Information on the following diseases can be found in the Related Disorders section of this report:

• Glucose-Galactose Malabsorption
• Sucrase-Isomaltase Deficiency
• Ulcerative Colitis
• Chronic Erosive Gastritis
• Irritable Bowel Syndrome

Individuals with a deficiency of lactase experience cramps, nausea, bloating, stomach rumbling (Borborygmi), gas (flatus) and/or diarrhea after eating or drinking lactose-rich foods, not all of which are dairy products. Symptoms are more severe when they occur in a newborn. The signs of congenital lactose intolerance are apparent soon after birth and usually include severe diarrhea, vomiting, abnormally low levels of body fluids (dehydration), and failure to thrive. Some infants may also have liver and kidney impairment.

Lactose intolerance is a prevalent disorder in adults, but it is rare in infants.
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Primary lactose intolerance may develop age a person ages. At birth and in early childhood, when milk, mother's or cow's, is the body's main source of food, the body produces large amounts of lactase. With age, the body's output of lactase decreases, especially since milk and milk products play less of a role in a person's diet. This gradual decline may cause symptoms of lactose intolerance.

Secondary lactose intolerance may become obvious if lactase production declines due to an injury to, or illness, or surgery on a person's small intestine. Intestinal diseases such as celiac disease, gastroenteritis or an inflammatory bowel disease, especially Crohn's disease are not infrequently accompanied by the symptoms of secondary lactose intolerance. This type of lactose intolerance may be transitory and last only a few weeks, after which the patient recovers from these symptoms. However, if it's caused by a long-term illness, it may be permanent.

Congenital lactose intolerance involves infants born with lactose intolerance. Congenital lactose intolerance is a rare disorder that is transmitted from generation to generation as an autosomal recessive trait. This means that both the mother and the father must pass on the defective form of the gene for a child to be affected. Infants with congenital lactose intolerance cannot thrive because they cannot metabolize or digest the lactose in their mothers' breast milk. Such baby's will have diarrhea from birth and require lactose-free infant formulas.

Genetic studies have determined that the mutated gene responsible for the congenital form of lactic intolerance is located at gene map locus 2q21. The disorder is transmitted as an autosomal recessive trait.

Chromosomes, which are present in the nucleus of human cells, carry the genetic information for each individual. Human body cells normally have 46 chromosomes. Pairs of human chromosomes are numbered from 1 through 22 and the sex chromosomes are designated X and Y. Males have one X and one Y chromosome and females have two X chromosomes. Each chromosome has a short arm designated "p" and a long arm designated "q". Chromosomes are further sub-divided into many bands that are numbered. For example, "chromosome 2q2" refers to band 21 on the long arm of chromosome 2. The numbered bands specify the location of the thousands of genes that are present on each chromosome.

Genetic diseases are determined by the combination of genes for a particular trait that are on the chromosomes received from the father and the mother.

Recessive genetic disorders occur when an individual inherits the same abnormal gene for the same trait from each parent. If an individual receives one normal gene and one gene for the disease, the person will be a carrier for the disease, but usually will not show symptoms. The risk for two carrier parents to both pass the defective gene and, therefore, have an affected child is 25% with each pregnancy. The risk to have a child who is a carrier like the parents is 50% with each pregnancy. The chance for a child to receive normal genes from both parents and be genetically normal for that particular trait is 25%. The risk is the same for males and females.

All individuals carry 4-5 abnormal genes. Parents who are close relatives (consanguineous) have a higher chance than unrelated parents to both carry the same abnormal gene, which increases the risk to have children with a recessive genetic disorder.

Congenital lactose intolerance is a rare disorder that affects males and females in equal numbers. Apparently, certain ethnic and racial groups show greater predisposition towards LI than others. It is estimated that 90% of Asian-Americans are lactose intolerant while about 75% of African Americans or American Indians are affected by the disorder.
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Symptoms of the following disorders can be similar to those of lactose intolerance. Comparisons may be useful for a differential diagnosis:

Glucose-Galactose Malabsorption (carbohydrate intolerance) is a rare inherited disorder characterized by the inability of the small intestine to transport and absorb glucose and galactose. The symptoms of this disorder in children may include diarrhea, dehydration, and failure to gain weight. In adults, symptoms of this disorder may include bloating, nausea, diarrhea, abdominal cramps, rumbling sounds caused by gas in the intestine (borborygmi), and/or excessive urination. (For more information on this disorder, choose "Glucose-Galactose Malabsorption" as your search term in the Rare Disease Database.)

Sucrase-Isomaltase Deficiency is a rare inherited gastrointestinal disorder that occurs because of low levels of the enzyme sucrase-isomaltase. The major symptom is diarrhea. Affected children may be unable to gain weight on a normal diet. Adults may experience abdominal cramps, bloating, and/or intestinal gas (flatus). Symptoms occur because of the ingestion of table sugar or certain other carbohydrates. (For more information on this disorder, choose "Sucrase-Isomaltase" as your search term in the Rare Disease Database.)

Ulcerative Colitis is an acute inflammatory bowel disease characterized by diarrhea and blood in the stools because of multiple, irregular ulcerations of the bowel. The initial symptoms of this disorder may include a general feeling of weakness (malaise) and fatigue. There may be abdominal discomfort, along with a change in the frequency and consistency of stools. Other symptoms may include abdominal pain, cramping, and urgency (tenesmus). Weight loss and a decrease in appetite are also associated with Ulcerative Colitis. (For more information on this disorder, choose "Ulcerative Colitis" as your search term in the Rare Disease Database.)

Chronic Erosive Gastritis is an inflammatory disorder characterized by multiple lesions in the mucous lining of the stomach. Symptoms of this disorder may include burning or a heavy feeling in the stomach, mild nausea, vomiting, loss of appetite and general weakness. In severe cases of Chronic Erosive Gastritis there may be bleeding from the stomach that can result in anemia. (For more information on this disorder, choose "Chronic Erosive Gastritis" as your search term in the Rare Disease Database.)

Irritable Bowel Syndrome, also known as Spastic Colon, is a common digestive disorder that involves both the small and large intestines. This disorder is characterized by abdominal pain, constipation, bloating, nausea, headache, and/or diarrhea. Spastic colon type is characterized by abdominal pain associated with periodic constipation or diarrhea. Those patients with Irritable Bowel Syndrome who have painless diarrhea may experience an urgent need to defecate upon arising. (For more information on this disorder, choose "Irritable Bowel Syndrome" as your search term in the Rare Disease Database.)

Other digestive diseases with symptoms that are similar to those of Lactose Intolerance include infectious diseases such as Yersinia Enterocolitica Infection, Amebiasis, chronic fungal bowel infections, Intestinal Tuberculosis, Pseudomembranous Colitis that is caused by excessive use of antibiotics, and certain venereal diseases. Ischemic Colitis and certain cancers such as abdominal lymphoma may also have symptoms that are similar to those of Lactose Intolerance.

Diagnosis
Lactose intolerance is usually diagnosed by means of a test that measures the levels of glucose in the blood after the ingestion of a specific amount of lactose. Since under normal conditions, the lactose taken in will be converted to galactose and glucose, measuring the amount of glucose in the blood after ingesting lactose determines whether there is enzymatic (lactase) activity. If the blood test finds little glucose, then LI is the likely diagnosis.

Another more sophisticated test known as a hydrogen breath test, may also be performed.
Normally no hydrogen is detectable in a person's breath. However undigested lactose leads to the formation of several gases, including hydrogen, as a result of bacterial activity. These gases enter the blood stream and are carried to the lungs from which they are exhaled. If the hydrogen breath test shows the presence of substantial amounts of hydrogen, then LI is the likely diagnosis.

Treatment
Infants born with congenital lactose intolerance must have a diet that is free of milk products and the removal of milk leads to rapid recovery. After six months of age, a normal diet including milk is usually tolerated, although some people remain lactose intolerant throughout their life.

Lactose intolerance that occurs during childhood or adulthood is easily controlled by limiting or eliminating milk products from the diet. People with this disorder usually avoid dairy products or choose special reduced-lactose products. Several lactose-reduced dairy products are now available in grocery stores including milk, ice cream, and cottage cheese.

The enzyme that breaks down lactose (lactase) is also available in tablets or liquid drops and is sold under several brand names. This product can be added to foods to make them more tolerable. The liquid products can be added to milk to break down lactose and make it digestible for people with lactose intolerance. The tablets can be taken within thirty minutes of eating dairy products. This replaces the missing enzyme, enabling patients to eat a normal diet.
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Research on genetic defects and their causes is ongoing. The National Institutes of Health (NIH) is sponsoring the Human Genome Project which is aimed at mapping every gene in the human body and learning why they sometimes malfunction. It is hoped that this new knowledge will lead to prevention and treatment of genetic disorders in the future.

Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. government funding, and some supported by private industry, are posted on this government web site.

For information about clinical trials being conducted at the NIH Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:

Tollfree: (800) 411-1222
TTY: (866) 411-1010
Email: prpl@cc.nih.gov

For information about clinical trials sponsored by private sources, contact:
www.centerwatch.com

MENDELIAN INHERITANCE IN MAN, 10th Ed.: Victor A. McKusick, Editor: Johns Hopkins University Press, 1992. P. 939.

THE METABOLIC BASIS OF INHERITED DISEASE, 6th Ed.: Charles R. Scriver, et al., Editors; McGraw Hill, 1989. P. 2988.

CECIL TEXTBOOK OF MEDICINE, 19th Ed.: James B. Wyngaarden, and Lloyd H. Smith, Jr., Editors; W.B. Saunders Co., 1992. P. 1187.

THE MERCK MANUAL, 16th Ed.: Robert Berkow Ed.; Merck Research Laboratories, 1992. P. 825.

BIRTH DEFECTS ENCYCLOPEDIA, Mary Louise Buyse, M.D., Editor-In-Chief; Blackwell Scientific Publications, 1990. Pp. 1025-27.

NELSON TEXTBOOK OF PEDIATRICS, 14th Ed.; Richard E. Behrman et al.; W.B. Saunders Co., 1992. P. 939.

GASTROINTESTINAL DISEASE, 4TH Ed.; Marvin H. Sleisenger, M.D. et al.; W.B. Saunders Co., 1989. Pp. 266, 1068, 1997-98.

DICTIONARY OF MEDICAL SYNDROMES, 3RD Ed.; Sergio I. Magalini, Sabina C. Magalini, and Giovanni de Francisci, Editors; J.B. Lippincott Company, 1990. P. 27.

CORRELATION OF LACTOSE MALDIGESTION, LACTOSE INTOLERANCE, AND MILK INTOLERANCE. A.O. Johnson; Am J Clin Nutr (March 1993; 57(3)). Pp. 399-401.

A COMPARISON OF SYMPTOMS AFTER THE CONSUMPTION OF MILK OR LACTOSE- HYDROLYZED MILK BY PEOPLE WITH SELF-REPORTED SEVERE LACTOSE INTOLERANCE. F.L. Suarez et al.; New Eng J Med (July 6 1995; 333(1)). Pp. 1-4.

LACTOSE INTOLERANCE. J.R. Malagelada. New Eng J Med (July 6, 1995; 333(1)). Pp. 53-4.

CONSUMER RESOURCES
National Digestive Diseases Information Clearing House. NIDDK. Lactose Intolerance. NIH Publication No. 02-2751. 2002:7pp.
www.niddk.nih.gov/health/digest/pubs/lactose/lactose.htm

National Digestive Diseases Information Clearing House. NIDDK. Why Does Milk Bother Me. NIH Publication No. 02-2751. 2002:7pp.
www.niddk.nih.gov/health/digest/pubs/whymilk/index.htm

NIH-Osteoporosis and Bone Related Diseases~National Resources Center. Fact Sheets. Lactose Intolerance. nd:2pp.

The American Gastroenterological Association. Lactose Intolerance. 2002:5pp.
www.gastro.org/public/lactose.html

Mayo Clinic. Managing lactose intolerance. 2002:3pp.
www.mayoclinic.com/invoke.cfm?id=HQ00566

Crohn's & Colitis Foundation. Diet, Nutrition &Fitness: What is lactose Intolerance?
www.ccfa.org/medcentral/library/diet/lactose.htm

US DHHS. Office of Women's Health. The National Women's Health Information Center. Lactose Intolerance. 2001:3pp.
www.4woman.gov/faq/lactose.htm

American Family Physician. Information. Lactose Intolerance. 2002:2pp.
www.aafp.org/20020501/1855ph.html