseling and is developing fears towards genetics due to lack of knowledge and the sensationalist reaction of the media to certain topics of genetic research. Genetic services are incorrectly perceived as an expensive, inextricably linked to high-tech laboratory tests and concerned only with rare and esoteric diseases.
Here is the basic science behind genetic disorders.
Gene is the unit for genetic information. Human being has about 30,000 genes distributed over 23 pairs of chromosomes. Every gene has a different function, controlling all kinds of biological activities including embryological development, fetal growth, metabolism, personality, cognition and proliferation. Chromosomes are the genetic material within a cell nucleus. Except some specialized cells like red blood cells and gametes, every cell in our body carries 23 pairs of chromosomes. Twenty-two pairs are known as autosomes and show no sex difference. The remaining pairs are known as sex chromosomes; females have a pair of X, while males have both an X- and Y-chromosomes. When the number or structure of chromosomes goes wrong, a genetic disease is the result. A classic example is Down syndrome, which is caused by trisomy (having 3 copies instead of 2) of chromosome 21. Another example is Turner syndrome, in which case affected females have monosomy (having 1 copy instead of 2) of X chromosome.
Genetic disease refers to one that is caused by abnormalities of the genetic material within gene at the stage of germ cell or early embryo.
Genetic diseases often have the characteristic of being heritable through generations but it does not mean every case must have a positive family history. It is not uncommon to see sudden appearance of a genetic disease in a family without precedents. The affected one becomes the first case in the family. One reason is that new mutations can arise when the genetic material is passed on from one generation to the next. Another reason is autosomal recessive inheritance. Genetic diseases can largely be divided into three categories:
- Chromosomal disorders – those that are caused by numerical or structural abnormalities of the chromosomes, e.g. Down syndrome, Turner syndrome. Baby With a Down Syndrome
- Single gene disorders – those that are caused by defects of individual genes, e.g. Thalassemia, Hemophilia. Gene defects are not detectable by chromosome analysis.
- Multifactorial disorders – those that are the result of the combined effect of genetic factors and environmental factors, e.g. diabetes mellitus, hypertension, psychiatric diseases and cancer.
By means of chromosome analysis, we can detect numerical or structural abnormalities of the chromosomes. Chromosomal disorders such as Down syndrome or Turner syndrome can then be diagnosed. Nevertheless, a normal result of chromosome analysis does not mean exclusion of genetic disease, because abnormalities with DNA sequence cannot be detected by chromosome analysis
Prevention based on reproductive options is best accomplished at the primary health care level, starting with the detection of genetic risk factors in the population. These include a positive family history for a birth defect or a genetic disorder, carrier detection of a recessive trait frequent in the community, maternal age, exposure to teratogens and prenatal screening for neural tube defects and Down syndrome by measurement of maternal serum biochemical markers and by fetal ultrasonography.