Atypical Patterns of Inheritance

Question 1

Fragile X Syndrome

Answer 1

Most common inherited form of mental retardation
CGG repeat at Xq27
Expansion from premutation to full mutation only occurs through female meiosis
Anticipation: severity & time of onset depends on # of repeats
Everted ears, long face, macroorchidism
Premature ovarian failure, Parkisonism
Loss of function of FMR1 gene, which is important for normal functioning of neuronal synapses

Question 2

Huntington Disease

Answer 2

CAG repeat -> toxic gain of function b/c huntingtin protein misfolds & aggregates in cell
Neurodegenerative disease characterized by involuntary jerky movements
Full mutation derived from premutation

Question 3

Leber Hereditary Optic Neuropathy

Answer 3

Mitochondrial inheritance

Neurodegenerative disease that causes progressive blindness

Question 4

Prader-Willi Syndrome

Answer 4

Absence of paternal imprint in chromosome 15
Could be due to: large deletion, mutation, maternal uniparental disomy, or imprinting defect
Mental retardation, hypogonadism, obesity, & hypotonia

Question 5

Angelman Syndrome

Answer 5

Absence of maternal imprint in chromosome 15
Could be due to: large deletion, mutation, paternal uniparental disomy, or imprinting defect
Severe mental retardation, ataxia, inappropriate laugh, & seizures