0 Members and 1 Guest are viewing this topic.
People with light-coloured eyes are over five times more likely to go deaf if they get meningitis than those with dark eyes, according to research.Scientists found a link between pigmentation and ear damage - suggesting that the more pigmentation a person has, the better their inner-ear is protected.But researcher Helen Cullington, a scientist at the Hearing and Balance Centre, based at the University of Southampton, admits her findings need a lot more work to establish their full value in the fight against meningitis.Ms Cullington studied the eye colour of 130 deaf patients aged between two and 80 and found that those with light coloured eyes, such as grey, blue, green and hazel were more at risk. Ms Cullington found that out of 98 patients whose deafness was not caused by meningitis 27% had dark eyes and 73% had light eyes.But among the 32 people who were deafened by meningitis the split was much more pronounced - just 6% had dark eyes and 94% had light eyes.Survival ratesMs Cullington said: "The difference in proportions of eye colour between the survivors of meningitis and the UK adult population was significant."The odds ratio showed that people with light eyes were 5.8 times as likely to be deafened by meningitis than those with dark eyes."But in the British Medical Journal (BMJ) research pointer Ms Cullington admitted the same research could also point to the fact that people with dark coloured eyes have a poorer survival rate from meningitis.She also suggested that people with light coloured eyes are more likely to contract meningitis than those with dark eyes.A spokeswoman from the Meningitis Research Foundation said more research was needed before the value of this research is known."It is certainly interesting and anything that can give us more help and information about meningitis is invaluable."But she said the BMJ study had been on a very limited number of people and that it was impossible to draw conclusions from this.
In humans, melanin is found in skin, hair, the pigmented tissue underlying the iris, the medulla and zona reticularis of the adrenal gland, the stria vascularis of the inner ear, and in pigment bearing neurons of certain deep brain nuclei such as the locus ceruleus and the substantia nigra. Melanin is the primary determinant of human skin color.The connection between albinism and deafness has been well known, though poorly understood, for more than a century-and-a-half. In his 1859 treatise On the Origin of Species, Charles Darwin observed that "cats which are entirely white and have blue eyes are generally deaf". In humans, hypopigmentation and deafness occur together in the rare Waardenburg's syndrome, predominantly observed among the Hopi in North America. The incidence of albinism in Hopi Indians has been estimated as approximately 1 in 200 individuals. Interestingly, similar patterns of albinism and deafness have been found in other mammals, including dogs and rodents. However, a lack of melanin per se does not appear to be directly responsible for deafness associated with hypopigmentation, as most individuals lacking the enzymes required to synthesize melanin have normal auditory function. Instead the absence of melanocytes in the stria vascularis of the inner ear results in cochlear impairment, though why this is is not fully understood. It may be that melanin, the best sound absorbing material known, plays some protective function. Alternately, melanin may affect development, as Darwin suggests.In Parkinson's disease, a disorder that affects neuromotor functioning, there is decreased neuromelanin in the substantia nigra as consequence of specific dropping out of dopaminergic pigmented neurons. This results in diminished dopamine synthesis. While no correlation between race and the level of neuromelanin in the substantia nigra has been reported, the significantly lower incidence of Parkinson's in blacks than in whites has "prompt[ed] some to suggest that cutaneous melanin might somehow serve to protect the neuromelanin in substantia nigra from external toxins.". Also see Nicolaus review article on the function of neuromalanins