hey everyone in this list want to talk about the genetic condition known as
albinism so in this lesson I want to talk about what causes albinism what are some
of the subtypes of albinism and we're also going to talk about the
pathophysiology and some of the preventive measures we can use to help
individuals with albinism so albinism is also known as ocularis albinism or OCA
and it is a group of rare inherited disorders of melanin biosynthesis so
that's key here disorders of melanin biosynthesis it is an autosomal
recessive condition which means that is rare and generally prevalence is around
one in 20,000 individuals now because it's autosomal recessive we'll take a
look at this chart here we have two unaffected parents both heterozygous
both having a recessive allele for this condition and they were to have four
children on average one in four or 25% of those kids would be affected carriers
so they'd have homozygous or they'd be homozygous for the recessive allele so
they would have this condition there would be two children that are
unaffected but our carrier so they carry the allele and there would be one
unaffected non carrier so in general it is one non carrier to unaffected
carriers and one affected carrier so that is the ratio of this condition now
there are actually seven different subtypes of ocular cutaneous albinism
and the one we generally think about the one with hypo pigmented skin and hyper
pigmentation is the one I like to call the classic OCA but it's actually type
one akio cutaneous albinism or OCA one this is the one that's actually
caused by deficiency of the enzyme tyrosinase due to mutation in the T Y
our gene and this one is located on chromosome 11 q1 4 to 11 q2 1 and this
is the one we're gonna be talking about most in this lesson but we'll also touch
on some of the other subtypes of ocular cutaneous albinism as well
so with regards to ocular continious albinism type one we can think about the
catecholamine biosynthesis pathway so at the beginning of the pathway we have
phenylalanine being converted into tyrosine via the enzyme phenylalanine
hydroxylase tyrosine itself is then acted on by either the enzyme tyrosine
hydroxylase or tyrosinase which is the key enzyme in OCA type 1 in a couple of
steps tyrosinase will lead to the production of melanin this is key for
our condition so again in type 1 a cutaneous albinism there is a deficiency
of the tyrosinase enzyme so that means that we're gonna have reduce production
of melanin and melanin is what gives our skin and hair and eyes a pigment so if
we have reduced melanin we're gonna have hypo pigmentation so that means we're
gonna have reduced melanin in our I rescind retina of the eyes or in a very
light colored eyes and there's gonna be reduced melanin production in the skin
and hair so we're gonna have hypo pigmentation so the skin will be very
fair this the hair will be very fair as well so the presentation of ocular
cutaneous albinism is due to this hypo pigmentation this reduced melanin
production we're gonna have hyperpigmentation of the hair eyes and
skin because it's ocular cutaneous in the name itself we can break it up into
ocular components and cutaneous ocular manifestations include sensitivity light
so melanin helps to actually protect our eyes or skin our hair from light waves
so if we don't have melanin if we have no melanin and all in our eyes we're
have some sensitivity to light also gonna have some poor vision we may have
strabismus as well so strabismus is when one eye is off-center to the other and
we're gonna also have a nystagmus and the cutaneous man
stations of albinism also include sensitivity to light because there's no
melanin in the skin they're gonna be very sensitive to light they're gonna
burn very easy on exposure to Sun and because they burn very easily they're
gonna have an increased risk of skin cancer so this is one of the things
we're gonna want to try to prevent and we'll talk about that a bit later in the
lesson so before I move on I want to just quickly talk about some of the
subtypes of albinism we talked about OCA one but I also want to touch on oca2
three in four and the other ones are very rare and very specific to only
certain families in certain areas of the world so these are the ones I want you
to really have a just a general understanding of so OCA one again we
talked about this before it's mutations in Tyr gene it's on chromosome 11 and
it's causes a tyrosinase deficiency there's actually two subtypes of OCA one
there's OCA one a this is actually the one we've been really talking about the
complete absence of melanin but there's also OCA 1b where there are maybe some
melanin presence so you may not have a complete deficiency in melanin but you
may have but you definitely be hypo pigmented but maybe not as completely
hypo pigmented as OCA 1a now OCA type 2 is caused by mutations in oca2 gene
that's easy and this one's actually on chromosome 15 and this one has nothing
to do with tyrosinase enzyme it has all to do with a mulana some'll membrane
protein and oca2 is actually the most common type of OCA in the world and this
is the one we actually call brown OCA so there they are hypo pigmented but they
aren't completely completely hypotension like you may see in OC 81 now with OCA 3
this one is caused by mutations in the tyr p1 gene and this one's located on
chromosome 9 and this one is related to tyrosinase enzyme and it stabilizes the
Tyra tonight's enzyme this one we call red
OCA in the last one OCA four is caused by mutations in SLC four five a to gene
it's on chromosome five and it is involved with membrane transport protein
with this one patients nearly have almost normal
levels of melanin they may have very slightly reduced levels of melanin but
generally normal and this is actually interestingly the most common in Japan
so I know there's a lot of little details with all these subtypes but
really what I want you to just get from this is that there's more than just one
ocular containing albinism there's actually seven but these are the four
that I want you to remember and kind of recognize but you don't really need to
remember all these details now how do we make the diagnosis and how do we treat
it well albinism is generally a clinical diagnosis so if we see decreased pigment
of the skin the hair the eyebrows and we compare it to the family and generally
the ethnic origins of the patient and they're generally less or hypo pigmented
compared to normal well that would maybe give it a way that this is a
presentation of albinism with regard to the eyes again the eyes have decreased
pigmentation there's going to be photophobia so sensitive to light and
there's gonna be nystagmus and I just want you to also realize that there are
some associated conditions or associated diagnosis related to albinism so you
think can think about Chediak-Higashi syndrome or Hermansky-Pudlak syndrome
and again you don't really need to know these in detail but I just want you to
remember that there are a couple of different syndromes that are associated
with albinism and you may do the clinical diagnosis but you could also do
genetics testing as well the see if there's any mutations in any of the
genes we talked about earlier so how do we treat it well unfortunately we can't
treat the condition because it's genetic condition but
treatment in this case really means prevention of consequences so we want to
absolutely have skin protection for these individuals so sunscreen we want
to avoid sunlight wear sunglasses everything we can do to help them with
regards to light sensitivity and reduce the risk for skin cancer or later in the
future and because there can be eye issues as
well we want to make sure that there are there is a examination so because there
may be poor vision we're gonna want to do corrective lenses if there's issues
again with strabismus we want to make sure that's corrected early in life
because we don't want to leat have consequences of that so these are the
things we want to do in albinism treatment again is a prevention of
consequences as opposed to just treating the condition itself so if you want to
learn more about other conditions and dermatological and genetic conditions
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