Albinism
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Albinism

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Albinism Presentation contents:

Albinism Presentation contents:
1- Introduction
2- Epidemiology
3- Biochemical bases
4- Management and Treatment

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Albinism Albinism Presentation Transcript

  • Prepared by:  epa ed by Yasser Sh. Barhoum Mohammed Bakeer  Supe sed by Supervised by: Prof. Abed Nasser Abu shahla  Master  Program of Biological Sciences, Al‐Azhar University‐Gaza (December, 2013)
  • INTRODUCTION
  • ALBINISM A S Definition: D fi iti •Is a congenital disorder characterized by   the complete or partial absence of  pg , melanin pigment in the skin, hair and  eyes. •D t b Due to absence or defect of tyrosinase  d f t ft i enzyme involved in the production of  melanin.
  • History i A man in the 17th century named  A i th 17th t d Balthazar Telez, who was an explorer,  came up with the name "Albino", which  g , means white negro, after he saw an  albino African tribe. Balthazar thought he  was seeing two different races of people.  was 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 amount  an organism with only a diminished amount of melanin.
  • Melanin i • Al Also called pigment, melanin is a substance  ll d i t l i i bt 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  tyrosine. t i • In the skin, melanin is formed by cells  , y called melanocytes.
  • There are three basic types of melanin: There 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 freckles. responsible 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  melanin in humans, as well as the form most likely to be  l i i h ll th f t lik l t b deficient in albinism.
  • Melanin have some benefits 1. Melanin provides a natural protection  against the harmful effects of ultraviolet  against 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  vision. ii
  • Types of A i i f Albinism 1)  Oculocutaneous Albinism (OCA) 1) 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 Have 4 types (1,2,3,4) 4t (1 2 3 4) 2)  Ocular Albinism (OA) ‐ Aff ti th Affecting the eyes only. l ‐ 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.
  • Genetics of Albinism G i fA i i Most types of albinism are inherited as an  Most types of albinism are inherited as an Autosomal recessive but some types are X‐ linked Recessive. linked 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  of being completely normal, a 50% chance of being  fb i l l l 50% h fb i a carrier, and a 25% chance of getting albinism.
  • 2) X‐linked Recessive: The exception: some types of ocular albinism, which is  The exception: some types of ocular albinism which is passed from mothers to their sons.
  • What if one gene is normal and one gene p does not produce the enzyme? The one functioning gene produces enough enzyme to make melanin for normal coloration
  • EPIDEMIOLOGY
  • Causes C • Albi i i Albinism is caused by mutation or an  db t ti alteration of the gene that makes the  melanin pigment. l i i • Albinism is inherited genetically as  previously stated, it is autosomal recessive  previously stated it is autosomal recessive and some types x‐linked recessive  inheritance. inheritance
  • Prevalence and Incidence P l d I id • The international average for albinism is about The international average for albinism is about  1 in 20,000. • I th U S 1 In the U.S., 1 person in 17,000 has some type  i 17 000 h t 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.
  • Prevalence and Incidence P l d I id • H Happens all over the world. ll th ld • 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.
  • Symptoms Skin and Hair ki d i Pale skin or  Pale skin or patchy  skin White hair White hair Eyes Usually pale blue or light  Usually pale blue or light brown, but can  sometimes appear pink‐ red Extremely poor vision Light sensitivity  (Photophobia)  Rapid eye movements  (Nystagmus) Strabismus b
  • Absence of normal pigments in eyes resulting in Ab f l i t i lti i pale blue, light brown or red eyes This is not because the iris is red, but because there is so little color that the blood vessels show through the iris.
  • Albinism in animals
  • Prognosis i • 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 the because they can't tolerate the  sun.
  • Complications C i i • Lack of skin pigmentation making more Lack of skin pigmentation making more  susceptible to sunburn and skin cancer. • Blindness. • Albinism may cause social problems,  because people with albinism look different  b l h lb l k d ff from their families, peers and other  members of their ethnic group.
  • BIOCHEMICAL BASIS
  • Biochemical Bases i i • Albi i i Albinism is caused by a genetic lack of  db ti l k f melanin. • Melanin is synthesized from the amino Melanin is synthesized from the amino  acid tyrosine. • Tyrosinase breaks down tyrosine.
  • Biosynthetic pathways i i • 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  to form the eumelanins: f h l i 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.
  • Interestingly, individuals with phenylketonuria can have light skin and hair at birth, because of low levels of tyrosine. However, phenylketonuriacs are not albinos, because they obtain sufficient amounts of tyrosine in their diets to support melanin biosynthesis.
  • DIAGNOSIS
  • Diagnosis i i • 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 albinism and Amniocentesis can identify albinism  during the second trimester of pregnancy.
  • Diagnosis i i • 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 melanin concentration. • 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  spectrophotometrically. spectrophotometrically • The value of this test is debatable since a negative result  indicates OCA1 but a positive result still leaves the  i di t OCA1 b t positi e res lt till l th possibility of OCA1, OCA2, OCA3, or OA1.
  • MANEGMENT  MANEGMENT and  and TREATMENT
  • 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. Skin Ski • 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 Eyes • 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  ophthalmologist. hh l l i
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