Resolving Perplexity: An Update

Have you EVER seen an albino water buffalo?   Anyway, as promised, here is the follow up to my last post, Perplexity and Why I Love Dan Meyer.

The question that my class set out to answer today: 

" O.k. so on my way home, I’ve seen yet another albino!  It seems like I see a lot of them here.  Is this because they are more noticeable here than in Caucasian populations or is there a biological explanation?  Just a lingering wondering..."

Last night on the doc, students essentially conducted  research in three main areas. 

  1. What is albinism?  What causes it specifically at a biochemical level?  How is it inherited? 
  2. How does the incidence of albinism in India compare to other parts of the world? 
  3. What psychological, social and cultural implications need to be considered when answering this question? 

Today I learned the following from my students: 

There are at least five types of albinism.  Albinism is caused by mutations in the genes that code for the enzymes involved in melanin metabolism in the skin hair and eyes including, the enzyme tyrosinase.  These mutations cause either and absence or defect in the enzymes of this pathway. Most of the forms of albinism are autosomal homozygous recessive conditions; however, ocular albinism is sex-linked.  If you want to know more, check out this link on the proteins of the biosynthetic pathway of melanin production that are involved in the various forms of albinism.

They also analyzed a great deal of data from different sources regarding the incidence of albinism in India.  Most of the sources, however were estimates or extrapolated due to issues with gathering this type of data in India.  This is largely due to the intersections between the cultural implications of the caste system, extreme poverty in slums and rural areas, and inefficiency in gathering this type of data through public health outreach in a population as large and disconnected as you find in developing nations like India and China.  Having said that, the estimates of prevalence in India exceed the extrapolated data by 20,000 to 30,000 affected individuals.  This source suggests that the incidence in India should be higher due to the prevalence of endogamy, which is is the practice of marrying within a specific ethnic group, class, or social group, while rejecting others on such basis as being unsuitable for marriage or other close personal relationships. In India, albinos are considered outcasts in some areas resulting in marital pairings of individuals that are homozygous for the mutations thereby increasing the frequency of recessive alleles in a familial group. 

There is also evidence to suggest that founder mutations have increased the incidence in India above the world average similar to situations found in tribal Africa.  In fact in some areas in Africa, the incidence of albinism is as high as 1 in 1000 individuals compared to a world average of 1 in 17,000 individuals.  This is due to inbreeding combined with the founder effect in small nomadic populations. 

While all of the literature suggests that there is a possibility of a higher incidence of albinism in India, the validity of the data is not reliable enough to confirm this hypothesis.  In a heavily populated area like Mumbai, it could just as easily boil down to the fact that you encounter more individuals on a daily basis compounded with the fact that individuals affected by albinism stand out more against individuals with dark pigmentation. 

Regardless, this research assignment was AWESOME!  I felt like Harvey Specter with an entire staff of paralegals and underlings solving the world's mysteries for me.  Keep the questions coming!