Albinism
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Transcript of Albinism
Prepared by: Supervised by:epa ed by
Yasser Sh. Barhoum
Mohammed Bakeer
Supe sed by
Prof. Abed Nasser Abu shahla
Master Program of Biological Sciences, Al‐Azhar University‐Gaza (December, 2013)
INTRODUCTIONINTRODUCTIONINTRODUCTIONINTRODUCTION
A SD fi iti
ALBINISMDefinition:•Is a congenital disorder characterized by the complete or partial absence of melanin pigment in the skin, hair and p g ,eyes.
D t b d f t f t i• Due to absence or defect of tyrosinase enzyme involved in the production of melanin.
iA i th 17th t d
HistoryA man in the 17th century named Balthazar Telez, who was an explorer, came up with the name "Albino", which means white negro, after he saw an g ,albino African tribe. Balthazar thought he was seeing two different races of peoplewas seeing two different races of people. This was the first discovery of albinism.
Albinism also called Hypo‐pigmentation, achromia, achromasia, or achromatosis
ALBINO:organism with complete absence of melanin.
ALBINOID or ALBINIC:an organism with only a diminished amountan organism with only a diminished amount of melanin.
iAl ll d i t l i i b t
Melanin• Also called pigment, melanin is a substance that gives the skin and hair its natural color.
• It also gives color to the iris of the eye, feathers, and scales.eat e s, a d sca es
• Melanin is synthesized from the amino acid t ityrosine.
• In the skin, melanin is formed by cells , ycalled melanocytes.
There are three basic types of melaninThere are three basic types of melanin:
1. Eumelanin: have black and brown color.
2. Pheomelanin: have red or yellow color, responsible for red hair and frecklesresponsible for red hair and freckles.
3. Neuromelanin: is found in the brain, though its function remains obscure.
Both pheomelanin and eumelanin are found in human skin and hair, but eumelanin is the most abundant
l i i h ll th f t lik l t bmelanin in humans, as well as the form most likely to be deficient in albinism.
Melanin have some benefits
1. Melanin provides a natural protection against the harmful effects of ultravioletagainst the harmful effects of ultraviolet rays of the sun.
2. Melanin is also a mechanism for absorbing heat from the sun.g
3. Melanin, also important for sharpness of i ivision.
f A i i1) Oculocutaneous Albinism (OCA)
Types of Albinism1) Oculocutaneous Albinism (OCA)‐ Affecting the eyes, skin and hair. ‐ People with this type of albinism have white or pink hair, skin, and iris color, as well as vision problems.‐Most severe type.H 4 t (1 2 3 4)‐ Have 4 types (1,2,3,4)
2) Ocular Albinism (OA)Aff ti th l‐ Affecting the eyes only.
‐ Skin color is usually normal or slightly lighter than the skin of other family members.skin of other family members.
‐ Eye color may be in the normal range but there is no pigment in the retina.‐ Have 3 types.
G i f A i iGenetics of AlbinismMost types of albinism are inherited as anMost types of albinism are inherited as an Autosomal recessive but some types are X‐linked Recessivelinked Recessive.
1) Autosomal Recessive:
• Most types of albinism are inherited when an individual receives the albinism gene from both parents.• If parents are carriers, the child has a 25% chance f b i l l l 50% h f b iof being completely normal, a 50% chance of being
a carrier, and a 25% chance of getting albinism.
2) X‐linked Recessive:The exception: some types of ocular albinism which isThe exception: some types of ocular albinism, which is passed from mothers to their sons.
What if one gene is normal and one gene does not produce the penzyme?
The one functioning gene produces enough enzyme to make melanin for normal coloration
EPIDEMIOLOGYEPIDEMIOLOGYEPIDEMIOLOGYEPIDEMIOLOGY
CAlbi i i d b t ti
Causes• Albinism is caused by mutation or an alteration of the gene that makes the
l i imelanin pigment.
• Albinism is inherited genetically as previously stated it is autosomal recessivepreviously stated, it is autosomal recessive and some types x‐linked recessive inheritanceinheritance.
P l d I idPrevalence and Incidence• The international average for albinism is about• The international average for albinism is about 1 in 20,000.
I th U S 1 i 17 000 h t• In the U.S., 1 person in 17,000 has some type of albinism.
• Research indicates that the first type, Oculocutaneous Albinism (OCA) happen by 1 per 40,000 of the population.
• While the second type, Ocular Albinism (OA)While the second type, Ocular Albinism (OA) happen by 1 per 15,000 of the population.
P l d I idPrevalence and Incidence
H ll th ld• Happens all over the world.
• Affects all vertebrates• Affects all vertebrates.
• Affects people from all races.p p
• Effects men and women of all ages.
• Albinism has been observed in many animals
also.
SSymptomski d i
Pale skin or Usually pale blue or light
Skin and Hair Eyes
Pale skin or
patchy skin
White hair
Usually pale blue or light brown, but can sometimes appear pink‐White hairred
Extremely poor vision
Light sensitivity (Photophobia)
Rapid eye movements (Nystagmus)
bStrabismus
Ab f l i t i lti iAbsence of normal pigments in eyes resulting in pale blue, light brown or red eyes
This is not because the iris is red, but because there is so little color that thebecause there is so little color that the blood vessels show through the iris.
Albinism in animals
iPrognosis• Growth development and intellectual• Growth, development and intellectual development in the albino child are normal.
• Vision is invariably severely impaired.
• Albinism does not affect the expected lifespan.
• People with albinism may be limited in their activities because they can't tolerate theactivities because they can't tolerate the sun.
C i iComplications• Lack of skin pigmentation making more• Lack of skin pigmentation making more susceptible to sunburn and skin cancer.
• Blindness.
• Albinism may cause social problems, b l h lb l k d ffbecause people with albinism look different from their families, peers and other members of their ethnic group.
BIOCHEMICALBIOCHEMICALBASISBASISBASISBASIS
i iAlbi i i d b ti l k f
Biochemical Bases• Albinism is caused by a genetic lack of melanin.
• Melanin is synthesized from the aminoMelanin is synthesized from the amino acid tyrosine.
• Tyrosinase breaks down tyrosine.
i iBiosynthetic pathways• The first step of the biosynthetic pathway for both eumelanins and pheomelanins is
catalyzed by tyrosinase:
Tyrosine → DOPA → dopaquinone
• Dopaquinone can combine with cysteine by two pathways to form pheomelanins:
Dopaquinone + cysteine → 5‐S‐cysteinyldopa→ pheomelanin
Dopaquinone + cysteine → 2‐S‐cysteinyldopa→ pheomelanin
• Also, Dopaquinone can be converted to leucodopachrome and follow two pathways f h l ito form the eumelanins:
Dopaquinone → leucodopachrome → dopachrome → 5,6‐dihydroxyindole‐2‐carboxylic acid (DHICA)→ quinone → eumelanin
Dopaquinone → leucodopachrome → dopachrome → 5,6‐dihydroxyindole (DHI)→ quinone → eumelanin
Albinism: mutation in tyrosinase, the first enzyme in the pathway that converts tyrosine to melanin
The result of no melanin is an albino.an albino.
Interestingly, individuals with phenylketonuria can have light skin and hair at birth,.low levels of tyrosinebecause of
However, phenylketonuriacs are not albinos, because they obtain sufficientamounts of tyrosine in their diets to support melanin biosynthesis.
DIAGNOSISDIAGNOSISDIAGNOSISDIAGNOSIS
i iDiagnosis• Albinism can first appear at birth because it is a• Albinism can first appear at birth because it is a
physical deformity that never changes.
• Detected at birth because of irregular pigmentation.Detected at birth because of irregular pigmentation.
• Diagnosis is based on careful history of pigment development and an examination of the skin, hair p ,and eyes.
• The most accurate way to determine albinism is• The most accurate way to determine albinism is genetic test, for example : Chorionic Villus Sampling Test(CVS) and Amniocentesis can identify albinismTest(CVS) and Amniocentesis can identify albinism during the second trimester of pregnancy.
i iDiagnosis• Hair from the scalp can be used to assess tyrosinase• Hair from the scalp can be used to assess tyrosinase
activity by determination the DOPA and melaninconcentration.
• DOPA and melanin assessed by a radioactive biochemical assay, in which the samples are incubated with a radiolabelled tyrosine precursor and the amount of radiolabel released after enzymatic conversion quantified spectrophotometricallyspectrophotometrically.
• The value of this test is debatable since a negative result i di t OCA1 b t positi e res lt till l thindicates OCA1 but a positive result still leaves the possibility of OCA1, OCA2, OCA3, or OA1.
MANEGMENTMANEGMENTMANEGMENT MANEGMENT andandand and
TREATMENTTREATMENTTREATMENTTREATMENT
MANEGMENT and TREATMENT
• There is no cure for albinism because albinism is a genetic• There is no cure for albinism, because albinism is a genetic disorder, treatment is limited.
• Treatments only reduce the symptoms.
• The skin and eyes must be protected from the sun.
SkiSkin
• The skin can be protected by using sunscreen creams .
• Always wear special UV protective clothing to reduce sunburn risk.
• Children should receive annual skin assessments to screen for skin cancer or lesions that could lead to cancer.
MANEGMENT and TREATMENT
EEyes• Many children will need to wear prescription Glasses or y p p
lenses, which can provide improvements in their vision.
• Wear dark Sunglasses (UV protected) may relieve photophobia.
• Eye muscle surgery is sometimes recommended to correct abnormal eye movements (Nystagmus)abnormal eye movements (Nystagmus).
• For strabismus, ophthalmologists prefer to treat infants starting at about six months of age, before the function of g g ,their eyes has developed fully.
• Children should receive annual examinations by an h h l l iophthalmologist.
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