Genetics of earwax

10. desember 2022
Have you ever taken time to think about earwax and wondered if everyone has the same type of earwax? Not a popular topic, but an interesting one when it comes to genetics. Living in the western part of the world I assumed this was a universal trait of all humans, this wet yellow-brown wax that seems so unnecessary, but vital in protecting the ear canal from bacteria and fungi. There are actually two types of earwax present in the human population; wet earwax and dry earwax. The gene responsible is called ABCC11. This gene codes for an ATP-binding cassette transporter, which is a membrane transporter that exports molecules from the inside of a cell. One single change in a nucleotide (single nucleotide polymorphism) decides weather the earwax is wet or dry, the wet trait being dominant. Meaning that to have dry earwax you would have to inherit both recessive allels from your parents. The dry earwax allel is more common in North- and East Asia.
This gene is not only responsible for our ears filling up with wax but also the presence of odored sweat caused by excessive apocrine secretion, which follows the wet type earwax. Because of this, badly odored sweat is not a common problem in Asia. This is the reason why it is reccommended that western people bring their own deodorant when traveling to Japan!

Facial Blindness (Prosopagnosia)

7. december 2022
Have you seen your mother today? If you were asked to point out your mother in a photo, most people would do so without any difficulties. People with facial blindness on the other hand might have some trouble doing so. In extreme cases they wouldn't be able to recognize her if she was staring straight at them.

Prosopagnosia is a fancy medical term for what is colloqialy known as facial blindness. Despite this congenital condition affecting roughly 2.5% of the population it usually goes unrecognized, with most people being diagnosed as adults, if they are diagnosed at all. Research has shown that the condition is associated with a portion of the brain called the fusiform gyrus. The fusiform gyrus is a part of the temporal and occipital lobes associated with "high-level" visual processing especially facial recognition. The degree to which people with this condition are affected varies. In severe cases people can be unable to recognize the faces of family members or even their own face in the mirror. Being unable to recognize faces constitutes a significant deficite for affected individuals particularly socially. To function in every day life they utilize a variety of identifying traits such as clothes, hair and skin color, body shape and voice to recognize others. As this condition regularly goes unrecognized in children, affected children often face difficulties making friends due to their inability to recognize those around them. Imagine never knowing who you are really speaking to. As they use unconventional ways to recognize their fellow man, they have an especially hard time recognizing the people they know outside of the place they recognize them from. For example meeting your classmate in the mall or a collegue at the grocery store. They are also likelier to enjoy animated shows over other forms of media as characters there generally have more well defined designs and character traits. Although most health care professionals have heard of this condition, its percieved scarcity often leads to misdiagnosis. In this regard the most common is likely Autism Spectrum Disorder (ASD) with overlaping symptoms of social dysfunction with both conditions. The diagnosis of Prosopagnosia is based on a test called The Benton Facial Recognition Test. It uses a series of photos of famous people, where both hair and clothes are cropped from the image, leaving only an image of that individuals face. Subjects are then asked to identify the people on the image. However, this test has a large drawback. As it relies on the identification of famous people, someone with limited interest or awareness of popular culture would have a difficult time with the test. This also limits the tests usfulness for diagnosis among children.

The root causes of facial blindness are unknown, but autosomal dominant inheritence has been implicated. One research team in Italy has been able to associate the condition to genetic variations in a gene called oxytocin receptor gene (OXTR), a gene associated with emotional traits, thinking and facial and emotional recognition. Another reasearch group have found an association to a mutation in the gene MCTP2. A gene which codes for a calcium binding transmembrane protein expressed in the central nervous system which is predicted to be involved in the regulation of neurotransmitter secretion.

In the news it has been stated that American actor Brad Pitt, suffers from facial blindness and one can only assume that there are many more. As with most human abilities, there can be found individuals on the other side of the spectrum which have a near super human ability to recognize even the most minute facial features. Prosopagnosia is a great reminder that everything that our brains percieve via our senses occurs along a normal curve, With each individual percieving our world slightly differently depending on our ablity to sence and process the information from those senses. Together we form a world were we assume that everyone experiences our surroundings in an "average" way and we forget that there are outliers in every corner. We ourselves are likely to be outliers in one way or another and we are simply unaware, like most people with facial blindness, because that is how things have always been.

X-ray of a brain Photo by cottonbro studio faceless crowd by DALL-E Photo by DALL-E