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USMLE Step 2 CK > Biochem & Genetics > Flashcards

Biochem & Genetics Flashcards

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USMLE® Step 1 flashcards
1
Q

Features of Lesch-Nyhan syndrome (purine salvage deficiency)

A 
Intellectual disability
Aggression, self-mutilation
Orange "sand" in diapers (hyperuricaemia)
Gout
Dystonia
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2
Q

Treatment of Lesch-Nyan syndrome

A

Allopurinol, febuxostat (2nd line)

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3
Q

Clinical feature of Adenosine deaminase deficiency

A

Lymphotoxicity (one of major causes of AR SCID)

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4
Q

What is the defect and inheritance of Kartagener syndrome?

A

Defect: defective dynein arm -> immotile cilia
Inheritance: Autosomal recessive

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5
Q

Features of Kartagener syndrome

A

Infertility (immobile sperm, blocked fallopian tubes)
Ectopic pregnancy
Lung infections (bronchiectasis, recurrent sinusitis)
Ear infections
Conductive hearing loss
*Situs inversus

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6
Q

Four main types of collagen in the body (and what disease occurs when defective/deficient)

A

Type I (90%): Skin and bones (Osteogenesis imperfecta type 1)
Type II: Cartilage
Type III: Blood vessels (Vascular type of Ehler Danlos syndrome)
Type IV: Basement membrane (Defective in Alport syndrome, attacked by antibodies in Goodpasture syndrome)

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7
Q

What type of collagen is involved in would healing?

A

Granulation by type III collagen, later replaced by type I

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8
Q

Defect and inheritance of osteogenesis imperfecta

A

Defect: Decreased production of NORMAL type 1 collagen (problem forming triple helix), most common gene defect in COL1A
Inheritance: Autosomal dominant (most common)

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9
Q

Features of osteogenesis imperfecta

A

Multiple fractures with minimal trauma (or even during birth)
Blue sclera
Opalescent teeth
Hearing loss (abnormal ossicles)

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10
Q

Treatment of osteogenesis imperfecta

A

Bisphosphonates to reduce fracture risk

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11
Q

Defect and inheritance of Ehlers-Danlos syndrome

A

Defect: Faulty collagen synthesis (defective cleavage and cross-linking)
- Classical type: Mutation in type V collagen
- Vascular type: Mutation in type III collagen
Inheritance: Can be AD or AR

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12
Q

Features of Ehlers-Danlos syndrome

A

Hyper extensible skin
Joint hypermobility/joint dislocation
Easy bleeding/bruising

a/w berry and aortic aneurysms, organ rupture

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13
Q

Which vitamin is essential in collagen synthesis?

What happens if it is deficient?

A

Vitamin C!

Scurvy!

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14
Q

Defect and inheritance of Marfan syndrome

A

Defect: Defective fibrillin (FBN1 gene mutation on chromosome 15)
Inheritance: AD

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15
Q

Features of Marfan syndrome

A

Tall with long extremities, arachnodactyly (tapering fingers and toes)
High arch palate
Pectus carinatum/excavatum
Joint hypermobility
Lens subluxation
Aortic/mitral regurgitation
Aortic dissection and aneurysms (cystic medial necrosis)

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16
Q

Features of McCune-Albright syndrome

A

Unilateral cafe-au-lait spots with ragged edges
Polyostotic fibrous dysplasia (bone replaced by collagen and fibroblasts)
At least one endocrinopathy (e.g. precocious puberty)

17
Q

Which copy of allele is deleted/mutated in Prader-Willi syndrome?

A

Paternal copy is deleted/mutated.

Maternal copy is imprinted/silenced - NORMAL

18
Q

Which chromosome is does the gene deletion/mutation occur on in Prader-Willi and Angelman syndrome?

A

Chromosome 15

19
Q

Features of Prader-Willi syndrome

A 
Intellectual disability
Obesity
Hyperphagia
Hypogonadism
Hypotonia
20
Q

Features of Angelman syndrome

A

Severe intellectual disability
Inappropriate laughter
Seizures
Ataxia

21
Q

Which copy of allele is deleted/mutated in Angelman syndrome?

A

Maternal copy is deleted/mutated.

Paternal copy is imprinted/silenced - NORMAL

22
Q

MELAS syndrome

1) What does it stand for?
2) What is its inheritance?
3) What does muscle biopsy show?

A

MELAS syndrome

1) Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes
2) Mitochondrial inheritance (i.e. only mother pass to children, variable expression)
3) Ragged red fibers

23
Q

Leber hereditary optic neuropathy

1) What is its inheritance?
2) What is its clinical feature?

A

Leber hereditary optic neuropathy

1) Mitochondrial inheritance
2) Bilateral vision loss in teens/young adults

24
Q

What is the genetic defect and inheritance of cystic fibrosis?

A

Genetic defect: Mutation in CFTR gene on chromosome 7 (commonly a deletion in Phe508)
Inheritance: Autosomal recessive

25
Q

What is the pathophysiology of cystic fibrosis?

A

Defective Cl- channel -> Cl- not secreted in lungs and GI tract -> Increased intracellular Cl- results in reabsorption of Na+ and H2O -> thick mucus formed

26
Q

What are the clinical features of cystic fibrosis?

A

Recurrent lung infections -> bronchiectasis
Pancreatic insufficiency -> malabsorption, steatorrhea, fat-soluble vitamin deficiency
Infertility
Meconium ileus in newborn

May present with contraction alkalosis and hypokalaemia

27
Q

How is cystic fibrosis diagnosed?

A

Increased Cl- concentration in pilocarpine-induced sweat test

Increased immunoreactive trypsinogen in newborn screening

28
Q

How is cystic fibrosis treated?

A

Chest PT, albuterol, hypertonic saline

Azithromycin used as anti-inflammatory agent.
Ibuprofen slows progression.

Ivacaftor and lumacaftor targets Cl- channels.

29
Q

What is the inheritance and defect in Duchenne Muscular Dystrophy?

A

Inheritance: X-linked recessive
Defect: Frameshift or nonsense mutation in DMD gene -> truncated or absent dystrophin protein -> myonecrosis

30
Q

What are the clinical features of Duchenne Muscular Dystrophy?

A

Onset < 5 years old.
Begins with pelvic girdle weakness and progresses superiorly
Calf pseudohypertrophy (muscles replaced by fatty tissues)
Gower sign (using upper extremities to help stand up)
Waddling gait

31
Q

How to confirm diagnosis of Duchenne?

A

Raised CK and aldolase

Confirm with genetic testing

32
Q

What is the difference between Duchenne and Becker muscular dystrophy?

A

Becker usually caused by non-frameshift mutations, is less severe, and onset in adolescence/early adulthood.

33
Q

What is the most common cause of death in Duchenne?

A

Dilated cardiomyopathy

34
Q

What is the inheritance and genetic defect in myotonic dystrophy?

A

Inheritance: AD

Genetic defect: CTG trinucleotide repeat

35
Q

Clinical features of myotonic dystrophy

A

Typically presents in middle age.

Facial appearance:

  • Bitemporal wasting
  • Weakness of facial muscle (leading to long haggard appearance)
  • Frontal balding
  • Ptosis

Profound muscle wasting and weakness:

  • Distal > proximal
  • Myotonic grip *****

Other features:

  • Cataracts
  • Intellectual disability
  • Gynaecomastia
  • Ovarian/testicular atrophy
  • Hyperglycaemia/DM
  • Cardiac arrhythmias or conduction defects
36
Q

What is the inheritance of Rett syndrome?

A

Sporadic. Seen almost exclusively in girls only.

37
Q

What are the clinical features of Rett syndrome?

A

Appears between 1-4 years old.

Developmental regression
Stereotyped hand-wringing ***
Ataxia
Seizures
Growth failure

USMLE Step 2 CK (6 decks)

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