Unit II Genetic Disorders Flashcards
Duchenne Muscular Dystrohpy: Inheritance
X- Linked Recessive
Duchenne Muscular Dystrohpy: Incidence
1/3000 males
Duchenne Muscular Dystrophy: clinical presentation
onset at 2 yrs, progressively lose motor function, wheelchair by 18 yrs. progressive myopathy, calf hypertrophy, + Gowers Maneuver, abnormal gait, high creatine kinase levels
Duchenne Muscular Dystrohpy: Mechanism
Deletion of multiple exons, Xp21.2 - dystrophin gene - loss-of-function
high mutation rate
in-frame deletion leads to Becker dystrophy
Hereditary Neuropathy with Liability to Pressure Palsies (HNPP): Inheritance
Autosomal Dominant
HNPP: Clinical Presentation
temporary (usually reversible) neuropathy when pressure applied to various nerves (i.e. “arm going to sleep” for days etc) Onset at 20-30 yrs
HNPP: Mechanism
deletion of PMP22 gene (PMP22 is integral to glycoprotein in nerurons)
Loss-of-Function mutation
(reciprocal mutation to CMT1A that is a duplication of PMP22)
Osteogenesis Imperfecta Type I: Inheritance
Autosomal Dominant
Osteogenesis Imperfecta Type I: Incidence
1/30,000-50,000
Osteogenesis Imperfecta Type I: Clinical Presentation
Brittle bones and increased fractures, blue sclerae, normal stature, progressive hearing loss in adults
Osteogenesis Imperfecta Type I: mechanism
nonsense/frameshift mutation in the COL1A1 gene that leads to premature termination (mRNA is unstable and degraded) - assembly of multimeric protein COL1A1 is disrupted, normal ratio of protein subunits is disrupted and protein not produced in sufficient quantities
Charcot-Marie-Tooth Type 1A: Inheritance
Autosomal Dominant
Charcot-Marie-Tooth Type 1A: Clinical Presentation
Demyelinating motor and sensory neuropathy; lower extremitiy weakness and muscle atrophy along with mild sensory loss, foot deformity known as hammertoes
Charcot-Marie-Tooth Type 1A: Mechanism
Duplication of PMP22 gene (17p11.2)
Gain-of-Function mutation (reciprocal mutation to HNPP that is a deletion of PMP22)
Osteogenesis Imperfecta Type II, III, IV: Inheritance
Autosomal Dominant
Osteogenesis Imperfecta Type II, III, IV: Clinical Presentation
Brittle bones, increased fractures, blue sclerae (usually a more sever phenotype than Type I)
Osteogenesis Imperfecta Type II, III, IV: Mechanism
Novel property mutation of the COL1A2 protein that results in different folding of COL1A2 protein that forms collagen trimer (1/2 collagen being abnormal is worse than 1/2 being produced but is normal)
Huntington Disease: Inheritance
Autosomal Dominant
Huntington Disease: Incidence
1/10,000
Huntington Disease: Clinical Presentation
Progressie neurodegenerative disorder with adult onset - fatal within 15 yrs of onset
Gene anticipation (earlier onset/more severe phenotype in subsequent generations)
parental origin helps determine onset
paternal origin = early onset, maternal origin = later onset
Huntington Disease: Mechanism
trinucleotide repeat disorder in an exon of the HTT gene on 4p16.3 leads to increased polyglutamine residues in huntington protein
Novel Property Mutation
Number of repeats - <27 = normal, >40 = 100% penetrant disease, >60 = Juvenile onset
Myotonic Dystrophy I: Inheritance
Autosomal Dominant
Myotonic Dystrophy I: Incidence
1/20,000
Myotonic Dystrophy I: Clinical Presentation
Adult-onset muscular dystophy (progressive muscle wasting and weakness), Droopy eyes, cataracts, intellectual disability, hypotonia, cardiac conduction defects