Microvillous atrophy


Microvillous atrophy

Description, Causes and Risk Factors:

Microvillous atrophy is a congenital and constitutive disorder of intestinal epithelial cells. It is characterized by the neonatal onset of abundant watery diarrhea persisting despite total bowel rest. Onset most often occurs within the first days of life. Secondary to the marked diarrhea, children with microvillous atrophy rapidly develop metabolic acidosis and signs of hypotonic dehydration. No other biological signs are associated with this disorder; however, most children are at risk of developing cholestasis and liver failure.

The precise etiology of microvillous atrophy is still unknown. A major defect in membrane trafficking in enterocytes has been proposed as pathogentic mechanism of microvillous atrophy, probably secondary to an altered structure of the cytoskeleton. However, the observation of morphologically normal microvilli on immature crypt cells in children with microvillous atrophy indicate that the microvillous changes seen in the differentiating and mature cells are of a secondray nature or rare a consequence of yet unidentified events within the cell. These events could include membrane recycling or mechanisms controlling endocytosis or exocytosis. However, analysis of the membrane targeting of disaccharidases, such as sucrase-isomaltase, revealed no abnormalities of the direct of indirect constitutive pathway. Very recent observation indicate a selective defect in glycoprotein exocytosis in patient with microvillous. This findings need further confirmation. Another hypothesis suggesting a defect in the autophagocytosis pathway was recently proposed to explain the morphological and functional abnormalities in microvillous atrophy.

In August 2008 it was discovered that it is the mutation of the MY05B gene that causes microvillous atrophy. The condition appears to be inherited on an auto recessive basis - i.e., where both parents are carriers of the defective gene. Any child born to parents who both carry the gene, has a 1 in 4 chance of being born with microvillous atrophy, a 50% chance of being a carrier and a 1:4 chance of not being affected and not being a carrier.

Microvillous atrophy is extremely rare congenital disorder. To date, no prevalance data are available, however, it can be estimated that there are no more than a few hundered children with microvillous in Europe. The prevelence is higher in counteries with a high degree of consanguinity, suggesting autosomal recessive transmission.

Symptoms:

Microvillous atrophy is characterized by chronic diarrhea, which in the majority of cases starts within the first week of life, usually within the first few days. The diarrhea is immediately life threatening and can become so severe that a child can lose up to 30% of his/her body weight and become extremely dehydrated.

Diagnosis:

The gold standard in the diagnosis of microvillous atrophy is a combined light/electron microscopic histological analysis of small bowel biopsies obtained during diagnostic gastrointestinal endoscopy. Macroscopic endoscopic analysis of the entire gastrointestinal tract remains completely normal, beside nonspecific minimal alterations, such as mild mucosal erythema and in rare cases, indirect signs of villous atrophy. The accumulation of PAS (periodic acid-Schiff (stain)) positive granules within the apical cytoplasm of immature enterocytes in the upper crypt is highly characteristic of microvillous atrophy. In parallel, on PAS staining, the brush border membrane looks pathological, with an enlarged intracytoplasmic band along the apical pole of enterocytes and an atrophic band instead of the normally well-defined small line representing the brush border.

Treatment:

To date, no causal treatment exists for microvillous atrophy. Trials with anti-inflammatory drugs including steroids and antisecretory medications did not significantly change stool volumes over a prolonged period. Therefore, all patients are dependent on supportive measures such as parenteral nutrition, which is the only way of stabilizing them. However, this treatment is often difficult to administer successfully as the diarrhea is very abundant and the patients can rapidly succumb to metabolic decompensation. Therefore, it is important that children with microvillous atrophy are transferred to highly specialized pediatric gastroenterology center. As discussed the long-term outcome is rather poor for children treated with parenteral nutrition. New treatment strategies for the management of microvillous atrophy are needed. Intestinal transplantation is a clear alternative to parenteral nutrition for children with microvillous atrophy. It can be performed is a clear alternative parenteral nutrition for children with microvillous. It can be performed as isolated small bowel or combined liver small bowel transplantation, if significant liver disease exists. A recent study revealed that the outcome for children who had undergone small bowel transplantation for microvillous atrophy was much better than that for children undergoing small bowel transplantation for other indications. Based on this observation and the fact that prolonged parenteral nutrition has a rather poor outcome, it is now appropriate to consider early small bowel transplantation as a first choice treatment of early onset microvillous atrophy, allowing the patients to obtain full intestinal autonomy. However, it is hoped that a curative treatment will be available in the near future.

NOTE: The above information is for processing purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.

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