Human Genetics - 2019

Attached as a PDF to an email addressed to two members of Congressman Mark DeSaulnier's staff
As you and the Congressman are probably aware, it is possible for private citizens to send in a saliva
sample and obtain a detailed sequencing of their DNA. Humans and our diseases are very

complicated: the super-category of 'blood cancers' is often divided into five categories:

/1/ Leukemias /2/ Hodgkin lymphomas /3/ non-Hodgkin lymphomas /4/ Myelomas
/5/ Others, such as myelodysplastic syndromes and myeloproliferative neoplasms.
Humans at present are estimated to have about 25,000 genes that code for proteins like insulin
and hemoglobin, and another 25,000 genes that have other functions. It is common to encounter
genes that control other genes, and there are epigenetic factors like methylization and histone
modifications that can also silence genes. After sampling the world-wide genetics grapevine it
would seem reasonable to say:
/1/ not all cases of leukemia have a genetic basis – the percentage of leukemias that do – even when
divided by type of leukemia – is an area of vigorous debate. That means someone could have a
condition somewhere on the wide-ranging leukemia spectrum without any obvious DNA problems.
/2/ there are currently over 160 genes associated with various named leukemia syndromes. The
number  of defined mutations of those genes is in the thousands - and growing. For example, the
 CEBPA gene on chromosome 19 in the q13.11 region is implicated in several types of acute myeloid
leukemia: if one has one of six mutations one group of leukemias results; if one has any of several
dozen other mutations one of a different group of leukemias usually results. Of course, some
mutations cause no known problems.
/3/ it is also the case that one can have known genetic effects but not display symptoms. It is poorly
understood why some genetic configurations result in early onset (childhood) leukemias and other
genetic configurations result in late onset (older than age 50) leukemias.
Were someone somewhere on Planet Earth fearful that they had leukemia a reasonable strategy
would be to search for a DNA sequencing company that has a panel (a list of genes) for leukemia.
Then the customer has to hope that the panel includes all of the 160-odd genes – or that the panel
at least has the gene involved in the customer's condition. Alas, things are more complicated than
that: the DNA sequencing company has to have lists of mutations for each gene so that the
company can report back that the customer's sequence for each of the 50,000 genes purports to be
normal or is implicated in leukemia. The lists of genes and their syndromes as well as the lists of
mutations of those genes change over time so a DNA sequence analysis done in 2019 might have
different results than one done months earlier.
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