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Genetics 101: How Some Retinal Diseases are Inherited

Egg and spermLong before the advent of genetic testing, or even knowledge of DNA and RNA, astute observers noticed that many traits were passed from one generation to another. But it still can be difficult to understand why some people inherit a genetic disease and others do not. Also, it’s often not clear which family members are at risk of inheriting a condition.

To understand heredity, you have to know a little about genetics. Below is a review of the three major genetic-disease inheritance patterns. But, first, a little background:

Genes and Mutations
Genetic conditions, including many retinal diseases, are caused by genetic variations, or mutations, passed down from one or both parents. Everyone has about 25,000 pairs of genes, which play a major role in determining who we are—our height, hair color, etc. We all have many variations and mutations in our genes, and most do not affect health or well-being. However, some cause problems and lead to diseases, including those of the retina.

Genes are wrapped in structures called chromosomes, of which humans normally have 23 pairs. We inherit one of each chromosome from our mother and father. Chromosomal pairs 1 through 22 are known as autosomal (non-sex) chromosomes. The X and Y chromosomes on pair 23 are known as the sex chromosomes, because one of their functions is to determine our sex.

Autosomal Dominant
To get an autosomal dominant disease, a child receives one copy of a mutated gene from an affected parent. It’s likely the affected parent knows he or she has the disease, or at least has related symptoms. The other parent is usually neither affected nor a carrier.

With dominant diseases, there’s a 50 percent chance that a child will receive the mutated gene and be affected by the disease. Dominant diseases frequently appear in several generations of a family, with many family members being affected.

Autosomal Recessive
To get a recessive disease, a child must inherit a mutated copy of the gene from both parents. With recessive conditions, each parent has one mutated copy and one normal copy of the relevant gene. Because each parent has only one mutated copy of the gene, they’re unaffected carriers of the condition. They usually have no idea that they’re carriers because they have no related vision problems.

If their child inherits only one mutated gene from one parent, then the child will only be a carrier of the disease and usually won’t experience any vision problems. If their child inherits a mutated copy from each parent, then the child will develop the disease and associated vision loss.

With recessive disease, there’s a 25 percent chance that the child will be affected and a 50 percent chance he or she will be an unaffected carrier. Recessive diseases are more likely to surprise a family because parents of an affected child usually don’t know they’re carriers.

X-Linked
Inheritance patterns for X-linked diseases are more complex than the others, because the gender of both parents and their children often determine if the disease will be passed down.

As mentioned previously, men have an X and Y chromosome and women have two Xs. In most cases, mothers pass X-linked diseases down to their sons. Daughters usually don’t get the disease, because they also have a healthy X chromosome from their fathers. However, researchers have found that women can sometimes have mild vision loss or, in rarer cases, severe vision loss from X-linked retinal diseases.

If an X-linked carrier mother has a son, there’s a 50 percent chance he will be affected. If an X-linked carrier mother has a daughter, there’s a 50 percent chance the daughter will be a carrier.

A Word on Age-Related Macular Degeneration (AMD)
AMD is the leading cause of blindness in people over 55 living in developed countries. It’s different from inherited retinal diseases, because risk of the condition is caused by a complex combination of genetic and lifestyle factors, including advancing age and smoking. The best way to determine risk of vision loss from AMD is through an examination of the retina by an eye doctor.

For more information, check out FFB’s Inheritance of Retinal Degenerations and About Genetic Testing booklets.

Image, above, courtesy of the National Institutes of Health.

 


28 Responses to 'Genetics 101: How Some Retinal Diseases are Inherited'

  1. deepak says:

    pls tell me the treatment of retinis pegmentosa.if treatment is a
    vailble pls reply my comments

  2. Laura Asplund says:

    Thanks for the primer on genetic inheritance. However, you need to correct the statement under the x-linked explanation that daughters “also have a healthy X chromosome from their fathers.” You meant from their mothers. The X chromosome they get from their fathers is the one with the disease.

    • EyeOnTheCure says:

      Both men and women can carry mutations on their X-chromosome. A father carrying a defective gene on his X chromosome can pass the X only to daughters, who will be carriers. Mothers who have a defective X chromosome have a 50% chance of passing the bad gene to either a daughter or son. If the daughter gets the bad X chromosome, she still has a good chromosome to compensate. If the son gets the defective X chromosome, since he only has one, he will most likely express the disease.

  3. SRIKANTH HS says:

    Can u tell me how to overcome night blindness and reducing eye sight from corner of eyes

  4. deepak says:

    pls tell me the treatnent of rp in india

  5. Lindales says:

    I’m undergoing treatment at Evergreen Eye Center, Auburn, for my dry eye. I need to know whether dry eye is genetic or not, because my mother had the same issue and is it common?

  6. melissa says:

    I have a son who is 13 and he has stargardtz disease im wondering if there are any clinical trials in the charlotte area we went to the vision walk this past weekend and my sons iep teacher said 53 kids were cured of blindness im wanting to know how to get on the list please contact me asap , thanks melissa

  7. Kevin says:

    As I read on, I realized that there’s only a few number of children who might obtain these vision problems. The possibility is somewhat 1:1000. But I know how severe these cases are when a child obtains them. The rareness defines the seriousness of the case. I just hope there’s an immediate way to heal all those patients who suffer.

  8. TASSOS says:

    These are called neurodegenerative eye diseases because they cause damage to the photoreceptors. The damage is due to inflammation in the retina caused by the genes. We canot change the genes but we can remove the neuroinflammation in a very simple way. This leads to improvement of photoreceptor function and results in visual acuity gain with stop of progression. No need for young people to go blind due to these diseases anymore. http://www.ophthalmiccentre.com

    • michelle anne dornan says:

      My mother is 82 and has Mackerel Degeneration i am 54 and have to wear 2 different pair.s of glass.s 1 for television and 1 pair for reading am i at risk of developing this condition?

      • EyeOnTheCure says:

        Researchers are discovering that genetics appears to be a major factor in more than half of the cases of AMD. In March 2005, three independent research groups — including one funded by FFB — discovered a gene called Complement Factor H (CFH) that appears to be linked to at least 50 percent of all cases of AMD. Prior to this landmark discovery, FFB-funded researchers discovered other genes that appeared to be linked to AMD, though these genes were implicated in a smaller number of cases than CFH.

  9. Jiggi says:

    As doctors said “you got eye disease from your parents” . but they are saying that no solution for this retina problem. i want to know where can i get treatment for this in INDIA. Please give suggestions . thanks Jiggi

    • EyeOnTheCure says:

      It is true that your eye disease originated from genes you received from your parents. However, you should know that there are three inherited forms of RP: recessive, dominant and X-linked. If you are not sure which type you have, you should ask your ophthalmologist. For information on inheritance types, please see the following web link to download a PDF document on inheritance:
      http://www.blindness.org/sites/default/files/inheritance_of_retinal_degeneration_-_july_2012.compressed.pdf
      If possible, you should consider genetic testing to try and identify the mutant gene responsible for causing the disease. If the gene is identified, medical databases such as PubMed can be searched to identify any research that is being conducted. With a molecular diagnosis, one may also qualify for gene therapy trials that are taking place. For information on genetic testing, please see the following web link to download a PDF document:
      http://www.blindness.org/sites/default/files/pages/pdfs/Genetic-Testing-Booklet-V5.2-20151023.pdf
      Whether the disease gene is identified or not, one should still consider participating in FFB’s “My Retina Tracker”, a free registry that monitors clinical trials that are recruiting for various retinal diseases. For more information on “My Retina Tracker” please see the following web link:
      https://www.myretinatracker.org/
      It may also be helpful to periodically check the website: http://WWW.CLINICALTRIALS.GOV which is maintained by the National Institutes of Health and contains a searchable list of clinical trials for most known diseases. Each clinical trial listing will provide you with information on what the study is about, the requirements for participating and contact information.

  10. sajjad says:

    Dear Sir, MY wife have eye problem (in VEP test)what test I should do for MY child before her pregnency.

    • EyeOnTheCure says:

      You should know that there are three inherited forms of RP: recessive, dominant and X-linked. If you are not sure which type you have, you should ask your ophthalmologist. For information on inheritance types, please see the following web link to download a PDF document on inheritance:
      http://www.blindness.org/sites/default/files/inheritance_of_retinal_degeneration_-_july_2012.compressed.pdf
      Your wife should consider genetic testing to try and identify the mutant gene responsible for causing the disease. If the gene is identified, medical databases such as PubMed (http://www.ncbi.nlm.nih.gov/pubmed/) can be searched to identify any research that is being conducted. With a molecular diagnosis, one may also qualify for gene therapy trials that are taking place. For information on genetic testing, please see the following web link to download a PDF document:
      http://www.blindness.org/sites/default/files/genetic_testing_booklet_201311rev.pdf

      Whether the disease gene is identified or not, one should still consider participating in FFB’s “My Retina Tracker”, a free registry that monitors clinical trials that are recruiting for various retinal diseases. For more information on “My Retina Tracker” please see the following web link:
      https://www.myretinatracker.org/

      It may also be helpful to periodically check the website: http://WWW.CLINICALTRIALS.GOV which is maintained by the National Institutes of Health and contains a searchable list of clinical trials for most known diseases. Each clinical trial listing will provide you with information on what the study is about, the requirements for participating and contact information.

  11. Dasa Vinayaga says:

    ​Dear friends:

    Please help this young lady (19) If you can tell us what her genetic eye disease is.

    Here is her description of her experience:

    I just remember it started when i was in grade 1 elementary ,the symptoms is first my eye sight something little cover on it that bother my eye sight can’t see good, it has something that i can’t take off i did tried wash water my eyes but still can’t take off after few minutes,it started ache,my eyes so hurt and i want to closed it cause if i open it hurts,then after few minutes my head starting ache too,usual i tried to sleep it so when i woke up its okay,sometimes can’t sleep and after that all start vomiting,i don’t know what makes it worst. I check years ago the doctor said i got high vision,my left eye is stronger than right eye,my left eye sights is blur,i need to put closely the paper on my left eye so i can see the letters,thats what i experience in school also,

    i sometimes faint and collapse,it was terrible i experience before but its not the same now like before now i feel that once a month or twice,when i wore glasses after one hour or few minutes my eyes hurt and i faint,i wore still my old glasses now when opening my cell phone,guess this glasses expired cause years pass since I bought it,i remember doctor said i have far sighted but now years I can’t see clearly in near too.

    Thank you. If you can recommend a good doctor or clinic for treating this condition, that would be wonderful.

    Dasa Vinayaga

    210 Market St. #201

    Kirkland, WA 98033

    425-737-6399

  12. shivkumar says:

    My eye side weak and ratina is weak . My specitals no is (-10)and I want to not spacitals doing use. Solution calls.

  13. Anna says:

    Thanks for sharing.

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