posted
A very acceptable and accurate alternative title for this thread could have possibly been; Physiological Realities that Drive Euro-Albinos to Madness.
The issue I always have with these studies is their consistent usage of misleading statements regarding the frequency of occurrence within a wide population. As example, this study shows the frequency of Waardenburg Syndrome as very rare with 1:10,000 annually. While this may be true for overall national population stats, had the incident rate been fine tuned another level to only include Non-Hispanic whites, the incident frequency would increase far outside of the boundaries of "rare". If the sample group were than narrowed to just the one group showing the most frequency, A. Jews, the incident rate would be in the single digits.
Waardenburg Syndrome
Waardenburg syndrome is named after Dutch eye doctor Petrus Johannes Waardenburg, who observed that individuals with differently colored eyes often had hearing loss as well. Indeed, a primary characteristic of Waardenburg is hearing loss - along with blue/brown eyes or two brilliant blue eyes. Another easily recognizable trait is white hair on the head.
There are four types of Waardenburg syndrome and many sub-types. They differ based on their physical characteristics and on their specific genetic causes. How rare is Waardenburg syndrome? According to the National Institutes of Health, approximately one in every 10,000 to 20,000 people will have Waardenburg. Plus, since the first two types (Types I and II) are more common and are associated with hearing loss, it can be assumed that the majority of individuals with Waardenburg will have hearing loss.
Different colored eyes
Type I Waardenburg
Type I Waardenburg is a more common type and is caused by a mutation in the PAX3 gene. The PAX3 gene is part of a gene family that is important in the development of tissues and organs. This gene makes a protein that controls other genes responsible for the development of specific cells and parts of the body, such as facial bones and melanocytes (cells that make the pigment melanin).
Melanin is responsible for the color of our eyes, hair and skin. Melanocytes are also needed in the inner ear for hearing. Therefore, a mutation in the PAX3 gene means that melanin pigment cells cannot develop properly, leading to various problems. These problems include patches of white hair, and patches or areas of skin that lack pigmentation. The eyes can also have patchy pigmentation. Lack of melanin also contributes to the sensorineural deafness associated with the syndrome. The amount of hearing loss can be anywhere from moderate to profound. Type I Waardenburg is generally autosomal dominant - it's inherited from just one parent.
Type II Waardenburg
Type II Waardenburg, also a more common type, may also have hearing loss in addition to the color changes in the hair, skin and eyes. The main difference between Type I and Type II is that in Type II, the eyes are not widely spaced. While this type is suspected to be caused by mutations in the PAX3 gene, it is also believed to be caused by mutations in the MITF (microphthalmia-associated transcription factor) and SNAI2 genes. Type II can be inherited in both the autosomal dominant manner (one parent) and in an autosomal recessive manner, meaning that two parents have to have the gene to be able to produce a child with Type II Waardenburg.
Type III Waardenburg
Then there is Type III, a very rare type. What distinguishes Type III (also caused by a mutation in the PAX3 gene) from the others is that in Type III, there are upper limb abnormalities, such as malformations in the arms and the hands. For example, fingers can be fused together. This type of Waardenburg is also known as Klein-Waardenburg syndrome. Type III can arise spontaneously (no genetic link; a mutation just happens) or can be inherited from one parent.
In one unusual case, specialists in India diagnosed Waardenburg Type III in a 7-year-old boy who had fused middle and ring fingers on both hands, plus two fused toes. One leg had a white skin patch. His eyes were different colors. He had a broad nasal root (the area between the eyes) and some white hair. The child's father was normal and had no symptoms. But the mother did have symptoms, including deafness. She was later diagnosed with Type I, not Type III.
Type IV Waardenburg
The final type of Waardenburg syndrome, also rare, is Type IV. This type is also known as Waardenburg-Shah syndrome. Besides the typical features of Waardenburg, this form also includes Hirschsprung disease, a digestive problem that causes constipation or intestinal blockage. Type IV is usually passed down from one parent, but it can also be inherited from both parents.
Posts: 4693 | From: Saturn | Registered: Apr 2012
| IP: Logged |
UBBFriend: Email this page to someone!
Printer-friendly view of this topic