Phenylketonuria (PKU) is a genetic disorder in which the individual cannot properly metabolize phenylalanine, an amino acid that naturally occurs in many food sources. It results from a recessive gene and occurs about once in every 10,000 to 20,000 live births. Today, phenylketonuria is easily detected in infancy, and it is treated by a diet that prevents an excess accumulation of phenylalanine (Rohde & others, 2014). If phenylketonuria is left untreated, however, excess phenylalanine Page 45 builds up in
the child, producing intellectual disability and hyperactivity. Phenylketonuria accounts for approximately 1 percent of individuals who are institutionalized for intellectual disabilities, and it occurs primarily in Whites.
How Would You…?
As a health-care professional, how would you explain the heredity-environment interaction to
new parents who are upset when they discover that their child has a treatable genetic defect? Sickle-cell anemia, which occurs most often in African Americans, is a genetic disorder that impairs functioning of the body’s red blood cells. Red blood cells, which carry oxygen to the body’s other cells, are usually shaped like a disk. In sickle-cell anemia, a recessive gene causes the red blood cell to become a hook-shaped “sickle” that cannot carry oxygen properly and dies quickly. As a result, the body’s cells do not receive adequate oxygen, causing anemia and early death (Derebail & others, 2014). About 1 in 400 African American babies is affected by sickle-cell anemia. One in 10 African Americans is a carrier, as is 1 in 20 Latin Americans. Recent research strongly supports the use of hydroxyurea therapy for infants with sickle-cell anemia beginning at 9 months of age (Yawn & John-Sowah, 2015). Other diseases that result from genetic abnormalities include cystic fibrosis, some forms of diabetes, hemophilia, Huntington disease, Alzheimer disease, spina bifida, and Tay- Sachs disease. Someday, scientists may be able to determine why these and other genetic abnormalities occur and discover how to cure them (Capurro & others, 2015; Tai & others, 2015; Wang & others, 2016; Williams & others, 2016).