Conclusions and future prospects
The monogenic diseases CF and α1-antrypsin deficiency are inherited in a recessive Mendelian fashion (i.e. mutations in both alleles are required for the disease to be present). However, the term ‘monogenic’ is an oversimplification, since the causal gene interacts both with other genes and with environmental exposures in the course of the disease. Indeed, several modifier genes influence the severity of the disease in CF, implicating gene–gene interactions in its development. Active and passive smoking have deleterious effects in subjects with α1-antitrypsin deficiency, implicating important gene–environment interactions in the pathogenesis of panlobular emphysema.
The most common chronic respiratory diseases – asthma and COPD – are complex airway diseases that result from interaction between multiple environmental exposures and many genetic risk factors. Thanks to the development of novel, powerful tools for genetic studies, many genetic loci have been discovered that are associated with asthma, allergy, smoking behaviour, lung function and COPD. Despite the impressive advances in the genetics of asthma and COPD in the past decade, major challenges remain. Firstly, a large proportion of the genetic variance in disease risk remains unexplained. Most genetic variants identified so far by genome-wide association studies confer relatively small increments in risk, and explain only a small proportion of familial clustering. The remaining, ‘missing’ heritability can be attributed to additional genetic variation as yet unidentified, including structural variation (e.g. copy number variation of genes) and rare sequence variation. Secondly, the biological pathways and molecular mechanisms involved in the pathogenesis of chronic airway disease need to be elucidated in order to translate these new genetic insights into better strategies for prevention and treatment.
| Gene | Gene name | Gene function |
|---|---|---|
| HHIP | Hedgehog-interacting protein | Lung development |
| GPR126 | G-protein-coupled receptor 126 | Unknown |
| ADAM19 | A disintegrin and metalloproteinase 19 | Cell migration and adhesion, cell-matrix interactions |
| AGER | Advanced glycation end products receptor | Receptor for danger signals, pro-inflammatory gene activation |
| FAM13A | Family with sequence similarity 13, member A | Signal transduction |
| GSTCD | Glutathione S-transferase, C-terminal domain containing |
Detoxification |
| HTR4 | 5-hydroxytryptamine receptor-4 | Receptor for serotonin, modulates release of neurotransmitters |
| PTCH1 | Patched 1 | Receptor for HHIP, lung development |
| MMP15 | Matrix metalloproteinase 15 | Breakdown of extracellular matrix |
| TGFB2 | Transforming growth factor-β2 | Embryonic development |
| HDAC4 | Histone deacetylase 4 | Transcriptional regulation, cell cycle progression and development |
| RARB | Retinoic acid receptor, beta | Transcriptional regulation, limits cell growth |
Table 4 – Genes associated with lung function.
Current and future applications of genetic testing in respiratory medicine encompass screening (e.g. newborn screening for CF), antenatal diagnosis, early diagnosis and prediction of disease risk (e.g. risk of recurrent venous thromboembolism according to underlying inherited thrombophilia). Pharmacogenetic and pharmacogenomic applications will improve our ability to use drugs more effectively and with less risk (e.g. optimising the dosing of the anticoagulant warfarin according to the genetic constitution of the patient). Finally, this genetic revolution will lead to the discovery of novel causal pathways, guiding mechanistic research in respiratory diseases and revealing new therapeutic targets.
