Irritable Bowel Syndrome: Genetics vs Environment a Twin Study
A new look at irritable Bowel Syndrome (IBS), published in the journal, Gut, suggests that the risk of developing IBS later in life increases significantly when fetal development is restricted in the womb. This 2006 study found that genetic factors appear to contribute to IBS in females more frequently than in males and that pairs of identical twins were more likely to either both have IBS or not have IBS than pairs of fraternal twins.
Involving an initial cohort of more than 12,700 Norwegian twins – born between 1967 and 1979 – who completed a disease questionnaire, researchers screened the list down to 7,392 subjects, identified as:
| Type of Twin |
No. of Pairs |
| Identical – Male | 504 |
| Identical – Female | 746 |
| Fraternal – Male | 379 |
| Fraternal – Female | 635 |
| Fraternal – Mixed Male & Female | 932 |
| Total Number of Twin Sets |
3196 |
The gastrointestinal maturation process is ongoing during fetal development and continues during infancy. When a premature birth interrupts the development process, long-term consequences occur, affecting both the gut immune system and intestinal motility. Past studies suggest that lack of nutrition and oxygen supply during fetal development may permanently affect the structure and function of physiological systems, including the digestive tract.
The researchers compared data from a large number of twins who were different weights at birth. Twins may differ dramatically in birth weight due to unequal distribution of nutrition and blood supply. Those who had a lower birth weight were more susceptible to IBS than their identical twin of greater weight, with the same gestational age. This variance was particularly evident when the low-weight twin was less than 1,500 grams at birth. These individuals had a 2.4-fold increased risk of developing IBS in adulthood than those with a birth weight of 2,500 grams or more. For the first time in IBS research, these findings suggest that restricted fetal growth in pregnancy, rather than premature birth, contributes to IBS.
This study also showed that IBS symptoms began about 8 years earlier in lower weight groups than in higher weight groups.
Looking at data for overlap from among 31 other chronic diseases, the researchers found that 21% of IBS subjects also suffered from dyspepsia.
The researchers suggest that a new classification of patients into IBS subgroups based on age at onset of symptoms, gender, familial resemblance, and birth weight might improve understanding of the pathophysiological mechanisms of IBS.