Hereditary Diseases

It's on my conscience that I did not reply to ukharassedmum, and I
don't want my conscience troubled for however long it is going to
take, if ever, to clear the clag from inside my one good eye. In view
of the replies she got, it is obvious there is a lot of
misunderstanding about the topic. I'll try to put it straight.

Most of us would have first heard of genetics at school and in terms
of Mendel and his laws, and using words like 'dominant' and
'recessive'. What we learned was in fact only a rough approximation
and a confession of ignorance. If Mendel's own results are looked at
very closely, they do NOT QUITE comply with his laws! And words like
dominant and recessive are only statements that we don't know how
genes work.

It is not always true that have gene = have disease. In the first
place many diseases depend on more than one gene and on environmental
triggers. In the second place many named diseases are not single
diseases but terms for a whole bundle of different diseases which have
some symptoms in common. Diabetes and cancer happen to be two
well-known examples of such packaged diseases. That is why, for
example. there never will be A 'cure for cancer' regardless of the
bull*** written by fundraisers and publicists. What may cure one kind
of cancer may have no effect at all on another kind. There is also the
problem that the body will sometimes cure itself. It isn't too
fanciful to regard the menstrual cycle in women as a process of
getting cancer and curing cancer once a month unless pregnancy
intervenes.

So it all begins to look complicated? You aint even started yet,
folks. Who actually had what in the past? Look up death certs? You
must be joking. We've been over it time and again but I'll illustrate
with my grandfather, who died in the early 1930's. That was the
pre-antibiotic era and meningococcal meningitis was fatal. His death
cert says so. Even if a sharp-eyed doctor had noticed he went down
unusually fast, it would have been shrugged off with some sophism like
'he was in a weak condition when he got the infection'. Dead is dead,
and a busy doctor has nothing to gain by doing intense studies on a
corpse when living people urgently need his attention. From the point
of view of hereditary diseases, Grandpa's meningitis is irrelevant. It
isn't inheritable. However if his life and behaviour prior to death
are explored there emerges the classic picture of undiagnosed Type II
diabetes. And that is inheritable as I know to my cost. That explains
the fast knockdown. Any bacterium landing in his blood would have
reacted as a starving man to a royal banquet. So much freebie glucose
to live on. There would have been explosive growth, and that means an
explosive rush of toxins. So the first bacterium which got there would
have killed him. It was a mere chance that it was a meningococcus. His
death cert is useless as an item in the study of hereditary diseases.
Ten years later people were stepping in front of bullets or having
bombs dropped on their it heads. All those death certs are useless
too.

Then there is another problem. The perennial question of 'what is the
modern equivalent of X in a death cert of a century or more ago' is a
nonsense. We know more now than we did then. So there are new words to
sort out what was lumped together then. Furthermore, the hereditable
diseases with a payback in old age wouldn't have been much in evidence
in a population with a life expectancy of around 40. The classic case
is a tribe of the Sioux, n whom there was no evidence of diabetes when
they were enduring intense cold, fighting wars, and generlly having a
hard life. A Sioux brave in that tribd who reached 40 was an old man.
Now? They all live to 70 and there is a 100% incidence of diabetes. In
terms of human lifetimes, no there is no easy 'computerised' way of
feeding in old data and out pops an accurate assessment of hereditary
disease.

Then there are the diseases which look genetic but are not. Much of
glaucoma fits this bill. In the peak locations for incidence of
glaucoma the common factor is diet. Humans are ingesting directly or
through the milk of their cows continuous small traces of an alkaloid
called sanguinarine. It occurs in all members of the Papaver and
Fumaria familes. Enjoy your poppy-seeded rolls if you want to go
blind, and when you do then don't blame your genetics. But there is
also a genetic component in some glaucoma.

Now we come to the fact that it is possible to have genes for a
disease, not have the disease, but pass those genes to a descendant
who does have the disease. My grandather's daughter who became my
mother did not exhibit diabetes. Maybe she was too busy dying of lung
bance for it to be noticed. But I got my diabetes from her. Similarly,
both my male cousin and I carry the breast cance genes from our mutual
grandmother. but neither of us have BC. On the other hand we both have
daughters who do.

And that leads on to how and why genes get switched on or off. Nobody
knows for sure. The problem ecists in your own body. Whether it is a
nerve cell in your brain, a liver cell, or a skin cell on your big
toe, it has the SAME genes. But those clls neither look the same nor
perform the same. Why? All the necessary genes are there. So it isn't
just have gene - have result.

Nor is that the end of the complications. Inheritance is a statistical
thing. You can't predict which genes you get from Dad and which from
Mum. They come across in clumps but it doesn't have to follow that the
breakdown into clumps is always the same. A lot can go wrong, and does
so more frequently than is realised. The process of getting rid of a
high proportion of the mistakes is called miscarriage. Since 'misses'
are not recorded there can be no historic information about what
genetic liabilities they indicate. And as I have said so often,
whereas stats about a population may give information anout
inheritability, or otherwsie, of disease, they are of absolutely no
use in making deductions or predictions about single cases.

In disentangling a field as complex as this there is no point in
expecting to sort it all in 50 plain words in Wikipedia. It needs a
whole new language of precisely defined terms in order to have an
intelligent discussion of the subtleties and complexities. A language
which takes years of intensive study to learn and become fluent. There
is no shortuct and no simple translator. Those who want to see what is
involved could do what ukharassedmum coyuld have done but evidently
did not do before she posted. Enter into Google search "Tourette's
+genetics" (without the quotes).. In the first page or two will be a
learned paper from a Harvard doctor. Try reading it. Papers written
like that are either by pretentious prats concealing their ignorance,
or by very solid and knowledgeable folk trying to put forward
precisely what they have found. Prats generally do not get through the
refereeing process in respectable journals. they publish where there
is no check.

In summary, if you want to get involved in genealogy as a poor, but
the only available, approximation to genetics in the study of disease
in humans, you have a binary choice. Give up and don't bother at all.
Or pay your dues with the equivalent of years of full-time study. It
is far too confusing for well-meaning amateurs.

In practical terms, ukharassedmum or anybody else in a like state
about something serious which their chld may have inherited, has a
simple course of action. Get their GP to refer them to a clinical
geneticist. Put beffore that geneticist the facts you have found,
answer his further question, and then sit back and let the oracle
speak from the benefit of 20 years or more of study.

Don

(This took more than three hours to type so I'm afraid there is no
prospect of me engaging in continued debate. If anybody is
sufficiently disturbed they are welcome to ring me .My phone remains
01626 821725. I am out a lot for hospital visits and treatments. but
it is a home number so I'm available at reasonable times outside
office hours. You can have the benefit of what is between my ears but
I CANNOT make any documentary references. I simply cannot read the
documents.)


.