View Full Version : What is the difference between Heredity and Genetic?


mildadhd
08-12-14, 04:59 AM
In your opinion, what is the difference between: ADHD is hereditary and ADHD is genetic?


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Dizfriz
08-12-14, 11:22 AM
In your opinion, what is the difference between: ADHD is hereditary and ADHD is genetic?

It is a good and somewhat difficult question and is discussed little in science sites. Mostly science based sites in this context focus on heritability as this is something that can be measured.

In the context of ADHD, (and these are my thoughts on this, based on my understanding of the subject and any errors are mine)

That a trait is heritable means that it can be or is passed from ancestor to descendent. It is usually expressed as a statistical measured of variance. In other words heritable means how much differences in genetic make up account for variation of traits in populations, the correlation between genetic make up and the phenotypic or trait make up of populations. The primary question is how well can genetic variation work as a proxy for phenotypic variation? What proportion of the phenotypic variation can be accounted for by genotypic variation?

It is not a set figure as sometimes environmental issues can account for much of variations. As an example, limited nutrition intake in childhood can have a big impact on human height where usually height is considered to be highly heritable.

In this context, describing a trait like ADHD as genetic is a much looser term, more colloquial and is often used to describe the genetics involving heritability, i.e. "ADHD is mostly genetic". Loosely stated but not totally wrong and I often tend to use this term as it gets the point across. I am working on not doing this though.

Using heritability the statement might be "many studies have shown ADHD to be have somewhere around .80 heritability" or "Those studies have found ADHD is mostly heritable". Much more accurate.

Many of us, and I am guilty too, use genetic as a synonym for heritable and it isn't. It is not so much wrong but imprecise. I am trying to be more careful.

In the study of genetics, genetic has a much more exact definition but I am not going to get into the research for a more complete picture thus the restriction to the context of ADHD.

Dizfriz


A good bit of this post was cribbed from: http://blogs.discovermagazine.com/gnxp/2007/08/genetic-vs-heritable-trait/#.U-og4mNups8

namazu
08-12-14, 12:37 PM
Also keep in mind that "heredity" and "heritability" sound a lot alike,
but the latter has formal technical / statistical meanings to people who do research in the field.

(Including distinctions between "genetic heritability" and "heritability due to shared environment"! How's that for confusing?)

"Heredity" seems to me to be a broader term
that refers to the passing-on of traits from generation to generation.

Of course, I'm sure for many people, "hereditary" does connote something primarily "in the blood" or "in the genes".

"Heritability", too, as I said above, can be divided into different components,
not all of which are purely genetic,
(and if you pick up a technical book on the subject, there's all kinds of partitioning of statistical variance going on every which way 'til Sunday).

But usually when the term is employed
in the context of inferring sources of disorders,
"genetic heritability" is the type they're primarily referring to.

These semantic differences create a lot of confusion
because people may think they're talking about the same concept,
when in fact one person has a specific definition in mind,
and another has another definition in mind.

SB_UK
08-12-14, 12:52 PM
To be honest I am surprised, what with the personal definitions of terms which the individual mind necessitates, that we ever communicate meaningfully.

Is a condition hereditary can be used to mean am I born with a death sentence ?

It doesn't matter whether someone chimes in with predisposition, or environmental interaction - people often don't see past heritable nature.

Why ?
Easier to see oneself as victim rather than as perpetrator ?

The environmental argument (to human suffering) does leave all people looking uneasily at one another -
- the genetic/heritable argument (no matter the qualification) can be used to comfort the irresponsible.

The rich are 'better' than the 'poor'.
Allowing the poor to be 'sick' and die prematurely removes their defective genes from the genepool.

There's all manner of nasty beliefs which perpetuate under the idea of heritable nature.

Dizfriz
08-12-14, 01:09 PM
Also keep in mind that "heredity" and "heritability" sound a lot alike,
but the latter has formal technical / statistical meanings to people who do research in the field.

(Including distinctions between "genetic heritability" and "heritability due to shared environment"! How's that for confusing?)

"Heredity" seems to me to be a broader term
that refers to the passing-on of traits from generation to generation.

Of course, I'm sure for many people, "hereditary" does connote something primarily "in the blood" or "in the genes".

"Heritability", too, as I said above, can be divided into different components,
not all of which are purely genetic,
(and if you pick up a technical book on the subject, there's all kinds of partitioning of statistical variance going on every which way 'til Sunday).

But usually when the term is employed
in the context of inferring sources of disorders,
"genetic heritability" is the type they're primarily referring to.

These semantic differences create a lot of confusion
because people may think they're talking about the same concept,
when in fact one person has a specific definition in mind,
and another has another definition in mind.
And it is confusing. I am not sure I have it all clear in my mind and I have a reasonable background on this. I can well understand the confusion for those with no education in statistics or genetics

Makes my head hurt.

Dizfriz

daveddd
08-12-14, 02:09 PM
can a mental disorder be both genetic and heritable , separately ?

mildadhd
08-12-14, 02:23 PM
I'm trying to figure out a good definition to explain what ADHD is, for ADHD awareness week.

Describing ADHD as epigenetic seems like it is the simplest most accurate description, of this complex topic.

Why don't we call ADHD epigenetic?

Opinion?


"Epigenesis: This biological principal suggests that individual development arise from gradual, individualized differentiation of each organism, a process that is now being understood at a genetic level.


While the mammalian genome (successive DNA base pairs) establishes the primal template for body and brain construction (genotype), a more complex and variable process of gene-expression controls the production of the final organismic forms (phenotype).


It is recognized that these developmentally variable "epigenetic" processes enable differential expressions of the genotype, allowing environmental control over the final phenotypes.


The biochemistry of epigenetics involves modifications in the degree to which gene expression can be controlled by histone methylation and related changes of nuclear chromatin, which provide for fine-tuning of patterns and intensities of gene expressions during development, along with the mechanisms by which gene expressions can be amplified or silenced."





- "From the Couch to the Lab: Trends in Psychodynamic Neuroscience", Chapter 9 Panksepp/Biven (Box 9.1 Definitions) p 146.


i!i

Greyhound1
08-12-14, 03:03 PM
Very good question P. I never gave it much thought. It interested me so I looked it up and found this. This seemed to explain the difference well.


Heredity and Genetics

Heredity is the passing on of characteristics from one generation to the next. It is the reason why offspring look like their parents. It also explains why cats always give birth to kittens and never puppies. The process of heredity occurs among all living things including animals, plants, bacteria, protists and fungi. The study of heredity is called genetics and scientists that study heredity are called geneticists.

Through heredity, living things inherit traits from their parents. Traits are physical characteristics. You resemble your parents because you inherited your hair and skin color, nose shape, height, and other traits from them.

Cells are the basic unit of structure and function of all living things. Tiny biochemical structures inside each cell called genes carry traits from one generation to the next. Genes are made of a chemical called DNA (deoxyribonucleic acid). Genes are strung together to form long chains of DNA in structures known as chromosomes. Genes are like blueprints for building a house, except that they carry the plans for building cells, tissues, organs, and bodies. They have the instructions for making the thousands of chemical building blocks in the body. These building blocks are called proteins. Proteins are made of smaller units called amino acids. Differences in genes cause the building of different amino acids and proteins. These differences cause individuals to have different traits such as hair color or blood types.

A gene gives only the potential for the development of a trait. How this potential is achieved depends partly on the interaction of the gene with other genes. But it also depends partly on the environment. For example, a person may have a genetic tendency toward being overweight. But the person's actual weight will depend on such environmental factors as how what kinds of food the person eats and how much exercise that person does.

namazu
08-12-14, 04:06 PM
I'm trying to figure out a good definition to explain what ADHD is, for ADHD awareness week.

Describing ADHD as epigenetic seems like it is the simplest most accurate description, of this complex topic.

If simplicity and accuracy are what you're after,
rather than speculate and use terms like "epigenetics"
that most laypeople won't understand,

just stick to the more basic description of ADHD --

a developmental disorder that affects a person's ability to
regulate their own behavior and responses.

Tell people how it affects your life and the lives of others you know with ADHD,
and what things you've done, or others have done, that have helped you deal with it in your own life.


Why don't we call ADHD epigenetic?

Opinion?
We don't call it "epigenetic" because we don't have enough evidence yet to support that assertion.

(Remember that epigenetics is not the only way genes can interact with the environment!)

We may have more evidence for it in the future, since we've just started looking into those epigenetic mechanisms, but we don't yet.

mildadhd
08-12-14, 04:41 PM
If simplicity and accuracy are what you're after,
rather than speculate and use terms like "epigenetics"
that most laypeople won't understand,

just stick to the more basic description of ADHD --

a developmental disorder that affects a person's ability to
regulate their own behavior and responses.

Tell people how it affects your life and the lives of others you know with ADHD,
and what things you've done, or others have done, that have helped you deal with it in your own life.



We don't call it "epigenetic" because we don't have enough evidence yet to support that assertion.

(Remember that epigenetics is not the only way genes can interact with the environment!)

We may have more evidence for it in the future, since we've just started looking into those epigenetic mechanisms, but we don't yet.



What are other ways that genes can interact with environment?

P

Dizfriz
08-12-14, 04:53 PM
What are other ways that genes can interact with environment?

P

A good example is the influence diet can have on height. Height is highly heritable but limited nutrition in childhood can change the genetic potential.

I doubt if we understand how this works but we know it happens and is real.

Dizfriz

Greyhound1
08-12-14, 04:55 PM
P.

I think Nam. makes a great point about keeping it simple.

Please try and mention in your awareness campaign the many comorbid conditions that accompany ADHD. I think that is the most important thing the average public has no idea about. They have no idea about the struggles we face with depression, anxiety, panic attacks and so many others. Most are unaware of our emotional dysfunctions.

Comorbids and 12 years of failed treatment attempts is the only reason my Dr. looked at ADHD as a possibility. I wasted so many miserable years because most people and many Drs. have no idea.

My biggest point I hope you can convey is that ADHD is way beyond focus and hyperactivity.

Cheers,
Hound

namazu
08-12-14, 05:33 PM
What are other ways that genes can interact with environment?
Well, to give a classic example, phenylketonuria (http://www.mayoclinic.org/diseases-conditions/phenylketonuria/basics/definition/con-20026275) is a disease that occurs in people who inherit two recessive alleles from their parents.

These people's genes are supposed to make an enzyme that helps metabolize certain kinds of food,
but their version of the gene doesn't make that enzyme properly.

People with PKU will experience problems if they consume the kinds of food that they can't break down properly,
but they don't have these problems if they avoid those certain foods.

This doesn't necessarily implicate any epigenetic mechanisms --
turning on or off of genes, or things like that.

It's just that the version of the enzyme that their genetic sequence encodes
is shaped funny, and doesn't work like it's supposed to.

So when they're in an environment (have a diet)
where they're exposed to phenylalanine (a chemical in some foods),
they have problems because they lack the functional enzyme they need to break down the phenylalanine,
so it hangs around and creates problems in the body.

When they're not exposed to phenylalanine,
they don't have these problems,
even though their enzyme is shaped funny because of their genes --
because they don't need the enzyme if they don't consume phenylalanine.

-----------------------------------------------------

Another example would be "sickle-cell" trait.
The gene involved there encodes hemoglobin molecules, which affect the shape of red blood cells.

The recessive allele encodes hemoglobin molecules that form crescent-shaped red blood cell (hence the name "sickle-cell").

--> )

The dominant allele encodes hemoglobin that forms a rounder, more Frisbee-shaped red blood cell (the "normal" kind of red blood cell).

--> O

If you get two dominant alleles,
you produce normal round red blood cells. O

If you get two recessive alleles,
you produce sickle-shaped blood cells, )
which aren't as good at carrying oxygen in the body.
This leads to painful crises (when they're not supplying parts of the body with the blood they need) and other medical problems. (This condition is called "sickle-cell disease" or "sickle-cell anemia".)

If you get one dominant and one recessive allele,
your body produces some normal round red blood cells, O
and some sickle-shaped red blood cells. )
Because you still produce some normal red blood cells,
you don't usually experience the severe problems that people who only have the sickle-shaped cells do.

OK, so that's genes leading to a phenotype related to red blood cells.

You with me still? :D

NOW, where does interaction with the environment come in?

Well, introduce mosquitos carrying malaria.
http://wwwnc.cdc.gov/travel/images/anopheles-mosquito.jpg
:eek:

Turns out, the malaria parasites like to hang out with human red blood cells.
When they do, people get sick with symptoms of malaria.

BUT...

People who have sickle-shaped red blood cells ) have some natural resistance to malaria.

Malaria likes people with "normal" round red blood cells. O
So, in an environment where malaria is common...

People who only make normal round red blood cells OO
have good ability to supply their bodies with oxygen through their blood
but they're more susceptible to malaria.

People who only make sickle-shaped red blood cells ))
suffer from painful crises and medical complications because of it,
but they're resistant to malaria.

People who make some normal and some sickle-shaped red blood cells O)
are usually phenotypically pretty normal (maybe not 100%) as far as circulating oxygen to the body,
because the round red blood cells do their job,
but they're also somewhat resistant to malaria,
because they have those sickle-shaped cells mixed in, which malaria doesn't latch onto as well.

So in this case, we see an interaction between the environment and genes in terms of resistance to malaria.

Again, this doesn't necessarily involve epigenetics, just how genes (and the proteins they encode) can have important and unusual influences when a person is in a specific environment.

Incidentally, sickle cell alleles are more common in people descended from groups who lived in areas where malaria was common. Some other genetic conditions, like some kinds of thalassemia (another blood disorder) are similar in this way.

Because of the interaction of the phenotype
(hemoglobin type/blood cell shape)
with certain environments,
the alleles that encode funny-shaped blood cells
(which are bad in terms of circulating oxygen through the blood)
are maintained in the population
(because they protect against malaria).

Again, no epigenetics here,
just the way genotype-encoded phenotypes
interact with environmental factors.

--------------------------------------------------------

Gene-environment interaction is broader than epigenetics alone.

And it's all really complicated! (Don't believe anyone who thinks they have it all figured out. Ask for evidence.)

Does that help at all?

Dizfriz
08-12-14, 05:49 PM
Namazu, excellent post, I find myself a little jealous as to the quality and clearness of your writing on this.

Dizfriz

mildadhd
08-12-14, 07:16 PM
Thanks Namazu,

There are determining epigenetic factors, in every example.

But I think your right to point out that epigenetic factors, may not be the only determining factors.

To clarify, I don't think the environment is the only determining factor.

But environment is one of the determining factors.

I need to learn a way to express that there is always more than one factor determining factor, when discussing ADHD.

Thanks.

If, (external environment) x (internal environment) x (genetic) x (genetic) = ADHD


(___________) x (internal environment) x genetic x genetic = ADHD


Focusing on (__________).

What terminology could we use to consider (__________)?


Opinions?




P

mildadhd
08-12-14, 07:32 PM
Behavioral epigenetics is the field of study examining the role of epigenetics in shaping animal (including human) behaviour.[1]

It is an experimental science that seeks to explain how nurture shapes nature,[2] where nature refers to biological heredity[3] and nurture refers to virtually everything that occurs during the life-span (e.g., social-experience, diet and nutrition, and exposure to toxins).[2]

Behavioral epigenetics attempts to provide a framework for understanding how the expression of genes is influenced by experiences and the environment[4] to produce individual differences in behaviour,[5] cognition[2] personality,[6] and mental health.[7][8]


http://en.wikipedia.org/wiki/Behavioral_epigenetics


i!i

daveddd
08-13-14, 11:46 AM
can namazu or someone help me interpret this to help understand my learning of genetics and adhd a little better



http://www.ncbi.nlm.nih.gov/pubmed/25055203

Genes (Basel). 2014 Jul 22;5(3):604-14. doi: 10.3390/genes5030604.
Functional gene-set analysis does not support a major role for synaptic function in attention deficit/hyperactivity disorder (ADHD).
Hammerschlag AR1, Polderman TJ2, de Leeuw C3, Tiemeier H4, White T5, Smit AB6, Verhage M7, Posthuma D8.
Author information

Abstract
Attention Deficit/Hyperactivity Disorder (ADHD) is one of the most common childhood-onset neuropsychiatric disorders. Despite high heritability estimates, genome-wide association studies (GWAS) have failed to find significant genetic associations, likely due to the polygenic character of ADHD. Nevertheless, genetic studies suggested the involvement of several processes important for synaptic function. Therefore, we applied a functional gene-set analysis to formally test whether synaptic functions are associated with ADHD. Gene-set analysis tests the joint effect of multiple genetic variants in groups of functionally related genes. This method provides increased statistical power compared to conventional GWAS. We used data from the Psychiatric Genomics Consortium including 896 ADHD cases and 2455 controls, and 2064 parent-affected offspring trios, providing sufficient statistical power to detect gene sets representing a genotype relative risk of at least 1.17. Although all synaptic genes together showed a significant association with ADHD, this association was not stronger than that of randomly generated gene sets matched for same number of genes. Further analyses showed no association of specific synaptic function categories with ADHD after correction for multiple testing. Given current sample size and gene sets based on current knowledge of genes related to synaptic function, our results do not support a major role for common genetic variants in synaptic genes in the etiology of ADHD.

Fraser_0762
08-13-14, 01:49 PM
"Genetic" is the biological term for "Heredity". They essentially mean the same thing.

SB_UK
08-13-14, 02:43 PM
can namazu or someone help me interpret this to help understand my learning of genetics and adhd a little better



http://www.ncbi.nlm.nih.gov/pubmed/25055203

Genes (Basel). 2014 Jul 22;5(3):604-14. doi: 10.3390/genes5030604.
Functional gene-set analysis does not support a major role for synaptic function in attention deficit/hyperactivity disorder (ADHD).
Hammerschlag AR1, Polderman TJ2, de Leeuw C3, Tiemeier H4, White T5, Smit AB6, Verhage M7, Posthuma D8.
Author information

Abstract
Attention Deficit/Hyperactivity Disorder (ADHD) is one of the most common childhood-onset neuropsychiatric disorders. Despite high heritability estimates, genome-wide association studies (GWAS) have failed to find significant genetic associations, likely due to the polygenic character of ADHD. Nevertheless, genetic studies suggested the involvement of several processes important for synaptic function. Therefore, we applied a functional gene-set analysis to formally test whether synaptic functions are associated with ADHD. Gene-set analysis tests the joint effect of multiple genetic variants in groups of functionally related genes. This method provides increased statistical power compared to conventional GWAS. We used data from the Psychiatric Genomics Consortium including 896 ADHD cases and 2455 controls, and 2064 parent-affected offspring trios, providing sufficient statistical power to detect gene sets representing a genotype relative risk of at least 1.17. Although all synaptic genes together showed a significant association with ADHD, this association was not stronger than that of randomly generated gene sets matched for same number of genes. Further analyses showed no association of specific synaptic function categories with ADHD after correction for multiple testing. Given current sample size and gene sets based on current knowledge of genes related to synaptic function, our results do not support a major role for common genetic variants in synaptic genes in the etiology of ADHD.

It's a negative study so won't help us understand ADHD really - but if we stick together variants in all genes identified as important in synaptic function - then the combination doesn't help us to separate ADDers from nonADDers.

Not too sure I'm looking for some global difference between ADDer synaptic function and nonADDer synaptic function - sounds like a real long shot.

ADDers aren't that different.

Just a slightly different reward system.

Yes it's easy to do stuff like that in mol genetics but there's no point.
We've ended up with the information in databases (gene ontology) and high throughput tech (NGS genotyping) but with no real need to use any of it.

The quote from 10 years ago relating to genetics then (which was a lot less high throughput than now)

- was 'there's a desperate nature to these types of studies'.

Point is - is that there was never really any need to look -- the actual aetiology could have been worked out by just thinking about it.

If you think about it - after years of genetics - and no useful results to show - we're just left in the same situation we were before.
We just (and still) have to think about it - if anybody wants a solution to the problem.

'Snot hard.

Human beings just aren't that complicated at least from the perspective of disease prevention.

Once we begin to break however - that's when the confusion begins.