PA10.1-5,PA11.1-3,PA12.1-3 | Infections, Genetic & Environmental Disease — Glossary

Host cell receptor used by SARS-CoV-2 spike protein for cellular entry; expressed on type II pneumocytes, enterocytes, endothelial cells, and renal tubular cells, explaining multi-organ tropism.

Lysosomal enzyme that degrades glycogen within lysosomes; deficiency causes Pompe disease, uniquely bridging the categories of glycogen storage disease and lysosomal storage disorder.

Cytokine secreted by adipose tissue; includes leptin (appetite regulation), adiponectin (insulin sensitisation, anti-inflammatory), TNF-α, IL-6, and resistin (pro-inflammatory, insulin resistance).

An anti-inflammatory, insulin-sensitising adipokine that is paradoxically low in obesity; its reduction removes a key brake on insulin resistance and systemic inflammation, contributing to metabolic syndrome.

Deviation from the normal diploid chromosome number (46 in humans), resulting from non-disjunction during meiosis or mitosis; trisomy (47) and monosomy (45) are the two principal forms.

Aggregates of ribosomal RNA visible as blue granules in red blood cells on Giemsa-stained peripheral blood smear; characteristic of lead poisoning (and also seen in thalassaemia and sideroblastic anaemia).

Thiamine (Vitamin B1) deficiency disease; wet beriberi presents as high-output cardiac failure; dry beriberi as peripheral polyneuropathy; both result from impaired pyruvate dehydrogenase activity.

Severe complication of P. falciparum malaria characterised by massive intravascular haemolysis, haemoglobinuria (dark urine), and acute tubular necrosis.

Haemoglobin bound to carbon monoxide instead of oxygen; CO has 250× the affinity of O₂ for haemoglobin, reducing oxygen delivery to tissues and contributing to tobacco-related cardiovascular disease.

Destruction of respiratory bronchioles in the central acinus, sparing peripheral alveoli; the pattern most strongly associated with cigarette smoking; results from elastase-mediated alveolar wall destruction.

Life-threatening complication of P. falciparum infection; caused by sequestration of infected RBCs in cerebral capillaries leading to ring haemorrhages (Dürck's granulomas), coma, and raised intracranial pressure.

Hexagonal bipyramidal crystals formed from eosinophil granule proteins (galectin-10/Charcot–Leyden crystal protein); found in tissues, stool, and sputum where eosinophils have degranulated; associated with helminthic infections and allergic conditions.

Fundoscopic finding in Tay-Sachs disease (and other neuronal storage disorders) in which the fovea appears bright red because the surrounding retinal ganglion cells, laden with GM2 ganglioside, appear pale; the thin fovea lacks ganglion cells, allowing the vascular choroid colour to show through.

Normal tissue present at an anatomically abnormal location (e.g., gastric mucosa in Meckel's diverticulum); a developmental anomaly, not a neoplasm.

Chromosomal deletion syndrome caused by loss of the short arm of chromosome 5 (5p-); hallmark is a high-pitched, cat-like cry in infancy due to laryngeal hypoplasia; associated with microcephaly and intellectual disability.

The larval (bladder worm) stage of Taenia solium; a translucent fluid-filled cyst (0.5–2 cm) containing an invaginated scolex; forms in intermediate hosts (human or pig) after egg ingestion.

Dysregulated, overwhelming systemic inflammatory response characterised by excessive production of pro-inflammatory cytokines (IL-6, TNF-α, IL-1β); causes multi-organ damage; a major mechanism of severe COVID-19.

Fibrin degradation product released when cross-linked fibrin is cleaved by plasmin; elevated in any state of active clot formation and lysis; markedly elevated in COVID-19 coagulopathy, correlating with microthrombus formation and mortality.

The pathological substrate of ARDS; caused by injury to type I and type II pneumocytes; characterised by exudative phase (hyaline membranes, oedema) followed by proliferative phase (type II pneumocyte hyperplasia, fibrosis).

Molecular cytogenetic technique using fluorescent DNA probes complementary to specific chromosomal loci to detect microdeletions, amplifications, or translocations with ~100 kb resolution, finer than standard karyotyping.

Modified acid-fast stain (Fite–Faraco method) used to demonstrate Mycobacterium leprae in tissue sections; uses milder decolourisation than Ziehl–Neelsen, as M. leprae is partially acid-fast and would be over-decolourised by standard ZN.

Alternating light and dark transverse bands on hair in kwashiorkor, reflecting alternating periods of protein deficiency (light, depigmented bands) and adequate nutrition (dark, pigmented bands).

True rosette in retinoblastoma in which tumour cells surround a central lumen (pseudo-lumen), recapitulating photoreceptor differentiation; distinguishes retinoblastoma from other SRBCTs.

Distended macrophages with abundant pale cytoplasm showing a 'crinkled tissue paper' or 'wrinkled silk' appearance due to accumulation of glucocerebroside fibrils; found in bone marrow, liver, and spleen in Gaucher disease.

Lysosomal enzyme (acid β-glucosidase) that cleaves glucose from glucocerebroside; its deficiency causes Gaucher disease, the most common lysosomal storage disorder.

Insoluble dark-brown crystalline byproduct of haemoglobin digestion by Plasmodium; accumulates in macrophages of spleen, liver, and brain; visible on Giemsa stain.

Tumour-like malformation consisting of disorganised but tissue-type-appropriate elements native to the site; grows proportionally with the body and does not metastasise; not a true neoplasm.

Leprosy; a chronic granulomatous infection caused by Mycobacterium leprae affecting peripheral nerves and skin macrophages; the clinical spectrum is entirely determined by host cell-mediated immunity.

Lysosomal enzyme responsible for degrading GM2 ganglioside; deficiency of its α-subunit causes Tay-Sachs disease, while deficiency of both α- and β-subunits causes Sandhoff disease.

Arrangement of neuroblastoma tumour cells around a central core of neuropil (fibrillary processes) without a true lumen; indicative of neuronal differentiation.

X-linked recessive MPS caused by iduronate sulphatase deficiency; phenotypically similar to Hurler but milder, without corneal clouding; survival into adulthood possible.

Autosomal recessive MPS caused by α-L-iduronidase deficiency; features include gargoyle facies, corneal clouding, hepatosplenomegaly, gibbus deformity, and severe intellectual disability; fatal in childhood without treatment.

Eosinophilic, glassy membranes lining alveolar walls in the exudative phase of diffuse alveolar damage (DAD); composed of precipitated plasma proteins and fibrin; hallmark of ARDS.

Low serum albumin (<3.5 g/dL); in kwashiorkor, caused by impaired hepatic synthesis due to protein deficiency, leading to reduced oncotic pressure and generalised oedema.

Negative staining technique where Indian (China) ink particles are excluded by the mucopolysaccharide capsule of Cryptococcus neoformans, creating a clear halo around the organism on a dark background in CSF; rapid screening test for cryptococcal meningitis.

Reduced responsiveness of target tissues (muscle, liver, adipose) to insulin; caused in obesity by inflammatory adipokines, excess free fatty acids, and ectopic fat deposition; drives hyperinsulinaemia, T2DM, and dyslipidaemia.

Softening and ulceration of the cornea due to severe Vitamin A deficiency; a leading preventable cause of childhood blindness in low-income countries.

A form of protein-calorie malnutrition caused by protein deficiency despite relatively adequate calorie intake; characterised by hypoalbuminaemia-driven oedema, fatty liver, flaky-paint dermatitis, and flag sign in hair.

Foamy macrophages in lepromatous leprosy packed with intact Mycobacterium leprae organisms (globi); macrophages have abundant foamy cytoplasm because they cannot kill the intracellular bacilli.

Skin test using killed M. leprae antigen (Mitsuda antigen); measures cell-mediated immunity (Th1 response); strongly positive in tuberculoid leprosy, negative in lepromatous; NOT a diagnostic test for active leprosy.

A state in which elevated circulating leptin fails to suppress appetite or increase energy expenditure despite intact leptin production; analogous to insulin resistance; key contributor to the pathogenesis of obesity.

White pupillary reflex (cat's eye reflex) in a young child, classically caused by retinoblastoma; also occurs in persistent fetal vasculature and cataracts; an ophthalmologic emergency.

A group of inherited metabolic disorders caused by deficiency of a lysosomal enzyme, leading to intralysosomal accumulation of undegraded substrate (lipid, glycoprotein, or glycosaminoglycan) and progressive organ dysfunction.

Severe malnutrition from total calorie and protein deprivation; characterised by extreme wasting of muscle and fat with a paradoxically preserved alertness and absence of oedema.

A cluster of cardiometabolic risk factors — central obesity plus any two of raised triglycerides, reduced HDL, raised blood pressure, and raised fasting glucose — driven by visceral adiposity and insulin resistance.

A family of lysosomal storage disorders caused by deficient degradation of glycosaminoglycans (heparan, dermatan, keratan sulphate); characterised by coarse facies, organomegaly, skeletal dysplasia, and (in some subtypes) intellectual disability.

Forms of leprosy with high bacterial load (BI 2–6); includes borderline lepromatous (BL) and lepromatous (LL); reflects weak/absent cell-mediated immunity and Th2 dominance.

Proto-oncogene on chromosome 2p24 whose amplification (>10 copies) in neuroblastoma confers high-risk disease and poor prognosis by driving uncontrolled cell proliferation.

Eosinophilic intracytoplasmic inclusion bodies found in neurons (especially hippocampal Purkinje cells) of rabies-infected brain; pathognomonic of rabies on histology; composed of viral nucleocapsid.

Infection of the central nervous system with Taenia solium larvae (cysticerci); the most common helminthic CNS infection and a leading cause of adult-onset acquired epilepsy in endemic regions.

Hepatic steatosis not due to alcohol; driven by excess free fatty acids from visceral fat in insulin-resistant individuals; spectrum from steatosis → NASH (steatohepatitis with inflammation) → cirrhosis.

Failure of homologous chromosomes (meiosis I) or sister chromatids (meiosis II) to separate correctly during cell division, producing aneuploid gametes or cells.

Repetitive upper airway obstruction during sleep due to pharyngeal fat deposition in obesity; causes chronic hypoxia and sleep fragmentation; itself worsens insulin resistance, creating a bidirectional link with metabolic syndrome.

The adult equivalent of rickets; Vitamin D deficiency causes softening of already-formed bone due to inadequate mineralisation of osteoid; presents with bone pain, proximal myopathy, and Looser zones on X-ray.

The ability of a microorganism to cause disease in a susceptible host, determined by virulence factors such as adhesins, toxins, and capsule.

Forms of leprosy with few or no demonstrable AFB on slit-skin smear (BI 0–1); includes tuberculoid (TT) and some borderline tuberculoid (BT) cases; reflects a strong Th1 immune response.

Niacin (Vitamin B3) deficiency disease characterised by the 3 Ds: photosensitive Dermatitis (Casal's necklace), Diarrhoea (with glossitis), and Dementia; common in maize-dependent populations.

Plasmodium falciparum erythrocyte membrane protein 1; expressed on surface knobs of infected RBCs; mediates cytoadherence to endothelium, causing sequestration in deep capillaries.

Particulate matter with aerodynamic diameter ≤2.5 μm; small enough to penetrate deep alveoli, trigger inflammation, and enter the bloodstream, causing both pulmonary and cardiovascular disease.

Lysosomal glycogen storage disease caused by acid maltase (α-glucosidase) deficiency; glycogen accumulates in cardiac and skeletal muscle lysosomes, causing fatal hypertrophic cardiomyopathy and hypotonia in the infantile form.

The pathophysiological mechanism of emphysema: tobacco smoke activates macrophages and neutrophils that release elastase and matrix metalloproteinases, overwhelming α₁-antitrypsin and other inhibitors, destroying alveolar walls.

Vitamin D deficiency in children causing failure of osteoid mineralisation; skeletal manifestations include bowing of weight-bearing bones, rachitic rosary, Harrison's sulcus, and craniotabes.

Fusion of two acrocentric chromosomes (13, 14, 15, 21, 22) at their centromeres with loss of short arms; balanced carriers are phenotypically normal but risk unbalanced offspring (e.g., familial Down syndrome with t(14;21)).

Molecular diagnostic test that detects viral RNA by converting it to cDNA and amplifying specific sequences; gold standard for COVID-19 diagnosis from nasopharyngeal swab specimens.

Vitamin C deficiency disease caused by failure of collagen synthesis (impaired hydroxylation of proline/lysine); hallmarks include perifollicular haemorrhages, corkscrew hairs, bleeding gums, and subperiosteal haemorrhages.

A group of paediatric malignancies characterised histologically by sheets of small, primitive-appearing cells with scant cytoplasm and round hyperchromatic nuclei; includes neuroblastoma, Wilms, retinoblastoma, Ewing sarcoma, and rhabdomyosarcoma.

The infective stage of Plasmodium injected by the Anopheles mosquito; travels to the liver to begin the hepatic (pre-erythrocytic) stage.

Bilateral fibrous streaks replacing the gonads in Turner syndrome; histologically show fibrostromal tissue without follicles; cause hypergonadrotropic hypogonadism and primary amenorrhoea.

Periportal fibrosis pattern seen in chronic hepatosplenic schistosomiasis (S. mansoni/japonicum); pale, thickened portal tracts resembling clay pipe stems on gross pathology; caused by granulomatous reaction to schistosome eggs in portal venules.

Mutation type in which a short DNA triplet motif (e.g., CAG in Huntington, CGG in Fragile-X) is amplified beyond a threshold copy number across generations (anticipation), silencing the gene or producing a toxic protein.

Pathognomonic pattern of Wilms tumour comprising three components reflecting arrested nephrogenesis: blastemal cells (small round blue cells), stromal cells (spindle cells/fibromuscular), and epithelial cells (tubules and glomeruloid structures).

Knudson's model for tumour suppressor gene inactivation: both alleles must be lost for cancer to develop; in hereditary retinoblastoma the first hit is germline and the second is somatic, producing bilateral/multifocal disease.

The degree or measure of a pathogen's ability to cause disease; a highly virulent organism causes severe disease at a low inoculum.

Glycogen storage disease caused by glucose-6-phosphatase deficiency; characterised by severe fasting hypoglycaemia, hepatomegaly, lactic acidosis, and doll-like facies due to glycogen and fat accumulation in liver and kidney.

Acute thiamine-deficiency syndrome characterised by the triad of confusion, ophthalmoplegia, and ataxia; pathology shows haemorrhagic necrosis of mamillary bodies and periaqueductal grey; medical emergency treatable with IV thiamine.

Wilms tumour suppressor gene on chromosome 11p13 encoding a zinc-finger transcription factor essential for normal kidney and gonadal development; biallelic loss predisposes to nephroblastoma.

Dryness and thickening of the conjunctiva and cornea due to Vitamin A deficiency; squamous metaplasia replaces goblet cells, progressing through Bitot's spots to keratomalacia if untreated.