Are you one of the more than 8 million people who've seen the Duracell Trust Your Power video?
The video features Seattle Seahawks offensive lineman Derrick Coleman, who will become the first legally deaf National Football League (NFL) player to play in a Super Bowl.
What is so inspiring is that Coleman became an NFL player at all.
Derrick became deaf about 20 years ago at the age of 3. Based on his medical and family history, Derrick's type of hearing loss is genetic and of the autosomal recessive, nonsyndromic variety. More about this below and in Part II of our story.
Growing up, Derrick was frequently taunted and bullied by other children. Because his hearing aids would pop out of his ears, his mother fashioned a support out of panty hose to hold them in place. High school coaches tried to get him to quit. But Coleman loved to play football and still persevered to become a professional player.
Derrick played well at the University of California Los Angeles, but was overlooked in the NFL draft. He was signed by the Minnesota Vikings as a free agent, but was cut a few months later. However, in December 2012, the Seattle Seahawks signed him, and now he's on his way to the Super Bowl.
Coleman can read lips, and quarterback Russell Wilson has been seen mouthing last-minute play changes to him. Coleman says his deafness can be an asset, especially when dealing with raucous crowds and rowdy fans when all players have to resort to hand signals and other forms of non-verbal communication.
“When it gets loud I feel like I have the advantage. I can tune that out.”
What are some of the genetic causes of deafness?
According to the , about 1 in 1,000 children in the US are born with profound deafness, with another 2-3/1000 born with partial hearing loss. More than half of these cases are caused by genetic factors. Around 70% to 80% of cases of genetic deafness are nonsyndromic, with the rest caused by specific genetic syndromes. Examples of the latter include and Syndromes.The causes of nonsyndromic deafness are complex. Since 1997 researchers have identified more than 30 genes that, when mutated or altered, are associated with deafness. Many genes related to deafness are involved in the development and function of the inner ear. Mutations in these genes contribute to hearing loss by interfering with critical steps in processing sound. in the same gene can be associated with different types of hearing loss, and some genes are associated with both syndromic and nonsyndromic deafness.
Mutations in the are a major cause of prelingual nonsyndromic deafness. This genetic location contains two genes, GJB2 and GJB6, encoding the proteins connexin 26 and connexin 30, respectively. These proteins form parts of the gap junctions, allowing communication between neighboring cells. Mutations in connexin proteins may affect the function or survival of cells that are essential for hearing.
X chromosome-linked deafness type 3 (DFN3) is the most prevalent X-linked form of hereditary deafness and is caused by mutations in the POU3F4 gene. In this condition, the stapes (one of the small bones in the middle ear) cannot move normally, and this stapes fixation results in conductive hearing loss.
We will describe other genes involved in hearing loss in Part II of our story.
What are the modes of inheritance of nonsyndromic deafness?
Nonsyndromic deafness can have different patterns of inheritance. Between 75% and 80% of cases are inherited in an autosomal recessive pattern, which means that patients are homozygous for the mutation. Although we don't know which particular deafness gene affected Derrick Coleman, his medical and family history indicates that his parents are heterozygous carriers.Another 20% to 25% of nonsyndromic deafness cases are autosomal dominant, which means that inheriting only one copy of the altered gene is sufficient to result in hearing loss. People with autosomal dominant deafness will have one parent who is also affected.
About 1% to 2% of cases show an X-linked pattern of inheritance.
Fewer than 1% of cases result from changes to mitochondrial DNA. The altered mitochondria are passed from a mother to all of her sons and daughters.
Types of nonsyndromic deafness are named according to their inheritance patterns. Autosomal dominant forms are designated DFNA, autosomal recessive forms are DFNB, and X-linked forms are DFN.
See the for more information on the full range of genes associated genetic deafness.
What are the prospects for personalized genomic medicine for deafness?
Part II of our article will feature an interview with Dr. Richard Smith, who directs the Iowa Institute of Human Genetics and the Molecular Otolaryngology & Renal Research Laboratories at the University of Iowa Carver College of Medicine. According to Dr. Smith, we have entered a new era in the precision diagnosis and treatment of genetic deafness, and he provides an exciting glimpse into this new world. He will teach us what a "genome era" patient workup looks like and how it leads to superior management of deafness disorders.