p.319 + genes pwpt & articles Flashcards
children should have HL diagnosed by
3 months of age
high-risk conditions
- ECMO or chemotherapy
- Cytomegalovirus infection
- Syndromes that have progressive HL
- Neurodegenerative disorders
- Trauma
- Postnatal infections associated w/ SNL HL
- caregiver concern
- Family Hx of HL
ECMO stands for
Extra Corporeal Membrane Oxygenation
ECMO is
procedure in which a machine outside of body delivers oxygen to a patient’s blood much like heart and lungs are supposed to (typically for infants in NICU who have health conditions complicating heart and/or lung fx)
cytomegalovirus
a member of the herpes virus family
One of the most common congenital infections & a leading cause of hearing loss at birth
If baby’s hearing loss is conductive
child may be referred to otolaryngologist and/or otologist
if baby’s HL is SL,
infant must be evaluated by otolaryngologist who specializes in children with HL
AND
infant & family should be referred for Genetics Consultation and to pediatric ophthalmologist for Visual Acuity Examination
origin of congenital or early-onset deafness
More than half are Genetic in origin
% of syndromic and nonsyndromic congenital genetic HL
25% syndromic
75%Nonsyndromic
Syndromic HL
occurs with other signs & symptoms
nonsyndromic HL
usually occurs as the only disability
chromosomal abnormalities
occur when there is either too much or too little genetic information
OR
material that is in wrong place
Genetic abnormalities also known as
mutations
genetic abnormalities
classified based upon whether they are located on an autosome or sex chromosome AND by inheritance pattern
dominant transmission
requires only one gene for the trait to be passed on
recessive transmission
requires that two copies of a gene are needed for a trait to be passed on
autosomal dominant disorders
have an inheritance pattern in which one parent has the genetic mutation,
expresses the disorder, and
has a 50% chance of passing it on to his or her children.
genotype
when a person has a trait in his or her genes (but doesnt necessarily present the trait)
phenotype
when a person presents the trait that in his or her genes
autosomal dominant HL
Not a surprise; knows it “runs in the family”
autosomal dominant HL is presents itself in
mild or severe form (variation in expressivity)
decreased penetrance
mild form of autosomal dominant disorder
autosomal recessive disorders
occurs when both parents are carriers of the genetic mutation, but
usually do not express it, and
have a 25% chance of having a child with the disorder, 50% chance of the child being a carrier, and 25% chance of child being normal.
autosomal recessive HL
is usually a surprise to parents
most common nonsyndromic cause of genetic HL
mutation of the connexin 26 gene (GJB2) (inherited mostly in autosomal recessive mode)
dual sensory impairment
simultaneous ocular and auditory impairment
a recessively transmitted genetic condition that includes congenital HL and a progressive loss of vision (dual sensory impairment)
Usher syndrome
most common sensory impairment in humans
deafness
incidence of HL in children
1:1000
how many genes involved in HL?
many different genes involved, but single gene mutations are most common
exogenous
outside the genes-acquired
endogenous
inside the genes
examples of exogenous causes of HL
- Ototoxicity
- Excessive Noise Exposure
- Inflammatory disease
- Trauma or Injury
examples of endogenous causes of HL
Inherited trait- (Genetic)
HL can be characterized as
congenital (at birth)
hereditary (genetic)
acquired (exogenous)
Approx 1/2 of all Auditory disorders are due to
Hereditary factors (endogenous)–genetic causes
Approx___#__ distinct syndromes can include hearing impairment
400
Pendred syndrome
- Thyroid/goiter
- abnormality in iodine
- severe HL overe 50% of the time
- need more comprehensive blood test to detect
- hearing problems at birth, gets worse in childhood
- Hearing deteriorates from minor knocks to head (mild loss can become profound if bumped into at school)
- swelling at neck caused by enlarged thyroid
Usher syndrome
Can leave people deaf & produce HL
Have 10 diff genes that cause mutation
Most severe & slow deterioration of sight & loss of vision by age 10 & profound HL at birth
*early cochlear implantation would be crucial due to loss of vision
Osteogenesis Imperfecta (OI)
Fractures in the absence of trauma (can be seen in family Hx)
- mobility impairments
- short stature (child not growing)
- predisposition to fractures
- little blue lining in pupil
- Has Disorder of the Sensory System
- Slow down of axonal to axonal reception
- problems w/ walking & balance
Modes of inheritance of hereditary deafness
Dominant Recessive X-linked Mitochondrial or other
One parent exhibits the inherited trait
50% chance that inherited trait will be transmitted
Presumed to cause 20% of endogenous deafness
Dominant inheritance
- Exhibits the inherited trait when the individual carries 2 similiar abnormal genes (1 from each parent)
- if no abnormal gene exists, child is normal
- if 1 abnormal gene exists, child is carrier of trait
- if 2 abnormal genes exist, child is carrier and exhibits
- Account for as much as 80% of childhood deafness
hereditary deafness
Defective traits are located on the X chromosome
Males affected through carrier females
Approx 2-3%deafness occurs
X-linked
Small organelles in our cells that have their own DNA are known as mtDNA (we inherit all of our mtDNA from our mothers)
Mitochondrial
doesnt follow same statistical probability as dominant/recessive patterns
mitochondrial
abnormal transcription (missense mutation)
1 letter is replaced w/ incorrect chemical unit
nonsense mutation
early stop in transcription
Connexin 26 genes can be
recessive or dominant
Hair cell degeneration & hereditary deafness
Hair cell degeneration not normally cause of hereditary deafness.
hair cells may have developmental or functional defects that cause hearing impairment & lead to 2ndary hair cell degeneration
gene therapy
permit productions or repression of ‘proteins’
- slow or increase rate of cell growth
- inhibit or induce viral replication
- increase or decrease cell death
gene mapping
identifying the chromosomal location of the gene
localization
isolating the defective gene (which may be in more than 1 place)
limitations of gene Tx development
- no side effects of a treatment be worse than disease being treated
- Hearing disorders tend not to be life threatening
Studies on gene Tx
- current studies involve genes that protect cochlea from degeneration
- difficult to find gene therapy approaches that can repair developmental defects in the embryo (complex development of inner ear)
- normally deals with genetic defects that result in degeneration of cochlear structures AFTER they have been developed
Genes are composed of a specific sequence of units of the following chemical units
Adenine (A)
Guanine (G)
Cytosine (C)
Thymine (T)
Genes are composed of a specific sequence of units of the following chemical units
Adenine (A)
Guanine (G)
Cytosine (C)
Thymine (T)
genes involved in the structure & f(x) of the ear
10% of 30,000 genes
genes involved in the structure & f(x) of the ear
10% of 30,000 genes
% of endogenous & exogenous causes of HL according to ASHA leader
50-60% endogenous (hereditary)
40-50% exogenous (acquired)
% of endogenous & exogenous causes of HL according to ASHA leader
50-60% endogenous (hereditary)
40-50% exogenous (acquired)
% of non-syndromic HL according to ASHA leader
60-70%
% of non-syndromic HL according to ASHA leader
60-70%
% of syndroming HL according to ASHA leader
30-40%
% of syndroming HL according to ASHA leader
30-40%
syndromic HL
HL from a gene that affects multiple organs
syndromic HL
HL from a gene that affects multiple organs
When recessive genes for deafness are located on X chromosome
trait is inherited as X-linked recessive
When recessive genes for deafness are located on X chromosome
trait is inherited as X-linked recessive
mitochondrial inheritance
inheritance of a genetic mutation in the genes contained w/in mitochondria (only inherited from mother-egg cell)
mitochondrial inheritance
inheritance of a genetic mutation in the genes contained w/in mitochondria (only inherited from mother-egg cell)