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Genetics Flashcards

1
Q

Classification of genetic diseases

A 
1. Single gene disorders:
 Mendelian: (4 types)
 Non Mendelian:
  Germ line mosaicism
  Trinucleotide repeat mutation
  Genomic imprinting
  Mitochondrial inheritance
2. Chromosomal disorders:
 Structural and Numerical
3. Multifactorial
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2
Q

Sperm mitochondrial DNA is eliminated. How

A

Ova eliminates all sperm mitochondrial DNA by ubiquitin proteasome pathway

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3
Q

The organs usually affected by mitochondrial inheritance are

A

Brain
Skeletal muscle
Eye, as they contain more amounts of mitochondria

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4
Q

Heteroplasmy

A

Presence of normal and mutant mitochondrial DNA in the same person

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5
Q

Examples of diseases of mitochondrial inheritance

A 
K. Kearns Sayre syndrome
L. Leigh syndrome,
 Leber Hereditary optic neuropathy
M. MELAS
N. NARP syndrome
O. CPEO
P. Pearson syndrome
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6
Q

Most common disease inherited through mitochondrial inheritance

A

MELAS

Mitochondrial Encephalopathy
Lactic Acidosis and
Stroke like episodes

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7
Q

Most common mitochondrial myopathy

A

CPEO
Chronic Progressive
External Ophthalmoplegia

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8
Q

Diseases due to trinucleotide repeat mutations in the coding region

A

Huntington’s disease CAG

Spinocerebellar ataxia CAG

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9
Q

Diseases due to trinucleotide repeat mutations in the non coding region

A

Fragile X syndrome CGG
Friedreich’s ataxia GAA
Myotonic dystrophy CTG

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10
Q

Cause of fragile X syndrome

A 
Mutation in FMR1 gene
➡️ increased CGG repeats 
5-40 CGG- normal
55-200 repeats- premutation
200-4000 repeats- full mutation
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11
Q

Anticipation/ Sherman’s paradox

A

CGG repeats increases with each generation

Increased CGG repeats causes fragile X syndrome

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12
Q

Why is fragile X syndrome called the way it is

A

When cells are cultured in a folate deficient media, constriction is seen in the X chromosome as if the X chromosome is broken

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13
Q

Clinical presentation of fragile X syndrome

A
  1. 2nd most common genetic cause of mental retardation
  2. Large head, everted ears, mandible
  3. Large testis/ macrorchidism- most distinctive feature
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14
Q

Fragile X tremor syndrome

A

Gene affected- FMR1
Gain of function mutation ➡️ intentional tremor
(Opposite effect of fragile X syndrome)

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15
Q

Gonadal mosaicism

A

Type of autosomal dominant disorder
Even if both parents are normal, child may be affected
Post zygotic mutation ➡️ mutation only in gametes, not in somatic cells

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16
Q

Examples of gonadal mosaicism

A

Tuberous sclerosis

Osteogenesis imperfecta

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17
Q

Genomic imprinting

A

Gene silencing/ inactivation
Either paternal/ maternal allele is inactivated ➡️ only one allele is functional
Normal phenomenon
Due to epigenetics

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18
Q

Epigenetics

A

Heritable modifications in DNA/ histone like DNA methylation or histone deacetylation ➡️ loss of expression of genes

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19
Q

Prader Willi syndrome

Cause

A

Maternal allele of chromosome 15q is usually silent, then
Paternal deletion: cause
Loss of function of SNORP gene

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20
Q

Features of Prader Willi syndrome

A 
Short stature
Hypotonia
Hypogonadism
Hyperphagy (increased ghrelin)➡️ obesity
Mental retardation
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21
Q

Causes of Angelman syndrome/ Happy Puppet syndrome

A

Paternal allele was silenced
The functional maternal is deleted then Angelman syndrome
Defect in ubiquitin ligase gene (UBE3A)

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22
Q

Features of Happy Puppet syndrome/ Angelman syndrome

A 
Inappropriate laughter
Ataxia
Seizures
Mental retardation
Hypotonia
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23
Q

Uniparental disomy

A

If both alleles come from same parent
Prader Willi syndrome: paternal deletion/ maternal disomy
Angelman syndrome: the opp

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24
Q

Autosomal dominant disorder characteristics

A

Usually have adult onset
Does not skip generations
Usually due to structural protein defects
1. Incomplete penetrance
2. Variable expressivity
Most common Mendelian mode of inheritance

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25
Examples of autosomal dominant disorders
``` He has a very dominant father H. Huntington’s disease H. Hereditary spherocytosis A. APKD V. VWF, VHL D. Dystrophia myotonica O. Osteogenesis imperfecta M. Marfan’s syndrome I. Intermittent porphyria N. NF-1 A. Achondroplasia N. NF-2 T. Tuberous sclerosis F. FAP, Familial hypercholesterolemia ```
26
Marfan’s syndrome | Cause
Autosomal dominant Defect in FBN-1 gene encoding for fibrillin-1 (defect in FBN-2 gene encoding for fibrillin-2 leads to congenital contractural arachnodactyly)
27
Clinical presentation of Marfan’s syndrome
``` 1. Skeletal defect: Tall stature Hyperextensible joints Dolicocephalic head 2. Ocular defects: Ectopia lentis Superotemporal dislocation 3. CVS: MV Prolapse (like Klinefelter’s) Aortic dissection ```
28
Most common cause of death in Marfan’s syndrome
CVS defect like aortic dissection
29
Diagnosis of Marfan’s syndrome
Revised Ghent’s criteria 1. Family history 2. Clinical signs and symptoms 3. Fibrillin-1 gene mutation
30
NF-1 or von Recklinghausen’s disease
Gene on chromosome 17 (letters) Encode for neurofibromin Can be associated with juvenile myelo monocytic leukaemia (JMML) Presentations: 1. Cafe au lait spots (>6 spots) 2. Lisch nodules: (pigmented iris hamartomas) 3. Neurofibromas: (meningeomas, pheochromocytoma)
31
NF-2
Gene on chromosome-22 Encodes for Merlin Associated with bilateral acoustic neuroma/ Schwannomas)
32
Ehler Danlos syndrome basics
``` AD and AR (type 6,7) Type 3 collagen mostly affected Most common : 3 Least common: 7 Most dangerous type of EDS: Type 4 (vascular) ```
33
AD types of Ehler Danlos syndrome
``` 1. Classical: Diaphragmatic hernia Mitral valve prolapse 3. Common, hypermotility: Loose skin (Rubberman syndrome) Thin skin (cigarette paper skin) 4. Vascular: Aorta may rupture ```
34
AR types of Ehler Danlos syndrome
``` 6. Kyphoscoliosis Defect in lysyl hydroxylase enzyme 7. a,b: arthrochalasia: Joint, bone defects c: Dermatosparaxis: Severe skin fragility ```
35
Autosomal recessive disorders
Young/ early onset usually Complete penetrance Usually due to enzyme deficiency Uniparental disomy (both alleles from a single parent) can also be seen
36
Examples of autosomal recessive disorders
``` A. Alkeptonuria, Ataxia, Albinism B. Beta thalassemia, sickle cell anaemia C. Cystic fibrosis, congenital adrenal hyperplasia D. Deafness E. Emphysema (α1 antitrypsin deficiency) F. Friedrich’s ataxia G. GSDs, Galactosemia H. Hemachromatosis, homocystinuria I. Inborn error of metabolism ```
37
All lysosomal storage disorders are autosomal dominant except
Fabry’s disease Hunter’s disease Autosomal recessive
38
Tay Sachs disease mnemonic
``` T. Tay Sachs A. Ashkenazi Jews Y. Young S. Spot- cherry red in macula A. AR C. CNS defects H. Hexosaminidase α defect (GM2 increases) S. Symptoms of motor neuron and mental retardation ```
39
Histopathology of Tay Sachs disease
``` Neuron: Ballooned Vacuolation (distended with lysosomes) Electron microscopy: Onion skin appearance ```
40
Onion skin appearance
``` X-ray: Ewing’s sarcoma e- microscopy: Tay Sachs disease Nerve biopsy: CIPD H and E: malignant hypertension, 1° sclerosing cholangitis Gross: spleen in SLE ```
41
Niemann Pick’s disease | Types
``` Defect in sphingomyelinase ➡️ accumulation of sphingomyelin Type A: Neuronal involvement Severe, early mortality Type B: Neuronal involvement absent Better prognosis Type C: most common, intermediate ```
42
Gaucher’s cell
Wrinkled/ crumpled tissue paper appearance PAS + Oil red O+ Perl’s +
43
Pseudo Gaucher’s cell
Seen in CML | Perl’s stain -ve
44
Types of Gaucher’s disease
``` 1. Non neuropathic: Adulthood Most common Bone involvement, pathological fractures Hepatosplenomegaly 2. Neuropathic: Infants Less common More severe CNS involvement 3. Intermediate ```
45
X-linked recessive disease examples
``` Lady. Lesch Nyhan syndrome Hardinge. Haemophilia A and B, Hunter’s disease College. Colour blindness Girls. G6PD deficiency Don’t. Duchenne muscular dystrophy Care. Chronic granulomatous disease About. Agammaglobulinemia Foolish. Fabry’s disease, Fragile X syndrome Words. Wiscott Aldrich syndrome ```
46
X-linked dominant disorders example
R. Rett’s syndrome A. Alport syndrome V. Vit D resistant rickets I. Incontinentia pigmenti
47
X-linked dominant properties
Mother: can give diseases to both sons and daughters Father: affects only daughters
48
Types of chromosomes
``` Metacentric: 1 Submetacentric: X Acrocentric: 13,14,15,,21,22,23Y Telocentric: does not exist in humans ```
49
Chromosomal disorders
``` 1. Structural: Deletion Insertion Translocation Ring chromosome Iso chromosome Inversion 2. Numerical: Aneuploidy; monosomy and trisomy ```
50
Reasons for aneuploidy
1. Meiotic non dysjunction | 2. Anaphase lag
51
Ring chromosome
Type of structural chromosomal abnormality Break at both ends Fusion of damaged ends Can be seen in Turner’s syndrome
52
Robertsonian translocation
Translocation between 2 acrocentric chromosomes (13,14,15,21,22,Y) t(14:21) Down’s syndrome
53
Isochromosome
When division of chromosome occurs transversely instead of longitudinally Two short or two long arms Most common isochromosome: iXq
54
Most common isochromosome in: Cancer Testicular tumour
In cancer: il7q In testicular tumour: i21p
55
Down’s syndrome pathogenesis
``` Most common chromosomal disorder Most common genetic cause of mental retardation 1. Meiotic non dysjunction: 95% Occurs in oogenesis in meiosis-I 2. Robertsonian translocation: 4% t(14:21) 3. Mosaics: 1% ```
56
Down’s syndrome screening tests for mothers
``` Triple test: AFP βBCG Unconjugated estradiol Quadruple test: Triple test + inhibin ```
57
Clinical features of Down’s syndrome
1. Most common cause of mental retardation 2. Face: mongoloid idiocy 3. Eyes: Brush field spots 4. Palm: (single) Simian crease, clinodactyly 5. Foot: Sandle gap/ saddle toe
58
Mongoloid idiocy
Facial features of Down’s syndrome 1. Flat facial profile 2. Upslanting/ oblique palpebral fissure 3. Prominent epicanthal folds 4. Flat occiput 5. Flat nasal bridge 6. Low set ears
59
Complications of Down’s syndrome
1. Acute leukaemia 2. Cardiovascular defect: M/C endocardial cushion defect, VSD 3. GIT: Annular pancreas Duodenal atresia Hirschsprung disease 4. Hypothyroidism 5. Premature Alzheimer’s disease (gene for the disease on chromosome 21)
60
Acute leukaemia and Down’s syndrome
M/C leukaemia- ALL M/C in children <3 years- AML M/C type of AML- AML M7
61
Common features of Patau’s syndrome and Edward’s syndrome
1. Mental retardation 2. CVS defect 3. Rocker bottom feet 4. Prominent occiput
62
Patau syndrome specific characteristics
``` Microcephaly Micro ophthalmia Umbilical hernia Polydactyly Left lip and palate ``` Meiotic non dysjunction occurs in meiosis-I 13 chromosome trisomy
63
Edward’s syndrome specific characteristics
``` Micrognathia Short neck Renal malformation Limited hip abduction Overlapping fingers ``` Meiotic non dysjunction occurs in meiosis-II (unlike others) 18 chromosome trisomy
64
Cat eye syndrome
Trisomy 22 | Multiple colobomas in the eye
65
Cat cry syndrome or Cri du chat syndrome
del 5p (short arm) Cat-like cry Behavioural abnormalities Developmental delay
66
Lyon’s hypothesis
Only one X chromosome of genetically active Other X, paternal or maternal, randomly becomes inactivated Inactivated X chromosome- Barr body of buccal mucosa having drumstick appearance (21 % of Xp and 3% of Xq escape inactivation)
67
Syndromes associated with advanced maternal age
Down’s syndrome | XXX syndrome
68
Syndromes associated with advanced paternal age
Marfan’s syndrome Osteogenesis imperfecta Achondroplasia
69
Klinefelter’s syndrome
Associated with both advanced maternal and paternal age Expected hormonal changes M/C cause of male hypogonadism M/C cancer: breast cancer M/C germ cell tumour: extragonadal GCT (teratoma)
70
Biopsy test for Klinefelter’s syndrome
Atrophy of seminiferous lobules Hyalinisation of lobules Leydig cell hyperplasia
71
Features of Klinefelter’s syndrome
1. Tall stature 2. Eunuchoid body habitus 3. Long extremities 4. Reduced 2° sexual characteristics 5. Gynecomastia 6. Frontal baldness absent 7. Poor muscle tone 8. Testicular atrophy- infertility
72
Turner’s syndrome basics
Most common female hypogonadism Only monosomy compatible with life Most common cause of primary amenorrhea M/C monosomy- monosomy 16
73
Pathology of Turner’s syndrome
1. Deletion of X chromosome 2. Ring chromosome 3. ISO chromosome
74
Common features of Turner’s syndrome | Mneumonic
C. Cardiac abnormalities, cubitis valgus, cystic hygroma L. Lymphadema O. streaked ovaries W. Webbed neck N. Normal intelligence, nipples widely spaced S. Short stature, short 4th metacarpal
75
CVS abnormalities of Turner’s syndrome
M/C CVS defect: bicuspid aortic valve M/C cause of death: preductal coarctation of aorta M/C cause of 1° amenorrhea Increased risk of developing gonadoblastoma
76
Noonan’s syndrome
Clinical features of Turner’s syndrome Normal karyotype Mutation in chromosome 12
77
Karyogram
Arrangement of chromosomes in descending order of length followed by sex chromosomes
78
Samples used for karyotyping
1. Amniotic fluid 2. Chorionic villi sampling 3. Skin fibroblasts 4. Peripheral blood lymphocytes Arrested the cell in metaphase using colchicine
79
Staining/ banding for karyotyping
1. Mc giemsa banding | 2. Q- banding (quinalrine)

Pathology MBBS (17 decks)

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