Secretory Diarrhea- Large volumes of water are normally secreted into the small intestinal lumen, but a large majority of this water is efficienty absorbed before reaching the large intestine. Diarrhea occurs when secretion of water into the intestinal lumen exceeds absorption.
Microvillus atrophy is the leading cause of secretory diarrhea in the first weeks of life.
The typical clinical presentation is watery profuse secretory diarrhea starting in the first hours of life. The peak age of onset is the early neonatal period. Although later-onset cases have been described, cases have never been described beyond the first 2-3 months of life.Three variants of the disease have been identified: congenital microvillus atrophy, late-onset microvillus atrophy, and atypical microvillus atrophy.In congenital microvillus atrophy, diarrhea starts in the first few days of life and is immediately life threatening. Oral alimentation in nutritionally significant amounts is impossible. In late-onset microvillus atrophy, diarrhea starts later in life, usually in the second month. Diarrhea tends to be less severe than in the other form, and some alimentation is possible. A few cases have been termed atypical microvillus atrophy, in which the onset can be congenital or late, but the histologic picture is different.
Microvillous inclusion disease, also known as Davidson's disease, congenital microvillous atrophy and, less specifically, microvillous atrophy, is a rare genetic disorder of the small intestine that is inherited in an autosomal recessive pattern.It is characterized by chronic, intractable diarrhea in new-born infants, starting in the first few days of life.This results in metabolic acidosis and severe dehydration.It is nearly always fatal unless, like short bowel syndrome patients, treated with parenteral nutrition or an intestinal transplant. The patient is often classified as being in "intestinal failure" and treated with the cohort of patients known as "short bowel syndrome" patients.It is caused by a congenital lack of apical microvilli in the epithelial cells of the small intestine.

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