American Medical Association Family Medical Guide - American Medical Association [673]
Diagnosis
Homocystinuria can be diagnosed from a physical examination, a health history, and various imaging and laboratory tests. A doctor may notice during a physical examination that a child has dislocation of the lens of the eye and nearsightedness. In this case, he or she will refer the child to an ophthalmologist for a more thorough eye examination. A child with homocystinuria may also have a history of blood clots. To confirm the diagnosis, a doctor may recommend X-rays of the bones to detect osteoporosis, a blood test to determine if the levels of methionine and homocysteine are high, a urine test to detect homocysteine, or a liver biopsy or skin biopsy to look for a deficiency of the enzyme cystathionine beta synthase.
Treatment
There is no cure for homocystinuria, but many people can control the disorder with a restricted diet. Infants are given a formula that is low in methionine. A low-protein diet must be followed throughout life. High doses of vitamin B6 along with a folic acid supplement (400 micrograms daily) can help lower the level of homocysteine in the blood in some people. For other people, supplements of a nutrient called betaine is used to reduce the level of homocysteine.
Alpha1-Antitrypsin Deficiency
Alpha1-antitrypsin deficiency is a recessive genetic disorder that causes the liver to make defective or inadequate amounts of the protein alpha1antitrypsin. Alpha1-antitrypsin normally protects the lungs against an enzyme (neutrophil elastase) released by white blood cells when fighting infections. When the lungs do not have enough alpha1antitrypsin, they become damaged by the enzyme and lose their ability to properly expand and contract. Smoking worsens the lung damage by irritating lung tissue, prompting the release of more of the harmful enzyme.
If alpha1-antitrypsin is defective, the liver cannot release it into the bloodstream and it stays in the liver, damaging it over time and eventually causing cirrhosis (see page 790). Not all people with alpha1antitrypsin deficiency have liver problems, but 12 to 15 percent of affected adults and a small percentage of young children with the disorder develop cirrhosis. Liver disease can occur at the same time as lung disease.
There are several different forms of alpha1antitrypsin deficiency that have varying degrees of severity, depending on the specific gene a person inherits. The condition is rare, affecting fewer than 100,000 people in the United States. However, an estimated 95 percent of affected people remain undiagnosed. To have alpha1-antitrypsin deficiency, a person must inherit one abnormal copy of the gene for the disorder from each parent. Inheriting only one defective gene makes a person an unaffected carrier—that is, he or she does not have the disorder but can pass the gene on to a child.
Symptoms
The primary symptom of alpha1-antitrypsin deficiency is shortness of breath during daily activities. Eventually, the person develops chronic emphysema (see page 656) by the third or fourth decade of life (earlier if he or she smokes). People who develop cirrhosis of the liver may have nausea, flatulence, weight loss, weakness, and abdominal pain.
Diagnosis
Alpha1-antitrypsin deficiency can be difficult to diagnose because the symptoms can mimic those of asthma (see page 640) or chronic bronchitis (see page 655), but a diagnosis of emphysema at an early age raises a red flag. A simple blood test can measure levels of alpha1-antitrypsin. If blood levels fall below 45 percent of normal, the doctor will order additional blood tests to identify the defective gene. The doctor will also order other tests of the lungs, including a pulmonary function test that measures how well the airways are working, a blood gas analysis that gauges the amount of oxygen in the blood, a chest X-ray, and exercise testing. An electrocardiogram (see page 559), which measures the electrical activity of the heart, may also be performed to confirm the diagnosis