Human Genomics in Global Health

Genetic laboratories and clinics

Prior to the development of modern genetic technologies, genetic services were limited to genetic counselling, where health professionals would attempt to characterize the genetic contribution of diseases based on family histories. With the discovery of DNA, genetic services have dramatically increased in quality and scope. Increasingly sophisticated technologies now permit new methodology and high quality preparations ensuring greater accuracy in diagnosis.

Today, the presence of genetic labs and clinics is prominent worldwide. Many hospitals with established genetics programmes do offer specialized laboratory testing and comprehensive diagnostic evaluation in addition to genetic counselling. In the absence of specialist genetic counsellor, nurses and other healthcare workers are often trained to counsel patients.

In addition to the work of independent genetic researchers, laboratories and clinics also address the needs of and provide services for the public. These range from detecting mutations, to analyzing predisposition to disease, to identifying illnesses in the unborn fetus, in addition to explaining the possible risks due to genetic influences in pregnancies and methods of their prevention.

Today a variety of genetic tests are available. These can be classified under five broad areas.

  • Carrier identification tests or screening involves tests for individuals (or couples who want to have children) with a family history of recessive genetic disorders such as they may not have a disease but may carry the gene for it. Three common carrier identification tests include those for cystic fibrosis, Tay-Sachs disease, and sickle-cell trait.
  • Prenatal diagnosis involves genetic testing of a fetus using reoutine In Vitro Fertilization methods. Here the child is suspected to be at the risk of possessing genes linked to mental retardation or physical deterioration, Down Syndrome being one of the most common genetic diseases to be screened by this method.
    • Four main diagnostic tests used in prenatal diagnosis are ultrasound, chorionic villus sampling (CVS), amniocentesis, and fetal blood sampling (cordocentesis), the latter three being invasive procedures. Of all these tests, however, only CVS testing produces reliable results during the first trimester.
    • Chorionic villus sampling involves use of a catheter through the cervix or a needle into the abdomen. The abdominal technique is possible throughout pregnancy if the placenta can be reached. CVS is beneficial because it can be used for DNA and various other biochemical studies to determine monogenic and other chromosomal disorders, though tests for congenital malformations and chromosomal disorders must be done in the second trimester
    • Ultrasound procedures are used to detect major deformations and are used to confirm gestation in the uterus and the duration of gestation. These tests normally are less than a half an hour. Over 90% of several anomalies can be detected in an ultrasound if done at a gestation period of 19 weeks, allowing organs to have sufficiently developed
    • Amniocentesis is another procedure often employed, in which amniotic fluid is removed. This test can be done at 15-16 weeks of gestation, though lab work may require two weeks time to produce results of chromosomal abnormalities. There may be some safety concerns about amniocentesis and its associated risks, and thus consultations with doctors and genetic counsellors may be appropriate.
    • Fetal blood sampling is primarily done after the completion of 18 gestation weeks. With the guidance of an ultrasound, a needle is punctured into the abdomen to sample some cells of the fetus. Its use ranges from detection of blood disorders to the karyotyping of fetal lymphocytes.
  • Newborn screening involves screening a newborn child as a preventative health measure. Phenylketonuria and congenital hypothyroidism are conditions for which this screening is frequently used. Benefits of this screening are significant where treatment is available.
  • Late-onset Disorders testing includes testing for diseases that may occur in late life. Adult diseases commonly screened are cancer and heart disease. These diseases are known to have genetic and environmental causation and genetic testing plots the susceptibility of the individual for these diseases.
  • Identity testing or DNA fingerprinting involves profiling the individuals genetic information from DNA test results of genetic markers in order to locate characteristics unique to the individual. Most commonly used by forensics in criminal investigations, this type of testing is increasingly gaining a lot of media attention and public recognition.