LACK OF THYROID HORMONE BLOCKS HEARING DEVELOPMENT
Fatigue, weight gain,
chills, hair loss, anxiety, excessive perspiration -- these symptoms are a few
of the signs that the thyroid gland, which regulates the body's heart rate and
plays a crucial role in its metabolism, has gone haywire. Now, new research from Tel Aviv
University points
to an additional complication caused by thyroid imbalance: congenital deafness.
The study, published
in Mammalian Genome, was conducted by Prof. Karen B. Avraham and
Dr. Amiel Dror of the Department of Human Molecular Genetics and Biochemistry
at TAU's Sackler School of Medicine. Using state-of-the-art imaging, the
researchers found that congenital deafness can be caused by an absence of a
thyroid hormone during development.
"Since our
laboratory mainly focuses on the system of the inner ear, the study of a system
such as the thyroid gland was new to us and therefore challenging," said
Dr. Dror. "My curiosity as to how these two systems interact together to
develop normal hearing led to this multidisciplinary study."
A colorful approach
The researchers used
mouse populations to study a form of congenital deafness that affects humans.
Harnessing electron microscopy at the Sackler Cellular & Molecular Imaging
Center, researchers tracked the inner hair cells of the cochlea (the auditory
portion of the inner ear) in two groups -- control (wild) mice and mutant
(congenitally deaf) mice. Inner-ear hair bundles in the affected mice were
labelled with bright colors to highlight the disorganization of the ear's hair
cells.
Examination of the
inner ear showed a spectrum of structural and molecular defects consistent with
hypothyroidism or disrupted thyroid hormone action. The researchers' analysis
of the images revealed defective formation of the mice's thyroid glands:
labelled thyroid follicles did not grow or grew incompletely.
"Our work
demonstrated that normal hearing fails to develop when thyroid hormone
availability is insufficient as a result of a genetic mutation," said Dr.
Dror. "Our model provides a platform to test therapeutic approaches in
order to prevent hearing loss before it occurs. There is still long way ahead
before we get to the point of practical treatments with our research, but we
believe we are moving in the right direction."
A lifelong commitment
"My attraction to
sound began very early as a child," said Dr. Dror. "I play string
instruments and pay great attention to sound quality and perception. As a
graduate student in the Avraham laboratory, I was exposed to the fascinating
world of genetics and the opportunity to combine two fields of research that I
am interested in: genetics and hearing. Now that I have continued this research
as a medical student, the direct interaction with patients with hearing
impairments encouraged me to explore the clinical significance of my
research."
As a physician, Dr.
Dror believes it is important to pursue research with clinical consequences for
his patients. "The basis of all advanced medicine relies on both basic
science and clinical research. I hope that our study will contribute a modest
part to global efforts for improved medical care and treatment of hearing
impairments," Dr. Dror said.
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