Non-BPD Mother-in-law has two pwBPD daughters (different fathers, neither BPD)?

[Our abuse recovery guide]

So recently I've been trying to grasp how it is that my mother-in-law is ostensibly not BPD - but has two children with BPD by different fathers...I guess I'm starting to question whether the mother-in-law is really non-BPD herself or simply undiagnosed.

MIL has Generalized Anxiety Disorder, but not BPD. She had two children; one child by an unknown father with unknown mental history, and the other child by a father who has been diagnosed as schizophrenic (presumably low-level, high-functioning, schizophrenia, and he disputes the diagnosis saying other doctors have spoken to him without making that finding).

Both children, now adults, have BPD. The one with an unknown father is also diagnosed with Bipolar and Agoraphobia alongside BPD, and to make things more baffling to me she never met either parent, having been given up for adoption at birth. The one with a potentially-schizophrenic father suggests she was "likely" sexually molested as a child but is only diagnosed with BPD (yes, I'm aware that's a commonly-held trigger for BPD in both meanings of the word).

So I guess I'm left wondering if anyone has any insight, scholastic or anecdotal, into how exactly a mother with two daughters with zero childhood overlap (never even knew each other existed; the one was given up for adoption at birth, the other stayed with the mother and father until she was an adult) can have both daughters diagnosed with BPD...but the mother seemingly does not have BPD (and she has apparently not avoided psychiatric testing - although expressed concern very early in motherhood about "passing on" unspecified mental problems to her offspring).

My best theory so far is just that it's a difference between both daughters having "low functioning Borderline Personality Disorder" which was easily diagnosed and pretty much spotted from a mile away, while the mother may have undiagnosed "high functioning BPD" that gets masked since she's taking the same medications for "Generalized Anxiety Disorder" that are commonly prescribed for BPD.

But I guess I want to hear that I'm wrong, or at least hear other possible theories that haven't occurred to me. I know all the parties intimately for about forty combined years, and I've seen the mother in just about every conceivable stressful situation and while she can react poorly at times (as can anyone), she's never really responded to even the most obvious triggers in a manner I'd deem consistent with BPD. But perhaps my judgement is clouded by living most intimately with low-functioning pwBPDs.

[PearlsBefore]

So recently I've been trying to grasp how it is that my mother-in-law is ostensibly not BPD - but has two children with BPD by different fathers...I guess I'm starting to question whether the mother-in-law is really non-BPD herself or simply undiagnosed.

MIL has Generalized Anxiety Disorder, but not BPD. She had two children; one child by an unknown father with unknown mental history, and the other child by a father who has been diagnosed as schizophrenic (presumably low-level, high-functioning, schizophrenia, and he disputes the diagnosis saying other doctors have spoken to him without making that finding).

Both children, now adults, have BPD. The one with an unknown father is also diagnosed with Bipolar and Agoraphobia alongside BPD, and to make things more baffling to me she never met either parent, having been given up for adoption at birth. The one with a potentially-schizophrenic father suggests she was "likely" sexually molested as a child but is only diagnosed with BPD (yes, I'm aware that's a commonly-held trigger for BPD in both meanings of the word).

So I guess I'm left wondering if anyone has any insight, scholastic or anecdotal, into how exactly a mother with two daughters with zero childhood overlap (never even knew each other existed; the one was given up for adoption at birth, the other stayed with the mother and father until she was an adult) can have both daughters diagnosed with BPD...but the mother seemingly does not have BPD (and she has apparently not avoided psychiatric testing - although expressed concern very early in motherhood about "passing on" unspecified mental problems to her offspring).

My best theory so far is just that it's a difference between both daughters having "low functioning Borderline Personality Disorder" which was easily diagnosed and pretty much spotted from a mile away, while the mother may have undiagnosed "high functioning BPD" that gets masked since she's taking the same medications for "Generalized Anxiety Disorder" that are commonly prescribed for BPD.

But I guess I want to hear that I'm wrong, or at least hear other possible theories that haven't occurred to me. I know all the parties intimately for about forty combined years, and I've seen the mother in just about every conceivable stressful situation and while she can react poorly at times (as can anyone), she's never really responded to even the most obvious triggers in a manner I'd deem consistent with BPD. But perhaps my judgement is clouded by living most intimately with low-functioning pwBPDs.

[zachira]

People with mental health problems often marry each other. Oftentimes people with mental health disorders meet the criteria for several disorders. When there are a lot of mental health disorders in a family, there tends to be a lot of environmental factors that make mental health problems more severe. I have several family members in both the immediate and extended families with BPD. Some do not have a parent with BPD. What seems to be more prevalent that triggers the BPD, are inherited problems with emotional dysregulation along with other mental health disorders and a highly dysfunctional family environment.

[Notwendy]

BPD compared to bipolar and schitzophrenia is less "inheritable" in terms of genetics from what I have read. I think in many ways, the symptoms of these mental disorders can overlapp.

Anxiety disorders can also run in families.

My guess ( and it isn't better than a guess)  is- considering that bipolar is the more strongly inheritable disorder- the child who has bipolar and a father with unknown mental disorder possibly has a father with bipolar.

Child #2 with the possible schitzophrenia father- perhaps the father has BPD and it looked like schitzophrenia at times?

It is also possible for parents who do not have BPD to have a child with BPD.

The mother in law might have BPD even if you haven't seen it. BPD affects the most intimate relationships the most, and that would be immediate family and intimate relationships. My mother is severely BPD but is able to "hold it together" with people outside the family. She's barely functional but has been able to get people to help her do things and it appears she has done them herself. People have known her for decades but have not seen what went on in our family behind closed doors. She also has managed to keep a lot of this from therapists by not being fully truthful with them. So it is possible your MIL is an undiagnosed BPD and you would not have seen all of her behaviors.

If she is your MIL, you must be married to one of her children. They would see her behaviors more but one problem is that - if this is what you grow up with- it can seem "normal" to a child. Her children may not recognize how dysfunctional she is.

Lots of possible guesses here, but we don't know for sure. If you are asking because you might be planning to have children- and wonder about inheritance, or just want to know more, it would be best to get the facts from a genetic counselor about the chances of inheriting any of these mental disorders, as the best we can do here is guess. They would do a more detailed analysis.

[Methuen]

Generally speaking from my reading and experience, my impression is that there can be certain genetic predispositions, but it is an environmental trigger such as  trauma which then develops into the mental health issue.  You can google "trauma and serious mental health disorders", and look for sites that end in .edu., .gov., .org., .ca ., and you'll find lots of good reliable info there from respected sources.

[PearlsBefore]

Zachira, I agree with your insights.

Notwendy, the problem I have is that while I agree the unknown father may well have had Bipolar thus causing the Bipolar in Daughter #1 - it wouldn't really explain a possible genetic root to the BPD except if the mother had it...and there's seemingly a genetic root where two sisters who have only one parent in common and were raised with zero overlap between their homelives (completely unaware each other existed). So the only alternative to "MIL somehow has high-functioning BPD but has managed to keep it hidden even from close relatives" is "MIL somehow had kids by two different men who had BPD, one of whom managed to keep it hidden albeit relatively easily since masked by schizophrenia". I don't know the MIL's childhood well, but I suppose it's possible MIL does not have BPD but had a close relative growing up with BPD and thus is instinctively drawn towards trying that type of person as a lifemate. Back to present-day, the daughters recognise the dysfunctionality and I have a pretty intimate picture of it from all sides; the thing is the dysfunctionality is not similar to that of her daughters' BPD instability which is what confuses me - although I admit it's possible I'm subconsciously not taking into account the fact that not every BPD engages in extreme risky behavior, or may not project their own faults onto everyone around them, or may never pick up a weapon or botch attempted felonies...that's just the special low-functioning demographic.

Methuen, I agree that the environmental trigger seems to be necessary - although I think having a BPD mother is one of the most common "triggers" activating genetic BPD; although in this instance it would be two sisters inheriting "genetic predisposition for BPD" despite having only the MIL in common, and that genetic predisposition being triggered by GAD rather than BPD which would just seem ironic/unlikely/contradictory. Not that GAD couldn't trigger it, but presumably it would be the trigger if the OTHER parent had been the genetic donor - but with two different fathers, one of whom I know intimately and is diagnosed with schizophrenia but BPD...I'm just not understanding the genetic component. Or else, of course - maybe there is no genetic component and I'm just overthinking a one-in-a-million coincidence...after all, those do happen to 7000 people daily.

[once removed]

the simplest way to explain this may be to look at BPD as "on a spectrum".

i had an old friend get in touch with me very recently. when she asked what id been up to, i mentioned my work here.

she was intrigued, and she told me shed been diagnosed with BPD.

i was frankly surprised.

ive known her since i was in 9th grade, when she dated my best friend. we were closer in high school, but have kept in touch on and off since. sure, id have pegged her as "bpdish". i would not have pegged her as diagnosable with a personality disorder. i have known lots of people that are "bpdish", some closer to a diagnosis, some not. she would have been one of the least extreme on my radar.

a diagnosis is complicated. to you and me, it may, frankly sound like semantics. it isnt, exactly, but for example, you can have a person who is a hell of a lot harder to love or deal with, that may have traits of BPD, vs someone who is a bit more self involved, or withdrawn, that might qualify for a diagnosis.

a diagnosis is mainly about how life is affecting you, rather than how you get on with others. things that tend to lead to a diagnosis of BPD are things like an eating disorder, a suicide attempt, a drug overdose. a major life crisis. driving everyone around you crazy is not considered the same thing.

in my friends case, i was surprised to learn things had gotten pretty bad for her (and ive kept up). she had a major commitment phobia so she had been acting out, was engaging in risky behavior, and she sought a psychiatrist whom, i suspect, saw someone who would not be particularly resistant to treatment, and made a diagnosis that wasnt going to require meds, or sussing out other underlying conditions, but that was pretty clear cut, and treatable, with a willing patient. i have known people who are objectively doing worse in life, doing worse to others, with clear cut BPD traits, who will probably never be diagnosed, and may not reach the threshold for a diagnosis. the posterperson for a diagnosis, quite often, while they may have pronounced or extreme traits, would not reach the threshold for a diagnosis. its the nature of diagnoses...they can be underdiagnosed, overdiagnosed, misdiagnosed, or you could have a real jerk of a person who is a jerk of a person with traits of a personality disorder that wouldnt reach the threshold for a clinical diagnosis of a personality disorder.

as to how a very difficult mother, with one difficult father, one without a known mental history, could have two children who never met turn out with BPD? its an odds game. its the same way some of the most loving parents (skim the Parenting board) could end up with a child with bpd.