University of Edinburgh
 

Medical Information on Albinism

by Dr Andrew Blaikie for VI Scotland

This document is written with the minimum use of medical terms and jargon. It is impossible to avoid all medical terms but where we have used them we have attempted to explain them as clearly as we can. Although the information is intended to describe most aspects of the condition each child is different and there will always be exceptions to the rule. As far as we can determine these pages are true and accurate and have been written in good faith.

What this information is not for

This document is not a substitute for a consultation with a Health Professional and should not to be used as a means of diagnosing a condition.

We hope the information will help you to:

  • Have a better understanding of the condition
  • Know what tests and treatments are normally available
  • Know when to seek professional advice
  • Be able to discuss the condition in a more informed way
  • Make the most of consultations with carers, teachers and health professionals
  • Be reassured and more able to cope

Due to staffing limitations we are not able to offer telephone or email advice to parents of children.

Medical Information on Albinism

What we see is made in the brain from signals given to it by the eyes. What we see is in fact made in the brain. The brain makes sight from signals given to it by the eyes.

What is the normal structure of the eye?

The eye is made of three parts.

  • A light focussing bit at the front (cornea and lens).
  • A light sensitive film at the back of the eye (retina).
  • A large collection of communication wires to the brain (optic nerve).

A curved window called the cornea first focuses the light. The light then passes through a hole called the pupil. A circle of muscle called the iris surrounds the pupil. The iris is the coloured part of the eye. The light is then focused onto the back of the eye by a lens. Tiny light sensitive patches (photoreceptors) cover the back of the eye. These photoreceptors collect information about the visual world. The covering of photoreceptors at the back of the eye forms a thin film known as the retina. Each photoreceptor sends its signals down very fine wires to the brain. The wires joining each eye to the brain are called the optic nerves. The optic nerves join together about halfway between the eyes and the brain and then splits apart again. This join is called the optic chiasm. At the optic chiasm about half of the visual information in each optic nerve swaps over to the opposite nerve. This swap makes it easier for the brain to make sense of all the visual information. The information then travels to many different special 'vision' parts of the brain. All the parts of the brain and eye need to be present and working for us to see normally.

What is Albinism?

The colour of our skin depends on how much melanin is in it. Melanin is a dark brown material (pigment) found in many parts of the body. The body parts that it helps colour include the skin, hair and eyes. Some children cannot make as much melanin as others and some cannot make any melanin at all. Children who do not make as much melanin as normal have Albinism. Most children with Albinism only have a problem making melanin in their eyes. These children have 'Ocular Albinism'. In other children the lack of melanin affects all parts of the body as well. They may have pale skin and blonde hair with light coloured eyes. These children have 'Oculo-Cutaeneous Albinism'. Children with any type of albinism also swap more information at the optic nerve join (chiasm) than normal. This difference in the way the eyes are 'wired' to brain can be used to help make the diagnosis if there is some doubt using special electrical tests. Children are born with Albinism. They cannot 'catch' it in later life.

Why are some children unable to make melanin?

Albinism is caused by a misprint in the child's genes. Genes are a chemical alphabet stored in the body. Genes contain the body's 'built-in' plan to make sure all the parts of the body work correctly. A child with Albinism has often been passed (inherited) a gene with a misprint in it from one or both parents. Sometimes by chance a new mistake occurs in the child’s genes and the parent's genes are normal. If a certain gene has a mistake in it then a special chemical called an enzyme may not work correctly. These enzymes are needed by the child to help make melanin. In children with Albinism they either don't have as much of the enzyme that helps them make melanin or they have none at all.

There are sifferent types of Albinism

There are many different types of Albinism. It can seem very complicated. Most experts would say there are three main types of Albinism that vary by:

  • Which parts of the body are mainly affected
  • How much melanin the child makes
  • Whether the child has any other associated conditions.

The two main types of Albinism are called:

  • Oculocutaneous Albinism (affects the eyes and the skin)
  • Ocular Albinism (only affects the eyes)

Oculocutaneous Albinism

In Oculocutaneous Albinism both the eyes and the skin are affected. 'Oculo' refers to the eyes and 'cutaneous' to the skin. There are two main types of Oculocutaneous Albinism that vary depending on how much melanin the child is able to make.

Tyrosinase Negative Oculocutaneous Albinism

In the first type the child cannot make any melanin at all. This is called 'Tyrosinase Negative' Albinism. Tyrosinase is the name of the enzyme that helps the child make melanin. These children do not have a working Tyrosinase enzyme because of a mistake in their genes. These children have white hair and pale skin. The eyes may appear pink or reddish. They also are likely to constantly move in a fast to-and-fro way (Nystagmus). Children with this type of Albinism normally have very impaired vision.

Tyrosinase Positive Oculocutaeneous Albinism

In the second type of Oculocutaneous Albinism children can make some melanin but not as much as normal. Their hair is blond and their skin is not as pale. Their eyes are usually pale blue. The children normally also have Nystagmus but their vision is not as impaired.

What types of conditions might also affect children with Tyrosinase Positive Oculocutaeneous Albinism

If a child with Albinism bruises easily they may also have a rare condition in which the blood does not clot well, leading to bruising. This is called 'Hermansky-Pudlak Syndrome'. These children may also become short of breath easily. This condition is inherited as an autosomal recessive condition. For a child to inherit this condition both parents must carry the gene. This condition is most commonly found in Puerto Rico. If a child with Albinism develops infections more often than is usual they may have a condition called 'Chediak-Higashi Syndrome'. In this condition children have a lower immunity to infection than other children.

Genes, Chromosomes and Inheritance

We inherit two sets of genes; one set from our mother and one set from our father. Genes determine everything about our make up; from eye and hair colour to our facial features and even our ability to roll our tongue.

Our genes are found on 23 pairs of chromosomes. 22 of these pairs are known as 'Autosomal' chromosomes and determine general characteristics. The 23rd pair is the Sex Chromosome; the one which determines the sex of a person (boy or girl). There are 2 types of sex chromosomes; an X chromosome and a Y chromosome. They are named by their shape when looked at down a microscope. We always inherit one X chromosome from our mother. We can inherit either an X or a Y from our father. If we inherit another X chromosome from our father then we are XX (a girl). If we inherit a Y chromosome from our father then we are XY (a boy).

The set of genes we inherit from our mother varies greatly from the one we inherit from our father. Some genes are stronger than others and therefore they are the ones that are expressed in our appearance. The stronger genes are said to be 'Dominant' and the weaker ones 'Recessive'. For example the 'Brown Eye Gene' is Dominant and the 'Blue Eye Gene' is Recessive. If we inherit a Brown Eye Gene from our mother and a Blue Eye Gene from our father, then we will have brown eyes. To have blue eyes, we must inherit the Recessive Blue Eye Gene from both our mother and father. This is the only way a Recessive Gene can be expressed.

The genetics of Oculocutaeneous Albinism (OCA)

The genes for OCA are located on autosomal chromosomes. Autosomes are the chromosomes that contain genes for our general body characteristics and are numbered from 1 to 22. This is in contrast to the sex chromosomes (X&Y) that are named by letters that are similar to their actual shape.

We normally have two copies of chromosomes (and the genes on them). One copy is inherited from our father, the other inherited from our mother. Neither of the two copies of the OCA genes work in children with OCA. This is because the genes have misprints which stop them working properly.

OCA is a recessive condition, so if only one of the two copies of the OCA gene is misprinted, a person can make pigment and appear near-normal but will still carry a misprinted gene. This is called carrying the albinism trait. Both parents must carry a misprinted OCA gene to have a child with albinism. When both parents carry the misprinted gene (and neither parent has albinism) there is a one in four chance at each pregnancy that the baby will be born with albinism. This type of inheritance is called autosomal recessive inheritance.

Ocular Albinism

In Ocular (eye) Albinism it is the eyes that are mainly affected. The skin and hair usually appears the normal colour for the race of the child or slightly paler. Typically only boys are born with this form of Albinism and the vision can be near normal or only moderately impaired.

In most cases ocular albinism is inherited through a misprinted gene on the X chromosome. This is why X-linked ocular albinism occurs almost only ever in boys. Boys do not have a back up copy of the X-chromosome to protect them from developing the gene. Boys have only one X chromosome and it is paired with a 'Y'. They are therefore much more likely to be affected than girls (XX) who have two copies of the X-chromosome. The second copy would also have to be misprinted for them to develop the condition. X-linked ocular albinism is passed from mothers who carry the gene to their sons. Each time a mother who carries the gene for ocular albinism gives birth to a son, there is a 1 in 2 chance that the son will have ocular albinism. Mothers who carry the gene may have slightly pale eyes, but do not have the full condition of ocular albinism. An Eye Doctor may be able to identify this slight paleness on examination in the clinic.

How does Albinism affect the way a child sees?

Albinism can affect vision in different ways in different children. Generally the less melanin pigment in the iris and retina of the child, the poorer their vision is. Some children may see very well while others may only see bright lights and large shapes. In Albinism it is usually only the central vision that is poor. The vision around the sides is often fine. Because of this although many children with Albinism have difficulty seeing small letters most have no difficulty seeing to get around.

In children with Albinism the iris is usually pale and thin with gaps in it. These are called 'iris transillumination defects'. Because of this more light than usual gets into the eye. The back of the eye is also less pigmented and less dark. The extra light that gets into the eye scatters and bounces around the inside of the eye causing blurred vision. Because too much light enters the eyes, children with Albinism nearly always dislike bright light. This is called photophobia.

The central part of the retina at the back of the eye does not develop properly in the womb in children with albinism. The central part of the retina is called the macula. The centre of the macula is called the fovea. Children with Albinism typically have foveal hypoplasia. Hypo means less and plasia growth. So foveal hypoplasia means the most central part of the retina has not gown fully or properly. This also leads to reduced sharpness of central vision.

The nerve that joins the eyes to the brain also does not develop normally in the womb. This does not seem to affect vision too much but can be used to help confirm the diagnosis by looking for it using special electrical tests or scans.

The eyes of children with Albinism tend to make fast 'to and fro' movements. This is called Nystagmus. Because the eyes are constantly moving (like camera shake) this can also lead to blurred vision. Nystagmus does not usually appear until the child is older than 3 months. Before this time the eyes can appear to have 'roving' eye movements or just look normal.

Children with Albinism often need spectacles to help see more clearly. Children may also later develop a squint or a lazy eye.

How is Albinism diagnosed?

Because the eyes, and often the hair and skin, are paler than normal a diagnosis can usually be made quite easily. An Eye Doctor can examine the child, and often their parents as well, and confirm the diagnosis. The iris often is pale blue or pink with gaps in it. The eyes often move quickly to and fro (nystagmus). Looking at the back of the eye with a special torch the retina often looks paler than normal. All these signs help an Eye Doctor to make a diagnosis.

If there is no family history of Albinism and the child is only mildly affected other tests can be done to help make a diagnosis. These can include special electrical tests, scans of the head and blood tests.

What can be done to help?

There is no known way to help children make more melanin. Lots of things can be done though to help children with Albinism.

Bright light often causes discomfort and reduced vision (photophobia). A sunhat and sunglasses may help reduce the symptoms of photophobia. Special lenses that get darker in brighter light (photochromic lenses) are useful. Sometimes specially made dark contact lenses can also help.

Problems at school may be due to some of the reading books being hard to see. This often means it takes longer and more effort to do the work. If the size of print is increased and a sloping board used most children will find schoolwork easier. Various Optical Aids are helpful to children with albinism and the choice of an optical aid depends on how a person uses his or her eyes in jobs, hobbies, or other usual activities. Some people do well using Bifocal Lenses which have a strong reading lens. Others use hand-held magnifiers or special small telescopes and some prefer to use screen magnification products on computers. Optometrists or ophthalmologists who are experienced in working with low vision patients can recommend various optical aids.

Who wrote these documents?

These pages are the consensus of opinion of many different people. They include parents of visually impaired children, visually impaired children themselves, Community Paediatricians, Ophthalmologists, Educationalists and Psychologists.

The main author and person responsible for their content is Dr Andrew Blaikie who was an Ophthalmology Research Fellow with Visual Impairment Scotland and is a member of the Royal College of Ophthalmologists.

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