Pathophysiology and mode of transmission

A defect in the membrane trafficking of immature and/or differentiating enterocytes has been discussed as an etiopathogenic mechanism in MVID.20,21 This membrane defect results, as a

Figure 1.2 Microvillus inclusion disease: CD-10 immunostaining. (a) Normal mucosa, normal CD-10, brush-border immunostaining; (b) abnormal accumulation of positive material in the apical cytoplasm of epithelial cells in microvillus inclusion disease.

direct functional consequence, in complete intestinal failure. It has been speculated that the disease is associated with a disorder of the enterocyte cytoskeleton, which produces an abnormal assembly of microvilli. Intestinal microvillus dystrophy was reported as being a hypothetic variant of MVID.24 The underlying pathogenesis of MVID is still unclear, although a cytoskeletal myosin deficiency has been found.25 When analyzing the turnover of sucrase-isomaltase, as a representative brush-border protein, there is clear evidence that the direct and indirect constitutive pathways are intact in MVID.21 Therefore, a defect in endocyto-sis is rather unlikely. More recently, by investigating the glycobiological nature of the epithelial accumulation of PAS, Phillips et al26 suggested that MVID involves a defect in exocytosis of the glycocalyx.26 The absence of glycocalyx might impair normal cell functions.

Considering the number of cases with affected siblings, and the frequency of consanguinity among patients in families of affected infants, this disease appears to be transmitted as an autosomal recessive trait.13,15,27 No candidate gene has been identified to date. MVID has been reported in a girl with autosomal dominant hypochondroplasia.28 The gene defect of this disease was recently localized on the chromosome region 4p16.3, which might help in elucidating the genetic basis of MVID.

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