My mom has had delusional disorder for probably around 7 years now. She never had negative symptoms, just a belief that her sister-in-law was spying on her through her phone. Nothing super out of the ordinary and we believed her for a few years as well. It has never progressed into hallucinations or anything like that (that I was aware of) and she has never received treatment for it. She is extremely high functioning, etc. Well, as her 22-year-old son, I’ve always been fearful of developing her mental illness or even schizophrenia. I do suffer a few mental illnesses myself, such as depression, OCD, anxiety, and I think my OCD has made me really anxious about developing psychosis. My sister is 28 and hasn’t shown any signs of developing psychosis but we both have an unfortunate history of drug use (cannabis, MDMA, amphetamines, LSD, alcohol). I think at this point I’m just waiting for the delusions/hallucinations to start.
The following table gives only very general figures for the chance of an individual developing schizophrenia
| RELATIONSHIP TO AN INDIVIDUAL WITH SCHIZOPHRENIA | **RECURRENCE RISK (%) *** |
|---|---|
| General population | 1 |
| Parents | 1-6 |
| Siblings | 7-14 |
| Offspring of one parent | 6-16 |
| Offspring of two parents | 35-46 |
| Second Degree Relative (e.g. Aunt /uncle) | 2-8 |
| Third Degree Relative (e.g. First cousin) | 1-6 |
Looks like your risk is 6-16% if one parent has schizophrenia.
Is your mom diagnosed with schizophrenia because delusions can also occur in persons with bipolar disorder with psychotic features. This is an important distinction.
As @smarti08 states schizophrenia and related disorders are believed to be heritable, but not a certainty. While easier said than done, passively waiting or getting bogged down in anxiety about an illness that may or may not come seems wasted effort. Better to focus on preparing mitigation and coping strategies, stress reduction and avoiding drugs and alcohol, especially cannabis which studies show is linked to the development of psychotic disorders in people with sensitivities.
I know a family with a history of retinitis pigmentosa (RP) where developing blindness in adulthood was a near certainty for females, and through them came to know other people with RP. Their young adulthood was focused on learning mitigation strategies including career, relationship and reproductive choices and training for life with progressive vision impairment.
I developed schizoaffective disorder in my mid twenties and like you, have an older sibling prone to substance abuse who developed Bipolar Disorder before my illness manifested. My father likely had some form of SMI while we were growing up, yet was high functioning and brilliant in his career. In many ways, I modeled my career choice and coping strategies from his example and my brother, who’s been less successful coping with his disease, served as an “anti-pattern” for how not to deal with a serious mental illness.
When I developed SZA, I approached it as a problem to be solved or mitigated, as I felt this was my best option. Were I to counsel my past self, I would tell him to avoid drugs, develop a robust social network, train for a career in a quiet lower stress environment, research the illness and where appropriate, develop relationships with psychiatrists, cognitive and talk therapists and embrace life and supportive relationships as best he could.
@summber - OK, issues are there but the fact that you are aware is a blessing. Live your life, take care of yourself and stay healthy. While it is believed that there is a genetic connection, it is also a hit or miss. So, don’t spend your time worrying about it but you can always prepare and educate yourself. Probably would provide some insight to your mother as well. I wish you a wonderful, productive future. Take care and be blessed! 
Excellent response! This is so true. Thanks for sharing.
Both my brother and paternal aunt have schizophrenia. Neither were functional.
My father had paranoid disorder.
My youngest brother committed suicide at age 24.
My mother, sister, and I suffer from depression.
None of us have a substance use disorder which is very helpful.
Knowing you genetic propensity towards mental illness is the starting point.
Then as you so graciously stated focusing on coping strategies, problem solving, and mitigating actions is a proactive approach that is a win win situation.
It makes me happy that you have been successful in ask your actions! This gives us all hope! Thanks for sharing!
She has never been officially diagnosed but I haven’t seen any symptoms that point towards bipolar disorder. Also was wondering if schizophrenia and delusional disorder are genetically related?
If there is any possible way to get your mother evaluated by a psychiatrist, then do this ASAP.
Unfortunately, we’ve been trying for all these years. Since she’s extremely high functioning, basically no one thinks anything is wrong with her except for me and my dad. They went to couples therapy and I feel like the therapist suggest seeing a psychiatrist but I’m pretty sure she refused (this was probably 6 years ago). Not only this but her siblings are supporting her delusions because they seem so real (we thought they were real for years because it’s so minor - some people that don’t even have schizophrenia feel like the government is spying on them through their phones).
Well it has now started to affect my half-brother, who is having delusions that are almost identical to the ones I used to have. He says the voices are telling him not to take meds and that he has a psychic gift or something. The next couple of years should be real fun for all of us 
No sense living in fear though, the chances are probably still low for you. My mom and her three sisters are unaffacted, as were my grandparents.
Yes, that is the belief. Delusional disorder is quite rare, however. Considering your mother is undiagnosed it may be more likely she lies somewhere on the schizophrenia or bipolar spectrum.
See:
“The fact that delusional disorder is more common in people who have family members with delusional disorder or schizophrenia suggests genes may be involved. It is believed that, as with other mental disorders, a tendency to have delusional disorder might be passed on from parents to their children.”