Comorbidity: The aetiological / genetic perspective

1. Comorbidity:The aetiological / genetic perspective Martina C. Cornel, professor of community genetics & public health genomics Clinical Genetics/ EMGO Institute for Health & Care Research

2. Definition “condition” Comorbidity: co-existent “conditions” • Etiology → pathology → manifestation • Disease → impairment → disability → handicap WHO, ICIDH, 1980 • Question of patient relates to consequences of disease: • Feel sad, apathy, headache, cannot go to work, do not manage to perform daily activities, diminished participation, lack of social integration

3. Definition “condition” • Comorbidity: co-existent “conditions”: • Etiology → pathology → manifestation • Disease → impairment → disability → handicap WHO, ICIDH, 1980 • Etiology or pathology or disease or impairment? Epilepsy, dementia, depression?

4. Etiological diagnosis in genetics • Down syndrome due to translocation of chromosomes #21 & 14, inherited from mother • Epicanthus, simian crease, congenital cardiac anomaly

5. Patterns of malformations in genetics • Syndromes: Consistent and recognizable patterns of abnormalities for which there will often be a known underlying cause (Down; one cause, several effects) • Sequences: Consequence of a cascade of events initiated by a single primary factor (Potter: renal agenesis → oligohydramnios → pulmonary hypoplasia and fetal compression → dislocation of hips and talipes). • Associations: non-random occurrence of abnormalities that cannot be explained on the basis of a sequence or syndrome. Emery, 2007

6. Comorbidity: Causes? Consequences? • Syndromes: One cause, several consequences • Sequences: Cause, consequence, consequence of consequence • Associations: recognized pattern in the absence of satisfactory underlying explanation

7. Recent developments in genetics/genomics • One gene, one disease (1990-2000) • Human genome sequenced (2001) • Genomics research (2001 →) • Function of genes • DNA, RNA, proteins, metabolites • High throughput • Common disorders • Multifactorial disorders

8. One gene, one disease Heutink 1994

9. One gene, one disease Heutink 1994

10. Common disease, common variant? Heutink 1994

11. Genome-wide association study of 14,000 cases of seven common diseases and 3,000 shared controls The Welcome Trust Case Control Consortium, Nature 2007

12. Contributing factors in causal models Janssens 2008

13. One disease, several genes; One gene, several diseases Frazer et al. Nat Rev Genet 2009

14. Common diseases, common pathways Zhernakova et al 2009

15. Comorbidity and genetics Monocausal • One genotype, several consequences (del 22q11→ cleft palate & schizophrenia & bipolar disorder) Multifactorial • Gene variant associated with increased risk of several multifactorial disorders • Gene function gives information about pathway (pathogenesis) • Treatment/prevention based on pathway

16. Comorbidity and genetics • The challenge in 2009 for common complex disorders: • Homogeneous subgroups (define phenotype) • Identify genes involved in multifactorial disorders • Identify common pathways • Develop treatment (or prevention) tailored to pathway → both co-existent disorders

17. Take home message • Comorbidity may reflect common etiological pathway • One gene/one cause or • Multiple susceptibility genes • Genetics/genomics can help to identify common pathways