Transcript Inner Ear Disorders

Inner Ear DisordersChildren
Lecture 15
Selected Causes of SNHL
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Genetic – Hereditary (congenital or late onset)
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Syndromic
Non Syndromic
Non – genetic – (congenital or late onset)
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Trauma
 Prematurity
 Anoxia
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Exposures/Infections
 Rh Factor
 Viral Infections (CMV)
 Rubella
Embryology of the Inner Ear
 3rd week – inner ear starts to develop
 6th -10th week – cochlear turns begin to
develop
 10th-12th week – organ of corti forms
 25th week – fully developed cochlea reaches
adult size
How do genes work
 Genes: road map for synthesis of proteins
 Chromosomes – comprised of genes
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humans @30-40,000
23 pairs of chromosomes
 22 pairs of autosomes
 1 pair of sex chromosomes
Hereditary Patterns
 One chromosome from each parent is inherited
Male XY - Female XX
Gene: basic physical and functional unit of heredity
comprised of DNA act as instructions to make proteins
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DNA is made up of 4 chemical letters.
Coding for DNA
(Deoxyribonucleic acid)
 Code is read in groups of 3 letters
 Each code means a specific amino acid
T- thymine
 A - adenine
 C – cytosine
 G – guanine
TTA, CCG, TAT, CAT etc
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Patterns of genetic codes
 Wildtype – common code/typical pattern
 Mutation - triplet codes can be changed by
substitution
deletion
insertion
 Outcomes:
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beneficial (rare)
neutral (common)
deleterious (rare)
Pre-natal Causes of HL:
 Autosomal Dominant:
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one gene required from parent for HL to be
inherited
 Autosomal Recessive:
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both parents are carriers for HL, but have
normal hearing
 X-linked:
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recessive alleles are carried on the X
chromosome, so HL occurs more in males
than females
 Mitochondrial : gene passed from mother
Autosomal Dominant
 Mutations occur on an autosome (1-22)
 Child needs to inherit one copy of dominant
trait to have disorder.
 50% chance of an affected parent passing
gene onto children
 Sometimes appears to “skip” generations
Autosomal Recessive
 Error occurs on autosome (Chr #1-22)
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Have to inherit a mutated gene from each
parent.
 Most common pattern of transmission
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Up to 80% of profound genetic HL
Half are associated with syndromes
 25% chance that the offspring will be affected
and manifest HL
X-linked Recessive:
 Recessive gene is carried on X chromosome
 Trait for HL is expressed in the presence of a single X
chromosome
 Occurs more in males because they have single X
 males have a single x chromosome
 females have 2 copies of the x chromosome
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even if they inherit the defective gene, the other x
chromosome will compensate .
 Sons have 50% chance of inheriting the trait and then
the disorder
 Daughters have a 50% chance of inheriting the trait
and being a carrier
Mitochondrial
 Mitochondria: powerhouse of the cell – also
contain DNA
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Sperm have no mitochondria
Only Mitochondria from mother’s egg passed
on
Only mothers can pass this on
Syndromic vs Non-syndromic HL
 NON-SYNDROMIC: Cases of hereditary HL
& no associated abnormalities
 SYNDROMIC: Hereditary HL also assoc w/
other abnormalities i.e.
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external ear, skull, facial deformities, cleft palate,
optic disorders, changes in eye, hair and skin
pigmentation,
thyroid disease,
disorders of the heart,
musculoskeletal anomalies,
mental retardation,
difficulty with balance
CHARGE Syndrome
 C= Coloboma of the
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eye
H= Heart defects
A= Atresia of
nasopharynx
R= retardation of growth
or development
G= Genital and/or
unrinary problems
E = Ear abnormalities
and deafness
 Etiology: AD
 CHL – Common
 SNHL – 90%
malformed cochlea
Waardenburg’s Syndrome
 Major Systems: intugement, ocular,
craniofacial, gastrointenstinal, CNS
 Etiology: AD
 Quick clues: white forelock, wide set eyes, bicolor eyes,
 Hearing Disorders: 25% congenital, bilateral
SNHL, mild to severe.
Usher Syndrome
(Retinitis Pigmentosa)
 Major Systems: Auditory, vestibular, ocular,
CNS
 Etiology: AR
 Quick clues: No external physical clues
Association between HL and visual
impairment, clumsy gait
 Hearing Disorders: Profound, bilateral SNHL
 Speech Disorders: Associated with HL
Usher Syndrome
 Type I: Profound SNHL, early onset, poor
vestibular function
 Type II: Severe SNHL, good vestibular
function, late onset
 Type III : Progressive, variable expression
and onset
Treacher Collins
 Major Systems: Craniofacial, respiratory
 Etiology: AD
 Quick Clues: Slanting eyes, small jaw,
malformed ears,
 Hearing Disorders: CHL, mild to moderate
 Feeding: sometimes cleft palate, small jaw
effects breathing and feeding issues
 S/L – crowding in oral cavity, normal IQ,
expressive/receptive delays assoc w hearing
loss
Jervelle Lange Nielsen
 Major Systems: Cardiovascular, auditory
 Etiology: AR
 Quick clues: electrocardiographic
abnormalities, fainting attacks, sudden
cardiac death
 Hearing Disorders: Profound, congenital
SNHL
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Flow of K+ ions disrupted in IE and cardiac
muscle
Genetic:Late onset SNHL in children
(Non-syndromic)
 Connexin 26 protein found on GJB2 gene
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Nonsyndromic, genetic cause of late onset HL
Most common (50% of Recessive genetic HL )
Mutation on GJB2 protein
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Screening tests are available
 Connexin 30
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Non-syndromic cause of late onset HL
Less common
Genetic Cause of Late onset SNHL
(Syndromic)
 Pendred’s (AR)
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Hypothyroidism
HL
Balance (ELVA)
Enlarged Vestibular Aqueduct
Syndrome
 Genetic origin
 Usually a later onset SNHL
 Vestibular aqueduct – last IE structure to
develop fully
 Sudden or fluctuating SNHL, progressive
 Aggravated by additional trauma to head
 Dxd with a CT scan and history
Non – genetic causes Childhood HL
Prematurity
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5% of children born before 32 weeks present
with HL by age of 5
Auditory system not fully developed if
premature
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VLBW
Aminoglycosides
NIHL
Oxygen supply
Prenatal causes of HL: Rh Factor
 Most people are Rh+
 If mother is Rh- and partner is Rh+
 Protein in “Rh” blood molecule is absent (negative) in
the mother, but present (positive) in the fetus.
 When Rh negative blood is exposed to Rh positive
blood, the Rh negative person begins producing
antibodies to fight off invading blood
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An Rh- mother will develop antibodies to protect
herself against the harmful effects of Rh + blood cells
of the fetus.
Her antibodies destroy the Rh + blood cells of the fetus
which can no longer carry oxygen to the cochlea
Rh incompatibility
 Tx
Early delivery
 Rhogam shots
Gives temporary immunity for subsequent
pregnancies
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Cytomegalovirus (CMV) si-to-MEGuh-lo-vi-rus
 Viral Infection – herpes group
 Transmission prenatally, perinatally or postnatally
 CMV spreads from person to person by direct
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contact.
CMV infection is usually harmless, it can cause
severe disease in persons with weakened immune
systems
Considered major cause of unknown etiology for
SNHL
Asymptomatic or Symptomatic CMV
31% of infants infected with CMV manifest HL
(Johnson et al, 1986)
Who is at risk for CMV?
 Babies born to women who have a first-time
CMV infection during pregnancy
 Pregnant women who work with infants and
children
 Persons with weakened immune systems,
including cancer patients on chemotherapy,
organ transplant recipients, and persons with
HIV infection
Non- genetic
 Anoxia: Oxygen deprivation
Damages cells in the cochlea
 Rubella: viral infection
vaccine since 1969
greatest impact if mother
contracted during 1st trimester
Meningitis
 Infection of the fluid around the spinal cord
 Causes inflammation of the meninges
 Viral – more common
 Bacterial – rare
 Outcome
 Viral: less severe
 Bacterial:
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1/10 – fatal
1/7 severe handicap
Meningitis
 Bacteria and viruses that infect the skin,
urinary system, gastrointestinal or respiratory
tract can spread through the bloodstream to
the meninges
 Spread by direct contact with the discharges
from the nose or throat of an infected person
 Not easily spread – not airborne
 10-25% of population is a carrier at any one
time
 Bacteria do not live outside the body
Possible outcomes from bacterial
meningitis
 SNHL
 Paralysis
 MR
 Seizures
 Coma/Death
Symptoms
 High fever
 Headache
 Stiff neck
 Nausea, vomiting, inactive
 Seizures in advanced stages
 Diagnosis: Spinal tap
“Acute congestion of the
stomach and brain”