Genetic Sucrase-Isomaltase Deficiency (GSID) is a rare genetic disorder where one lacks the enzymes needed to digest sucrose and maltose due to low or absent levels of the enzymes sucrase and isomaltase. This causes undigested sugars to enter the large intestine, where bacteria ferment them causing gas, diarrhea, abdominal pain and other gastrointestinal issues. GSID symptoms range from mild to severe and include gas, diarrhea, vomiting and weight loss. The condition is diagnosed through tests like endoscopy and breath tests and is treated through a lifelong sucrose-free diet and enzyme replacement therapy.

2. Genetic Sucrase-Isomaltase Deficiency (GSID)
Sucrose or table sugar is a disaccharide that is made up of two simple sugars linked together by
glycosidic bonds. The two simple sugars are glucose and fructose. Maltose is also another disaccharide
made up of two glucose molecules.
Human beings cannot absorb sucrose or maltose directly from the small intestines to the blood stream.
Therefore, two enzyme known as Sucrase and Isomaltase are needed to cleave sucrose and maltose into
glucose and fructose which are simple sugars (monosaccharide) that can be absorbed from the digestive
track to the blood stream. If there is absence or low levels of sucrose and isomaltase, then a person is
unable to break down sucrose or starch.
What is GSID?
Genetic Sucrase-Isomaltase Deficiency (GSID) is a rare genetic disorder that affects one’s ability to digest
sucroseor maltose due to low levels or absence of two digestive enzymes, Isomaltase and Sucrase.
Sucrase and Isomaltase are two enzymes that are associated with digestion of starch and disaccharides.
Isomaltase is one among several enzymes involved in digestion of starches. Sucrase is usually produced
in the small intestines (Ileum) and is involved in conversion of Sucrose into fructose and glucose.
Some children can be born with GSID after their genes produce a defect version of Sucrase-Isomutase
which is involved in breakdown of sugar and starch. The child can inherit the defect gene from both the
father and mother in order to develop the disorder. However, the type of gene alteration can determine
the severity of GSID symptoms.
If a person lacks sucrose-Isomaltase, then sucrose is not converted into glucose and fructose. As a result,
the small intestines hold a high concentration of sucrose creating a high osmotic pressure that draws
water into the intestines. This can in turn result to frequent and severe watery diarrhea.
How to distinguish GSID from other digestive track disorders
Majority of people who suffer GSID, lack sucrase, an enzyme involved in digestion of sucrose. People
with GSID are unable to digest sucrose and therefore develop digestive track symptoms after taking
food rich in sucrose. Many people with GSID also have irregular amounts of starch digestive enzymes
such as isomaltase, palatinase and maltase. Such people may experience digestive track symptoms after
taking foods rich in starch.
Symptoms of GSID
People with GSID may experience digestive tract symptoms that may range from mild to severe after
sucrose moves through the ileum undigested. The undigested sucrose enters the large intestines which
contain bacteria colonies. The bacteria feed off the increased amount of sucrose causing fermentation.
As a result, one may experience increased gas production and osmotic diarrhea. Symptoms of GSID may
differ between adults, children and infants.

3. Symptoms in Infants and Children
Symptoms of GSID do not manifest in infants until they start consuming sucrose and starch containing
foods such as solid foods, juices, baby formula and medications sweetened with sucrose. This means
that infants who are breastfed only, cannot experience GSID symptoms until they are introduced to
other foods in addition to mother’s milk. Common GSID symptoms in infants include:
 Colic
 Gassiness
 Abdominal distension (swelling)
 Irritations and abrasions in the buttocks
 Vomiting
 Diaper rash
Other rare signs and symptoms of GSID include muscle wasting, dehydration, body weakness and
malnutrition which may require hospitalization.
Symptoms of GSID in children may be more severe than those of adults since they have shorter
gastrointestinal tracks. GSID in infants may sometimes be misdiagnosed. It may be confused with
Irritable Bowel Syndrome since it also has symptoms such as gas, cramps, intermittent diarrhea cramps
and abdominal pain. Other conditions that may be mistaken with GSID in children and infants include
food allergies, lactose intolerance and nonspecific diarrhea.
Symptoms in Adults
Symptoms of GSID in adults are almost similar to those in children and infants, but bearing in
mind that they have a longer digestive track than infants, their symptoms are likely to be more
severe. In adults, many can learn to live with the symptoms and assume that their GI issues are
normal. Major and recurrent symptoms of GSID in adults include:
 Chronic diarrhea
 Gassiness
 Bowel movements
 Abdominal pain with unknown cause
 Constipation (bloating)
 Weight loss
 Abdominal distension
Abdominal distension and vomiting are symptoms which should not be ignored as they may
vary in different adults. GSID in adults may be misdiagnosed with Irritable Bowel Syndrome
when some symptoms such as constipation and diarrhea alternate. Any recurring GI symptoms
should be addressed to a gastroenterologist.
Severity of symptoms may be affected by some factors such as:

4.  Quantity of sucrose or starch consumed
 Bacterial activity in the colon
 Absorptive capacity of the large intestine
 Small bowel transit time
 The rate of gastric emptying
GSID Diagnosis
Diagnosing GSID in a patient is not as simple as many would think. Starting with your primary
care physician, you can be diagnosed with more common causes of abdominal distension and
diarrhea such as intestinal infections and Irritable Bowel Syndrome. When the treatment for
these two conditions does not relieve your symptoms, your primary care physician will definitely
refer you to a gastroenterologist, a doctor who specializes in digestive issues. The
gastroenterologist will perform physical examination and as well acquire for diet, family and
clinical history. Based on the patient’s information, tests will be ordered. Diagnosis for GSID is a
systematic process which involves elimination of other common GI disorders which have
symptoms similar to GSID.
Tests used to diagnose GSID include:
 Upper gastrointestinal endoscopy with biopsy- This is considered the most accurate test for
GSID. It involves a small tissue sample taken from the small intestine to test for enzymatic
activity.
 Sucrose hydrogen breath test
 Stool PH test
 Free S/Genetic test
 Oral sugar challenge test
 Sucraid therapeutic trial
The test your physician may choose to order may be affected by factors such as patient overall health
and age.
GSID Treatment
Treatment for GSID involves a strict and life-long sucrose free diet. However, in the world of today it is
very difficult to adhere to that since much of the processed food we buy contain sucrose. It is
problematic for both children and adults to adhere to a sugar free diet.
Enzyme replacement therapy is another new treatment for GSID that can be used to compensate for the
lack of natural functioning digestive enzymes. Such supplementation allows one to take normal diet
without development of symptoms.