Usmle Biochem Diseases

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Orotic Aciduria

Back 1

Defect in Orotic Acid Phosphoribosyl Transverase

Higher orotic acid in urine --> megaloblastic anemia (not treatable with B12 or folate) and failure to thrive

Treat w/ oral uridine

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Adenine Deaminase Deficiency

Back 2

ADA in purine salvage pathway

Causes SCID (2nd most common)

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Lesch-Nyhan Syndrome

Back 3

Defect: HGPRT (XLR)

Lab: Increase uric acid production

Sx:Gout, chreoathetosis, retardation, selfmutilation, agression, hyperuricemia

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Xeroderma Pigmentosum

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Defect in Endonuclease = defect in Nucleotide Excision repair or Base Excision repair

See: Dry skin w/ melanoma and other cancers ->cant repair UV damage

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Hereditary Nonpolyposis colorectal Cancer (HNPCC)

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Defect: Mismatch repair --> proofreading ability defective

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I Cell Disease (Inclusion cell disease)

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Lysosomal Storage D/O

Defect: failure of adding mannose-6-P to lysozyme proteins

Sx: coarse facial features, clouded corneas, restricted joint movemnt, high plasma levels of lysozyme enzymes

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Chediak-Higashi Syndrome

Back 7

Defect: in MT polymerization
--> cant phagocytize

Sx:
Recurrent pyogenic infections, partial albinism, peripheral neuropathy

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Kartagener's Syndrome

Back 8

Defect in Dynein Arm --> immotile cilia

Sx:
Male and femal infertility
Bronchiectasis
Recurrent sinusistis

*Associated w/ sinus invertus

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Ehlers-Danlos Syndrome

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Defect: forming lysine crosslinks during collagen synthesis (mostly Type III)

Causes:
-Hyperextensible skin
-Hypermobile joints
-Tendency to bleed (bruise easily)

Assoc w/ joint dislocation, berry aneurysms, organ ruptures

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Osteogenesis Imperfecta

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AD
Defect: in forming triple helix of procollagen (mostly Type I)

Results in:
Multiple Fractures
Blue Sclerae
Hearing loss
Dental imperfections

Type II is fatal in utero

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Alports Syndrome

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XLR
Defect: Abnormal type IV collagen

Results:
-Progressive hereditary nephritis
-Deafness

Assoc w/ ocular disturbances

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Marfans Syndrome

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AD
Defect: mutation in Fibrillin gene

Sx: tall long extremities, pectus excavatum, hyperextensive joints, long, tapering fingers and toes, cystic medial necrosis of aorta, floppy mitral valve, subluxation of lenses

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Emphysema

Back 13

alpha1-antitrypsin deficency --> cant inhibit the breakdown of elastin

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Prader Willi Syndrome

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Deletion of normal active Paternal allele on Chromosome 15

Sx: Mental retardation,hyperphagia, obesity, hypogonadism, hypotonia

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Angelman Syndrome

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Deletion of normally active Maternal gene on Chromosome 15

Sx: Mental retardation, seizures, inappropriate laughter, ataxia

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Hypophosphatemic Rickets

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Inherited disorder--> Phophate wasting at proximal tubule

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Leber's hereditary Optic neuropathy

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Degeneration of retinal ganglion gells and axons
- Mitochondrial Inheritance

Sx: Acute loss of central vision (bilaterally)

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Mitochondrial Myopathies

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Mitochondrial Inheritance
-MELAS = Mitochondrial Encephalomyopathies w/ Lactic Acidosis and Stroke-like symptoms

- Myoclonic epilepsy w/ Ragged Red fibers

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Achondroplasia

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AD
Defect: FGF receptor 3

Sx: Dwarfism (short limbs, but head and trunk normal)

Assoc. w/ advanced paternal age

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Autosomal Dominant Polycystic Kidney disease (ADPKD)

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AD
Defect: Mutation in APKD1 (chromosome 16)

Bilateral massive kidneys w/ cysts

Sx: flank pain, hematuria, HTN, progressive renal failure

Assoc. w/ Polycystic liver disease, berry aneurysm*, mitral valve prolapse

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Familial Adematous Polyposis

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AD
Defect: deletion on chrom 5 (APC gene)

Colon becomes covered w/ adematous polyps after puberty

Progresses to colon cancer

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Familial Hypercholesterolemia (Hyperlipidemia type IIa)

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AD
Defect: LDL receptor --> increase in LDL levels

Sx: Severe atherosclerotic disease early in life, tendon xanthomas, may have MI before age 20

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Hereditary Hemorrhagic Telangectasia

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AD
Defect: Blood vessel disorder

Sx: Teleangectasia, recurrent epistaxis, skin discolorations, AV malformations

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Hereditary Spherocytosis

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AD
Defect: spectrin or ankyrin

Sx: hemolytic anemia (increase MCHC)

Tx: Splenectomy

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Huntingtons Disease

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AD
Defect: CAG repeat on Chrom 4

Sx: depression, progressive dementia, choreiform movements,caudate atrophy, decrease levels of GABA and ACh in brain

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Neurofibromatosis Type 1

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AD
Defect: on long arm of Chrom 17

Sx: cafe-au-laits spots, neural tumors, Lisch nodules

Assoc. w/ skeletal d/o, optic pathway gliomas, pheochromocytomas, increase tumors

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NF Type 2

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AD
Defect in NF2 gene on chrom 22

Sx: bilateral acoustic neuromas, juvenile cataracts

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Tuberosclerosis

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AD - incomplete penetrance

Sx: facial lesions, hypopigmented "ash leaf spots" on skin,angiomyolipomas, cardiac rhabdomyomas, increase incidence of astrocytomas

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Von Hippel-Lindau

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AD
Defect: Deletion of VHL gene on chromosome 3

Sx: hemangioblastomas of retina/cerebellum/medulla, 1/2 affected w/ mutiple bilateral renal cell carcinomas

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interesar

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to interest

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Cystic Fibrosis

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AR
Defect: mutation on CFTR gene on chromosome 7 (mostly deletion of Phe 508)

Sx: Secretion of abnormally thick mucous due to defect Cl- channel

Tx: N-acetylcysteine

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Duchennes Muscular Dystrophy

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Xlinked

Defect: Frameshift mutation --> deletion of dystrophin gene


Sx: weakness starting in pelvic girdle --> superiorly, pseudohypertrophy of calf muscles, Gowers maneuvers

Dx: increase CPK and muscle biopsy

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Beckers Muscular Dystrophy

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X link
Defect: mutation in dystrophin gene

Not as severe as Duchennes MD

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Fragile X syndrome

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X-linked
Defect: Trinucleotide repeat = CGG --> defect in methylation and expression of FMR1 gene

Sx: eXrta large testes, jaw, ears, mental retardation (2nd most common)

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Cri-du-chat Syndrome

Back 35

Microdeletion of short arm of Chrom 5

Sx: microcephaly, mod to sev mental retardation, high pitched crying, epicanthal folds, cardiac abnlties

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Williams Syndrome

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Congenital microdeltion of long arm of chromosome 7 (deleted region includes elastin gene)

Sx: distinctive elfin facies, mental retardation, hyperCa, well-developed verbal skills, extreme friendliness w/ strangers, Cardiovascular probs

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Glycolytic Enzyme Deficiency

Back 37

Hemolytic anemia


Rememeber: RBCs depend solely on glycolysis for energy - cant maintain NaK pump --> lysis

Front 38

Pyruvate Dehydrogenase Deficiency

Back 38

Backup of substrate --> lactic acidosis

Sx: neuro defects
Tx: increase intake of ketogenic nutrients (Lys and Leu) --> ketogenesis

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G6PD deficiency

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XLR

Cant form NADPH in RBCs --> hemolytic anemia due to poor RBC defense against oxidizing agents

See: Heinz bodies and Bite cells

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Fructose Intolerance

Back 40

AR
Defiency of aldolase B

Sx: hypoglycemia, jaundice, cirrhosis, vomiting
Tx: Decrease intake of fructose and sucrose

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Essential Fructosuria

Back 41

AR
Defect in fructokinase --> benign ASx condition

Sx: Elevated Fructose in blood and urine

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Classic Galactosemia

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AR
Absence of galactose-1-P uridytransferase

Sx: Failure to thrive, jaundice, hepatomegaly, infantile cataracts (due to accumulation of galactitol in eye), mental retardation

Tx: Exclude galactose and lactose in diet

Front 43

Galactokinase deficiency

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AR
Deficient in Galactokinase

Sx: more mild --> elevated galactose in blood and urine, infantile cataracts, may present as failure to tract objects or develop a social smile

Front 44

Ornithine Transcarbamoylase (OTC) deficiency

Back 44

XLR
Defect: Cant eliminate ammonia

Sx: Orotic Acid in blood and urine, low BUN, Sx of hyperammonemia

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Phenylketouria

Back 45

Defect in phenyalanine hydroxylase or its cofactor BH4

Sx: Mental retardation, growth retardation, seizures, fair skin, eczema, mousy body odor

Tx: decrease phenylalanine and increase tyrosine

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Alkaptonuria (Ochronosis)

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AR
Deficiency in homogentisic acid oxidase (degradative pathyway of tyrosine)

Sx: Dark CT, pigmented sclera, **urine turns black on standing

Front 47

Albinism

Back 47

Defiency of tyrosinase (AR) or defective tyrosine transporter --> decrease amount of melanin

*ex: of locus heterogeneity
Can be XLR (ocular albinism)
Can be a result of lack of neural crest migration

Front 48

Homocystinuria

Back 48

AR
3 forms: Cystathionine synthase deficiency, decrease affinity of cystathionine synthase for Pyridoxal phosphate, Homocysteine transferase deficiency

Sx: high homocysteine in urine, **mental retardation, osteoperosis, tall stature, kyphosis, lens subluxation, **atherosclerosis

Front 49

Cystinuria

Back 49

AR
Defect of renal tubular amino acid transporter in PCT of kidneys

XS cysteine in urine --> cystine kidney stones

Front 50

Maple Syrup Urine Disease

Back 50

Defect: Decrease a-ketoacid dehydrogenase --> cant degrade branched amino acids (Isoleucine, Leucine, Valine)

Sx: Severe CNS defects, mental retardation, death

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Hartnup Disease

Back 51

AR
Defective neutral amino acid transporter on renal and intestinal epithelial cells

Sx: Increase tryptophan excretion in urine --> PELLAGRA; rashes, neuro probs