The Facts of Life: Examining Reproductive Health

Childbirth

Birth Defects

Normally, each person should have 23 pairs of chromosomes and a pair of genes for every feature or trait. The father contributes one set of 23 chromosomes with its DNA in his sperm. The mother contributes another set of 23 chromosomes with its DNA in her egg. The egg and sperm combine at fertilization. Thus we get one or more genes from each parent for every inherited trait. An inherited trait is any feature such as eye or hair color, height, or a disease which can be passed from parent to child. For any feature or disease to be passed to the next generation, the code for that trait must be in the DNA.

32. 23 chromosome pairs

Birth Defects
Birth defects have been noted for thousands of years in primitive drawings, carvings, and descriptions on clay tablets. Today, they are known to be caused by chromosome errors, altered genes, teratogens, or by a combination of genetic and environmental factors.

Chromosome Errors

Chromosome errors can occur, particularly during the formation of reproductive cells. As a result, the fertilized egg cell may contain chromosomes in abnormal number, structure, or arrangement. The most common birth defect resulting from a chromosomal error is called Down syndrome.

33. Microscopic photograph of chromosomes

Down Syndrome
Down syndrome is one of the most common genetic conditions. It affects people of all races and economic levels. Approximately 1 in 800 to 1,000 babies are born with the condition. In approximately 95% of people with Down syndrome, there is an extra number 21 chromosome in each cell. The extra chromosome may be passed to a child from either the mother or the father. When this happens, it is known as trisomy 21. Though it is known that the cause of Down syndrome is an error in cell division, it is not known why the error occurs.

A child with Down syndrome has delays in physical and mental development. Typical characteristics include: low muscle tone, upward slanting eyes, low-set ears, and a single horizontal crease on either palm. Children with Down syndrome may face health complications beyond the usual childhood illnesses. Problems such as heart defects, can be life threatening. Other health problems are of less significance. There are programs to help children with Down syndrome develop to their utmost potential. Many of these children attend school, and learn to read and write. Adults with Down syndrome may hold jobs and live semi-independently in their communities.

A woman age 35 or over may want to consider having prenatal testing that may reveal if an unborn baby is likely to have Down syndrome. Prenatal tests include a blood test called alpha- fetoprotein (AFP) screening, amniocentesis, or chorionic villus sampling. Though the chance of having a baby with Down syndrome increases significantly with age, statistics indicate that the majority of children with Down syndrome are born to women younger than 35.

Gene Errors
There are hundreds to thousands of genes within each chromosome. Some inherited diseases are caused by altered genes. Diseases caused by an altered gene may be passed from one generation to the next through different inheritance patterns. Some examples of diseases due to an altered gene are Sickle Cell Disease, Duchenne Muscular Dystrophy, and Huntington disease.

Sickle Cell Disease
In the United States, those at the highest risk of having sickle cell disease are African-Americans. Approximately 1 in every 400 to 600 black people has sickle cell disease. Hispanics of Caribbean descent, and people of Arab, Greek, Maltese, Italian, Sardinian, Turkish, and South Asian ancestry also have an increased risk.

Sickle cell disease is an inherited condition in which both parents are carriers of the sickle cell gene. Carriers have 1 copy of the sickle cell gene but do not have symptoms of the condition. To have sickle cell disease, a person must have 2 copies of the sickle cell gene. When both parents are carriers, each of their children will have a 50% chance of being a carrier, a 25% chance to have the disease, and a 25% chance of not being a carrier or having the disease. A disease that is inherited in this manner is called autosomal recessive.

Sickle cell disease affects a protein in red blood cells called hemoglobin. Hemoglobin carries oxygen from the lungs to every part of the body. A change in the hemoglobin causes sickle cell disease. Red blood cells are normally round and flexible in order to pass easily through blood vessels. However, for those who have the disease, the cells become distorted, forming a rigid banana or sickle shape. These cells pile up and clog tiny blood vessels, causing a shortage of oxygen rich red blood cells to nearby tissues. Areas of the body receiving inadequate oxygen start to hurt. This is the source of pain that comes from sickle cell disease.

A person with sickle cell disease is often pale, short of breath, and easily tired. Infections may worsen the disease. People with sickle cell disease are also especially vulnerable to infections. Bacterial infections, such as those that cause meningitis and pneumonia, are the leading cause of death among children who have the disease. However, early diagnosis and treatment can reduce the risk of death.

At this time there is no known cure or therapy to prevent or correct the disease carrying gene. Researchers are studying the possibilities of gene therapy for the future. There has been great progress in reducing pain and improving the quality of life for those who are affected.

Duchenne Muscular Dystrophy
Duchenne muscular dystrophy (DMD) is the most common and severe form of muscular dystrophy. Usually, the symptoms that suggest DMD are identified by the time a male child is 5 years old. Early signs of DMD include a tendency to fall, difficulty rising from a sitting or lying position, and a waddling gait. Another feature is enlargement of the calf muscles. This is due to an accumulation of fat and connective tissue in the muscle. Blood tests may show an elevation of CPK (creatinine phosphokinase), which is an important muscle enzyme that leaks from damaged muscle. The muscle weakness progresses over a period of 10 to 20 years. A wheelchair is usually necessary by the time a boy reaches adolescence. Breathing becomes affected in the latter stages of the disease, which leads to premature death before 30 years of age.

DMD is inherited in an X-linked recessive manner. X-linked conditions affect males almost exclusively, so that boys who inherit the gene always develop the disease. Women who have the gene for DMD are known as carriers. A carrier can pass on the gene to her children. Her sons have a 50% chance of being affected, and her daughters have a 50% chance of being a carrier. Researchers have identified the altered gene on the X chromosome that, when defective, is responsible for DMD. This gene's failure to make a vital muscle protein called dystrophin is the cause of the disease. With these discoveries, scientists can now attempt to create therapies aimed at fixing the gene, replacing the missing protein, or preventing key steps in the disease's development.

Prenatal diagnosis is available for most women concerned about passing DMD to their sons. An amniocentesis is done to determine if the baby has an alteration in the dystrophin gene. The alteration may be a deletion or duplication of genetic material on the X chromosome. Specialized genetic testing is used to determine these small rearrangements. Since the testing is quite complex and the inheritance pattern is difficult to explain, genetic counseling is usually recommended.

Huntington Disease
Huntington disease (HD) is a genetic condition that has been found in all races and all parts of the world. The origin of the HD gene was probably in Europe and the disease was then inherited through generations until it was present worldwide. The disease affects approximately 1 in 10,000 individuals of European descent. It is interesting to note, though, that there has been a much higher number of cases in places like the Lake Maracaibo region of Venezuela. Woody Guthrie, the famous American folk singer, had Huntington disease.

HD is a fatal neurological disease that progresses at a variable rate. The initial symptoms usually appear in the fourth to fifth decade of life; however, the range of age of onset is broad. The first symptoms are often mild and can include clumsiness, falling, dropping objects, problems with balance, impaired driving, slurred speech, or altered handwriting. The classic symptom of Huntington disease is uncoordinated movements that the affected individual cannot control. There is also progressive intellectual impairment and often psychiatric and behavioral disturbances.

In virtually all cases, HD is inherited from a parent. If either the mother or father has HD, each of their children will have a 50% chance of developing HD. A disease that is inherited in this manner is called autosomal dominant.

On March 23, 1993, during a press conference at Massachussets General Hospital, the discovery of the HD gene was announced. This occurred after 10 years of intensive research. The HD gene is located on chromosome number 4. In fact, a small portion of DNA on chromosome 4 is often repeated approximately 40 to 80 times in individuals who have HD. Since the discovery of the HD gene, it has now become possible to do presymptomatic testing. Presymptomatic testing, through a blood test, is available to those individuals with a family history of the disease. Individuals who choose to have the testing must carefully consider the consequences of learning that they may or may not be likely to develop the disease.

Teratogens
Teratogens are any environmental hazard that can harm a developing baby. These include maternal illness, prenatal drug or alcohol use, and some medications or chemicals.

Fetal Alcohol Syndrome
Alcohol is a known teratogen. This means that alcohol consumption by a female while she is pregnant can harm a developing baby. When a pregnant woman drinks alcohol, it crosses the barrier of the placenta. Research has shown that 2 or more drinks per day can be detrimental to a developing baby. Women who have a habit of drinking alcohol may be taking the risk that their baby will be born with Fetal Alcohol Syndrome or FAS.

Babies with FAS may:

• be born too small
• be mentally retarded
• have a cleft lip or unusual facial features
• have heart problems

Some babies have a few, but not all of these problems. This is called Fetal Alcohol Effects or FAE. Women who have a habit of drinking alcohol are also at greater risk of having a miscarriage or stillborn baby. No one knows how much alcohol will put an unborn baby at risk. The safest choice is to not drink alcohol if you are a woman planning a pregnancy soon or if you think you may be pregnant.

Multifactoral Conditions
Sometimes a child is born with a birth defect that is believed to be caused by the interaction of many genes and environmental factors. Examples of multifactoral conditions are cleft lip/palate and spina bifida.

Spina Bifida
Spina bifida, often called "open spine," is caused by the incomplete closure of the backbone when a fetus is developing inside itÕs motherÕs womb. It is one of a group of birth defects known as neural tube defects. The neural tube is the structure that develops into the brain and the spine. Spina bifida is one of the most common birth defects in the United States. Approximately 1 in 2,000 babies are born with spina bifida. It occurs more frequently in white people of European descent.

Hydrocephalus, otherwise known as "water on the brain," occurs in 70 to 90 percent of severe cases of spina bifida. When this happens, the spinal fluid is unable to drain properly. As a result, the head becomes enlarged and creates pressure on the brain. Treatment is often critical to prevent seizures, mental retardation, or even death.

Although the cause of spina bifida is not well understood, scientists believe that a combination of genetic and environmental factors cause neural tube defects, including spina bifida. Approximately 90 to 95 percent of babies with spina bifida are born to parents with no family history of the condition. However, if parents have had one child with spina bifida, there is a 1 in 40 chance that their next child will have a neural tube defect. If 2 of their children have the condition, there is a 1 in 20 chance that their next baby will have a neural tube defect. Prenatal tests may reveal whether an unborn baby is likely to have spina bifida. These include the alpha-fetoprotein (AFP) screening test and an ultrasound examination of the fetal spine. If the diagnosis is positive for spina bifida, health care providers can plan the delivery so that any necessary surgery or treatment will be immediately available for the baby. A cesarean delivery may be necessary.

Studies have shown that an adequate intake of folic acid can prevent neural tube defects, including spina bifida. A female can lower her risk of having a child with spina bifida by making sure she gets 0.4 mg of folic acid each day. The RDA (recommended daily amount) of folic acid is 0.4 mg. Some of the best sources of folic acid are leafy green vegetables, spinach, peanuts, okra, broccoli, cauliflower, avocados, brussels sprouts, rye, corn, papaya, and oranges. Some cereals are also fortified with folic acid. Most over-the-counter multivitamins have this amount of folic acid in them. If a woman chooses to take multivitamins she should begin taking them a month before she is planning to get pregnant. No more than one multivitamin should be consumed each day. Too much of some other vitamins, like vitamin A, could harm an unborn baby.

Links of interest:

• Iowa Registry for Congenital and Inherited Disorders