Understanding Albinism and Prenatal Testing

The provided text delves into various aspects of albinism, including its identification through tests such as chorionic villus sampling, hairbulb pigmentation testing, and tyrosinase testing. It explains that these procedures can reveal specific types of albinism but highlights the importance of considering individual circumstances for effective treatment. The document also discusses treatments for eye problems associated with albinism, including surgery to correct nystagmus, strabismus, and refractive errors. Overall, it provides a comprehensive overview of albinism and its management options.

COMSATS UNIVERSITY, ISLAMABAD
Task: Semester project
Topic: Albinism (Genetic Disorder)
Submitted By:
Manal Rizwan
REG NO:
SP19-BSE-066
Submitted to:
Mam Saira Amir
Date:
21DEC,2019
1

COMSATS UNIVERSITY, ISLAMABAD
Department of Computer Science
Albinism
FINAL SEMESTER
PROJECT
2

Contents
Albinism……………………………………….……………………………………………………………………………………………1
Types of Albinism………………………………………………………………………………………………………………………2
Symptoms…………………………………………………………………………………………………………………………………..3
Visual Problems……………………………………………………………………………………………………………………………4
Diagnosis……………………………………………………………………………………………………………………………………….5
Treatment……………………………………………………………………………………………………………………………………..6
Pedigree………………………………………………………………………………………………………………………………………..8
References…………………………………………………………….………………………………………………………………………..8
3

Albinism
Albinism is a heterogeneous condition inherited through either autosomal recessive or sex-linked
recessive genes that affects approximately 1 in 17,000 people. Albinism is a defect of melanin
production that results in little or no color (pigment) in the skin, hair and eyes. Melanin is a
natural substance that gives color (pigment) to hair, skin, and the iris of the eye. It is produced by
cells in the skin called melanocytes. The enzyme tyrosinase is missing from the melanocytes.
Tyrosinase is a catalyst in the conversion of tyrosine to melanin. When the enzyme is missing no
melanin is produced. Thus, it caused diseases albinism.
There are 2 main types of albinism:
i) Oculotaneous albinism
ii) Ocular albinism.
Oculotaneous albinism (OCA) describes a phenotype that lacks pigment in the skin, hair, and
eyes. It is of 4 types- OCA1(OCA1A, OCA1B), OCA2, OCA3, OCA4.
Ocular albinism occurs when the phenotype only lacks pigment from the eyes, the hair and skin
appear normal in these individuals. Thus, oculotaneous albinism is typically more prominent.
Oculocutaneous albinism type1 (OCA1) - It is tyrosinase - related albinism results from a genetic
defect in an enzyme called tyrosinas. This enzyme helps the body to change amino acid tyrosine
into the pigment. There are 2 subtypes of OCA1 (OCA1A and OCA1B):
a) OCA1A - In OCA1A, the enzyme is inactive and no melanin is produced, leading to white
hair and very light skin.
b) OCA1B - In OCA1B, the enzyme is minimally active and small amount of melanin is
produced, leading to hair that may darken to blonde, yellow/ orange or even light brown, as well
as slightly more pigment in the skin.
Oculocutaneous albinism type2 (OCA2) - it is a P-gene albinism results from a genetic defect in
the p-protein that helps the tyrosinase enzyme to function. Individuals with OCA2 make a
minimal amount of melanin pigment and can have hair color ranging from very light blonde to
brown.
4
Simple flow chart to show to
production of melanin from
tyrosine.

Oculocutaneous albinism type3 (OCA3) - It is rarely desribed and results from a genetic defect
in TYPR1, a protein related to tyrosinase. Individuals with OCA3 can have substantial pigment.
Oculocutaneous albinism type4 (OCA4) - It results from a genetic defect in the SLC45A2
protein that helps the tyrosinase enzyme to function. Individuals with OCA4 make a minimal
amount of melanin pigment similar to persons with OCA2.
Ocular albinism (OA1) - It is caused by a change in the GPR143 gene that plays a signalling role
that is especially important to pigmentation in the eye. OA1 follows a simpler pattern of
inheritance because the gene for OA1 is on X chromosome. Female has 2 copies of X
chromosomes while males have only 1 copy (another Y chromosome). To have Ocular albinism,
a male only need to inherit one changed copy of the gene for ocular albinism from his carrier
mother. Therefore almost all the people with OA1 are males.
The Biochemical Pathway That Is Affected By Albinism
5
Example showed that albinism is
caused by sex-linked recessive
gene.

Melanin synthesis starts with the amino acid tyrosine, which is oxidized to
dihydroxyphenylalanine (DOPA) by the enzyme tyrosinase. DOPA is then oxidized to
dopaquinone by the same enzyme. Dopaquinone is spontaneously transformed to
leucodopachrome, and then to dopachrome. The latter is decarboxylated to 5,6-dihydroxyindole,
and then oxidized to indole 5,6-quinone. Indole-quinone is converted to melachrome, and then
polymerizes to eumelanin (pigment with brown to black color). Dopaquinone can react with
cysteine under high concentrations of the latter to form cysteinyl-dopa, which is oxidized to
pheomelanin (yellow to red color pigment). DOPA can also react with glutathione to form
pheomelanin (brown to black pigment). When the absence of enzyme tyrosinase, it prevents the
synthesis of melanin pigment by melanocytes.
Symptoms
Most oculocutaneous albinistic humans appear white or very pale as the melanin pigments
responsible for brown, black, and some yellow colorations are not present. Ocular albinism
results in pale blue eyes, and may require genetic testing to diagnose.
Individuals with albinism have skin that partially or entirely lacks the dark pigment melanin,
which helps protect the skin from the sun's ultraviolet radiation, their skin can burn more easily
from overexposure and increase the risk of skin cancer
The human eye normally produces enough pigment to color the iris blue and lend opacity to the
eye. However, there are cases in which the eyes of an albinistic person appear red or purple,
depending on the amount of pigment present, due to the red of retina being visible through the
iris. Lack of pigment in the eyes also results in problems with vision, both related and unrelated
to photosensitivity. The albinistic are generally as healthy as the rest of the population, with
growth and development occurring as normal, and albinism by itself does not cause mortality.
Visual problems
Development of the optical system is highly dependent on the presence of melanin, and the
reduction or absence of this pigment in albinistic individuals may lead to:
 Decussation (crossing) - Misrouting of the retinogeniculate projections, resulting in
abnormal of optic nerve fibres.
 Photophobia - decreased visual acuity due to light scattering within the eye (ocular
straylight).
 Foveal Hypolasia - Reduced visual acuity and possibly light-induced retinal damage
 Nystagmus - Irregular rapid movement of the eyes back and forth, or in circular motion.
 Refractive errors such as myopia or hyperopia and especially astigmatism.
 Amblyopia - Decrease in acuity of one or both eyes due to poor transmission to the brain,
often due to other conditions such as strabismus. - muscle imbalance of the eyes "crossed
eyes" (esotreopia), "lazy eye" or an eye that deviates out (exotropia).
6

 Optic nerve hypoplasia - underdevelopment of the optic nerve where the nerve signals from
the retina to the brain does not follow the usual routes.
Diagnosis
a) Chorionic Villus Sampling (CVS)
A chorionic villus sampling (CVS) test during the fifth week of pregnancy may also reveal some
types of albinism. But, chorionic villus sampling is not recommended for women who have
vaginal bleeding or spotting during the pregnancy. It is not typically recommended for women
who have Rh sensitization from a previous pregnancy.
Overall, this prenatal testing procedure involves taking a sample of the chorion frondosum—that
part of the chorionic membrane containing the villi—for laboratory analysis. The chorionic
membrane is the outer sac which surrounds the developing fetus. Chorionic villi are microscopic,
finger-like projections that emerge from the chorionic membrane and eventually form the
placenta. The cells that make up the chorionic villi are of fetal origin so laboratory analysis can
identify any genetic, chromosomal, or biochemical diseases of the fetus.
b) Hairbulb Pigmentation Test
Hairbulb pigmentation test is used to identify carriers by incubating a piece of the person's hair
in a solution of tyrosine, a substance in food which the body uses to make melanin. If the hair
turns dark, it means the hair is making melanin (a "positive" test); light hair means there is no
melanin. This test is the source of the names of two types of albinism: "ty-pos" and "ty-neg."
c) Tyrosinase Test
The tyrosinase test is more precise than the hair bulb pigmentation test. It measures the rate at
which hair converts tyrosine into another chemical (DOPA), which is then made into pigment. In
hair, tyrosine converts with the help of "tyrosinase." In some types of albinism, tyrosinase
doesn't do its job, and melanin production breaks down.
Treatment
There is no treatment that can replace the lack of melanin that causes the symptoms of albinism.
Doctors can only treat eye problems that often accompany the lack of skin color.
Treatment of the eye conditions consists of visual rehabilitation. Surgery is possible on the
ocular muscles to decrease nystagmus, strabismus and common refractive errors like
astigmatism. Nystagmus-damping surgery can also be performed, to reduce the "shaking" of the
eyes back and forth. The effectiveness of all these procedures varies greatly and depends on
individual circumstances.
Glasses and other vision aids, large-print materials as well as bright but angled reading lights,
can help individuals with albinism, even though their vision cannot be corrected completely.
7

Some people with Albinism do well using bifocals (with a strong reading lens), prescription
reading glasses, and/or hand-held devices such as magnifiers or monocular. Contact lenses may
be colored to block light transmission through the iris. But in case of nystagmus this is not
possible, due to the irritation that is caused by the movement of the eyes. Some use bioptics,
glasses which have small telescopes mounted on, in, or behind their regular lenses, so that they
can look through either the regular lens or the telescope.
Pedigree:
References
1. Elias I. Traboulsi, W. Richard Green. (2006). An Overview of Albinism and Its Visual
System Manifestations (Chapter 38, Volume 4). Lippincott Williams & Wilkins.
2. Retrieved from website http://www.elmhurst.edu/~chm/vchembook/635pku.html
3. Retrieved from website http://medical-dictionary.thefreedictionary.com/Albino+people
4. Retrieved from website
http://medical-dictionary.thefreedictionary.com/Chorionic+Villus+Sampling
Retrieved from website http://powerofthegene.com/joomla/index.php/genetically-inherited-
diseases/dermatological-disorders/oculocutaneous-albinism
8