Microvillus inclusion disease is an extremely rare inherited intestinal disorder (enteropathy) that is typically apparent within hours or days after birth. The disorder is characterized by chronic, severe, watery diarrhea and insufficient absorption (malabsorption) of necessary nutrients due to incomplete development (hypoplasia) and/or degeneration (atrophy) of certain cells of the wall of the small intestine (e.g., hypoplastic villus atrophy, defective brush-border assembly and differentiation). In infants with microvillus inclusion disease, chronic diarrhea and malabsorption may result in severe dehydration, deficiency of necessary nutrients (malnutrition), a failure to grow and gain weight at the expected rate (failure to thrive), and/or disturbance of the body's balance of acids and bases, which is essential in regulating the body's composition of bodily fluids (acidosis). Microvillus inclusion disease is inherited as an autosomal recessive genetic trait.
Microvillus inclusion disease is characterized by severe, large amounts of watery diarrhea appearing at birth or within seventy-two hours. Symptoms of a rare late onset form may not occur until two or three months after birth. Diarrhea persists even after oral feeding is stopped and does not decrease with age. Diarrhea often worsens after feeding because of insufficient absorption (malabsorption) of necessary nutrients. The diarrhea often results in life-threatening complications, specifically severe dehydration and metabolic acidosis, which may cause kidney failure, requiring the infant to be hospitalized. There may also be related weight loss, growth retardation and developmental delay.
Infants affected by this disorder require total intravenous hydration and total parenteral nutrition (TPN). TPN may be associated with an increased risk of developing blockage of the liver or bile ducts preventing the normal flow of bile (cholestasis) and liver failure.
Microvillus inclusion disease is thought to be caused by a basic defect in the cells in the intestinal wall of the small intestine and colon. Some researchers believe that it is inherited as an autosomal recessive trait. The specific genetic mutation involved has not yet been identified.
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 a few 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.
Fewer than 100 cases of microvillus inclusion disease had been reported in the medical literature. The true prevalence of this disorder is unknown. Most cases become apparent soon after birth, but it is also believed by some that there is a later-onset form that becomes apparent six to eight weeks after birth in infants that, until then, have appeared healthy. Microvillus inclusion disease affects more females than males with a sex ratio of about 2:1.
Microvillus inclusion disease was first described in the medical literature in 1978.
The diagnosis of microvillus inclusion disease may be based upon electron microscopy of a tissue sample (biopsy) from the intestine of an ailing child, which depicts microscopic findings characteristic of the disorder. Before a biopsy is performed, other causes of dehydration and diarrhea in infants are ruled out.
No effective drug treatment is available. Treatment of microvillus inclusion disease is accomplished through intravenous feeding often called total parenteral nutrition (TPN).
However, chronic TPN carries with it high risks of infection (sepsis), liver damage and other organ disorders. Therefore, the affected child must be carefully monitored by a physician.
Some children with severe disease have been treated with transplantation of a part of the small intestine.
Other treatment of microvillus inclusion disease is symptomatic and supportive. Genetic counseling will be of benefit for affected individuals and their families.
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