Birth defects: Challenges and solutions

(Professor of Anatomy, Assam Medical College, Dibrugarh Phone: 9435034595)

Approximately 15% of new borns are born with minor birth defects. The presence of an extra finger in the hand or feet, a small ear, or a pigmented spot on the skin is not detrimental to the survival of the baby but may be an indication of an underlying severe malformation. It is estimated that babies with one minor defect have a 3% chance of having a major birth defect, those with two minor defects have a 10% chance, and those with three or more minor defects have a 20% chance of having a major defect. Therefore, minor birth defects may serve as a clue for diagnosing more serious underlying major defects.

Process of Normal Development

To understand birth defects, we must first understand the process of normal development. Our body develops from a single cell called a zygote. This single cell rapidly divides to form a multicellular individual. Normal development occurs through three synchronized processes. 1. cellular proliferation; 2. cell differentiation; and 3. growth.

n Cell Proliferation: Our body is made of millions of cells, all derived from a single zygote.

Cell proliferation is a process of cell division that increases the number of cells from a single cell to millions. Cell division occurs through a process called mitosis. The rate of cell division is very fast in the early days of development and occurs in geometric progression. It is most rapid in the first two weeks of development, which gradually stabilizes during adulthood and continues to some extent throughout the life of an individual.

n Cell differentiation: Differentiation is the process of specialising cells to take up a specific function. From the second week of development onward, the cells place themselves in a specific position to take up a specific action or function. As we take up specific professions just after the completion of higher secondary classes, these cells also start taking up specific functions (professions). Cells doing the same action come together to form a group; such groups are now called organs. Different organs come together to complete the action to a logical result; such a group of organs is called a system. e.g Nephrons are made up of cells that are supposed to clean our blood. Several nephrons come together to form a bean-shaped organ called the kidney. Organs like the kidney, ureter, urinary bladder, and urethra come together to form a system called the excretory system, or urinary system, to clean blood and excrete waste products out of the body. The cell differentiation to form an organ is completed within 6–8 weeks of development. That means that by the time the mother becomes aware of her pregnancy, the organ has already started taking shape.

3. Growth: Growth means an increase in bulk, which may take place in one of the three ways

4. An increase in the size of the body due to an increase in the number of cells is known as multiplicative growth.

5. Increase in cell size (auxetic growth)

6. Increase or accumulation of intercellular substance, that is, increased substance in between the cells (accretionary growth). An increase in the girth of our abdomen during middle age is due to the accumulation of fat.

The period of development of a foetus in the womb can be divided into three distinct periods.

1. Germinal period: It extends from the first to the third week of development, when rapid cell proliferation occurs.

2. Embryonic period or period of embryogenesis: This period extends from the 4th week to the 8th week, when most of the tissues and organs of the body are formed.

3. The foetal period extends from the third month to the delivery of the baby and is characterised by rapid growth of the foetus and maturation of the organs.

We must have pondered that our brain always lies in the upper part of the body and our legs are always in the lower part. Why the opposite never occurs. There are some factors that determine the position of each organ in the body. These regulatory factors, which help in determining the position of different organs, are known as organizers. Organisers act by means of the liberation of a chemical, the chemical nature of which is not known. Any abnormality in the release of these chemicals results in abnormalities in the body.

The structural defects may occur due to incomplete or excess development or failure to eliminate the excess cells. e.g., the presence of additional fingers in the hand or feet or the absence of one or more fingers are such examples. The increase and decrease in the development of an organ occurs due to an abnormal increase or decrease in cell proliferation or failure in the programmed death of the excess cells.

The formation or disappearance of an organ and its maturation and function follow a calendar. These events, which follow a calendar, are called mile stones. Disappearance or involution of the thymus, appearance of milk teeth or permanent teeth, standing, walking, speaking a few meaningful words, starting of menstruation (puberty) or menopause, appearance of the breast, or greying of the hairs all follow a timeline.

The blue print of life of a new individual is stored within the nucleus of the zygote as genes or DNA, and the embryogenesis gradually unfolds the coils of life under the direction of the genetic code. In the early stages of development, each cell is capable of forming a complete embryo (an individual); these types of cells are called totipotent cells (stem cells). Gradually, they lose their totipotent character and become specific for specific organs.

Any deviation from the normal process of development may result in a birth defect.

Types of birth defects

Birth defects can be broadly classified into three categories.

1. a) Structural defects

2. b) behavioural and functional defects and

3. c) Metabolic defects

4. a) Structural defects

All structural defects occur due to an assault on the mechanism of normal structural development.

Depending on the time of assault, the defects are classified into four categories.

1. Malformations: The first cell of our body is known as the zygote. A zygote is formed by the union of sperm from the father’s side and ovum from the mother’s side. This first cell rapidly divides through a process of cell division called mitosis. During the first two weeks of development, the number of cells increases in a geometric progression, and from the third week onward, these cells organise themselves in a certain manner to differentiate into organs. The nervous system is the first to develop, followed by the circulatory system, and so on. Within the 6th to 8th weeks of development, most of the organs can be identified by their shape and function (although immature in function). They are visible in ultrasound and other non-invasive imaging techniques. Any assault or restriction during this period may result in the complete or partial absence of a structure or alteration of the normal configuration. The assaults may be in the form of an environmental factor, a genetic factor, or both occurring in tandem. Absence of a kidney, absence of an ovary or uterus, failure in the development of a lobe in the thyroid gland, etc. are some of the examples of malformation.

2. Disruptions: Disruption is a form of birth defect occurring in an already-formed structure. (To be continued)