PART-III
Dr. Giriraj Kusre
(Professor of Anatomy, Assam Medical College, Dibrugarh Phone: 9435034595)
Once an organ is formed, it differentiates into its
mature form and grows in size. Any assault occurring during this period results
in some morphological changes in the organ or system. One of the common causes
of disruption is obstruction of blood supply to the organ. The presence of some
abnormal amniotic bands may compress the organ and restrict the growth and
differentiation of the organ or system.
2. Deformations: This is a type of birth defect occurring due to mechanical pressure on a part of the foetus over a prolonged period. These mechanical forces deform the shape of the anatomical structure. Clubfoot is one of the most common examples of this type of defect. The musculoskeletal system is the most common system involved, and these deformations can be treated postnatally.
3. Syndromes: These are groups of defects occurring together due to a specific common cause. In these cases, the risk of recurrence is known or can be predicted. Downs syndrome, Turner syndrome, etc.
5. Association: the non-random appearance of two or more anomalies that occur together more frequently than by chance alone is called association.
Causes of birth defects: The causes of birth defects fall into two major groups.
1. Genetic: As has been mentioned, the blue print of the life of a new individual is stored.
Within the nucleus of the zygote as the genes, or DNA. These genes, or DNA, which maintain a calendar, sometimes show some minor or major changes occurring naturally or under the influence of some environmental factors. These changes are called mutations. These changes may be passed on from the parents to their children. These inherited mutations cause a change in the development of an organ or may change the calendar of the individual.
Failure in the appearance of menstrual bleeding at the time of puberty or premature ageing are some of the examples of defects in the calendar.
2. Environmental factors: Environmental factors play a significant role in the occurrence of a birth defect. The Thalidomide tragedy, which was observed in 1961 by W. Lenz, where the use of a sedative drug called Thalidomide during pregnancy caused a limb defect in the newborn baby, highlighted the role of environmental factors in the occurrence of birth defects. Gradually, other environmental factors were identified, which proved to be causing birth defects.
In 1941, a Sydney ophthalmologist, Norman McAlister Gregg, observed an increase in cases of congenital cataracts (problem in the lens of the eye) in infants born to mothers who had rubella infection during pregnancy. The relationship between infection or drugs and the occurrence of birth defects established the role of environmental factors in birth defects. These factors were called teratogens. Environmental factors are classified as:
1. Infectious agents: bacteria, viruses, or protozoa such as syphilis, rubella, cytomegalovirus, herpes virus, toxoplasma, etc.
2. Physical agents: X-rays, high temperature (hyperthermia), etc.
3. Chemical agents: various drugs such as thalidomide, lithium, valproic acid, alcohol, industrial solvents, organic mercury, lead, etc.
4. Hormones: maternal diabetes, androgenic agents, diethylstilbesterol, etc.
5. Nutritional factors: maternal iodine deficiency, folic acid deficiency, hypervitaminosis A, etc.
6. b) Functional defects
Functional or developmental birth defects are related to a problem with how a body part or body system works or functions. These problems can include:
1. Nervous system or brain problems: intellectual disabilities, behavioural disorders, difficulties in speech and language, and movement problems These defects can be described as a problem of wiring in the brain.
2. Congenital deafness or blindness
3. Degenerative disorders are conditions where an individual may be normal at birth but may steadily get worse due to the loss of functions of some tissues or cells. Muscular dystrophy is such an example.
Normally, functional or behavioural defects are not visible at the time of birth and are manifested in the later part of life. Most of these defects have a genetic cause. Some functional or behavioural defects, such as defects of the nervous system, occur due to the failure of the nerves to establish connections with the adjacent nerves, resulting in reduced intellect or behaviour problems. These defects occur in the later part of pregnancy or during the neonatal period. In some of the degenerative defects, such as muscular dystrophy, muscles lack some proteins that protect them from injury or help to repair them after injury. The muscles are normal at the time of birth, but repeated injury during use of these muscles results in gradual loss of the muscle cells. By the time the individual reaches adulthood, most of the muscle cells die, making the muscle weak enough to carry out its normal function.
1. c) Metabolic defects
Metabolism is a complex set of chemical reactions occurring in the body and is important to maintain a normal life. A normal level of secretion of hormones and enzymes is required to complete certain chemical reactions. A decreased or increased level of these hormones and enzymes may either reduce the speed of a reaction, result in the production of excess by-products, or cause the accumulation of abnormal molecules in the cytoplasm of the cell.
Some of the common inherited metabolic disorders are
1. a) G6PD deficiency
2. b) Congenital hypothyroidism
3. c) Familial hypercholesterolemia
4. d) Phenylketonuria (PKU)
5. e) Gaucher disease
6. f) Hunter syndrome, etc.
Prevention and treatment of birth defects
The occurrence of birth defects is a natural phenomenon, and if left to nature, it will keep occurring in the community. To prevent these defects, we must understand the processes of normal development and teratogens.
1) Birth defects due to genetic causes
There are some common conditions in which heredity plays an important part but where there is no simple mode of inheritance. In such conditions, the risk of recurrence is empirical. For example, the empirical risk for acute leukaemia in childhood in the general population is 1 in 3000, 1 in 700 in siblings, and 1 in 5 in monozygotic twins. Depending on the risk of recurrence, counselling can be done.
In conditions inherited by autosomal recessive genes (genes that do not manifest when the genes are inherited from one parent), marriage in the same family or blood relatives increases the chance of inheritance. So, consanguinity plays an important role in the inheritance of autosomal recessive disorders.
Autosomal dominant genes can cause a birth defect when inherited from any of the parents. In this type of inheritance, the offspring may manifest the severe form of the defect, while the parent may have the milder form. A prenatal diagnosis can help in the identification of defects before the birth of the baby, and an option can be given to the parents to continue or terminate the pregnancy.
Some of the genetic causes have a predictable risk, and premarital pre-marital counseling can help the couple make a decision before or after marriage. Genetic diseases (such as haemophilia and duchenne muscular dystrophy) where the carrier state can be recognised with a high degree of certainty Detection of the carriers in the family should be done, and a prenatal diagnosis can be advised once the carriers get pregnant.
2) Avoidance of teratogens
As it is well known that exposure to certain teratogens during pregnancy may increase the chances of birth defects, no drugs or harmful agents should be taken during pregnancy unless prescribed by a competent physician. The state of pregnancy must be inquired about by every radiologist before exposing any woman of childbearing age to radiation. Alcohol and addictive substances should be avoided during pregnancy.
If the woman is taking a known tertagogenic drug for an existing disease, such as epilepsy, hyperthyroidism, depression, or TB, a risk-benefit analysis must be done before prescribing the drug. An option for a non-tertogenic drug, even if of lesser efficacy, should be explored.