CSID Phenotypes

The molecular basis of CSID is still not elucidated. However, it has been proposed that different molecular defects or mutations in the SI gene are responsible for CSID. This hypothesis has been strongly supported by the analysis of several cases of CSID, which has led to the identification of five different phenotypes of SI.

 

 

 

Phenotypes I and II

Phenotypes I and II, for instance, are characterized by an intracellular accumulation of mannose-rich SI in the ER and the Golgi, respectively.

 

Phenotype III

In phenotype III an enzymatically inactive, but transport-competent, SI is expressed.

 

Phenotype IV

Phenotype IV expresses a partially folded, mannose-rich SI molecule that is missorted to the basolateral membrane.

 

Phenotype V

Finally, phenotype V reveals an SI species that undergoes intracellular degradation leaving behind the isomaltase subunit that is correctly targeted to the brush border membrane.

This genetic variability may account for the range in the severity of symptoms encountered by patients affected by the disease