The classification of IDI is probably incomplete, since other forms with abnormal small-bowel mucosa have been described. These include mitochondrial DNA rearrangements; congenital ente-rocyte heparan sulfate deficiency, phosphoman-nose isomerase deficiency; and a carbohydrate-deficient glycoprotein syndrome with hepatic-intestinal presentation.54-59 Rare diseases involving the immune system and small-bowel mucosa,60 or severe intractable enterocolitis of infancy,6 seem clearly different from the above-described diseases. The so-called 'pheno-typic diarrhea' that is an IDI syndrome associated with phenotypic abnormalities and immune deficiency is one of these rare diseases recently reported. The patients present with diarrhea starting within the first 6 months of life (< 1 month in most cases), and have several features in common.
They are small for gestational age and have an abnormal phenotype.11 All have facial dysmor-phism with prominent forehead, broad nose and hypertelorism. They have a distinct abnormality of hair, tricorrhexis nodosa, in which the hair is woolly, difficult to manage, easily pulled out and poorly pigmented, even in children of Middle-Eastern origin. Among the congenital forms of hair dysplasia, tricorrhexis nodosa is very common, and can be present in several pathological conditions.61-64 In addition, the previously reported patients had defective antibody responses despite normal serum immunoglobulin levels, and defective antigen-specific skin tests despite positive proliferative responses in vitro.12 Small-bowel biopsy specimens of the patients with diarrhea syndrome show moderate or severe villus atrophy with inconstant mononuclear cell infiltration of the lamina propria, and absence of epithelial abnormalities. Histologically, there are no specific abnormalities. The prognosis of this type of intractable diarrhea of infancy is poor, since most patients have died between the ages of 2 and 5 years - some of them with early onset of liver disease.12 The cause of this diarrhea is unknown, and the relation between low birth weight, dysmorphism, severe diarrhea, trichor-rhexis and immune deficiency is unclear. The coexistence of morphological, trichological and immunological abnormalities with early-onset intractable diarrhea disproportionate to the mucosal architectural abnormality (consistent with a primary enterocyte abnormality) suggests either mutation within several genes, inherited together by linkage disequilibrium, or, more probably, interference with a higher level of control, such as a patterning gene. The characteristic hair abnormalities may allow a more focused search for candidate mutations, as relatively few genes have been implicated in hair development.
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