Starch Digestion Consortium (SDC) workshop

Published: January 3, 2012

Congratulaton for the successful Starch Digestion Consortium (SDC) workshop was held by Dr. Buford Nichols on Dec 21-22 at the USDA/ARS Children's Nutrition Research Center (CNRC) at Baylor College of Medicine and Texas Children's Hopital at Houston, TX. The main research groups of SDC include Dr. Buford Nichols, Dr. Bruce Hamaker, Dr. Amy Hui-Mei Lin, Dr. Hassan Y. Neim, Dr. Roberto Quezada-Calvillo, Dr. David R. Rose and Dr. Mario Pinto. The Theme of this workshop is 50 Years of Progress since Congenital Sucrase-Isomaltase Deficiency (CSID) Recognition.

RATIONAL:

This is the 8th workshop of the Starch Digestion Consortium (SDC). It is to be a multidisciplinary workshop which blends clinical medicine with nutritional and food sciences. From the historical perspective, we recognized the passing of 50 years since the discovery of Congenital Sucrase-Isomaltase (SI) Deficiency (CSID) and review progress toward clinical diagnosis and management of SI enzyme deficiency. The nutritional and food technological objectives of this CSID/ SDC workshop were:

1. To define the roles of SI enzyme complex in human starch digestion to glucose (?-glucogenesis).

2. By study of SI deficient CSID patients envision approaches to botanical and technological alterations in food that will benefit all human populations.

What is Congenital sucrase-isomaltase deficiency (CSID)? This is an autosomal recessive intestinal disease caused by mutations of the SI gene. Duodenal mucosal histology is always normal. CSID patients have different phenotypes of enzymatic activities associated with SI, ranging from reductions of sucrase activity to total absence, as well as variable absence, of isomaltase activity. Low sucrase activity leads to maldigestion of sucrose, resulting in dyspeptic-like symptoms such as diet related chronic osmotic diarrhea and abdominal pain. The severity of symptoms is related to the amount of sucrase activity and quantity of sucrose fed. A reduced maltase activity is expected to occur in patients with CSID because both subunits in the SI complex contribute to the total mucosal maltase activity. The low maltase activity can lead to maldigestion of starch products, which may contribute to symptoms of dyspepsia and chronic abdominal pain. Because presently there are no practical and noninvasive methods for specific confirmation of SI deficiency conditions, we developed and validated a sucrose breath test for screening and confirmation of CSID using a novel noninvasive 13C-sucrose labeled substrate. It has been demonstrated that primary sucrase deficiency can be confirmed using 13C-sucrose breath test and that the effectiveness of sucrase replacement therapy can be proven by the same noninvasive method. Investigation of the same CSID patients with 13C-starch breath test confirmed that starch is poorly digested when mucosal sucrase activity is low. This genetic deficiency of SI provides a confirmation of a dominant role of sucrase enzyme complex in human starch digestion and provides a human model for investing the complexities of mucosal ?-glucogenesis from the many varieties of food starches.

What are the roles of mucosal sucrase-isomaltase activities in starch digestion? Food starches constitute a major source of energy in the diet of many humans. Starches exist as semicrystalline energy storage granules in more than 400 species of food plants. They are branched (amylopectin) and linear (amylose) polymers of glucose. The process of digestion of food starches to free glucose is here called dietary ?-glucogenesis. This process is dependent on a combination of six salivary, pancreatic and intestinal brush border ?-glucosidase enzyme activities. Two secreted luminal activities are called amylases (Amy), which hydrolyze internal ?-1,4 glucose bonds of linear starch polymers and polymer branches to produce soluble dextrins. Additional enzyme activities are bound to the luminal surface of small intestinal enterocytes. These activities were first described as maltase. Subsequent investigations have distinguished four different maltase activities. Two were associated with the signature activities of a twined catalytic complex named sucrase-isomaltase (SI). Two activities were not associated with any identifying substrate specificities and were named maltase-glucoamylase (MGAM). It has become recognized that these maltase activities extend to all linear ?-glucoside substrates and are thus described as mucosal ?-glucosidases. Amy activity amplifies the activity of the SI ?-glucosidases by producing very short dextrins and Amy produced dextrins slow the activity of MGAM but not SI. In vitro studies show that the SI enzyme complex accounts for more than 80% of the mucosal ?-glucosidase activity but in vivo studies show that about 40% of Amy produced starch oligomers are resistant to SI ?-glucogenesis. SI is thus the constraining enzyme for normal mucosal starch digestion rates and CSID patients are deficient in this dominant ?-glucogenic activity.

AGENDA:

Name

Agenda and location

time, min

Clock Schedule

pages mms

Breakfast

12/21/2011: Fomon Room

8:30

Plenary

Howland Auditorium CNRC

Gilger

Presiding

Nichols

CSID Early History

45

9:00

7

Treem

CSID Clinical Care

45

10:00

7

Naim

CSID Molecular Mutations

45

11:00

7

Hamaker

Slow Starch Digestion

45

12:00

7

Lunch

Fomon Room

1:00

Investigators

Fomon Room CNRC

Hamaker

Presiding

Baker

Frequency of Sucrase deficiency

25

2:00

3

Slawson

CSID Support Group

25

2:30

3

Opekun

CSID-Breath Tests

25

3:00

3

Chumpitazi

CSID family genetics

25

3:30

3

Scott

CSID mutation screening

25

4:00

3

McMeans

CSID dietary management

25

4:30

3

Zimmer

Celiac: Secondary deficiencies

25

5:00

3

Shulman

RAP: Secondary deficiencies

25

5:30

3

Money

IBS: Secondary deficiencies

25

6:00

3

Evening

Recess: Fomon Room

6:30

Dinner

Lobby of CNRC

7:00

Breakfast

12/22/2011: Fomon Room

8:30

Investigators

Fomon Room CNRC

Hamaker

Presiding

Rose

New inhibitors to MGAM and SI

45

9:00

6

Ao

Digestion of resistant starch

25

10:00

3

Lin

Digestion of limit dextrins

25

10:30

3

Lee

Substrate specificity

25

11:00

3

Quezada

MGAM splicing

25

11:30

3

Lunch

Fomon Room

12:00

End

1:00

Total

660

11.00 hr

68

Proceedings of SDC workshop will be published at Journal of Pediatric Gastroenterology and Nutrition (JPGN) as a supplement.

Special thanks to QOL Medical, the supplier of Sucraid® oral enzyme supplements for treatment of CSID sucrase deficiency, for the contribution of travel and local arrangements of speakers.