CHILD DEVELOPMENT
CHAPTER 4: BIRTH DEFECTS
SECTION 1: SIGNS AND SYMPTOMS OF BIRTH DEFECTS
There are thousands of birth defects, each with its own unique signs and symptoms. Defects can affect nearly any part of the body, and generally have an effect on the body’s structure, function or metabolism. They may occur alone or in groups. Some birth defects are obvious immediately after birth, while others may not be discovered until later childhood or even adulthood. Some may not demonstrate any signs or symptoms, or may not show signs or symptoms until childhood or adulthood. Because of the wide range of birth defects, nearly any problem (e.g., poor feeding, unresponsiveness, irritability) could potentially be a sign or symptom of a birth defect. Some other common signs and symptoms of birth defects include:
- Abnormal physical structure. Structural defects result in abnormal physical properties. These may be external, such as misshapen ears or too many fingers or toes. They may be internal, such as with missing or malformed organs. Many structural defects may be obvious both internally and externally, such as with defects in the skull that cause an abnormal shape of the head or face. Musculoskeletal problems or paralysis may be less apparent before a child learns to crawl.
- Mental impairment. Many birth defects result in learning disabilities or mental retardation. These defects may not become apparent until an infant gets older and appears to be missing developmental milestones associated with a given age. Learning disabilities may not be noticed until a child is 4 or 5 years old.
- Sensory impairment. Blindness and/or deafness may occur due to a birth defect. This may be due to structural defects in the eyes and/or ears or problems with the central nervous system.
- Irregular heart rhythms. Murmurs and irregular heart rhythms may be caused by heart defects.
Hormone or enzyme deficiencies. Many birth defects result in hormone or enzyme deficiencies. Many of these may be detected in blood, urine or fecal tests. Some enzyme disorders may not be detected until much later, when the child suffers some sort of attack or experiences mental retardation because of malfunctioning enzymes.
SECTION 2: CAUSES OF BIRTH DEFECTS
Some birth defects are caused by a single, well-documented factor, such as a missing or abnormal gene or chromosome. Many are caused by a combination of several factors. However, the causes of 70 percent of all birth defects are not known, according to the U.S. Centers for Disease Control and Prevention (CDC).
Many birth defects are the direct result of genetic disorders. These are often chromosomal conditions, such as an absent or extra chromosome. Even a single abnormal gene can cause a birth defect. In normal development, a baby receives half of its genes from the mother and half from the father. Genes may be dominant or recessive. For example, if one parent has the recessive gene for the enzyme associated with phenylketonuria (PKU) and the other parent has a dominant gene for the PKU enzyme, the baby will have functioning enzymes and will not develop PKU. Many genetic disorders such as PKU can occur only when both parents contribute a recessive gene, leading to expression of the defect.
Genetic birth defects can also result from a spontaneous mutation in a gene or during embryonic development. Some genes only increase an infant’s risk of a birth defect. These can be passed down for many generations before the defect actually occurs.
Other causes of birth defects include environmental factors affecting the fetus and the mother. These environmental factors may be divided into categories such as:
- Teratogens. These are harmful substances that the mother takes in and that pass through the placenta into the fetal bloodstream. Among the best known of these harmful substances is alcohol, which causes fetal alcohol syndrome in about one out of every 1,000 infants, according to the March of Dimes. Fetal alcohol syndrome (FAS) is a collection of birth defects that occur when a fetus is exposed to alcohol. These range from learning and behavioral difficulties to mental retardation. A woman who drinks at any point during pregnancy puts the fetus at risk of FAS. Generally, the more alcohol consumed during pregnancy, the greater the risk of FAS and the more severe the symptoms. However, exactly how much alcohol causes defects is not known, and appears to vary from person to person and from pregnancy to pregnancy.
About 1,200 children are born with FAS every year. The U.S. Department of Health and Human Services estimates that 40,000 babies are born every year with some signs of prenatal exposure to alcohol. FAS is not diagnosed until after a child is born.
Children with FAS will have certain distinctive facial abnormalities, physical growth deficiency (e.g., height or weight) as well as central nervous system problems. There is no cure for FAS. Most treatment focuses on addressing the special education or medical needs of children with FAS. However, the physical, mental or behavioral defects in children with FAS are lifelong, irreversible problems.
- Smoking. Maternal smoking has also been linked to many birth defects, including cleft lip and palate, heart defects, clubfoot and other limb defects.
- Illegal drugs. Recreational drugs are also dangerous to the fetus. The March of Dimes reports that infants whose mothers used cocaine in early pregnancy are five times more likely to have urinary tract defects and damage to the central nervous system.
- Medications. Many medications have also been linked to birth defects. However, while women are encouraged to avoid alcohol, nicotine and recreational drugs while pregnant, they may not be able to avoid all medications. All women who are or may be pregnant should discuss all of their medications, including over-the-counter medications, with their doctor.
- Infections and illnesses. Women with diabetes or high blood pressure have an increased risk of having a child with a birth defect, particularly if these conditions are not under control during the pregnancy. Infections during pregnancy may also lead to birth defects. Rubella carries the highest risk, although it is much less common now that the rubella vaccination is available. According to the March of Dimes, infants have a 25 percent chance of displaying at least one feature of congenital rubella syndrome if the mother is infected during the first trimester of pregnancy. Other infections that may result in birth defects include cytomegalovirus, toxoplasmosis and chickenpox. Sexually transmitted diseases (e.g., syphilis, genital herpes) may also lead to birth defects.
- Maternal nutrition. Infants born to women who are particularly stressed, obese, or malnourished also have an increased risk of birth defects, particularly neural tube defects. Many neural tube defects are linked to a deficiency in the B vitamin folic acid before and during pregnancy.
In addition to the known causes, some maternal risk factors increase the likelihood of birth defects. These include:
- Age. Infants born to teenagers and women over age 35 have a higher risk of birth defects, particularly chromosomal defects (e.g., Down syndrome).
- Pregnancy history. Women with a history of miscarriage or who have had previous children with birth defects also have a higher risk of having another child with a birth defect.
- Premature birth. Infants born prematurely have a greater risk of having some birth defects, such as cerebral palsy.
- Multiple pregnancies. Infants in multiple pregnancies, especially higher order multiple pregnancies (three or more babies) are more likely to have birth defects.
Vaccines are another concern for pregnant women. Any vaccination containing live viruses may cause the same birth defects that are associated with an active infection with the virus. Such live virus vaccines include those for measles, mumps and rubella. Women should receive any live virus vaccines before they become pregnant.
SECTION 3: DIAGNOSIS METHODS FOR BIRTH DEFECTS
Many birth defects can be detected before birth. According to the American Academy of Family Physicians (AAFP), around 250 birth defects can be diagnosed prenatally. Some are obvious when the infant is born or are discovered through newborn screening tests. Most birth defects are discovered in infancy, within the first year of life. Others may not be detected until childhood or even adulthood.
Prenatal screening tests are used to determine the chance that a particular fetus has a birth defect. They are safe, noninvasive and typically painless. They are not exact, but may be used to determine if prenatal diagnostic tests are necessary. Screening tests may be more accurate when performed earlier in the pregnancy. Some women may not wish to undergo prenatal screening. However, others find that these tests can give them peace of mind or time to prepare for a child with special needs.
Prenatal screening tests include:
- Maternal blood tests. Identify and measure substances in the mother’s blood that reveal information about her fetus. There are a number of these tests available, including the triple screen test and alpha fetoprotein plus, which detect different substances.
- Detailed ultrasound. Uses sound waves to create an image of the inside of a mother’s womb. This can be used to identify the physical features associated with some birth defects. Ultrasound is particularly useful in the diagnosis of structural defects affecting areas such as the heart and spinal cord.
If screening tests indicate a potential problem, a physician may recommend a diagnostic test. Prenatal diagnostic tests are around 99 percent accurate in identifying Down syndrome and other chromosomal conditions, according to the AAFP. The diagnosis of many other birth defects may not be as accurate. These tests are associated with complications, including a risk of miscarriage and preterm labor. They are typically only recommended for women with a high risk of having a child with a birth defect, including those over the age of 35 years, those with a family history of birth defects or genetic problems, and those who have had abnormal results on screening tests. Parents may use the results of diagnostic tests to prepare for the birth of a special needs child or to consider terminating the pregnancy.
Prenatal diagnostic tests include:
- Amniocentesis. With the aid of continuous ultrasound guidance, a needle is inserted through the abdomen and into the uterus. Then, a small amount of amniotic fluid (the fluid in the uterus) is removed for testing. This test is generally performed between 16 and 20 weeks into the pregnancy.
- Chorionic villus sampling (CVS). A sample of the placenta is removed for testing. It may be obtained using either a needle through the abdomen (as in amniocentesis) or a tube inserted through the vagina. This test can be performed between eight and 12 weeks of pregnancy.
- Percutaneous umbilical blood sampling (PUBS). A needle is used to remove a sample of blood from the fetus' umbilical cord. This test carries higher risks of complications than amniocentesis or CVS and is typically used only when diagnosis must be made very quickly. It is typically performed late in pregnancy, after 20 weeks.
After an infant is born, newborn screening tests are typically performed. These tests are used to detect metabolic disorders, often called inborn errors of metabolism (IEMs), that are not otherwise apparent at birth. They typically require a small sample of blood be taken from the infant’s heel.
An infant’s first well-child exam typically includes a thorough evaluation for birth defects, including a detailed physical examination and an evaluation of the infant’s family history. Hearing and vision tests are also usually performed. If there is any suspicion that a birth defect may be present, other tests (e.g., x-rays, CAT scans) may follow. Pediatricians also observe infants at other regular examinations to determine if they are meeting developmental milestones.
SECTION 4: TREATMENT OPTIONS FOR BIRTH DEFECTS
Birth defects range from mild to very serious. Some require little treatment at all and some cannot be treated or will result in early death regardless of treatment attempts. However, most birth defects lie somewhere between these two extremes and are treatable to some degree.
Specialists may be helpful or necessary for the treatment of certain birth defects. For example, skeletal defects may require the expertise of a pediatric orthopedist and neural tube defects typically require assistance from a pediatric neurologist and a surgeon.
Some birth defects can be treated before birth. For example, injections of blood products (immunoglobulin-Rhogam) are used to treat Rh disease of the newborn. Heart medications may be given to women carrying infants with certain heart defects and extra vitamins may be taken by women carrying infants with enzyme deficiencies. In some cases, birth defects may even be treated using surgery before birth. Prenatal surgery has been used to repair urinary tract blockages, lung tumors, neural tube defects (e.g., spina bifida) and congenital diaphragmatic hernia (an opening in the muscle between the chest and abdomen). However, these surgeries remain experimental and require further research.
Many structural defects are corrected through surgery in early infancy. Such surgery is often effective enough that the defect is completely cured, as is the case with many heart defects. Many birth defects can also be treated through nonsurgical means. Medications are often quite useful for metabolic defects, for example. Physical and occupational therapy may help infants with birth defects to overcome or correct some defects and build and maintain muscle tone and coordination. Speech therapy may also be useful for some individuals.
Early intervention services can help children with many problems associated with birth defects. These may include feeding support and nutritional services. It usually includes information on assistive technology (e.g., leg braces) and social work services that may help accommodate a child living with birth defects as he or she ages.
Finally, counseling may be an option. Mental health or genetic counseling may be important for parents, particularly immediately after learning of a child’s birth defect. Support groups may also be beneficial. They allow children with birth defects and their parents to meet other people with similar conditions.
SECTION 5: PREVENTION METHODS FOR BIRTH DEFECTS
Some birth defects are easily preventable. For example, fetal alcohol syndrome can be prevented by avoiding alcohol during pregnancy. However, not all birth defects can be prevented. Healthy parents who do everything their physicians recommend can still have an infant with a birth defect. Many birth defects occur before most women discover that they are pregnant. Women may unknowingly expose their fetuses to conditions that they would otherwise avoid (e.g., drinking alcohol, smoking) if they only realized that they were pregnant.
Pregnancies that are planned have a reduced risk of birth defects. Genetic counseling is common during pregnancy planning. Here, a genetic counselor discusses an individual couple’s chances of having a child with a birth defect. This can help establish realistic expectations. In addition, couples who are carriers of known serious genetic conditions may want to use methods of assistive reproductive technology to minimize the risk of a fetus that will develop a serious or fatal birth defect.
Women who plan their pregnancies tend to take care of themselves as though they were pregnant. This is particularly beneficial because many steps to prevent birth defects are best initiated before conception. For example, taking 400 micrograms of folic acid (a type of B vitamin) daily has been shown to reduce the risk of neural tube defects by 70 percent, according to the American Academy of Family Physicians (AAFP). However, it must be taken both before and during pregnancy. Planning a pregnancy also allows women to treat or control any conditions (e.g., obesity, diabetes, seizures, high blood pressure) before their pregnancy.
SECTION 6. HEREDITARY DISEASES
Most babies are born healthy, but some are not. Genes carry all of the information about a person, including any diseases they might have. It is possible to pass diseases on to your children through the genes in your eggs or sperm. These types of inherited diseases that are passed on from generation to generation are called hereditary diseases or genetic diseases. Hereditary diseases can be passed on in any gene in an egg or sperm cell. The majority of genetic diseases are passed on by a gene in one of the 22 autosome chromo-somes. However, between 40 and 60 hereditary diseases are passed on to children through the sex chromosomes. These diseases are called sex-linked or X-linked diseases because they are passed on through the X chromosome in eggs or sperm. The Y chromosome doesn’t seem to carry any genetic diseases. If a parent has a genetic disease, their child may either be healthy and normal, be a carrier for it, or have the disease and be a carrier for it. To see how this works, let’s look at an example.
Hemophilia is a hereditary disease in which a person’s blood doesn’t clot normally. A person can bleed to death if they get cut or injured. About 1 in 10,000 people have hemophilia. Hemophilia is carried and passed on by the X chromosome. Let’s say a man has hemophilia. He’ll have an X chromosome that carries the hemophilia disease (Xa) and a healthy Y chromosome. If his wife has two healthy X chromosomes (XX), you can see from the following Punnett square which of their children will be carriers, and which will have the disease:
Xa
Dad’s sperm
Y
|
Mom’s egg
X X |
|
XXa carrier girl |
XXa carrier girl |
|
XY normal boy |
XY normal boy |
|
As you can see, all of their daughters be carriers (XXa). However, none of their daughters will be a hemophiliac because the healthy X chromosome will be dominant over the recessive Xa chromosome. Their sons will be totally normal (XY) and will not have the disease or be carriers.
Now, let’s assume that one day one of their daughters has children. She is a carrier, so she has an XXa chromosome. If her husband is normal, he’ll have an XY chromosome. The following Punnett square shows what their children will likely be:
X
Dad’s sperm
Y
|
Mom’s egg
Xa X |
|
XXa carrier girl |
XX normal girl |
|
XaY hemo- philiac son |
XY normal son |
|
In this case, half of their daughters will be normal (XX). Half of their daughters will be carriers (XXa). None of their daughters will be a hemophiliac because their healthy X chromosome will by dominant and mask the disease. Half of their sons will be normal (XY). Half of their sons will be hemophiliacs and will have the disease (XaY). In this latter case, there isn’t a healthy X chromosome to mask the disease, so the disease shows up. These sons will also be carriers of the disease. Since girls have a normal X chromosome to mask the disease, they can only show the disease if they get a hemophilia gene from both parents (XaXa). This is extremely rare. Since boys don’t have another X chromosome to mask the disease, almost every case of hemophilia occurs in males.
X-LINKED HEREDITARY DISEASES
As these examples show, X-linked hereditary diseases can be passed down from either the mother or the father, but they are always passed on the X chromosome. There are other X-linked hereditary diseases besides hemophilia. Here is a brief definition of some of the most common ones:
1. COLOR BLINDNESS: the person sees everything in shades of gray. They can’t tell the difference between colors. They don’t know what blue, red, green or yellow looks like.
2. DUCHENNE MUSCULAR DYSTROPHY: this is the most common and severe type of muscular dystrophy. It is an X-linked recessive disease, so girls are usually just carriers, but boys have the disease. This disease shows up when toddlers start to crawl and walk. This disease prevents the joints and muscles from developing right so, the person has trouble walking, talking, and using their other muscles. The disease slowly damages all of the muscles in a person’s body, including the heart. Most people usually die in their twenties or early thirties from a heart attack or respiratory tract infections.
3. DIABETES INSIPIDUS: in this disease, the kidneys don’t absorb water right, and the person urinates a lot and is always thirsty. The disease affects about 1 in 10,000 to 20,000 people. There usually aren’t any problems as long as the person drinks plenty of fluids.
4. RICKETS: in this disease, children don’t absorb Vitamin D correctly. Vitamin D is needed for healthy bones. Children with this disease have bones that are weak and don’t grow straight. They often walk bow-legged.
OTHER HEREDITARY DISEASES
As mentioned before, only a few of the genetic diseases are passed to a child on the X chromosome. The majority of diseases are passed on one of the other 22 chromosomes in an egg or sperm. Here is a brief definition of some of the most common ones:
1. PKU (PHENYLKETONURIA): this disease affects mostly white babies. In this disease, the baby is missing an enzyme that works in the liver. This enzyme turns a substance called phenylalanine into tyrosine. Without this enzyme, phenalanine builds up inside a person’s blood. This can cause retardation, seizures, rashes, vomiting, hyperactivity, and failure to thrive. The problem is present at birth, but the signs show up until the baby is about 6 months old. Most babies with this problem have white skin, blond hair, and blue eyes. About 1 in 10,000 to 20,000 babies have this disease. A blood test at birth can show if the baby has the disease, and steps can be taken to make the effects of the disease less severe.
2. ALBINISM: this disease affects all races. About 1 in every 5,000 to 20,000 people have it. In this disease, the person lacks an enzyme that helps form melanin, which is what gives skin its color or pigment. People with this disease have very white skin, fine white hair, and pink or light blue eyes. They have many problems with their eyes and typically have very bad eyesight. There is no treatment or cure.
3. TAY-SACHS DISEASE: this disease affects mostly Jewish people. In this disease, a certain type of lipid accumulates in the neurons in the central nervous system. Most babies with the disease appear normal at birth. Between four and six months old, they start to get apathetic and listless and lose motor and social skills. In addition, they gradually go blind and get dementia (go insane). Most children with this disease die by the age of 3 or 4. Sometimes tests can show if a fetus has this disease.
4. DIABETES MELLITUS: this disease is a more severe type of diabetes. Estimates are that 2% of people have this disease. The basic problem is that the person doesn’t produce the right amount of insulin, so the body doesn’t aborb sugar correctly. People are born with this defect, but the symptoms can start any time after birth. In fact, the majority of people don’t show symptoms until after they turn 30. If a parent has this disease, there is a 5% to 10% chance they’ll pass it on to their children. People with this disease eat a lot, drink a lot, and urinate a lot. The disease can’t be cured. However, the symptoms can be greatly controlled by daily shots of insulin and a careful diet with very little or no sugar.
5. CYSTIC FIBROSIS: this disease affects mostly white babies. Almost 1 in 1,500 to 2,000 babies have it. Basically, the person’s mucus glands secrete too much mucus. The mucus clogs their pancreas. This keeps pancreatic enzymes from getting to the intestines. Without these enzymes, food is not absorbed properly, and the person can’t get enough nutrients. These people are very skinny and don’t grow well. The mucus also clogs their lungs, causing mild to severe breathing problems. The mucus in their lungs also provides an excellent place for bacteria to grow. This bacteria often develops into lung infections. There are some treatments for the problems associated with this disease. However, the majority of people die from chronic lung problems by their late teens or early twenties.
6. SICKLE-CELL ANEMIA: this disease affects mostly black people, and 1 in 500 to 600 black people have it. In this disease, a person’s red blood cells are shaped oddly, like a crescent moon or sickle. These abnormal red blood cells don’t carry oxygen very well. They also clog up the arteries and veins. The lack of enough oxygen in the body causes anemia. A child first begins to show symptoms around 2 to 4 years old. The child will be pale, tired, not eat well, and have aches and pains in their back, arms, and legs. Through-out their life, people with this disease will have aches, pains, and cramps from lack of oxygen and infections from the clogged arteries. If arteries in their brains get clogged, people can die from this disease. There is no cure for this disease but painkillers can be given to ease the pain. People can take a very easy blood test to see if they are a carrier for this disease and might pass it on to their children.
7. DEAFNESS: inherited deafness and other hearing disorders are common. One reason it’s so common is because deaf people tend to marry other deaf people, which increases the chances that one or both parents will pass on a hearing disorder to their children. Since hearing problems are caused by recessive genes, it is possible for people with hearing disorders to have normal children or children with hearing problems.
8. VISION PROBLEMS: there are various disorders of the eyes that are inherited including color blindness, cataracts, nearsightedness, farsightedness, and blindness. Inherited eye problems are very common. In most vision disorders, parents detect the problem in their children when they start school or start to read. Depending on the problem, there are a variety of treatments. The most common one is eyeglasses.
9. DOWN’S SYNDROME: this disease is caused when the chromosomes don’t separate right and the person gets an extra chromosome. Instead of 46 chromosomes, the person has 47. They accidentally get 3 number 21 chromosomes instead of 2 of them. In most cases, the extra chromosome comes from the mother. As a woman gets older, she is more likely to have chromosomes that don’t separate right. This is why women over 35 are more likely to have a child with Down’s Syndrome. The chances of having a baby with Down’s Syndrome are 1 in 10,000 for young mothers, 1 in 300 if the mother is 35 to 39, and 1 in 30 if the mother over 40. The reason a mother’s age matters is because all of a woman’s eggs are formed by the time she’s born. By the time she is 30, her eggs are 30 years old, too, and older eggs have more defects.
It is usually obvious at birth when a baby has Down’s Syndrome. The babies are short, round, and have small, low-set ears, flat noses, and slanted eyes. They have small mouths and their tongues stick out. They have short, broad hands with stubby fingers. They have flabby muscles. In addition to these physical deformities, the babies are retarded. They generally need someone to take care of them for the rest of their lives. Half of the babies have heart problems, which causes many of them to die during the first year. They are also likely to have kidney and intestinal problems and to develop leukemia. There is no cure for Down’s Syndrome. People with Down’s Syndrome rarely have children. Males with the disease are almost always born sterile. Women with the disease start having periods much later than normal, have irregular periods, and go through menopause at an earlier age. However, some women with the disease have been able to have children, and there is a 50% chance that they’ll pass the disease on to their children. A pregnant woman can have an amniocentesis test to find out if her fetus has Down’s Syndrome.
Genetic counselors help people determine if genetic diseases run in their families, and if they are likely to pass them on to their children. By using blood tests, you and your spouse can see what the chances are of your children having a genetic disease. These tests can’t predict all genetic diseases, but they can be a great help to parents who know that a particular disease runs in their family.
End of Chapter 4.
The homework assignment is shown below. Students would complete the multiple-choice study questions, then use them as a study guide to prepare to take a test over this chapter’s material.
Each ½ credit course consists of 16 chapters with homework assignments/exams, two quarter exams, and a semester final.
Each 1 credit course consists of 32 chapters with homework assignments/exams, four quarter exams, and a course final.
CHILD DEVELOPMENT
CHAPTER 4: HOMEWORK QUESTIONS
1. Seven common signs and symptoms of birth defects are:
1. __________________________________________________
2. __________________________________________________
3. __________________________________________________
4. __________________________________________________
5. __________________________________________________
6. __________________________________________________
7. __________________________________________________
2. Learning disabilities are often not noticed until a child is ________ or _________ years old.
3. Many birth defects result in _______________________ or __________________________ deficiencies, which can be detected by
__________________ , __________________ , or __________________ tests.
4. Some birth defects are caused by a missing or abnormal ______________ or ______________________ , but the cause of ________ % of birth defects is unknown.
5. In genetic birth defects, the cause is often an __________________ or __________________ chromosome.
6. These six environmental factors may also cause birth defects:
1. _________________________________
2. _________________________________
3. _________________________________
4. _________________________________
5. _________________________________
6. _________________________________
7. A pregnant woman’s use of alcohol causes fetal alcohol syndrome in _____________ out of every ______________ infants. Infants with FAS suffer everything from _______________________ and ______________________ difficulties to __________________________________ .
8. It is estimated that every year __________________ babies are born in the United States with some signs of prenatal exposure to alcohol, and about ___________________ babies are born with fetal alcohol syndrome.
9. Smoking by a pregnant woman may cause these birth defects: _____________________________ , _______________________________ ,
_________________________ and other ______________________________ .
10. Is this statement true OR false? Legal medications, such as those prescribed by a doctor or that can be bought over-the-counter and taken by a pregnant woman are safe and can’t cause birth defects. __________________
11. A woman’s age also affects the chances that her baby with have birth defects. Specifically, infants born to ___________________ and women over age ___________ have a higher risk of birth defects.
12. About ___________ birth defects can be diagnosed before the baby is born.
13. These five types of tests can be used to determine if a fetus has a birth defect:
1. _________________________________
2. _________________________________
3. _________________________________
4. _________________________________
5. _________________________________
14. These four methods can be used to treat some birth defects before birth:
1. ________________________________
2. ________________________________
3. ________________________________
4. ________________________________
15. Diseases passed to a fetus through the mom’s or dad’s chromosomes are called __________________ or ____________________ diseases.
16. Genetic diseases passed to a fetus through the sex chromosomes are always carried by the _______ chromosome, never the ______ chromosome.
17. List five genetic diseases that are passed by a sex chromosome:
1. _______________________________
2. _______________________________
3. _______________________________
4. _______________________________
5. _______________________________
18. If a pregnant woman takes care of herself before and during her pregnancy—eats right, doesn’t smoke or drink, doesn’t take legal or illegal drugs, etc.--there is no chance that she will have a baby with a birth defect. Is this statement true OR false? _____________________
Match each of the following genetic diseases listed on the left with the correct description listed on the right. Some descriptions may not be used.
________19. PKU A. red blood cells aren’t formed correctly, leading to a lack of oxygen in the body; results in anemia; mostly affects black babies
________20. sickle-cell anemia B. hearing disorder caused by a recessive
gene
_______ 21. Down’s syndrome C. mucus glands secrete too much mucus,
causing breathing problems and lung infections
_______ 22. diabetes mellitus D. Vitamin D is not absorbed properly,
resulting in bone growth problems
_______ 23. deafness E. excess lipid in the central nervous
system causes blindness, dementia, and death; mostly affects Jewish babies
_______ 24. Tay-Sacks disease F. person is missing an enzyme to make
their liver work correctly; results in retardation, seizures, and failure to thrive; mostly affects white babies
_______ 25. cystic fibrosis G. person’s body doesn’t produce enough
insulin, so sugar isn’t absorbed correctly
H. infant has an extra chromosome, more
likely to happen when the pregnant woman is over the age of 35
