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Vitamin A deficiency vs excess?
Answer: Deficiency: night blindness (nyctalopia), xerophthalmia, dry skin. Excess: teratogenic (do not give to pregnant women), pseudotumor cerebri, dry skin/hair.
Vitamin A (retinol) is a component of visual pigments and used for epithelial cell differentiation; isotretinoin (acne drug) is a vitamin A derivative and is teratogenic.
Vitamin D deficiency vs excess?
Answer: Deficiency: rickets (children) / osteomalacia (adults), hypocalcemic tetany. Excess: hypercalcemia, hypercalciuria, loss of appetite, stones.
Vitamin D increases intestinal Ca2+ and phosphate absorption; excess can be seen in granulomatous diseases like sarcoidosis (activated macrophages make 1-alpha-hydroxylase).
Vitamin E deficiency vs excess?
Answer: Deficiency: hemolytic anemia, ataxia, peripheral neuropathy (mimics vitamin B12 deficiency but no megaloblastic anemia). Excess: enhances warfarin's anticoagulant effect, risk of hemorrhage.
Vitamin E is an antioxidant that protects erythrocyte membranes from free-radical damage.
Vitamin K deficiency — findings and mechanism?
Answer: Neonatal hemorrhage, bleeding diathesis with increased PT and PTT; vitamin K is required to gamma-carboxylate (activate) clotting factors II, VII, IX, X and proteins C and S.
Deficiency occurs in newborns (sterile gut, poor placental transfer) or with warfarin therapy/antibiotics that kill gut flora.
Vitamin B1 (thiamine) deficiency — syndromes and cofactor role?
Answer: Causes Wernicke-Korsakoff syndrome (confusion, ophthalmoplegia, ataxia + confabulation, memory loss) and beriberi (wet = cardiac, dry = neuro); it is a cofactor for pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, transketolase, and branched-chain ketoacid dehydrogenase.
At-risk: alcoholics and malnourished patients; give thiamine before glucose to avoid precipitating Wernicke's.
Vitamin B2 (riboflavin) deficiency findings?
Answer: Cheilosis (inflammation of lips, scaling/fissures at corners of mouth) and corneal vascularization.
The 'Bs' of B2: Cheilosis, Corneal vascularization.
Vitamin B3 (niacin) deficiency — classic triad and special cause?
Answer: Pellagra: diarrhea, dermatitis, dementia (the 3 D's); can also be caused by Hartnup disease (decreased tryptophan absorption) or carcinoid syndrome (tryptophan diverted to serotonin).
Niacin can be synthesized from tryptophan; isoniazid can also cause niacin deficiency. Excess causes flushing.
Vitamin B5 (pantothenic acid) role and deficiency?
Answer: Component of coenzyme A and fatty acid synthase; deficiency is rare but can cause dermatitis, enteritis, alopecia, adrenal insufficiency.
Vitamin B6 (pyridoxine) deficiency — causes and findings?
Answer: Peripheral neuropathy (classically from isoniazid therapy), sideroblastic anemia, convulsions; it's a cofactor in transamination, decarboxylation, and heme synthesis reactions.
Isoniazid inhibits pyridoxine kinase, so B6 is co-administered with INH.
Vitamin B7 (biotin) deficiency — cause and findings?
Answer: Dermatitis, alopecia, and enteritis; classically caused by eating raw egg whites (avidin binds biotin) or antibiotic use.
Biotin is a cofactor for carboxylation reactions (e.g., pyruvate carboxylase, acetyl-CoA carboxylase).
Vitamin B9 (folate) deficiency — findings and clinical importance?
Answer: Macrocytic, megaloblastic anemia and neural tube defects in the fetus; no neurologic symptoms (unlike B12 deficiency).
Folate is required for one-carbon transfers/DNA synthesis; supplementation is recommended for women of childbearing age.
Vitamin B12 (cobalamin) deficiency — findings?
Answer: Macrocytic, megaloblastic anemia plus neurologic symptoms (subacute combined degeneration — demyelination of dorsal columns, lateral corticospinal tracts, spinocerebellar tracts).
Causes include pernicious anemia (lack of intrinsic factor), strict veganism (slow onset due to liver stores), and Diphyllobothrium latum infection.
Vitamin C deficiency and function?
Answer: Scurvy: swollen gums, bruising, poor wound healing, corkscrew hairs, hemarthrosis. Vitamin C is required for hydroxylation of proline and lysine in collagen synthesis and is an antioxidant.
Also enhances dietary iron absorption by reducing Fe3+ to Fe2+.
Tay-Sachs disease: enzyme, inheritance, accumulated substrate, classic finding?
Answer: Enzyme: hexosaminidase A. Inheritance: autosomal recessive. Substrate: GM2 ganglioside. Finding: cherry-red spot on macula, progressive neurodegeneration, NO hepatosplenomegaly.
Higher frequency in Ashkenazi Jewish population; absence of hepatosplenomegaly distinguishes from Niemann-Pick.
Niemann-Pick disease: enzyme, inheritance, substrate, classic finding?
Answer: Enzyme: sphingomyelinase. Inheritance: autosomal recessive. Substrate: sphingomyelin. Finding: hepatosplenomegaly, cherry-red spot, foam cells (lipid-laden macrophages).
Distinguished from Tay-Sachs by presence of hepatosplenomegaly.
Fabry disease: enzyme, inheritance, substrate, classic finding?
Answer: Enzyme: alpha-galactosidase A. Inheritance: X-linked recessive. Substrate: ceramide trihexoside. Finding: peripheral neuropathy of hands/feet, angiokeratomas, cardiovascular/renal disease.
One of the few X-linked recessive (not AR) lysosomal storage diseases.
Krabbe disease: enzyme, inheritance, substrate, classic finding?
Answer: Enzyme: galactocerebrosidase. Inheritance: autosomal recessive. Substrate: galactocerebroside. Finding: peripheral neuropathy, destruction of oligodendrocytes, optic atrophy, globoid cells.
Gaucher disease: enzyme, inheritance, substrate, classic finding?
Answer: Enzyme: glucocerebrosidase (beta-glucosidase). Inheritance: autosomal recessive. Substrate: glucocerebroside. Finding: hepatosplenomegaly, aseptic necrosis of femur, bone crises, Gaucher cells (macrophages that look like crumpled tissue paper).
Most common lysosomal storage disease.
Metachromatic leukodystrophy: enzyme, inheritance, substrate, classic finding?
Answer: Enzyme: arylsulfatase A. Inheritance: autosomal recessive. Substrate: cerebroside sulfate (sulfatides). Finding: central and peripheral demyelination with ataxia and dementia.
Hurler syndrome: enzyme, inheritance, substrate, classic finding?
Answer: Enzyme: alpha-L-iduronidase. Inheritance: autosomal recessive. Substrate: heparan sulfate and dermatan sulfate. Finding: corneal clouding, developmental delay, gargoylism (coarse facial features).
A mucopolysaccharidosis.
Hunter syndrome: enzyme, inheritance, classic finding, and how it differs from Hurler?
Answer: Enzyme: iduronate sulfatase. Inheritance: X-linked recessive. Finding: mild Hurler-like features plus aggressive behavior, but NO corneal clouding.
Mnemonic: Hunters need to see (no corneal clouding) and aim (aggressive); X-linked.
Von Gierke disease (GSD type I): enzyme and classic findings?
Answer: Enzyme: glucose-6-phosphatase. Severe fasting hypoglycemia, lactic acidosis, hepatomegaly, hyperuricemia, hyperlipidemia (increased glycogen and fat in liver).
Glucose-6-phosphatase is needed for the last step of gluconeogenesis/glycogenolysis to release free glucose.
Pompe disease (GSD type II): enzyme and classic findings?
Answer: Enzyme: lysosomal alpha-1,4-glucosidase (acid maltase). Cardiomegaly, hypertrophic cardiomyopathy, systemic findings, and early death.
Pompe trashes the Pump (heart, liver, muscle) — the only GSD that's a lysosomal storage disease.
Cori disease (GSD type III): enzyme and how it differs from Von Gierke?
Answer: Enzyme: debranching enzyme (alpha-1,6-glucosidase). Milder than Von Gierke disease; gluconeogenesis is intact, so fasting hypoglycemia is less severe.
McArdle disease (GSD type V): enzyme and classic findings?
Answer: Enzyme: skeletal muscle glycogen phosphorylase (myophosphorylase). Painful muscle cramps, myoglobinuria, and arrhythmia with strenuous exercise; increased glycogen in muscle but cannot break it down.
'McArdle = Muscle' — affects muscle, not liver, so no hypoglycemia.
Phenylketonuria (PKU): enzyme deficient, inheritance, classic findings, treatment?
Answer: Enzyme: phenylalanine hydroxylase (or deficient tetrahydrobiopterin/BH4 cofactor). Autosomal recessive. Findings: intellectual disability, growth retardation, fair skin, eczema, musty body odor. Treatment: decrease phenylalanine, increase tyrosine in diet.
PAH converts phenylalanine to tyrosine; without it phenylalanine accumulates and is shunted to phenylketones.
Alkaptonuria: enzyme, inheritance, classic findings?
Answer: Enzyme: homogentisate oxidase. Autosomal recessive, generally benign. Findings: dark connective tissue, black urine on standing/exposure to air, and debilitating arthralgias (ochronosis).
Blocked in the tyrosine degradation pathway, causing homogentisic acid to accumulate.
Homocystinuria: enzyme, inheritance, classic findings, treatment?
Answer: Enzyme: cystathionine beta-synthase (classic cause). Autosomal recessive. Findings: lens subluxation (downward), intellectual disability, osteoporosis, and thrombosis/atherosclerosis. Treatment: decrease methionine, increase cysteine, increase B12 and folate in diet.
Can also be caused by decreased affinity of cystathionine synthase for pyridoxal phosphate (responsive to vitamin B6).
Maple syrup urine disease: enzyme, inheritance, classic findings?
Answer: Enzyme: branched-chain alpha-ketoacid dehydrogenase. Autosomal recessive. Blocks degradation of branched-chain amino acids (isoleucine, leucine, valine), causing CNS defects and urine that smells like maple syrup/burnt sugar.
Mnemonic: 'I Love Vermont maple syrup' (Ile, Leu, Val).
Ornithine transcarbamylase (OTC) deficiency: inheritance, mechanism, and lab findings?
Answer: X-linked recessive (most common urea cycle disorder). Excess carbamoyl phosphate is converted to orotic acid instead of entering the urea cycle. Findings: hyperammonemia, increased orotic acid in blood/urine, DECREASED BUN; no megaloblastic anemia.
Contrast with hereditary orotic aciduria (UMP synthase deficiency), which has increased orotic acid but NO hyperammonemia and megaloblastic anemia that does not respond to B12/folate.
Lesch-Nyhan syndrome: enzyme, inheritance, classic findings?
Answer: Enzyme: HGPRT (hypoxanthine-guanine phosphoribosyltransferase) deficiency. X-linked recessive. Findings: hyperuricemia/gout, intellectual disability, self-mutilation, dystonia, choreoathetosis.
HGPRT normally salvages purines; its absence causes excess uric acid production via de novo purine synthesis.
Adenosine deaminase (ADA) deficiency — consequence?
Answer: Causes one form of severe combined immunodeficiency (SCID); excess ATP and dATP accumulate and are toxic to lymphocytes, causing lack of both B and T cell maturation.
One of the few causes of SCID that is primarily a biochemical/metabolic defect.
Hereditary orotic aciduria: enzyme, inheritance, findings, and key distinguishing feature?
Answer: Enzyme: UMP synthase (orotate phosphoribosyltransferase/orotidylate decarboxylase). Autosomal recessive. Findings: increased orotic acid in urine, megaloblastic anemia that does NOT improve with B12 or folate, failure to thrive; NO hyperammonemia.
Distinguishes it from OTC deficiency, which causes hyperammonemia along with increased orotic acid.
Ehlers-Danlos syndrome — defect and classic findings?
Answer: Defective collagen synthesis/structure (commonly type III collagen; vascular type involves type V/COL3A1). Findings: hyperextensible skin, joint hypermobility, easy bruising/bleeding, and risk of organ/vessel rupture and berry aneurysms.
Several subtypes exist with different collagen gene defects and severity.
Osteogenesis imperfecta — defect, inheritance, classic findings?
Answer: Defective type I collagen synthesis (most common form: decreased amount of otherwise normal collagen). Autosomal dominant. Findings: multiple fractures with minimal trauma, blue sclerae (thin connective tissue reveals underlying choroidal veins), hearing loss, and dental imperfections.
'Brittle bone disease'; can mimic child abuse on presentation.
Marfan syndrome — defect, inheritance, classic findings?
Answer: Mutation in fibrillin-1 (FBN1 gene), which normally scaffolds elastin. Autosomal dominant. Findings: tall stature with long extremities, pectus excavatum, hypermobile joints, lens subluxation (upward and temporally), aortic root dilation/dissection, mitral valve prolapse.
Fibrillin defect leads to excess activation of TGF-beta signaling, weakening connective tissue.
Xeroderma pigmentosum — defective repair pathway, inheritance, classic findings?
Answer: Defective nucleotide excision repair (cannot repair UV-induced thymidine dimers). Autosomal recessive. Findings: extreme photosensitivity, dry skin with early skin freckling/pigmentation changes, and high risk of skin cancer.
Ataxia-telangiectasia — defective gene/pathway, inheritance?
Answer: Defective ATM gene, which encodes a kinase involved in detecting and repairing double-stranded DNA breaks. Autosomal recessive. Findings: cerebellar ataxia, spider angiomas (telangiectasias), immunodeficiency, and increased cancer risk.
Hereditary nonpolyposis colorectal cancer (Lynch syndrome) — defective repair pathway, inheritance?
Answer: Defective DNA mismatch repair. Autosomal dominant. Markedly increased risk of colorectal cancer (typically proximal colon) without extensive polyp formation, and increased risk of endometrial/ovarian cancer.
Bloom syndrome — defect, inheritance, classic findings?
Answer: Defective DNA helicase (BLM gene), leading to genomic instability. Autosomal recessive. Findings: short stature, photosensitivity, and increased risk of malignancy.
What are the trinucleotide repeat expansions and inheritance for Fragile X, Huntington disease, myotonic dystrophy, and Friedreich ataxia?
Answer: Fragile X: CGG repeat in FMR1 gene, X-linked. Huntington disease: CAG repeat, autosomal dominant. Myotonic dystrophy: CTG repeat, autosomal dominant. Friedreich ataxia: GAA repeat in frataxin gene, autosomal recessive.
Mnemonic: 'Try hunting for my fried eggs' — Try(nucleotide) Hunting(ton CAG) for(ragile X CGG) My(otonic dystrophy CTG) Fried(reich GAA) eggs.
Fragile X syndrome — classic clinical findings?
Answer: Macroorchidism (enlarged testes), long face with large jaw, large everted ears, autism spectrum features, mitral valve prolapse; second most common cause of genetic intellectual disability (after Down syndrome).
CGG repeat expansion causes hypermethylation and silencing of the FMR1 gene.
Huntington disease — classic clinical findings and pathology?
Answer: Chorea, behavioral/personality changes, and dementia, typically presenting in the 30s-40s; caused by atrophy of the caudate nucleus (loss of GABAergic/ACh neurons) with cerebral atrophy.
Exhibits anticipation (repeat expands and disease worsens/presents earlier in successive generations), especially with paternal transmission.
Myotonic dystrophy — classic clinical findings?
Answer: Myotonia (sustained muscle contraction, delayed relaxation), progressive muscle wasting, frontal balding, cataracts, and cardiac arrhythmias.
Friedreich ataxia — mechanism and classic clinical findings?
Answer: GAA repeat expansion in the frataxin gene impairs mitochondrial iron metabolism/function. Findings: ataxia, loss of vibratory/proprioceptive sense, hypertrophic cardiomyopathy (common cause of death), diabetes mellitus, and kyphoscoliosis.
Unlike the other trinucleotide repeat disorders, it does not typically show anticipation and is autosomal recessive (intronic repeat, not in a coding exon).
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