How Hereditary Illnesses Work

Happily, most children arrive in this world normal and healthy. By adulthood, children have had their share of colds, coughs, stomachaches, and other minor illnesses. Compared with the usual childhood ailments, hereditary diseases are rare, but they do occur, and all parents should be informed about the more common ones. Genetic counseling is advisable for parents who are in certain high-risk groups.

Central to any discussion of hereditary diseases is an understanding of the basis of heredity -- the gene. Genes are bits of chemical information that determine all of our inborn characteristics. They are carried in structures called chromosomes within the nucleus of all cells.

Genes are composed of varying arrangements of molecules of deoxyribonucleic acid (DNA), which makes up the chromosomes. Each gene, by virtue of its unique DNA sequence, holds the code for a specific trait.

Except for the sex cells (eggs and sperm), each cell in the body contains 46 chromosomes. Forty-four of the chromosomes are called autosomes. The two remaining chromosomes are the sex chromosomes.

The autosomal chromosomes are paired. For each pair, one chromosome comes from an individual's mother, the other from the father. Each gene on one chromosome is matched to a corresponding gene on the other chromosome. Thus, for every genetic trait, there are two genes.

The two genes that provide the code for a trait may not be identical. For example, if a gene pair governs eye color, one gene may code for blue eyes, the other for brown eyes. Because the gene for brown eyes is dominant, the eyes will be brown. The gene for blue eyes is recessive. A person with brown eyes may also have two genes for brown eyes. For a dominant trait to be expressed, however, only one dominant gene is necessary. A person with blue eyes must have two genes for blue eyes. To express any recessive trait, a double dose of recessive genes is necessary. A person with only one copy of a recessive gene exhibits no evidence of the trait.

Like eye color, certain illnesses are genetically determined. In some instances, the defective gene has been passed from generation to generation within a family by carriers who show no symptoms of the illness. Parents may be aware of a family history of hereditary disease. Whether their baby develops that illness depends upon the inheritance of dominant or recessive genes.

The better known genetic disorders include sickle cell anemia, Tay-Sachs disease, and cystic fibrosis, which are more prevalent among certain demographic groups. Other diseases include Phenylketonuria, autosomal dominant disease, hemophilia, muscular dystrophy and may include conditions like cleft lip, spina bifida and Down syndrome. Read about genetic diseases next.

This information is solely for informational purposes. IT IS NOT INTENDED TO PROVIDE MEDICAL ADVICE. Neither the Editors of Consumer Guide (R), Publications International, Ltd., the author nor publisher take responsibility for any possible consequences from any treatment, procedure, exercise, dietary modification, action or application of medication which results from reading or following the information contained in this information. The publication of this information does not constitute the practice of medicine, and this information does not replace the advice of your physician or other health care provider. Before undertaking any course of treatment, the reader must seek the advice of their physician or other health care provider.

There are several different categories of genetic diseases that are divided by the type of gene or chromosome that transmits the disease.  The most common are autosomal recessive, autosomal dominant, multifactorial, x-linked recessive and chromosomal abnormalities.

In most cases, a woman who inherits a defective recessive gene from one parent and a normal dominant gene from the other parent does not exhibit any symptoms of that illness but is a carrier of that abnormal gene. However, if she has children with a man who is also a carrier, their children have a 50 percent chance of inheriting one defective gene and being nonsymptomatic carriers, and a 25 percent chance of inheriting two defective recessive genes and expressing the disease. This pattern is called autosomal recessive inheritance. The better-known of these disorders include sickle cell anemia, Tay-Sachs disease, and cystic fibrosis.

Sickle cell anemia:

Anemia is sometimes caused by a deficiency of hemoglobin. Hemoglobin is the substance in red blood cells that carries oxygen to the other cells in the body. In sickle cell disease, the hemoglobin is abnormal. People who carry only one defective recessive gene usually have no symptoms of the disease. People who inherit two sickle cell genes develop many problems due to the structure of their abnormal hemoglobin.

This defective hemoglobin molecule causes the normally round blood cell to sickle (assume a crescent shape). Anemia occurs because sickled red blood cells are more fragile, hence more easily destroyed. Sickled cells are also less able to bend as they squeeze through tiny blood vessels. Thus, these cells become trapped and obstruct small vessels.

Episodic clogging of the vessels with sickled blood cells causes tissue damage and pain, especially in the hands, feet, joints, and abdomen. Children with sickle cell anemia are prone to more frequent infections than children without the condition.

At present, no cure for sickle cell anemia exists. Treatment includes administration of painkillers and antibiotics as necessary. Children with sickle cell anemia who develop a fever should be seen by their doctor as soon as possible to determine treatment, which may include hospitalization for intravenous fluids and antibiotics. More children with sickle cell anemia are surviving into adulthood because of improved therapy and new, effective vaccines for many illnesses. Such vaccines are vital because children with sickle cell anemia are at increased risk for certain bacterial infections.

Because sickle cell anemia is most common among black persons, black adults are encouraged to undergo screening to determine if they are carriers of sickle cell anemia. Carriers can be identified by means of a simple blood test. Approximately eight percent of black people in the United States are carriers.

If both parents are carriers, they have a one in four chance of giving birth to a child with sickle cell disease. Sickle cell disease can be diagnosed before birth with the use of amniocentesis (see page 14 for an explanation of this procedure). In many states, most newborn babies are screened for sickle cell disease at birth by means of a blood test.

Tay-Sachs disease: Tay-Sachs disease is a metabolic disorder marked by the accumulation of a type of fatty acid in the liver, spleen, and brain. It is caused by a deficiency in the enzyme that normally degrades this fatty acid. After four to six months of normal development, children with Tay-Sachs exhibit deterioration in neurologic development. The disease progresses to mental retardation, blindness, and convulsions. Death usually occurs by age three or four. No treatment exists.

Preventive measures are available. The Ashkenazim, the Jews of eastern Europe, are disproportionately affected by Tay-Sachs, with nearly 100 times the rate of occurrence as other groups. Carriers have no symptoms of the disease and sometimes have no family history of the disease. It is recommended that all Jewish couples of eastern European descent undergo screening for the Tay-Sachs gene before they start their families. If both parents are carriers, diagnosis of Tay-Sachs disease in the baby can be made during pregnancy with the use of amniocentesis.

Cystic fibrosis: Cystic fibrosis is a serious childhood illness that causes the glands of the body to secrete abnormal sweat and mucus. The sweat glands secrete too much salt. The abnormally thick, sticky mucous secretions accumulate in and obstruct the lungs and pancreas. Since the pancreas is an important organ for digestion, these children fail to grow properly. The thick mucus in the lungs makes breathing difficult and leads to infections. Death is usually due to respiratory failure. Although no cure exists, improved treatment has brightened the prognosis of children with cystic fibrosis, giving them a good chance for survival into adulthood.

Cystic fibrosis is much more common in white people of northern European extraction. In the United States, approximately 1 in 29 white people are carriers. One infant in every 3,000 live births has cystic fibrosis. Traditionally, the disease has been diagnosed on the basis of sweat test results obtained only after the appearance of the symptoms. However, now diagnosis can be made before birth with amniocentesis.

Phenylketonuria: Phenylketonuria (PKU) is a rare disorder that can cause severe mental retardation. It is caused by an inability to convert an amino acid called phenylalanine into another amino acid called tyrosine. (Amino acids are the building blocks of proteins.) At elevated levels, phenylalanine damages brain cells, causing retardation.

In the United States, all newborns are screened for PKU by means of a blood test. Early detection and prompt treatment can prevent the mental retardation. Treatment consists of limiting a child's dietary intake of phenylalanine. If this dietary regimen is followed, children with PKU can have essentially normal development. Pregnant women who have PKU need to stick to this special diet to protect the baby's developing nervous system. All people with PKU must completely avoid the artificial sweetener aspartame, which contains phenylalanine. New research is in progress to help identify carriers of PKU and to diagnose PKU prenatally.

This information is solely for informational purposes. IT IS NOT INTENDED TO PROVIDE MEDICAL ADVICE. Neither the Editors of Consumer Guide (R), Publications International, Ltd., the author nor publisher take responsibility for any possible consequences from any treatment, procedure, exercise, dietary modification, action or application of medication which results from reading or following the information contained in this information. The publication of this information does not constitute the practice of medicine, and this information does not replace the advice of your physician or other health care provider. Before undertaking any course of treatment, the reader must seek the advice of their physician or other health care provider.

Another category of hereditary disease is called autosomal dominant disease. Because the defective gene is dominant, the disease is expressed even if only one gene is defective. A normal gene cannot mask the harmful effects of an abnormal gene as it can in autosomal recessive disease. If one parent has an autosomal dominant disease, the chances are 50 percent that each child will inherit the disorder.

Huntington chorea: An example of an autosomal dominant disease is Huntington chorea, a brain disease marked by abnormal body movements and mental deterioration beginning in middle age.

Although a few medicines have been found to make the symptoms more tolerable, the disease has no cure. Researchers have been able to identify carriers in families with Huntington chorea with a genetic test. It is hoped this procedure will be perfected and also extended to prenatal diagnosis.

Multifactorial Genetic Diseases

Multifactorial genetic diseases are illnesses that tend to run in families. These diseases are not due simply to the inheritance of a single defective gene. Rather, a cluster of faulty genes is inherited, which predisposes the person to a disease. Given the appropriate environmental factors, the person may actually develop that disease. Examples of illnesses that run in families include such chronic adult diseases as coronary heart disease, high blood pressure, and stomach ulcers, as well as birth defects, such as cleft lip and palate and spina bifida.

Cleft lip and palate: In cleft lip, the upper lip is divided by a vertical fissure. In cleft palate, the roof of the mouth is split by a longitudinal fissure. These two birth defects can occur alone or together. They are the result of incomplete fusion of the components that form the lip and mouth during fetal development.

Spina bifida: Spina bifida is a failure in the closure of the bony vertebral column with or without protrusion of the nerve tissue of the spinal cord. Paralysis below the defect often accompanies spina bifida if the spinal cord does protrude. When the spinal cord does not protrude, the vertebral defect may go unnoticed. Clues to indicate the presence of this form of spina bifida are abnormalities of the skin and tufts of hair overlying the spine in the lower part of the back.

During pregnancy, spina bifida in the fetus can be diagnosed by means of ultrasound study and detection of elevated levels of a substance called alpha-fetoprotein in the mother's blood and in the amniotic fluid that bathes the fetus. Spina bifida can be caused by a folate deficiency in the mother during pregnancy or exposure of the pregnant woman to certain drugs that interfere with folate.

Chromosomal Abnormalities

Sometimes the structure or the number of chromosomes is not normal. The risk of having a child with chromosomal abnormalities increases with increasing maternal age (and to some extent with increasing paternal age as well). If chromosomal abnormalities occur in the sex cells (eggs and sperm), the offspring may have physical and mental disorders.

Down syndrome: Formerly called mongolism, Down syndrome is a condition caused by a chromosomal abnormality. Due to the failure of the chromosomes to divide evenly during cell division, the person with Down syndrome has an extra chromosome (a total of 47). The presence of this extra chromosome causes a characteristic physical appearance and delayed physical and mental development. Other ailments, such as defects in the heart and digestive system, can accompany this syndrome. Despite their disabilities, children with Down syndrome usually have pleasant dispositions and can do quite well if given special therapy.

The cause of the chromosomal abnormality leading to Down syndrome is unknown. A genetic predisposition may exist. The incidence of Down syndrome increases with increasing maternal age. The condition can be diagnosed prenatally with the use of amniocentesis. For these reasons, women who have previously given birth to a baby with a chromosomal abnormality or who are older than 35 years of age are encouraged to undergo amniocentesis.

In sex-linked inheritance, the gene responsible for the disease is located on the X chromosome. Usually, the abnormal gene is recessive. For these reasons, the resultant disorder is called an X-linked recessive disease. In a woman with such a defective gene, the effects of the abnormal gene are masked by those of the normal gene on the other X chromosome. Although she does not have the disease herself, she is a carrier, capable of transmitting the defective gene to her children.

In X-linked recessive disease, the Y chromosome lacks the corresponding normal gene to mask the harmful effects of the abnormal gene on the X chromosome. Thus, all male offspring of a woman who is a carrier of an X-linked recessive disease have a 50 percent chance of having the condition. All female offspring have a 50 percent chance of being carriers. Following are examples of X-linked recessive disorders:

Color blindness: A person with the most common form of color blindness cannot distinguish red from green hues.

Hemophilia: In hemophilia, the blood does not clot properly. Persons with hemophilia bleed excessively, even from minor cuts. There are several forms of hemophilia, each caused by a deficiency of a different protein called a clotting factor. The disease is managed by giving transfusions of the deficient clotting factor and of whole blood to replace blood losses. Research continues toward the accurate identification of carriers and prenatal diagnosis of this disease.

Duchenne muscular dystrophy: Muscular dystrophy refers to a group of rare diseases characterized by progressive muscular weakness. Duchenne type muscular dystrophy is the most common. Between the ages of two and six years of age, children with this condition develop weakness first in their legs, then in their arms and trunk. The weakness rapidly worsens. Most children die during their second decade, usually as a result of severe weakness of the muscles of respiration. The disease has no cure. Treatment includes physical therapy, braces, and, occasionally, surgery.

Newer techniques and better understanding of the genes involved have made prenatal testing possible. Advances in genetic testing are soon likely to make it possible to detect the recessive trait in carriers as well.

In recent years, tremendous progress has been made in the development of genetic tests to diagnose heritable diseases. You may wish to consult your physician about genetic counseling if any of the following risk factors apply to you:

If you have any concerns or questions regarding heritable diseases, ask your physician. If you are considered to be at risk for passing on a hereditary disease to your children, you can receive genetic counseling. A genetic counselor asks you about your personal and family medical history. Blood tests may be necessary to help determine whether you are a carrier of a heritable disorder. You are advised about the chances of transmitting hereditary illness to your offspring. If you are pregnant, the well-being of your fetus can be assessed by several procedures:

Remember that the diseases described in this section are rare. Most expectant parents can look forward to the arrival of a healthy baby. If you are pregnant or hope to be and have any worries about the well-being of your child, don't hesitate to address them with your doctor. If your child does have a hereditary disease, however, it's important to confront and accept the realities of this challenge. Keep the lines of communication open within your family, seek out support groups, and avoid bearing all the guilt for your child's disease. Read about coping with a child who has a hereditary illness next.

Until two centuries ago, the death of a baby was an accepted, although tragic, risk of childbirth. Infectious diseases claimed many young lives. In mid-seventeenth century Europe, only one in four children survived to celebrate his fifth birthday. As recently as the late nineteenth century in the United States, one in five children died before the age of one year. Largely due to improved hygiene, immunizations, and antibiotics, babies in developed nations now die infrequently.

Although infant death is an uncommon occurrence, families sometimes have to cope with babies who have serious, chronic, and even fatal illnesses. Parents may walk an emotional tightrope between hope and despair for the long months that their child is ill.

Upon facing the diagnosis of serious illness in their infant or child, parents may at first feel nothing except shock and disbelief. Grief follows as a response to any loss. This loss may be the dissipation of their dreams of a healthy child. If the disease is expected to be fatal, parents may mourn in anticipation of the child's death. Despair, fear, anger, remorse, and loneliness are all emotions of the normal grieving reaction.

Dealing With Guilt

Guilt is another emotion many parents feel when they learn their infant is gravely ill. Parents can torment themselves or each other with feelings of responsibility for the illness. If the baby has a hereditary disease, feelings of self-blame may be especially overwhelming.

Self-reproach can be destructive. Negative feelings about oneself make it difficult for a parent to nurture the sick baby and the other members of the family. Guilt-ridden parents may either lavish excessive attention on the baby or turn away from her. Both responses amplify an older infant's or toddler's sense that something is wrong with her.

Parents may suffer further if communication between husband and wife is impaired. Their coping styles may be incompatible. Resentments may arise if one parent quits working to undertake the care of the sick child.

Sadly, having a child with a chronic or fatal disease can add enormous stress to a marriage. While it is safe to say that no marriage is the same after a child is diagnosed with a serious illness, families that recognize this stress are better equipped to cope. Marriage or family counseling is a vital part of coping with the stress, and your child's doctor or nurses can refer you to a therapist.

Helping Siblings to Cope

Parents often wonder whether their other children are too young to be told about the fatal illness or death of their sibling. Most psychologists feel it is crucial that the other children be told the truth in a straightforward manner that they can understand. Children who are not informed will still know something is frightfully wrong and may invent their own fantastic explanations.

A child's ability to comprehend death and dying depends on his age and prior experience with death (of a friend, family member, or pet). Before the age of two years, infants and toddlers are unable to grasp the concept of death. However, even very young children do react with distress to prolonged separations from loved ones.

After two years of age, given proper assistance from an adult, children are able to achieve a basic and concrete understanding of death. Still, they may have difficulty comprehending the permanence of death. Active imaginations lead to wild fantasies about where the deceased has gone. Because it is normal for children to have occasional negative feelings about their siblings, they may worry that their own thoughts or actions caused the illness. This sort of magical thinking and self-blame is especially common in children between the ages of five and eight.

A young child's response to the death of a sibling may be exasperating for parents. Using denial as a defense, he may act overtly as though nothing were wrong. Clues to inner turmoil include demanding, clinging behavior; regression to infantile behavior, such as lapses in toilet training; and increased aggression. Your warmth, understanding, and sharing of thoughts and feelings help him to grieve in a more appropriate fashion.

By 8 to 12 years of age, a child's understanding of death is similar to an adult's. However, the severe illness or death of a sibling may make him overly fearful of his own mortality.

This information is solely for informational purposes. IT IS NOT INTENDED TO PROVIDE MEDICAL ADVICE. Neither the Editors of Consumer Guide (R), Publications International, Ltd., the author nor publisher take responsibility for any possible consequences from any treatment, procedure, exercise, dietary modification, action or application of medication which results from reading or following the information contained in this information. The publication of this information does not constitute the practice of medicine, and this information does not replace the advice of your physician or other health care provider. Before undertaking any course of treatment, the reader must seek the advice of their physician or other health care provider.

As the family grapples with the serious illness and perhaps imminent death of the baby, the infant must also cope with the consequences of her ill health. An infant's need to be cuddled is just as great as her requirement for food. She thrives on consistent care from her parents. A baby quickly comes to know and love these special people.

Separations, such as during hospitalizations, can be very distressing for an infant. Parents of children with chronic diseases can sometimes arrange to care for the child at home with or without the assistance of a nurse. Should parents decide to bring their dying baby home, many communities have resources to assist them during this period (such as visiting nurses, home care nursing, and hospice care).

During necessary hospitalizations, most hospitals allow parents unrestricted visiting privileges and often provide facilities for parents to room-in with the child. This gives parents the opportunity to participate in the care of their sick baby. Caution must be exercised not to spend so much time with the ill child that the well-being of the parents and other family members suffers.

To help you cope with an ill or dying baby, do the following:

However, it is important for new parents to keep in mind that this is the worst-case scenario. The overwhelming majority of children are born health or with only minor genetic fluctuations that are easily corrected. While it is a good idea to stay informed to all of the possibilities, there is also no reason to focus on the negative.