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What are the odds?

Last post 10-12-2009 6:36 PM by Jennamooney. 20 replies.
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  • 10-11-2009 12:46 AM In reply to

    Re: What are the odds?

    May I ask what makes it clincally different then OCA2? I will go back and correct the info with it.

    I dont think it meant that OCA4 only happenes in Japanese people. Only that 18% of people with it are Japanese. Just like OCA2 is more common in Black people then OCA1. Bryn has OCA2 and we are not African.

    • Post Points: 20
  • 10-11-2009 6:51 AM In reply to

    • wilsone8
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    • Joined on 10-11-2009
    • Posts 4
    • Points 50

    Re: What are the odds?


    Out of curiousity, where did you come up with the 1 in 70 statistic?  I've seen 1 in 10,000 quoted for OCA1.  Are you counting all the different forms? 

    I'm just going by what I have learned here. Quote:"Her risk for carrying the gene for albinism is the same as everyone else in the world, 1:70. Assuming that she would be that lucky 1:70 AND that he too was a carrier AND that her albinsim gene was the same as her husbands, then their babies would have a 25% chance of having albinsim. .." Is this not correct? I'm confused now, that's not hard to do. :) You all are so great, I appreciate you taking the time out of your busy schedules to try to educate me. I am forever grateful to you all, you have touched my heart.

    Oh sorry, I was actually asking the person who originally quoted that number: mktighe.

    I think the odds should be calculated as follows:

    Albinism occurs in the US in 1 in about 17,000 people.  Working backwards from that, we can calculate that the odds of being a carrier as 1 / 17,000 / 4 = 1 / 4250 for any type of albinism.

    The son-in-law has a 50% chance of being a carrier (each of his parents is a carrier).  Your daughter has a 1 in 4,250 chance of having any albinism related genetic defect based on the instances in the general population.  Even if both are a carrier, there is only a 1/4 chance that their child will inherit the defect from both parents.  So their odds are:

    1 / 4250 * 1/2 * 1/4 = 1 / 34,000

    And that's actually properly overestimating the odds.  From what I understand, in order for albinism to be present both carrier must have related defects.  The odds above assume that all combinations of defects will cause albinism, but that's not true in reality.

    • Post Points: 20
  • 10-11-2009 8:33 AM In reply to

    Re: What are the odds?

    I found this info about the odds

    Albinism can affect people of all ethnic backgrounds and has been extensively studied. Approximately one in 17,000 people have one of the types of albinism [1]. This suggests that about 1 in 70 people carry a gene for OCA.

      OCA1 has a prevalence of approximately 1 per 40,000 [3] in most populations but is very uncommon among African-Americans

    In contrast, OCA2 is the most common type of albinism in African Black OCA patients. The overall prevalence of OCA2 is estimated to be 1:36,000 in the USA, but is about 1:10,000 among African Americans [4]. It affects 1 in 3,900 of the population in some parts of the southern part of Africa [5].

    OCA3 or Rufous oculocutaneous albinism has been reported to affect 1:8,500 individuals in Africa, whereas it is very rare in Caucasians and Asiatic populations [6].

    Recently, mutations in a fourth gene were shown to be the cause of albinism, OCA4, [7] and were reported to explain the disease in approximately 5–8% of German patients with albinism [8] but 18% of Japanese patients [9].




    • Post Points: 5
  • 10-11-2009 2:58 PM In reply to

    • Summer
    • Not Ranked
    • Joined on 12-02-2008
    • Frisco, Texas
    • Posts 12
    • Points 240

    Re: What are the odds?

    It is clinically different due to the fact that the mutation occurs on a completely separate gene compared to OCA2. I was just stating that we are not of Japanese decent as it has been commonly thought that OCA4 is only in people of Japanese decent. They were certain my daughter had HPS rather than OCA4 due to the fact that we have no Japanese decent. After further testing for OCA4 it was conclusive. My daughter is one in fewer than 100 people in the U.S. diagnosed with OCA4. Well I should say that when she was diagnosed at 4 months old and is now about to be 2 she was 1 in about 100.

     Hope that helps! Most people don't even know about OCA4... it is that rare!

    • Post Points: 35
  • 10-11-2009 4:12 PM In reply to

    Re: What are the odds?

    Albinism is wild! I still want to get my son tested. I think we are going to do that study at the NIH and find out what Andy has and how he got it And if it is a new mutation or one from my and hubby!

    • Post Points: 5
  • 10-12-2009 6:36 PM In reply to

    Re: What are the odds?

    Oh, I was thinking clinically meant visually, sorry. I see. Thanks for the info!

    I bet that was scary info to have so few people with what she has.

    I still have yet to find another child with both chromo issues my DD has. Its scary b/c I dont have any clear guidelines to go off of KWIM??

    • Post Points: 5
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