TY - JOUR T1 - Genetics and pulmonary medicine: asthma JF - Thorax JO - Thorax SP - 65 LP - 69 DO - 10.1136/thx.54.1.65 VL - 54 IS - 1 AU - I P Hall A2 - Britton, J Hopkin, J Y1 - 1999/01/01 UR - http://thorax.bmj.com/content/54/1/65.abstract N2 - It has been known for centuries that asthma is a disease which runs in families. Initial attempts to quantify the contribution of the heritable element of asthma or its intermediate phenotypes were performed in extended pedigrees. These were complemented by twin studies which examined the risk of asthma developing in monozygotic or dizygotic twin siblings of an asthmatic individual. If the development of asthma is genetically determined, one would predict that the risk of a monozygotic twin sibling developing asthma would be greater than that of a dizygotic twin sibling. This is because monozygotic twins are completely identical for all genetic factors and dizygotic twins share on average half their genes: the contribution of environmental factors should be the same for both monozygotic and dizygotic twins. The estimates of heritability of asthma itself from twin studies have agreed reasonably well with those obtained in family studies and have ranged from around 30% to 70%. In one large study of 7000 same sex twin pairs concordance rates were 19% for asthma in monozygotic twin pairs compared with 4.8% for asthma in dizygotic twin pairs.1 In addition to studying asthma per se, estimates for heritability can also be derived for intermediate phenotypes. The major intermediate phenotypes that have been studied are total IgE, atopy, and bronchial hyperresponsiveness. In general, the heritability of total IgE appears to be greater than for atopy, asthma or bronchial hyperresponsiveness, with estimates of the genetic component of the variability of IgE around 70% whilst figures of 30–50% are typical for the other intermediate phenotypes. It can be seen that these values agree reasonably well with those obtained from twin studies.Although it was clear from these early studies that there is a major heritable component in asthma, remarkably little progress was made in attempting to define … ER -