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Pathology > Genetics > Flashcards

Genetics Flashcards

1
Q

Polymorphism

A

Refers to the existence of more than one “normal” allele (form) of a gene. Polymorphism can also refer to SNP’s (single nucleotide polymorphs), which are the most common form of this phenomenon.

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2
Q

Pleiotropism

A

Refers to the ability of a single gene mutation to have more than one phenotypic affect.
Marfan syndrome is another disorder in which a single gene mutation can cause many different phenotypic changes.
The gene mutation causing Neurofibromatosis 1, for example, can cause pigment changes in the skin (café au lait macules), neurofibromas and Lisch nodules.

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3
Q

Genetic Heterogeneity

A

Refers to the ability of different gene mutations to cause the same phenotypic change.
Childhood deafness is another example and can be caused by 16 different types of autosomal recessive mutations.
Retinitis pigmentosa, caused by abnormal retinal pigmentation, can be caused by several different, unique gene mutations.

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4
Q

Huntington disease

A

AD disorder, gain-of-function mutation

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5
Q

Autosomal Dominant Disorders - Nervous System

A

Neurofibromatosis (von Recklinghausen disease)
Huntington disease*
Myotonic dystrophy*
Tuberous sclerosis (Bourneville’s disease)

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6
Q

Autosomal Dominant Disorders - Skeletal

A

Marfan syndrome
Ehlers-Danlos syndrome*
Osteogenesis imperfecta
Achondroplasia

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7
Q

Autosomal Dominant Disorders Gastrointestinal

A

Familial polyposis coli

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8
Q

Autosomal Dominant Disorders Hematopoietic

A

Hereditary spherocytosis

von Willebrand disease

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9
Q

Autosomal Dominant Disorders Metabolic

A

Familial hypercholesterolemia

Acute intermittent porphyria

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10
Q

Autosomal Dominant Disorders Urinary System

A

Adult (Autosomal Dominant) polycystic kidney disease

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11
Q

Neurofibromatosis Type 1

A

(von Recklinghausen disease) Autosomal dominant disorder - Up to 50% are new mutations. Results from defect of NF-1 gene which is found on chromosome 17q11. NF-1 is a tumor suppressor gene producing the protein neurofibromin.
Clinical Findings: Neurofibromas (multiple) malignant nerve tumors in ~3% of patients, cafe au lair macules 90%, Lisch nodules >94%

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12
Q

Marfan Syndrome

A

Autosomal Dominant
Due to defective fibrillin protein. Fibrillin gene found on chromosome 15. Fibrillin, together with elastin, provides stability to elastic tissue.
Clinical features:
Aortic dilatation -> aortic valve incompetence
Cystic medial necrosis -> aortic dissection
Mitral valve prolapse
Increased stature and arachnodactyly
Dislocated lens (ectopia lentis)
Premature aging changes; mucopolysaccharide deposition often pronounced.

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13
Q

Ehlers-Danlos Syndrome

A

Autosomal dominant disorder
Heterogenous group of disorders that result from various defect in collagen synthesis or structure (12 variants) of collagen IV, VI, VII
Mode of inheritance encompasses all 3 Mendelian patterns
Clinical Findings:
Very stretchable skin and hypermobile joints (contortionists)
Abnormal connective tissues are more easily injured and healing is delayed/abnormal

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14
Q

Pleiotropism

A

Refers to the ability of a single gene mutation to have more than one phenotypic affect.
Marfan syndrome is another disorder in which a single gene mutation can cause many different phenotypic changes.
The gene mutation causing Neurofibromatosis 1, for example, can cause pigment changes in the skin (café au lait macules), neurofibromas and Lisch nodules.

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15
Q

Genetic Heterogeneity

A

Refers to the ability of different gene mutations to cause the same phenotypic change.
Childhood deafness is another example and can be caused by 16 different types of autosomal recessive mutations.
Retinitis pigmentosa, caused by abnormal retinal pigmentation, can be caused by several different, unique gene mutations.

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16
Q

Huntington disease

A

AD disorder, gain-of-function mutation

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17
Q

Autosomal Dominant Disorders - Nervous System

A

Neurofibromatosis (von Recklinghausen disease)
Huntington disease*
Myotonic dystrophy*
Tuberous sclerosis (Bourneville’s disease)

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18
Q

Autosomal Dominant Disorders - Skeletal

A

Marfan syndrome
Ehlers-Danlos syndrome*
Osteogenesis imperfecta
Achondroplasia

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19
Q

Autosomal Dominant Disorders Gastrointestinal

A

Familial polyposis coli

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20
Q

Autosomal Dominant Disorders Hematopoietic

A

Hereditary spherocytosis

von Willebrand disease

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21
Q

Autosomal Dominant Disorders Metabolic

A

Familial hypercholesterolemia

Acute intermittent porphyria

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22
Q

Autosomal Dominant Disorders Urinary System

A

Adult (Autosomal Dominant) polycystic kidney disease

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23
Q

Neurofibromatosis Type 1

A

(von Recklinghausen disease) Autosomal dominant disorder - Up to 50% are new mutations. Results from defect of NF-1 gene which is found on chromosome 17q11. NF-1 is a tumor suppressor gene producing the protein neurofibromin.
Clinical Findings: Neurofibromas (multiple) malignant nerve tumors in ~3% of patients, cafe au lair macules 90%, Lisch nodules >94%

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24
Q

Neurofibromatosis Type 2 (NF-2)

A

Much less frequent than Type 1. Gene found on chromosome 22 and produces the protein merlin. Also a tumor suppressor gene.
Clinical findings:
Bilateral acoustic neuromas
Multiple meningiomas
May have neurofibromas and café au lait macules
No Lisch nodules

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25
Q

Marfan Syndrome

A

Autosomal Dominant
Due to defective fibrillin protein. Fibrillin gene found on chromosome 15. Fibrillin, together with elastin, provides stability to elastic tissue.
Clinical features:
Aortic dilatation -> aortic valve incompetence
Cystic medial necrosis -> aortic dissection
Mitral valve prolapse
Increased stature and arachnodactyly
Dislocated lens (ectopia lentis)
Premature aging changes; mucopolysaccharide deposition often pronounced.

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26
Q

Familial Hypercholesterolemia

A

Autosomal dominant disorder
Results from a defective LDL receptor, an important regulator in cholesterol metabolism
May be the most frequent Mendelian disorder; estimated to occur in 1 in 500
Clinical manifestations result from high levels of total and LDL cholesterol
Five distinct types of mutations can cause this entity
Clinical Manifestations:
Xanthelasma - lipid accumulations around the eye
Xanthomas

27
Q

Autosomal Recessive Disorders Metabolic

A 
Cystic fibrosis
PKU
Galactosemia
Homocystinuria
Lysosomal storage diseases
Alpha-1-antitrypsin deficiency
Wilson disease
Hemochromatosis
Glycogen storage diseases
28
Q

Cystic fibrosis (CF)

A

Pathophysiologic lesion is a defect in c-AMP-regulated ion transport across apical membranes of affected epithelial cells.
The most common fatal autosomal recessive disease affecting the Caucasian population
The CF gene has been localized to a single locus on the long arm of chromosome 7
The gene product is a protein called CF transmembrane conductance regulator (CFTR), which is a chloride channel that fails to be activated by c-AMP
Heterozygous states may have a relative resistance to diarrheal diseases, especially cholera
The impairment of transport here is failure of resorption of chloride through the duct epithelial cells.

29
Q

CF Respiratory airway and pancreatic duct cells

A

In these systems, there is a failure to transport chloride into the lumen of the airways and ducts. This is coupled with increased sodium resorption, the combination of which greatly decreases the water content in the lumens of these systems resulting in thick, viscid secretions which are difficult to clear. The viscid secretions lead to obstruction with parenchymal destruction. In the lungs, this also predisposes to infection; in particular a propensity to become infected with mucoid strains of Pseudomonas.

30
Q

CF Pancreas

A

Early on there is cystic dilatation and direct plugging of the exocrine glands and ducts with inspissated (thickened or congealed) eosinophilic secretions. Acinar atrophy with rupture, inflammation and progressive fibrosis ensues. Later, there is extensive fatty and fibrous replacement of the exocrine pancreas with relative sparing of the islet cells, although they may ultimately become involved as well and cause secondary diabetes mellitus

31
Q

CF Lungs

A

Show plugging of the submucosal tracheal mucous glands and ducts. The bronchioles often become distended with thick mucus, often associated with marked hyperplasia and hypertrophy of the mucus-secreting cells and inflammation. Atelectasis and emphysema ensue. Superimposed infections give rise to severe chronic bronchitis and bronchiectasis, and, in many cases, lung abscesses develop.

32
Q

CF Liver

A

Liver involvement follows the same basic pattern of duct involvement as in the pancreas. Early on, there is bile duct hyperplasia with mucus plugging of the bile canaliculi. Focal biliary cirrhosis is characteristic, but diffuse hepatic nodularity is seen only in a small percentage of patients.

33
Q

Alkaptonuria

A

Autosomal recessive disorder
Results from lack of homogentisic oxidase causing build-up of homogentisic acid
Large amount excreted in urine which causes urine to turn black upon standing
Ochronosis: homogentisic acid binds to collagen in tissues imparting black-blue pigmentation to these tissues
Seen especially over ears, nose and cheeks
Arthropathies occur

34
Q

Autosomal Recessive Disorders Endocrine

A

Congenital adrenal hyperplasia

35
Q

Autosomal Recessive Disorders Skeletal

A

Ehlers Danlos syndrome (some variants)

Alkaptonuria

36
Q

Autosomal Recessive Disorders Neural

A

Friedreich ataxia*
Neurogenic muscular atrophies
Spinal muscular atrophy

37
Q

Sickle Cell Anemia

A

The mutated allele is recessive, meaning it must be inherited from each parent for the individual to have Sickle Cell disease. This is a type of missense point mutation. Inheritance of a single mutant allele results in Sickle Cell trait ≈ 60% Hemoglobin A and 40% Hemoglobin S (protective against malaria.

38
Q

Phenylketonuria (PKU)

A

Autosomal recessive disorder
Affects people of Scandinavian descent; rarely seen in African or Jews
Due to a severe lack of phenylalanine hydroxylase causing hyperphenylalaninemia and PKU. Unable to convert phenylalanine to tyrosine due to phenylalanine hydroxyls (PAH); results in metabolites that are excreted in the urine and sweat, producing a characteristic “mousy” odor.
Infants are normal at birth, but within a few weeks develop increasing plasma levels of phenylalanine and toxic metabolites
Seizures, eczema and decreased pigmentation of hair and skin (due to the lack of tyrosine, which is largely produced from phenylalanine) often accompany the mental retardation

39
Q

Maternal PKU

A 
Anomalies can include
Cardiac defects
Microcephaly
Low birth weight
Mental retardation
Slow development
Language deficits
40
Q

Galactosemia

A

Autosomal recessive disorder
Deficiency in ability to convert galactose to glucose – deficient in galactose-1-phosphate urydil transferase
May clinically result in hepatomegaly/ hepatic steatosis with jaundice, cataracts, non-specific CNS changes, failure to thrive, vomiting and diarrhea
May be prevented by early removal of galactose from the diet (until at least age 2)

41
Q

Tay-Sachs Disease

A

Autosomal Recessive Disorder
Results from mutations affecting hexosaminidase enzyme complex
A deficiency of hexosaminidase A alpha subunit causes GM2-ganglioside accumulations in the neurons of CNS and ANS
Blindness with retinal cherry red spot
Most common in Jews of Eastern European origin

42
Q

Niemann-Pick Disease

A

Results from the accumulation of sphingomyelin and cholesterol. Affected NPC-1 gene controls cholesterol trafficking.
Types A, B and C (C is most common type)
Types A and B common in Eastern European Jews
Type A is the severe infantile form and is associated with the following:
Neuronal death with resultant brain shrinkage
Retinal cherry red spot
Hepatosplenomegaly and lymphadenopathy
Death at 1-3 years of age
Heterogeneous clinically
Hydrops fetalis and still births
Neonatal hepatitis
Chronic form with progressive neurologic damage

43
Q

Gaucher Disease

A

Characterized by mutations involving the glucocerebrosidase gene, resulting in decreased levels or activity of this enzyme – leading to accumulations of glucocerebrosides
Type I: (99%) Involves the mononuclear phagocytes in body but not the CNS
Spleen and skeletal changes common
Seen in Eastern European Jews

44
Q

Hunter/Hurler Syndromes

A 
Mucopolysaccharidoses - MPS I - MPS VII
All autosomal recessive, except Hunter syndrome which is X-linked recessive
Common features include
Coarse facial features
Clouding of the corneas
Joint stiffness
Mental retardation
45
Q

Glycogenoses

A 
Result from some metabolic defect in the synthesis or catabolism of glycogen
Hepatic type (von Gierke disease, type I)
Myopathic type (McArdle syndrome, type V)
Miscellaneous types (Pompe disease, type II)
46
Q

Pompe Disease

A

Deficiency of lysosomal acid maltase, therefore both a glycogen storage and lysosomal storage disorder
Lysosomal accumulation of glycogen in multiple organs, especially the heart
Early death

47
Q

Alkaptonuria

A

Autosomal recessive disorder
Results from lack of homogentisic oxidase causing build-up of homogentisic acid
Large amount excreted in urine which causes urine to turn black upon standing
Ochronosis: homogentisic acid binds to collagen in tissues imparting black-blue pigmentation to these tissues
Seen especially over ears, nose and cheeks
Arthropathies occur

48
Q

X-Linked Recessive Disorders Musculoskeletal

A

Duchenne Muscular Dystrophy

Becker Muscular Dystrophy

49
Q

X-Linked Recessive Disorders Hematopoietic

A

Hemophilia A & B
Glucose-6-phosphate dehydrogenase deficiency
Chronic granulomatous disease

50
Q

X-Linked Recessive Disorders Neural

A

Fragile X syndrome*

51
Q

X-Linked Recessive Disorders Metabolic

A

Lesch-Nyhan syndrome

Diabetes insipidus

52
Q

Multifactorial Inheritance

A

Disorders or defects associated with multifactoral inheritance includes cleft lip/palate, congenital heart disease, coronary heart disease, hypertension, gout, diabetes mellitus and pyloric stenosis

53
Q

Mosaicism

A

defined as the presence of two or more populations of cells with different genotypes in a single individual

54
Q

Trisomy 21

A

Clinical findings:
Flat facial profile
Oblique palpebral fissures
Epicanthic folds
Congenital heart disease (40%), especially endocardial cushion defects
Acute leukemia (10-20X increased risk)
GI atresia, Alzheimer disease (in patients older than 40), and immunodeficiencies

55
Q

Klinefelter Syndrome

A

Male hypogonadism that occurs when there are two or more X chromosomes and at least one Y chromosome (needed for the male phenotype). 1:660 male births
82% are of the “classic” form; 47,XXY
Slightly low IQ, increased risk of mental retardation with additional copies of the X chromosome
Atrophic testes, hypospadias, cryptorchidism, infertility, gynecomastia, female distribution of fat and skeletal abnormalities
Increased breast cancer and autoimmune disorders

56
Q

XYY Males

A

47,XYY or 48,XYYY etc.
1:1000 live-born males
Phenotypically normal except may be tall and have increased acne
Normal intelligence

57
Q

Turner Syndrome

A

Results from complete or partial monosomy of the X chromosome
Characterized primarily by hypogonadism in phenotypic females
Other phenotypic changes can also be present
Clinical findings:
Short stature
Coarctation of aorta
Edema
Cystic hygromas
Webbing of the neck
Broad (shield) chest with widely spaced nipples
Streak ovaries
Nevi
Primary amenorrhea (causes up to 1/3 of all cases of primary amenorrhea)
Infantile genitalia
Hypothyroidism (50%)
Insulin resistance - can cause a form of diabetes mellitus

58
Q

Triplet Repeat Mutations

A

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

59
Q

Fragile X Syndrome

A

Prototype of diseases in which the mutation is characterized by a long repeating sequence of 3 nucleotides. CGG is the trinucleotide repeat at this location
FMR-1 (familial mental retardation-1 gene), located on the X chromosome, is the gene involved
Named Fragile X syndrome because the triple repeats give the X chromosome a “broken” appearance on G banding. FMR-1 protein is widely expressed, but most highly in the brain and testes, possibly explaining the syndromes most common features. In the brain, FMRP complexes with mRNA to form mRNP-FMRP complexes, which are transported down the axons and regulate transcription of specific mRNA’s.
Characteristic phenotype: Long face with large mandible, large, everted ears, and macroorchidism (large testis) in 90% of post-pubertal males

60
Q

Mitochondrial Mutations

A

Mitochondrial DNA is maternally inherited
mtDNA encodes for genes necessary for oxidative phosphorylation
Therefore, mutations affect organs most dependent on oxidative phosphorylation, including the CNS, skeletal muscle, cardiac muscle, liver and kidneys

61
Q

Leber Hereditary Optic Neuropathy

A

Mitochondrial Mutations

62
Q

Genomic Imprinting

A

Selective inactivation of either the maternal or paternal allele, e.g. maternal imprinting refers to transcriptional silencing of the maternal allele
Prader-Willi syndrome
Angelman syndrome

63
Q

Prader-Willi syndrome

A

Chromosome 15 partial deletion with loss of expression of seven genes (paternal)
1 in 10,000 to 1 in 25,000 live births
Signs and symptoms
Poor muscle tone with weak cry and poor suckling
Lack of eye coordination and almond shaped eyes
Excessively sleepy
Hyperphagia with obesity and diabetes
Short stature with extreme flexibility
Hypogondaism
Learning disabilities

64
Q

Angelman syndrome

A 
Chromosome 15 partial deletion (Maternal)
1 in 10,000 to 1 in 20,000 live births
Signs and symptoms
Movement disorder/ataxia
Developmental delays
Speech impairment
Seizures with characteristic EEG changes
Hypopigmented skin
Sleep disturbances and hyperactive tendon reflexes

Pathology (5 decks)

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