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ayesha
06-20-2017, 10:53 AM
Hello,
I wanted to know how people with no medical history whatsoever - like an adopted child or an orphan - fill in the gaps of their family history? Does anybody know the kind of details that are revealed by genetic testing? For example, I have a friend who lost her entire family during an earthquake as a child and has no records available of either of parents family medical history. But she remembers blurry stories about her mother possibly being a vanishing twin survivor and now that she's getting married, she's worried she might have inherited it. Will complications like that be revealed via early testing?

cornflake
06-20-2017, 11:08 AM
Hello,
I wanted to know how people with no medical history whatsoever - like an adopted child or an orphan - fill in the gaps of their family history? They don't, unless they search for biological relations. Does anybody know the kind of details that are revealed by genetic testing? For example, I have a friend who lost her entire family during an earthquake as a child and has no records available of either of parents family medical history. But she remembers blurry stories about her mother possibly being a vanishing twin survivor and now that she's getting married, she's worried she might have inherited it. Will complications like that be revealed via early testing?

I'm not sure I understand the question. Inherited what? Twins do sometimes run in families, but it depends on what type of twins and other things. As far as I know, there's no test for inheriting the propensity to produce twins, specifically.

Do you mean complications like losing one of multiples? That's a random thing. Early testing during a pregnancy will show if it happened, if it showed two embryos and then one....

Cindyt
06-20-2017, 04:37 PM
I've always been under the impression that twins skip a generation. But it may depend on family gene pool.

autumnleaf
06-20-2017, 08:35 PM
Fraternal twins run in families; if your mother or grandmother had fraternal twins, you're more likely to have them also. It can "skip a generation", for example, if a woman passes down the "twinning" gene to her son, he's no more likely than any man to have twin offspring, but his daughter has an above-average chance of becoming the mother of twins.

The incidence of identical twins does not run in families, but seems to be pretty random.

Tsu Dho Nimh
06-21-2017, 05:27 AM
"Vanishing twin" is not heritable that I can find.

It is currently thought that the twin that vanishes became non-viable because of a severe defect and because the other fetus is healthy enough to keep the pregnancy going, the dead twin is resorbed or disposed of by phagocytes.

Had it not bee a twin it would have been a miscarriage.

With total lack of medical records, a good physical exam and a test for the major genes involved in things like breast cancer would be useful.

chompers
06-21-2017, 05:57 AM
I think the skipping a generation thing is a myth. But I do think you are more likely to have twins run in the family.

I have a friend who's a twin, and he has twin sons. (I already thought the skipping thing was a myth, but this kind of proved it. He is an identical twin, and so are his sons.)

Cyia
06-21-2017, 06:04 AM
Anecdotally, we've had at least 3 "vanishing twins" various generations of my family. One cousin (male) also has twins. Genetic testing isn't going to tell you if you'll have twins ahead of time, though.

Fraternal twins and identical twins aren't formed the same way. One is two distinct eggs, while the other starts off as one and splits either directly following the fertilization stage or at the blastocyst stage.

How young was your friend when she lost her family? If she was eight or nine, then she might have legit memories of overheard conversations. If she was four, then it's more likely she's assimilated other information into her real memories.

neandermagnon
06-21-2017, 10:33 AM
I think the skipping a generation thing is a myth. But I do think you are more likely to have twins run in the family.

I have a friend who's a twin, and he has twin sons. (I already thought the skipping thing was a myth, but this kind of proved it. He is an identical twin, and so are his sons.)

The skipping a generation thing comes from recessive genes. Anything that's caused by recessive genes can skip a generation and can also not skip a generation. It can also skip multiple generations. This is because you need two copies of the gene to get the characteristic.

For example, ginger hair. My mum has ginger hair, I have brown hair and one of my daughters has ginger hair. You need two copies of the gene to have ginger hair, because it's recessive. I have one copy (if I didn't, I wouldn't be able to have a ginger child) but the other gene is dominant (in this case for brown hair) and determines my hair colour. Traits coded for by dominant genes show in each generation, but those that are coded for by recessive genes can skip generations - or not as the case may be. Someone who's ginger can have a ginger child, if the child gets two copies of the ginger gene. And if both parents are ginger all the kids are ginger. So it's not that it skips every single time, or only affects (say) every other generation, but traits skipping generations is a very real thing.

Back to the OP:

AFAIK identical twinning is random, but non-identical twins tends to run in families. It's the double ovulation that runs in families and is more common in some ethnic groups. Non-idential twins happen when two eggs are released instead of one. Sometimes this can just happen randomly but it can also run in families (i.e. genes that make people more likely to double ovulate). Identical twins come from the same egg, where the embryo splits in two at an early stage. Although the way this happens is known, the reason why it happens isn't fully understood and it appears to be random and not related to genetics. Anything that's random can happen more than once in the same family by chance. Also, genetics isn't the only thing that increases the likelihood of twin pregnancies. There are multiple other factors. And if double ovulation runs in a family, it doesn't happen every time they ovulate, so not every pregnancy in someone who's inherited this tendency will be a twin pregnancy. And sometimes women who haven't inherited this trait can double ovulate anyway.

Vanishing twin is where one twin dies at an early stage of pregnancy and is reabsorbed by the body. In the past, people wouldn't have known this was happening and they would've assumed it was a singleton pregnancy all along. As mentioned upthread, if the mother had been pregnant only with the non-viable twin, the pregnancy would've ended in an early miscarriage. Some researchers believe that vanishing twins are more common than previously thought (possibly as common as 1 in 8 pregnancies), but in most pregnancies, they don't know that one of the twins was ever there at all. Most routine scans are done too late to tell as it happens so early in pregnancy.

Vanishing twin isn't genetic. The only thing that is possibly genetic is the tendency to double ovulate. So if your friend's worried about this being genetic, it's not. The only thing she may have inherited is a tendency to double ovulate, but given that many twin pregnancies are due to random factors and not genetics, you cannot say with any certainty that she may have inherited the tendency to double ovulate.

frimble3
06-21-2017, 11:05 AM
http://absolutewrite.com/forums/images/misc/quote_icon.png Originally Posted by ayesha http://absolutewrite.com/forums/images/buttons/viewpost-right.png (http://absolutewrite.com/forums/showthread.php?p=10193826#post10193826) Hello,
I wanted to know how people with no medical history whatsoever - like an adopted child or an orphan - fill in the gaps of their family history? They don't, unless they search for biological relations. Does anybody know the kind of details that are revealed by genetic testing?

And not even then, if the relations are as tight-lipped as mine.
Some families don't talk, some people don't discuss 'personal' stuff.
And, small children have no context or background - who knows how she came to the conclusion that it was a 'vanishing twin'?
I think in many cases the whole 'most people know their family histories, even specifically medical history, and that those who don't are unusual' thing is optimistic assumption more than reality.

blacbird
06-21-2017, 11:11 AM
I was an adopted child, and know nothing of my biological parents, except their names, which I only found out via some papers left to me at my adoptive mother's death 24 years ago. And, frankly, I don't care to know. My birth parents are almost certainly long dead, and even at that time a quarter century ago, the likelihood of discovering anything useful about their medical histories would have been minuscule. But, perhaps useful to you: A few years ago, to complete the process of applying for an academic position, I needed to get a birth certificate. It turned out that the state in which I was born (Iowa) had, some years back, passed a regulation requiring that all birth certificates for adopted children be sent from their original county recorder's offices to the state's office in the capital. It was a minor hassle to obtain one from there, but doable and didn't cost much. Point being mainly that a lot of such stuff is dependent on state rules, which certainly vary.

caw

autumnleaf
06-21-2017, 02:07 PM
For example, ginger hair. My mum has ginger hair, I have brown hair and one of my daughters has ginger hair. You need two copies of the gene to have ginger hair, because it's recessive. I have one copy (if I didn't, I wouldn't be able to have a ginger child) but the other gene is dominant (in this case for brown hair) and determines my hair colour. Traits coded for by dominant genes show in each generation, but those that are coded for by recessive genes can skip generations - or not as the case may be. Someone who's ginger can have a ginger child, if the child gets two copies of the ginger gene. And if both parents are ginger all the kids are ginger. So it's not that it skips every single time, or only affects (say) every other generation, but traits skipping generations is a very real thing.

The genetics of hair color are a lot more complicated than that. The existence of red pigment (pheomelanin) is determine by a single gene, but the amount of brown pigment (melanin) comes from different genes, and the brown pigment can mask the red (https://udel.edu/~mcdonald/mythredhair.html). So it is actually possible for two flame-haired parents to have an auburn or brown-haired child. (I think this also partially explains why some men have dark head hair but red beards.)

autumnleaf
06-21-2017, 02:24 PM
Does anybody know the kind of details that are revealed by genetic testing?

Getting back to the OP.... There are currently tests for single genes, such as BRCA (increases chances of breast cancer -- this is what Angelina Jolie has), hemophilia (mainly found in males but females can be carriers), cystic fibrosis, Tay-Sachs disease etc. Maybe she remembers something about an uncle who was very sick and needed "blood treatment". So possibly he had hemophilia and she's worried that this might happen to her baby?

ap123
06-21-2017, 03:38 PM
For the most part, we don't fill in the gaps. We tell drs we don't have a medical history and why, and they make a note of it, end of story. I'm not sure how these new tests/companies--like ancestry?--play in When seeing a geneticist, if there is a reason for broad testing and gene mapping (which there generally is, otherwise why would you go, not to mention insurance isn't going to pay otherwise), they will often only disclose the results that specifically, directly relate to the reason you're there.

The field of genetics is truly growing by leaps and bounds. So much more is known than used to be, but there is still much that is unknown, including things that are seen but not yet understood. Geneticists, and the highly specialized labs that run these tests, will keep results on file, so if testing yields an unknown variant they will hold/flag, waiting to see if someone else eventually tests with that same variant and then if there are the same symptoms = a new syndrome/disorder.

FYI, these tests thousands of dollars, and full results take many months to come in.

cornflake
06-21-2017, 07:32 PM
Mostly people who see geneticists still go, afaik, for the reasons they have traditionally (for the past few decades) -- to test for things they think they really might have for one reason or another, either in their genes possibly to affect offspring or to affect them directly.

Ashkenazi Jews marrying others test for Tay-Sachs, people with Huntington's in the family test to see if they'll be affected or if they're carriers, people with various other congenital things do the same, people who've had one child with a rare congenital condition go for testing to find out the likelihood of it happening in subsequent pregnancies and decide whether to do selective IVF, etc.

I think what Frimble says is true for a lot of people, not just those with tight-lipped families. Grab 10 people off the street and ask them what their grandparents died of and at what ages and if they had basic conditions, and I don't think you'll get that many complete answers. Some families discuss that stuff, are aware of those things, lots of people aren't at all educated about even their own medical conditions (I've been on line at the pharmacy counter more than once and heard otherwise coherent-seeming adults not know what medication they're taking, be surprised when the pharmacist says something about side effects or dosage...)

I also have a family member who was adopted and it's just not known. *shrug* If there were some condition that had cropped up that would have been helped by trying to find out some biological information or people, steps would have been taken I'd imagine, but it didn't so....

Los Pollos Hermanos
06-21-2017, 08:56 PM
I've had my exome (the "coding" part of the genome) screened, in addition to 23andMe (I'm a DNA geek and also teach secondary school science). I'm also a genealogy geek, so know loads about my family tree and recent ancestral causes of death.

No family history of the eight or so "dodgy" recessives I've uncovered (as you'd likely expect). From what I've read, I think these "home DNA tests" - especially 23andMe and similar - are proving more and more popular with adoptees wanting to learn more about their origins and their health. If I'd been adopted, I'd definitely have been getting every test under the sun done!

Mum is "genetically ginger" - two different ginger alleles (R160W and V92M - I've got V92M from her), but had mid-brown hair before it went grey. I did some googling and learnt that certain modifier genes can somehow inhibit the red. She's really pale and freckly though, and turns tomato red very quickly in the sun - I call it "ginger skin syndrome" ;-) . I found a research paper where someone had exactly the same R160W and V92M alleles, but displayed a red-headed phenotype. Dad had to be an obligate red carrier as my Granny was ginger - he has the rare R142H allele, which he sadly didn't pass on to me. I love red hair and wish I had a fiery mane (it's very dark brown with noticeable red highlights), so always insist on having ginger cats instead - haha!

ayesha
06-22-2017, 05:36 AM
Hello,
Thank you so much for the detailed answers.
To answer some of your questions, my friend was around 9 when she lost her family and there are a few things she remembers. Her father had a non-identical and possibly diabetic twin - she remembers stories of her grandfather being the same but since he died before she was born, she can't be 100% sure. She had a one year old brother - his twin died during childbirth - and her mother lost a baby before that as well. She also remembers her mother being severely ill in the aftermath of her brothers birth but has no recollection or knowledge of what the complication was, of course. She is quiet sure though that all the births, including hers, were premature - her father used to tease her for always being in such a rush that she was born before time. So far in her life, she hasn't had any health issues but the recollections of her mother kind of scare her to death.

cornflake
06-22-2017, 07:03 AM
Hello,
Thank you so much for the detailed answers.
To answer some of your questions, my friend was around 9 when she lost her family and there are a few things she remembers. Her father had a non-identical and possibly diabetic twin - she remembers stories of her grandfather being the same but since he died before she was born, she can't be 100% sure. She had a one year old brother - his twin died during childbirth - and her mother lost a baby before that as well. She also remembers her mother being severely ill in the aftermath of her brothers birth but has no recollection or knowledge of what the complication was, of course. She is quiet sure though that all the births, including hers, were premature - her father used to tease her for always being in such a rush that she was born before time. So far in her life, she hasn't had any health issues but the recollections of her mother kind of scare her to death.

There's nothing there that really indicates anything specific. If her grandmother and mother both had fraternal twins, she could be prone to having twins, but anyone can have twins.

Her mother losing a baby, having early births (premature is one thing, early is another and that doesn't seem specific to me), could be due to something that could affect her, theoretically, like a physical abnormality or insufficiency, but that stuff can also be caused by smoking, environmental factors, just random things, bad assessment of gestation...

blacbird
06-22-2017, 10:46 AM
I'm now so ol chronologically successful that I suspect I carry vampire genes.

During the day the coffin helps, though.

caw

Rachel
07-03-2017, 06:19 PM
Hello,
I wanted to know how people with no medical history whatsoever - like an adopted child or an orphan - fill in the gaps of their family history? Does anybody know the kind of details that are revealed by genetic testing? For example, I have a friend who lost her entire family during an earthquake as a child and has no records available of either of parents family medical history. But she remembers blurry stories about her mother possibly being a vanishing twin survivor and now that she's getting married, she's worried she might have inherited it. Will complications like that be revealed via early testing?

To answer this question, I need to know what kind of family history? Just medical? Or is this person trying to track down other information about relatives? Both are possible now.

23andMe is a service that will check for various known genetic traits.
Ancestry.com also now has a genetic testing component that can get you details of where you came from generally (not sure if it will help you narrow down actual family members unless you have other information to try to start building a tree, and other people in said family also have genetic information). I have a friend who only did the genetic testing and found out she's a viking. She's very excited.

In a novel, I think we've reached the point where you can say such a service exists commercially. The "details" are quite interesting on 23andMe. If you hit up their site, the first things you may see are "lactose intolerance" and "sweet vs. salty preference." More importantly, there are several options for your genetic test. You can get a carrier test, to see if you carry 40+ conditions you could potentially pass on, and a health risk test for yourself. Then there are ancestry ones, probably similar to the one you get from ancestry.com (price comparison unknown), and others.

Hope that helps. If you are curious about anything else, I can hit up my genetic PhD friends here at school. They all just took comprehensive exams so supposedly they know stuff. ;)

WeaselFire
07-06-2017, 03:48 AM
Hello,
I wanted to know how people with no medical history whatsoever - like an adopted child or an orphan - fill in the gaps of their family history? Does anybody know the kind of details that are revealed by genetic testing? For example, I have a friend who lost her entire family during an earthquake as a child and has no records available of either of parents family medical history. But she remembers blurry stories about her mother possibly being a vanishing twin survivor and now that she's getting married, she's worried she might have inherited it. Will complications like that be revealed via early testing?

Genetic testing doesn't work that well. Yet at least. You can find some very general things out, such as whether you're predisposed to diabetes or sickle cell anemia, but the science of genetics is new enough not to have reliable long-term data. And there is no absolute link that if you have this gene you will get that disease.

And yes, I'm adopted, no family medical history, and have had some genetic testing done. And, I'm 1/64th vampire, I sneeze in bright sunlight. :)

Jeff