I am aware that the past few posts have been quite heavy, they have been
hard to write and I know some of you have found them hard to read. So now for a little light relief with some
science (HA!)
I mentioned in a previous post that Alfie’s condition is
genetic. An initial diagnosis was given to us before we had any
genetic testing done. The initial diagnosis was a keratin 1 mutation
because during the first week the skin on Alfie’s palms and soles had
peeled. During our first appointment at Birmingham Childrens
Hospital when Alfie was about a month old, blood was taken and was sent off to
Dundee for testing. We were told that the results could take up to a
year to come back. The results actually came back a few months later
but reported a mutation on the kertatin 10 gene and not 1 as first thought –
meaning that his palms and soles were not affected.
Different type of ichthyosis are caused by errors on different
genes. Genes can either be inherited autosomal
recessively, autosomal dominantly or x-linked and to try to explain
this I will use 3 examples: EI (Alfies type of ichthyosis), Lamellar Ichthyosis
(LI) and x-linked ichthyosis (XLI).
In LI, the genes that cause the condition are inherited
recessively. Both parents need to be a carrier of the gene (and will
not necessarily have the condition themselves). Any child they have has a 25%
chance of presenting with the condition, a 50% of their child carrying the gene
and a 25% chance of them not passing the gene on at all. Because the
gene is recessive, in order to inherit the condition the child would need to
have a copy of the gene from both parents.
In XLI the mutation is present on the X chromosome only and is passed on
from the mother. The majority of people affected by this type of
ichthyosis are male. This is because females inherit 2 X chromosomes
(one from mother and one from father) and
the unaffected chromosome compensates for the affected one. Males
carry an X and a Y chromosome so if the male inherits the affected X chromosome
from their mother, they will present with the condition because they do not
have an additional unaffected X chromosome to compensate for
it. When a mother is a carrier, any daughters they have will have a
50% chance of being a carrier and any sons have a 50% chance of being
affected. Fathers that are affected by XLI will not pass this on to
their sons because they only pass the Y chromosome on but daughters will have a
50% chance of being a carrier.
In EI (Alfie’s type), the genes that are responsible for causing the
condition are dominant which means that only one parent has to carry the gene
for it to be passed on. As the affected gene is dominant, the carrier
is affected. If someone with EI goes on to have children, their
child will have a 50% chance of also having the condition.
Just to confuse matters even more, those of you that know us will know
that neither Lee or I have EI which means we don’t carry the mutated
gene. So how did Alfie end up with it if we haven’t passed it down
to him? After his diagnosis was confirmed, we were sent to see a
geneticist. He explained that in a small number of EI cases, the
parents do not present with widespread ichthyosis but sometimes have a small
patch on their skin. On examination, neither of us had this...i was
confused!! He then went on to explain that in a lot of EI cases, the
condition is caused by a random mutation on the keratin gene and no one knows
how or why it happens. You can think of it as a kind of typo on the
gene when it is being copied. So in our case, as neither parent has
the condition or has a small patch that could have caused it, we assume that it
is just a random thing that happened to Alfie before he was born. We
don’t know why the random mutations happen or what may have caused
it. Since Alfie does have EI, any children he goes on to have
would have a 50% chance of inheriting it from him. If he had
children that were not affected then that is where the genetic inheritance would
end (unless there was another random mutation).
Baffled? Me too although my A-level biology teachers would be so proud
that I finally took an interest!
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