Sucrase isomaltase deficiency is a disorder that affects normal carbohydrate digestion and therefore absorption, and leads to sucrose intolerance. Intolerance is described as clinical symptoms that are caused by sugar malabsorption (Scriver et al, 2001), in the case of sucrose intolerance this refers to the inability to digest and absorb sucrose, leading to several abdominal symptoms. Although sucrase isomaltase deficiency is not a fatal condition, it can cause suffers discomfort and therefore changes to the diet need to be made in order to avoid the symptoms caused by the deficiency.
Carbohydrate accounts for about half of the energy humans get from food. Carbohydrate digestion and ...view middle of the document...
The sucrase subunit is responsible for all sucrase activity and hydrolyses sucrose into glucose and fructose. The isomaltase subunit hydrolyses alpha-1, 6 glycosidic bonds in isomaltase to form two glucose monomers. While collectively both subunits are responsible for 80% of maltase activity, which breaks maltose into two glucose molecules (Lieberman et al, 2007).
Once the polysaccharides and disaccharides have been hydrolysed into monosaccharaides they can be transported across the brush-border membrane and absorbed into the blood. Both glucose and galactose are absorbed across the apical membrane using the sodium-glucose SGLT symporter and across the basolateral membrane using the GLUT 2 transporter (Silverthorn, 2010). While fructose is absorbed by facilitated diffusion using the GLUT 5 transporter across the apical membrane and over the basolateral membrane using the GLUT 2 transporter (Silverthorn, 2010).
Sucrase isomaltase deficiency is a rare congenital disorder that affects the digestion and absorption of certain carbohydrates. The main clinical symptom of sucrase isomaltase deficiency is watery osmotic fermentative diarrhoea, caused by the build-up of sucrose, which is then broken down by colonic bacteria into glucose and fructose, this increases the solute potential and increases the movement of water into the lumen of the colon, thus resulting in watery diarrhoea (de Zoeten, 2008).Other symptoms may include; abdominal pain and cramps, flatulence, vomiting, dehydration, malnutrition and occasionally failure to thrive (Scriver et al, 2001). Due to the lack of active or fully functional sucrase isomaltase, patients suffering from this disorder have no sucrase activity and greatly reduced maltase activity. The activity of isomaltase is heterogeneous, as it can vary from being greatly reduced to unaffected; this is dependent on the phenotype of the patient, however it is often reduced (Scriver et al, 2001).
There are five phenotypes of sucrase isomaltase deficiency, resulting from different genetic mutations. These include faults in; post transcriptional modification, intracellular transport and enzyme activity (Keiser et al, 2006). In Phenotype I, misfolded sucrase isomaltase (SI) is retained in the Endoplasmic reticulum (Ouwendijk et al, 1996). Phenotype II is characterised by SI retention in the cis compartment of the Golgi apparatus, due to a point mutation at position 1098 causing glutamine to be changed to proline meaning SI is incorrectly folded (Keiser et al, 2006). Phenotype III is caused by inactive SI on the brush-border membrane, while in phenotype IV partially folded SI is transported to the basolateral membrane, not the apical membrane. Intracellular degradation cleaves sucrase isomaltase in phenotype V, causing only isomaltase to be present and active in the brush-border membrane (Ouwendijk et al, 1996).
Congenital sucrase isomaltase deficiency (CSID) is hereditary and is an autosomal recessive trait (Belmont et al,...