Biochem - genetics

Question 1

Cafe au lait spots, polyostotic fibrous dysplasia, precocious puberty

Answer 1

McCune Albright

mutation affecting G-protein signaling, example of mosaicism

Question 2

Locus vs allelic heterogeneity

Answer 2

locus - mutations at different loci = similar phenotype (eg. albinism)

allelic - different mutations in same locus = same phenotype (eg. B-thalassemia)

Question 3

Hyperphagia, obesity, intellectual disability, hypogonadism, hypotonia

Answer 3

Prader-Willi (paternal gene deleted + maternal imprinting/silenced through methylation)

25% of cases due to maternal uniparental disomy

Question 4

Inappropriate laughter, seizures, ataxia, severe intellectual disability

Answer 4

Angelman (paternal imprinting + maternal gene mutated)

Question 5

Most common mutation of CFTR

Answer 5

F508 (phenylalanine)

Causes misfolded protein, which is then retained in RER and not transported to cell membrane, causes decr. Cl secretion

Question 6

Reproduction in CF

Answer 6

males - absent vas deferens

females - amenorrhea, abnormally thick cervical mucus

Question 7

Muscular dystrophy genetic mutations

Answer 7

Duchenne: frameshift –> truncated dystrophin protein

Becker: non-frameshift mutation –> partially function dystrophin protein

Dystrophin = anchor muscle fibers, connects actin cytoskeleton to transmembrane proteins which connect to ECM (loss results in myonecrosis)

Question 8

Four Trinucleotide repeat expansion diseases

Answer 8

Fragile X syndrome (CGG)
Friedrich ataxia (GAA)
Huntington disease (CAG)
Myotonic dystrophy (CTG)

Show genetic anticipation (incr. severity, decr. age of onset)

Question 9

Autosomal trisomies

Answer 9

Down: 21 (Drinking age)

Edwards: 18 (Election age), low-set ears! death w/in 1 yr

Patau: 13 (Puberty) cleft lip, polydactyly, holoprosencephaly, death w/in 1 yr