Factors Influencing Development

This is the first post in another mini-series, this time about growth and development of the individual after birth! (For more info about the reproductive system and birth, go here, here, here or here.)

So... factors influencing development. There are a myriad of factors influencing how an individual develops. Some are genetic, some environmental (the old nature-nurture debate!). Genetic influences have to do with the chromosomes passed down to the child- half of them from the mother's ovum, the other half from the father's sperm. Environmental influences are quite varied- while the child is in the womb, pretty much the only environmental influences are related to the mother's diet and consumption of other substances that cross through into the placenta, but outside the womb, influences include other people, culture, climate, food and so on. There are many traits that can be linked to both genetics and the environment. For example, our potential heights might be determined genetically, but whether or not we reach our potential is often determined by other outside influences, such as nutrition.

Congenital disorders are diseases or defects which are present at birth due to either defective genes or environmental factors. If DNA copies incorrectly during cell division, a gene mutation, or a change in a single gene, might occur. If a cell receives too many or too few chromosomes, or parts of chromosomes, this is called a chromosomal mutation. Most mutations are harmful, many resulting in natural abortion of the pregnancy early on or in some kind of birth defect. However, not all mutations are harmful. Other congenital disorders involve environmental influences, including diseases, nutrient deficiencies or drugs, all of which can affect the developing individual.

Mutagens are agents that can increase the rate at which mutations occur. (They do not cause mutations as far as we know.) Mutagens include mustard gas, sulfur dioxide, X-rays, radiation from radioactive waste, and so on. Hence, doctors try to avoid using X-rays during the early stages of pregnancy.

Teratogenic agents are chemicals that cause physical defects in the developing embryo. These include alcohol (which might cause foetal alcohol syndrome), smoking (which is associated with a higher risk of SIDS), thalidomide (a chemical that used to be in morning sickness pills until it was found to result in children with malformed limbs), heroin, LSD, and many medicinal drugs. Care has to be taken to avoid taking medication that might interfere with the development of the foetus.

Here's a brief list of some birth defects:

• Cleft palate- This occurs when the bones of the hard palate (the front part of the roof of the mouth) don't come together before birth. This disorder is associated with cleft lip, a split in the upper lip. Cleft palate and cleft lip can be rectified with surgery.
• Down syndrome- Also known as trisomy-21, since it's caused by having 3 of the chromosome number 21. Symptoms include mental retardation and malformation of the heart, ears, hands and feet. The risk of Down Syndrome increases as the mother reaches the end of her child-bearing period.
• Muscular dystrophy- A genetic disease in which the muscles waste away (due to uncontrolled cell necrosis IIRC. Lalalalalaaaaa I clearly can't remember much from Year 10 Skills Week...). As the child grows, more and more muscle tissue wastes away and is replaced by fatty substances. Death inevitably results from the wasting away of the muscles in the lungs or heart.
• Phenylketonuria (PKU)- A genetic disorder that can result in severe mental retardation. The gene controlling the production of an enzyme that breaks phenylalanine down is affected, so toxic levels of phenylalanine accumulate in the blood, resulting in damage to the growing brain. A special diet, restricting phenylalanine intake, can be used during the first 5 years of life. After this period, brain development is more or less complete, so phenylalanine levels are no longer a cause for concern.
• Thalassaemia- A genetic form of anaemia in which there are defects in the formation of the haemoglobin molecule. People with thalassaemia need frequent blood transfusions, as well as medication to remove the excess iron in their bodies.
• Spinal bifida is a neural tube defect in which the vertebrae of the spinal column don't fully "close up" around the spinal cord. In severe cases, parts of the spinal cord and nerves may be pushed through the gap in the spine. Spina bifida can be treated with surgery in order to prevent further damage to the spinal cord. Spina bifida, and other neural tube defects, are less likely to occur if the woman has had adequate intake of folic acid (folate) before and during pregnancy.

There are several ways in which birth defects can be detected early so that the parents can decide whether or not to have an abortion, and so that they can make preparations if they do decide to keep the child with the birth defect. Some methods involve looking at images of the baby, while others involve analysing chromosomes. (Random fun fact: a photograph of all of the chromosomes displayed in order is called a karyotype.)

Without further ado, here's a quick list of methods:

• Ultrasound uses inaudible, high-frequency sound waves, which are reflected by the foetal tissues, to produce an image of the foetus. This image can then be analysed to check for malformed body parts.
• Amniocentesis involves the removal of 10-20mL of amniotic fluid, which contains some living cells from the foetus. These can be checked for abnormalities in biochemistry or in number/structure of chromosomes. Amniocentesis is usually done between the 16th and 20th weeks of pregnancy.
• Chorionic villus sampling (CVS) is kind of like amniocentesis, but instead of removing amniotic fluid, foetal cells from the chorion are checked instead. There are several advantages to this method- firstly, the foetal tissue can be tested more quickly and secondly, testing can be done a little earlier in the pregnancy- at 8-12 weeks.
• Blood tests- A special blood test can be used to detect genetic disorders 6 weeks after conception. The blood sample is treated with antibodies which only adhere to the foetal cells in the mother's blood. The antibodies have magnetic beads attached to them, allowing them (and the foetal cells) to be removed via the use of a magnet. The foetal cells can then be examined for genetic abnormalities.
• Fetoscopy- A small, telescope-like instrument is inserted into an incision made in the abdominal wall, allowing doctors to have a look at the developing foetus. The procedure als allows doctors to take samples (of skin tissue, umbilical cord blood etc.) for further analysis. This is a relatively high-risk procedure, so it is generally only done if there is high risk of a defect.(See http://www.fetoscope.net/fetoscopy/ for more details)
• Marker proteins- Some proteins are more common in certain defects, and thus testing for the presence of these proteins helps to detect abnormalities. For example, alphafetoprotein (AFP) is high in foetuses with spina bifida.
• DNA probe technology is used to look for and identify abnormal genes. Genetic disorders such as Duchenne muscular dystrophy and thalassaemia can be tested for using this method.

Genetic counselling services are sometimes used to help determine the risks of having a baby with a birth defect. Genetic counsellors look at family history of the disorder to advise parents of potential risks. If parents decide to take the risk, one or more of the above diagnostic techniques can be used to determine whether or not the foetus is affected.