Congenital Disorders

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Congenital disorders are those present at birth (birth defects). They fall into two categories: developmental disorders that occur during growth of the fetus and hereditary (familial) disorders that can be passed from parents to children through the germ cells. Genetic disorders are caused by a mutation (change) in the genes or chromosomes of the cells. They may involve changes in the number or structure of the chromosomes or changes in single or multiple genes. The appearance and severity of genetic disorders may also involve abnormal genes interacting with environmental factors. Examples are the diseases that "run in families," such as diabetes mellitus, heart disease, hypertension, and certain forms of cancer. Display 15-1 describes some of the most common genetic disorders.

A carrier of a genetic disorder is an individual who has a genetic defect that does not appear but that can be passed to offspring. Carriers of some genetic disorders can be identified using laboratory tests.

DISPLAY 15-1

Common Genetic Disorders*

DISEASE

CAUSE

DESCRIPTION

albinism

recessive gene mutation

lack of pigmentation

cystic fibrosis

recessive gene mutation

affects respiratory system, pancreas, and sweat glands; most common hereditary disease in white populations (see Chapter 11)

Down syndrome

extra chromosome 21

slanted eyes, short stature, mental retardation, and others; incidence increases with increasing maternal age

hemo_philia_ he-mo-FIL-e-a

recessive gene mutation on the X chromosome

bleeding disease passed from mothers to sons

Huntington disease

dominant gene mutation

altered metabolism destroys specific nerve cells; appears in adulthood and is fatal within about 10 years; causes motor and mental disorders

Klinefelter syndrome

extra sex (X) chromosome

lack of sexual development, lowered intelligence

Marfan syndrome

dominant gene mutation

disease of connective tissue with weakness of the aorta

neurofibromatosis nu-ro-fi -bro-ma-TO-sis

dominant gene mutation

multiple skin tumors containing nervous tissue

DISPLAY 15-1 Common Genetic Disorders*, continued

DISEASE

CAUSE

DESCRIPTION

phenylketonu r ia ( PKU)

recessive gene mutation

lack of enzyme to metabolize an amino acid; neu

fen-il-ke-to-NU-re-a

rologic signs, mental retardation, lack of pigment; tested for at birth; special diet can prevent retardation

sickle cell anemia

recessive gene mutation

abnormally shaped red cells block blood vessels; mainly affects black populations

Tay-Sachs disease

recessive gene mutation

an enzyme deficiency causes lipid to accumulate in nerve cells and other tissues; causes death in early childhood; carried in Jewish populations in eastern Europe

Turner syndrome

single sex (X) chromosome

sexual immaturity, short stature, possible lowered intelligence

*A dominant gene is one for a trait that always appears if the gene is present; that is, it will affect the offspring even if inherited from only one parent. A recessive gene is one for a trait that will appear only if the gene is inherited from both parents.

*A dominant gene is one for a trait that always appears if the gene is present; that is, it will affect the offspring even if inherited from only one parent. A recessive gene is one for a trait that will appear only if the gene is inherited from both parents.

Teratogens are factors that cause malformation of the developing fetus. These include infections, such as rubella (German measles), herpes simplex, and syphilis; alcohol; drugs; chemicals; and radiation. The fetus is most susceptible to teratogenic effects during the first 3 months of pregnancy. Examples of developmental disorders are atresia (absence or closure of a normal body opening), anencephaly (absence of a brain), cleft lip, cleft palate, and congenital heart disease. Spina bifida is incomplete closure of the spine, through which the spinal cord and its membranes may project (Fig. 15-13). This usually occurs in the lumbar region. If there is no herniation of tissue, the condition is spina bifida occulta. Protrusion of the meninges through the opening is a meningocele; in a myelomeningocele, both the spinal cord and membranes herniate through the defect, as seen in Figure 15-13D and Figure 15-14.

Many congenital disorders can now be detected before birth. Ultrasonography (Fig. 15-15), in addition to being used to monitor pregnancies and determine fetal sex, can also reveal certain fetal abnormalities. In

Meningocele And Myelomeningocele

FIGURE 15-13. Spinal defects. (A) Normal spinal cord. (B) Spina bifida occulta. (C) Meningocele. (D) Myelomeningocele. (Reprinted with permission from Pillitteri A. Maternal and Child Health Nursing: Care of the Childbearing and Childrearing Family. 4th Ed. Philadelphia: Lippincott Williams & Wilkins, 2003.)

FIGURE 15-13. Spinal defects. (A) Normal spinal cord. (B) Spina bifida occulta. (C) Meningocele. (D) Myelomeningocele. (Reprinted with permission from Pillitteri A. Maternal and Child Health Nursing: Care of the Childbearing and Childrearing Family. 4th Ed. Philadelphia: Lippincott Williams & Wilkins, 2003.)

FIGURE 15-14. A myelomeningocele. (Reprinted with permission from Pillitteri A. Maternal and Child Health Nursing: Care of the Childbearing and Childrearing Family. 4th Ed. Philadelphia: Lippincott Williams & Wilkins, 2003.)

ft amniocentesis (Fig. 15-16), a sample is withdrawn from the amniotic cavity with a needle. The fluid obtained can be analyzed for chemical abnormalities. The cells are grown in the laboratory and tested for biochemical disorders. A karyotype is prepared to study the genetic material. In chorionic villus sampling (CVS), small amounts of the membrane around the fetus are obtained through the cervix for analysis. This can be done at 8 to 10 weeks of pregnancy, in comparison with 14 to 16 weeks for amniocentesis.

Week Old Fetus
FIGURE 15-15. Transvaginal sonogram showing a 9-week-old fetus. (Reprinted with permission from Erkonen WE, Smith WL. Radiology 101: Basics and Fundamentals of Imaging. Philadelphia: Lippincott Williams & Wilkins, 1998.)
Week Old Fetus

adrenal

adrenal

Key Clinical Terms

DISORDERS

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Responses

  • Folco
    How spina bifida forms?
    7 years ago
  • Everard
    Can albinism be detected prenatally?
    2 years ago

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