In the past, asthma was believed to be chiefly caused by environmental factors such as allergens, tobacco smoke, and pollution. Recent studies have consistently supported the possibility that genetics may play a larger role in the development of asthma than previously believed. Statistical studies comparing the prevalence of asthma among monozygotic twins and dizygotic twins show a significant difference between these two groups. The data from these studies have shown that if one of the identical twins had asthma 59% of the time the other twin also had asthma. Unlike identical twins, if one the dizygotic twins had asthma the other twin developed asthma only 24% of the time.

In another study determining whether parents having asthma increased the likelihood of their children developing asthma, the data showed that a correlation could be made linking asthma to genetic factors. When neither parent has asthma, 6% of their children develop asthma. When one of the parents have asthma, the percentage of their children developing asthma jumps to 20%. When both parents have asthma, the percentage of their children developing asthma is a staggering 60%. As the numbers suggests, genetic factors may play a large role in determining whole develops asthma.

An interesting study took place at the island of Tristan DA Cunha in an attempt to discover a genetic link to asthma. The human population of the island is highly inbred and the high frequency of asthma makes the island an ideal place to search for genes that may attribute to the development of asthma. In their search, the researchers collected data that provided support for a gene cause to the high prevalence of asthma on the island. Historical records also indicate that 2 of the original 15 settlers were asthmatic. Furthermore, sensitivity tests conducted on the islanders to different allergies revealed that 40% of the population was sensitive to cat dander. This is an important find because most of the people found sensitive to cat dander had never been exposed to a cat their entire lives. Since the sensitivity to cat dander arose without pre-exposure, the only other cause is due to a genetic predisposition to an allergic reaction.

With the understanding that environmental factors may not be the only cause of asthma, the next hurdle facing researchers is determining the genes responsible for the increased risk of asthma. Unlike other illnesses that may be attributed to a variation at just one gene locus, all cases of asthma can not be linked to a specific gene. Using linkage analysis techniques, several loci have located that may make individuals more susceptible to developing asthma. Of these loci, the Adam33 gene was the first to be identified as a possible candidate for causing asthma and it is found on chromosome 20. It is hypothesized that the Adam33 helps to model the airway in utero as well as remodel the airway passages after birth. Besides Adam33, other gene loci that may attribute to the development of asthma have been found on chromosomes 5, 6, 11, and 12. The genetics of asthma may not be limited to susceptibility. Different mutations at different gene loci may be responsible for increased severity of asthma symptoms. All these recent findings have only complicated the asthma problem and there seems to be no real solution on the horizon.