Screening for Substance Abuse Comorbidity in the GPC

The GPC is primarily designed as a resource for genomic studies. However, it is also a large population in which to explore the clinical phenotypes and a variety of possible environmental risk factors, including substance abuse. We thus included 14 items on smoking, alcohol use, and subtance use in the screening questionnaire.^10,24,25 The items are:

• 1. Do you often have more than four drinks in one day (for women) or more than five drinks in one day (for men)?
• 2. Have you been under the influence of alcohol three or more times in situations where you could have caused an accident or gotten hurt?
• 3. Have you often had a lot more to drink than you intended to have or do you often drink to calm your nerves?
• 4. Have you ever wanted to quit or tried to cut down on your drinking and found that you couldn’t?
• 5. Have people annoyed you by criticizing your drinking?
• 6. Have you ever had a drink first thing in the morning to steady your nerves or get rid of a hangover (eye-opener)?
• 7. Over your lifetime, have you smoked more than 100 cigarettes? Include cigars, pipes, and chewing tobacco.
• 8. Have you ever had a period of 1 month or more when you smoked cigarettes every day?
• 9. Do you usually smoke your first cigarette within 1 hour after waking up?
• 10. Have you ever wanted to quit smoking or have tried to quit smoking and found that you couldn’t?
• 11. Have you ever smoked marijuana more than 21 times in a single year?
• 12. Have you ever used recreational (street) drugs or prescription drugs more than 10 times to feel good or get high?
• 13. Have you ever tried to cut down or quit using drugs and found that you couldn’t?
• 14. Has your drug use ever caused you any problems?

The prevalence of substance use in GPC controls was consistent with other population-based samples. However, patients suffering from psychosis, regardless of DSM-IV diagnosis, had a 4-6 times increase in prevalence (Table 16.2). These observations were consistent across gender, ethnic group, race, and age.²¹

Pooling across cases and comparing cases with controls, we found that all of the ORs were significantly elevated (Table 16.3), which demonstrates excess comorbidity of substance use symptoms in individuals with psychotic illnesses. Substance use may be an important environmental risk factor that might significantly increase the penetrance or expression of a psychotic phenotype. However, these results may also be indicative of a shared genomic risk(s)

Table 16.2 Prevalence of substance use symptoms across psychiatric diagnoses

Reprinted with permission.²¹

Table 16.3 Comparisons of Genomic Psychiatry Cohort (GPC) cases with chronic psychotic illness with controls, adjusted for diagnosis, gender, race, age, and data collection site

aOR * 95% CI**

*aOR = adjusted odds ratio **All p values were <0.0001 Reprinted with permission.²¹

that may contribute to the development of both phenotypes. This cohort allows us to explore this observed association and attempt to determine whether or not there is an etiologic relationship between substance abuse or misuse and psychosis.