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Medical Genetics Flashcards

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Biology 101 flashcards USMLE® Step 1 flashcards
1
Q

Carbamoyl phosphate synthetase deficiency

A

Urea cycle disorder that results in the accumulation of N-acetyl glutamic acid due to CP synthetase deficiency

Lethargy, coma

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2
Q

Ornithine transcarbamoylase deficiency

A

Urea cycle disorder that results in the accumulation of carbamoyl phosphate

Most common urea cycle defect (X linked)

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3
Q

Argininosuccinate synthetase deficiency

A

Urea cycle disorder that has an accumulation of citrulline

Lethargy, coma

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4
Q

Arginosuccinase deficiency

A

Urea cycle disorder characterized by a buildup of argininosuccinate due do deficiency of enzyme

Lethargy, coma

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5
Q

Cystinuria

A

Defect in Cystine transporter in the kidneys

Cystine is a dimer of cysteine, precipitates out of soln in high conc, leading to repeated kidney stones

Drink lots of H2O and take drugs to incr pH in urine to make cystine more soluble

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6
Q

Wilson Disease

A

Defect in copper excretion to biliary tract

Cu accumulates in liver, causing progressive liver disease and neurologic dx

Sx include liver dx, dysarthria, arthropathy, cardiomyopathy, kidney damage, hypoparathyroidism, Kayser-Fleischer ring around iris of eye

Single missense mutation in 40% of Northern European cases

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7
Q

Hereditary Hemochromatosis

A

Excessive iron absorption in intestine

Accumulates in liver, kidney, heart, joints, pancreas

Common in Northern Europenas, delayed onset (after 40 in men and 60 in women)

Fatigue common, bronzing of skin

Diagnose w/ liver biopsy and hemosiderin staining

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8
Q

Retinoblastoma

A

Autosomal dominant disorder

Tumors form in the retina and fill the eye if untreated

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9
Q

Postaxial polydactyly

A

Autosomal disorder characterized by multiple fingers/toes

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10
Q

Achondroplasia

A

Autosomal dominant disorder characterized by very short limbs

Disease seen in heterozygotes; homozygotes not viable

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11
Q

Albinism

A

Autosomal recessive disorder characterized by the inability to produce melanin from tyrosine

Hypopigmentation of skin, hair

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12
Q

Cystic fibrosis

A

Autosomal recessive disorder

Disrupted chloride transport results in thickened mucus secretions in lungs and the inability of pancreatic secretions to reach the intestine

Chloride sweat test

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13
Q

Delayed age of onset

A

Disorders not evident until adulthood

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14
Q

Reduced penetrance

A

Phenotype is mild or nonexistent in some individuals bc they hae other modifying genes that may affect presentation of this phenotype

Children of these ppl may have much more severe forms of the disease

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15
Q

Variable expression

A

Severity of a disorder depends on expression

Genes can be modified to limit their expression

Expression may be different in offspring

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16
Q

Neurofibromatosis

A

Autosomal dominant disorder w/ variable expression characterized by cafe au lait skin lesions

Some pts get a few lesions; others have large tumors

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17
Q

Pleiotropy

A

Multiple effects from one mutation

Ex. Marfan’s syndrome - defect in fibrillin, leads to multiple effects such as hypermobile joints, incr risk for aortic dissection, displaced lenses in eye, etc.

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18
Q

Allelic Heterogeneity

A

Multiple mutant forms of one type of disorder

Ex. Hb disorders sickle cell anemia and B-thalassemia are caused by dif mutations; have similar effects on pt

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19
Q

Locus heterogeneity

A

Multiple genes affect one pathway

Ex. Urea cycle disorders

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20
Q

Anticipation

A

Dominant disorders are more severe in later generations

Ex. Huntingdon’s disease

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21
Q

Hemophilia A

A

X linked recessive disorder characterized by excessive bleeding due to low levels of factor VIII

Can range from mild to moderate to severe

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22
Q

Duchenne Muscular dystrophy

A

X linked recessive characterized by severe, progressive muscular dystrophy caused by defective dystrophin protein

Show up around age 5 in males; pts confined to wheelchair by age 11

High levels of creatine kinase; Positive Gower’s sign, pseudohypertrophy of calves

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23
Q

Red-Green Colorblindness

A

X linked recessive disorder based on opsin proteins

One red opsin followed by several green opsins genes on X chromosome

Colorblindness caused by unequal crossing over of X chromosomes

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24
Q

Hypophosphatemic rickets

A

X linked dominant disorder

Kidneys cannot reabsorb phosphate, leading to decr ossification of bones (bones are soft, so the bend and distort)

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25
Q

Incontinentia pigmenti

A

X linked dominant

Abnormal skin pigmentation and teeth

Only found in females because males w/ this phenotype are not viable

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26
Q

Rett syndrome

A

X linked dominant

Autism, ataxia, MR

Most males do not make it to term, so it is more freq seen in females

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27
Q

Leber Hereditary Optic Neuropathy (LHON)

A

Mitochondrial inherited disease

Optic nerve death in 3rd decade leading to blindness

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28
Q

Myoclonic epilepsy w/ ragged red fibers (MERRF)

A

Mitochondrial inherited disease

Epilepsy, ataxia, dementia, myopathy

Highly variable expression due to heteroplasmy (some mitochondria may be affected in a cell and others may be normal)

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29
Q

Mitochondrial encephalomyopathy and stroke-like episodes (MELAS)

A

Mitochondrial inherited disease

Many stroke like episodes w/ variable expression

30
Q

Fragile X

A

Most common inherited MR

Affects females twice as often as males; shows up in families w/o prior history; normal transmitting males are not likely to be affected but are likely to have unaffected daughters and affected granddaughters because the CGG repeat expands only in female meiosis

If repeat gets over 230, then disease is present

Long face, prominent jaw, large ears

31
Q

Prader-Willi Syndrome

A

Genomic imprinting disease caused by deletion of part of the paternal copy of chromosome 15

Characterized by morbid obesity, intellectual defects

32
Q

Angelman Syndrome

A

Genomic imprinting disease caused by a deletion on part of the maternal copy of chromosome 15

Leads to uncontrollable laughter and puppet-like movements

33
Q

Classic Galactosemia

A

Missense mutation in gene that codes for GAL-1-P-uridyl transferase, leading to inability to convert galactose to glucose-1-phosphate

Causes buildup of galactose, leading to incr synthesis of galactitol, leading to cataracts in infants. Also causes failure to thrive, developmental delay. Screened for at birth

34
Q

Hereditary Fructose intolerance

A

Defect in fructose 1,6 bisphosphate aldolase

Inability to digest fructose; prevalent in 1/20,000

35
Q

Von Gierke Disease

A

Glycogen storage dx due to defect in glucose-6-phosphatase

Results in the inability to utilize broken down glucose, causing hepatomegaly and hypoglycemia

36
Q

PKU

A

Inability to metabolize Phe, resulting in its buildup

Causes defects in myelination, protein synthesis, and eventually MR

Dietary restrictions to limit symptoms

37
Q

Maple Syrup Urine Disease

A

Cannot metabolize branched chain ketoacids from branched chain amino acids

Highly prevalent in Menonites of Lancaster County

Odor of urine; can lead to death if not accounted for

38
Q

MCAD Deficiency

A

Deficiency in medium chain acyl coenzyme A dehydrogenase

Inability to break down medium chain FA and long chain FA when they are converted into medium chain FA

Cause hypoglycemia after fasting due to inability to make ketone bodies; brain needs ketone bodies for energy when blood glucose gets low

Tx is to avoid fasting, have a diet high in glucose

39
Q

Congenital Adrenal Hyperplasia

A

Block in corticoid synthesis (aldosterone, cortisol)

Intermediates build up, leading to excess synthesis of androgens

Can cause development of male-like sex characteristics in a fetus w/ high androgens

May also lead to wt loss, lethargy, dehydration, death

Many forms are less severe

40
Q

Zellwegger Syndrome

A

Severe peroxisome disorder

Buildup of toxins leads to neonatal hypotonia, white matter disease, distinctive face, death in infancy

Not to be confused with Renee Zellwegger, a condition in which one has the facial similarities of an anteater

41
Q

Mucopolysaccharidoses

A

Inability to degrade GAGs

All are autosomal recessives except Hunter, which is X linked

MR occurs in some (Hunter, Hurler, Sanfilippo)

42
Q

Sphingolipidoses

A

Inability to degrade sphingolipids

Gaucher disease occurs mainly in Ashkenazi Jews (B-glucosidase deficiency)

Also Tay-Sachs and Niemann-Pick disease are sphingolipidoses

43
Q

I-Cell Disease

A

Lysosomal storage dx characterized by inability to add mannose-6-P to proteins destined for lysosomes

These proteins are instead secreted, and inclusion bodies build up due to defective lysosomes

44
Q

Linkage disequilibrium

A

Mutations and specific alleles may be inherited together, resulting in a higher than normal frequency of a person with a mutant gene carrying a specific linked allele

45
Q

Genetic association

A

Some specific allele significantly incr the risk of a person being affected with a particular disease, even though linkage between the two is not known or not a factor

46
Q

FGFR3 Mutations

A

Cause skeletal dysplasias

Most are autosomal dominantly inherited (think about how achondroplasia is inherited)

47
Q

Camptomelic dysplasia

A

Genetic disorder caused by mutation of SOX9, which is no longer able to activate DAX, thereby preventing testes from properly forming

Leads to short limbs and sex reversal

48
Q

Hirshsprung Disease

A

Enteric neurons do not properly form, so colon cannot move digested material through, causing severe constipation

Due to SOX10 mutation

49
Q

Osteogenesis imperfecta

A

Mutation in glycine residues of a collagen chain disrupts fibril formation, leading to malformed, brittle bones

50
Q

Marfan’s syndrome

A

Fibrillin-1 mutation that results in defective elastin, leadng to abnormal heart and large blood vessels, longer than normal arms and legs, lens dysfunctions, hypermobile joints

51
Q

Junctional epidermolysis bullosa

A

Defect on laminin that normally anchors cells to ECM

Defect results in large blisters on skin due to epithelium being unable to attach

52
Q

HOX genes

A

Determine anterior/posterior axis development

53
Q

Dorsal/Ventral Axis development

A

Dorsalized in presence of noggin and choridin

Ventralized w/o those two, allowing expression of BMP4

54
Q

Holt-Oram syndrome

A

TBX5 mutation resulting in thumb and radius defects

55
Q

Ulnar-mammary syndrome

A

TBX3 mutation, affecting posterior digits and ulna

56
Q

Neurofibromatosis 1

A

NF1 normally downregulates RAS signaling by hydrolyzing GTP

Defect leads to constitutively activated RAS, leading to constant gene activation

Appearance of skin lesions called cafe au lait spots are characteristic

57
Q

Li-Fraumeni syndrome

A

Mutation in p53, resulting in much higher prevalence of various cancers

Early age, multiple primary tumors

58
Q

Familial adenomatous polyposis coli

A

Many polyps, most do not progress to cancer, but some can

Due to APC mutation, followed by other defects such as K-Ras activation, p53 mutation, SMAD4 alteration

59
Q

Heridatry non-polyposis colon cancer

A

Fewer polyps, but they have a much higher chance of developing cancer

Due to mutations in DNA mismatch repair genes MSH2 and MLH1

60
Q

BRCA genes

A

Normally repair double stranded DNA breaks

Mutations can lead to a variety of different cancers, mainly breast cancer

61
Q

Liability Distribution

A

Individuals at one end of the distribution curve are affected

62
Q

Threshold of Liability

A

Limit that separates normal from affected; may differ by sex or other factor

63
Q

Multifactorial inheritance

A

More likely to be affected by a disease if you have more affected relatives, if affected relative is of the less affected sex, and if there is an early age of onset for an affected relative

64
Q

Familial Hypercholesterolemia

A

Quantitative trait w/ autosomal dominant inheritance

Accelerates atherosclerosis due to very high blood cholesterol, produces fatty deposits, high risk for CAD and MI, homozygotes severely affected

Caused by mutation in LDL receptor

65
Q

Stroke

A

Multifactorial due to mitochondrial disorder MELAS; mutations in NOTCH3, Protein C and S; Factor V Leiden (hypercoagulability of factor V)

66
Q

Hypertension

A

Some single gene mutations can cause one symptom:

Liddle syndrome due to defective epilthelial Na channel

Gordon syndrome due to incr renal salt reabsorption

Excess corticosteroid production or renin-angiotensin system mutation

67
Q

Type I Diabetes

A

Destruction of beta cells of pancreas, leading to decr insulin

Shows a genetic component, but also autoimmune

Shows association w/ HLA DR3 or DR4

68
Q

Type II Diabetes

A

High concordance rate in MZ twins

Environment plays a large role

Recurrence risk is higher if first degree family member is affected

69
Q

MODY

A

Mature onset diabetes of the young

Glucokinase mutations in 50% of cases

Also many txn factor mutations that are normally involved w/ pancreatic dvmt or insulin reg

70
Q

Alzheimer’s

A

Risk doubles if first-degree relative is affected

Mostly sporadic

cleavage of APP precursor can be a gain of fxn mutant, leading to Alzheimer’s

Medical Genetics (1 decks)

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