genetics 3

Question 1

define Anticipation

Answer 1

• genes rendered abnormal by amplification of CG-rich units
• these diseases get worse from generation to generation as amplification continues
• the disease appears sooner in the son than in the father (anticipation)

Question 2

describe Fragile X syndrome

Answer 2

• leading cause of INHERITED mental imapirment
• X-linked DOMINANT (with reduced penetrance)
• Assocaited with CGG repeats in FMR1 gene on X chromosome (>200 Cgg repeats)
• Diagnosed via southern blot or PCR

Question 3

define intermediate range

Answer 3

• refers to a range of repeats that is normally stable

Question 4

define premutation range

Answer 4

• always changes in size (usually an expansion)

- expansion from pre- to full mutation only occurs through FEMALE Meiosis

Question 5

describe the clinical characteristics of Fragile X syndrome

Answer 5

• CGG repeats
• severity of disease correlates with # of repeats
• Big ears, Big upper jaw, Big testicles
• mental retardation, behavior problems, long, characteristic face (prominant Jaw and protruding ears)
• High arched palate
• large gonads
• AFFECTED FEMALES TEND TO HAVE MILDER FEATURES

Question 6

describe Huntington’s disease (HD)

Answer 6

• HD gene on chromsome 4 encodes for HUNTINGTIN (protein widely expressed by neurons and glia of CNS)
• HD is an AUTOSOMAL DOMINANT condition caused by expression of CAG trinucleotide repeats in the HD gene
• people with HD have >36 CAG repeats

Question 7

describe the clinical characteristics of HD

Answer 7

• progressive disorder of motor, cognitive, and psychiatric changes
• mean age = 36-44

Question 8

describe EARLY stage of HD

Answer 8

• sublt changes in coordination, minor chorea (involuntary jerky movements), difficulty mental planning and often a depressed or irritable mood

Question 9

describe Middle stage

Answer 9

• Chorea becomes more prominent with increasing difficulty with voluntary activity and worsenign dysarthria and dysphagia

Question 10

describe late stage of HD

Answer 10

• behavior problems are gradually lessened; motor disability becomes severe and the individual is often totally dependent, mute and incontinent

Question 11

describe late stage of HD

Answer 11

• behavior problems are gradually lessened; motor disability becomes severe and the individual is often totally dependent, mute and incontinent

Question 12

Describe Edwards syndrome

Answer 12

• chromosomal disorder caused by the presence of all or part of an extra CHROMOSOME 18 due to NONDISJUNCTION during meiosis
• low rate of survival resulting from heart abnormalities, kidney malformations and other internal organ disorders

Question 13

Patau syndrome

Answer 13

• extra genetic material from CHROMOSOME 13
• -> full extra copy or extra partial copy (robertsonian translocation) of chromosome
• 80% of die within first year of life (physical development and muscle devleopment is slower)

Question 14

describe turner syndrome

Answer 14

• 45, X
• Monosomy X results when an individual inherits ONE X chromosome and no second sex chromosome
• Individuals are FEMALE

Question 15

describe the clincial features of turner syndrome

Answer 15

• Prenatal = common cause of miscarriage; some patients are detected by finding icnreased fluid, swelling, CYSTIC HYGROMA about the neck, or hydrops
• Birth = residua sings of prenatal lymph blockage including webbed neck, puffy hands and feet, low-set, rotated ears

Question 16

Cystic hygroma

Answer 16

• characteristic feature of turner syndrome
• not a true neoplasm, but failrue of lymphatics to forma nd drain properly
• eventually forms the webbed neck feature of women with turner syndrome

Question 17

Describe the characteristics of people with turners syndrome

Answer 17

• absence of second dose of genetic ifnormation contained on the short arm of the X-chromosome
• short stature
• absence of ovaries and failure to proceed through puberty (sexual infantilism)
• characteristic facial features (traingle-shaped face, posteriorly rotated ears)
• broad webbed neck
• broad sheild like chest
• short 4th metacarpal
• FAILURE TO MENSTRUATE (Amenorrhea)

Question 18

describe Klinefelter sydrome (KS)

Answer 18

• 47, XXY

- presence of an EXTRA X chromosome (1-1000 boys)

Question 19

describe the characteristics of Klinefelter syndrome

Answer 19

• be taller than average
• longer arms and legs than usual
• develop breast tissue during teen years (gynecomastia)
• HYPERESTROGENISM (icnreased risk of berast cancer!!!)
• have smaller genitals that average (hypogonadism)
• atrophy of seminiferous tubules leads to sterility
• learning diabilities and social immaturity

Question 20

describe the characteristics of Klinefelter syndrome

Answer 20

• be taller than average
• longer arms and legs than usual
• develop breast tissue during teen years (gynecomastia)
• HYPERESTROGENISM (icnreased risk of berast cancer!!!)
• have smaller genitals that average (hypogonadism)
• atrophy of seminiferous tubules leads to sterility
• learning disabilities and social immaturity

Question 21

define imprinting

Answer 21

• given gene has methyl groups attached to its cytosine nucleotides (methylated)
• methylated genes are NOT actively transcribed and translated into protein, so these genes are essentially TURNED OFF (inactivated)
• deviation of the normal methylated genes can cause genetic disease

Question 22

describe Prader-Willi syndrome

Answer 22

• patients lack the normal gene from their FATHERS
• -> inherited dads mutant (typically deleted) gene (del of 15q11)
• Truncal obesity, hypogonadism, small hands
• overeat, incorrigibly stealing and hiding food and become very obese
• prone to a outbursts of extreme violence

Question 23

describe angelman syndrome

Answer 23

• patients lack the normal gene from their MOTHERS
• -> inherited moms gene deletion (del of 15q11)
• wide stance, arm position, spasticity
• severely retarded, with microcephaly and huge jaws
• they have jerky, puppet like movements and laugh a lot
• NO SPEECH
• severe ataxia
• paroxysmal laughter