genetics Flashcards
Dominant inheritance
when a mutation is passed in a dominant way; only 1 mutation is needed to cause hearing loss. every child has a 50% chance of a loss
recessive inheritance
mutations in both copies of a gene (one from each parent)
if each parent has 1 recessive mutation, each child has a 25% of having HL and 50% chance of being an unaffected carrier
Dominant inheritance
when a mutation is passed in a dominant way; only 1 mutation is needed to cause hearing loss. every child has a 50% chance of a loss
genetic causes of hearing loss
can be syndromic or nonsyndromic
1/3 of genetic HL is syndromic (associated with additional medical problems)
majority of children have no associated medical problems (nonsyndromic)
x-linked inheritance
if 1 x chromosome has a recessive mutation, the 2nd chromosome can provide a functioning copy of a gene, HL would not develop. HL resulting from x-linked mutations is usually seen in males
recessive inheritance
mutations in both copies of a gene (one from each parent)
if each parent has 1 recessive mutation, each child has a 25% of having HL and 50% chance of being an unaffected carrier
mitochondrial inheritance
only from the mother.
nonsyndromic genetic HL
only clinical finding is HL except some patients with vestibular symptoms (early cue to vestib problems is delay in walking)
DFN followed by “A” = dominant
DFN followed by “B” = recessive
no additional letter for x-linked
genetic causes of hearing loss
can be syndromic or nonsyndromic
1/3 of genetic HL is syndromic (associated with additional medical problems)
majority of children have no associated medical problems (nonsyndromic)
Connexin HL
first recessive HL identified in ‘94
mutation in the GJB2 gene (most common cause of SNHL)
-congenital
-mild to profound
-if it is dominant, SNHL is early onset, moderate to severe, progressive
DFNB4 HL
SLC26A4 gene associated with syndromic Pendred syndrome as well as nonsyndromic form called DFNB4.
DFNB4 pateitns have autosomal recessive SNHL and englarged vestibular aqueducts (EVA) and Mondini malformations but do NOT manifest the thyroid abnormalities like Pendred syndrome.
HL is congenital, bilateral, severe-profound SNHL
x-linked inheritance
if 1 x chromosome has a recessive mutation, the 2nd chromosome can provide a functioning copy of a gene, HL would not develop. HL resulting from x-linked mutations is usually seen in males
DFNB4 HL
SLC26A4 gene associated with syndromic Pendred syndrome as well as nonsyndromic form called DFNB4.
DFNB4 pateitns have autosomal recessive SNHL and englarged vestibular aqueducts (EVA) and Mondini malformations but do NOT manifest the thyroid abnormalities like Pendred syndrome.
HL is congenital, bilateral, severe-profound SNHL
mitochondrial inheritance
only from the mother.
Mitochondrial HL
associated with neuromuscular disease.
2 nonsyndromic forms
may develop HL on when exposed to aminoglycoside antibiotics
-based on geographic/ethnic origin
Auditory dys-synchrony/neuropathy
environmental causes: hyperbilirubinema, prematurity, hypoxia.
- prelingual
- moderate to profound (flat, rising, sloping, bowl-shaped)
- do well with cochlear implants
nonsyndromic genetic HL
only clinical finding is HL except some patients with vestibular symptoms (early cue to vestib problems is delay in walking)
DFN followed by “A” = dominant
DFN followed by “B” = recessive
no additional letter for x-linked
syndromic forms of genetic HL
30% of patients with childhood HL have additional problems
Connexin HL
first recessive HL identified in ‘94
mutation in the GJB2 gene (most common cause of SNHL)
-congenital
-mild to profound
-if it is dominant, SNHL is early onset, moderate to severe, progressive
alport syndrome
characteristic is hematuria (blood in the urine) that progresses to renal disease. also eye lens defect is common.
-non congenital, HL starts in HF
