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PA10.1-5,PA11.1-3,PA12.1-3 | Infections, Genetic & Environmental Disease — Graded Quiz
Graded
12 questions · Untimed · 2 attempts
Click any question card to reveal the correct answer.
A 7-year-old child from a P. falciparum–endemic district develops sudden-onset confusion, seizures, and decerebrate posturing 3 days after fever onset. Blood glucose is 1.8 mmol/L. Peripheral smear shows >5% parasitaemia with ring forms and 'appliqué' trophozoites. Fundoscopy reveals retinal whitening and haemorrhages. Which mechanism BEST explains the neurological complications in this patient?
A
P. falciparum schizonts rupture synchronously → mass release of merozoites into CSF → direct parasitic invasion of neurons
B
Parasitised erythrocytes express PfEMP-1 (CIDR domain) → cytoadherence to ICAM-1 on cerebral microvascular endothelium → sequestration → mechanical obstruction + cytokine (TNF-α) release → endothelial dysfunction and tissue hypoxia
✓
C
P. falciparum exotoxin crosses the blood-brain barrier directly, triggering excitotoxic neuronal death without vascular involvement
D
Hypersplenism from falciparum malaria → platelet sequestration → DIC → cerebral haemorrhage as the primary cause of neurological findings
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A 26-year-old man from Bihar presents with new-onset seizures. MRI brain shows three cystic lesions (8–12 mm) in the parietal cortex and one in the fourth ventricle. The cortical lesions have a bright eccentric scolex on T1. One lesion shows a rim of surrounding oedema and enhancement — consistent with a dying cyst. A fourth, calcified lesion is seen. Which statement BEST predicts the clinical significance of the enhancing vs non-enhancing lesions?
A
Enhancing lesions indicate live viable cysts with intact scolex; non-enhancing calcified lesions indicate developing cysts
B
Enhancing lesions represent dying/degenerating cysts where the host immune response is active; they are the primary cause of perilesional oedema and seizures; calcified lesions are burnt-out inactive disease
✓
C
All lesions carry equal risk of rupture; enhancement pattern does not correlate with inflammatory activity or seizure risk
D
Non-enhancing viable cysts produce the most intense perilesional inflammatory response and are most likely to cause seizures
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A 28-year-old woman from Kerala presents with three hypopigmented anaesthetic skin patches: a single large patch on the left arm (borders ill-defined, AFB smear strongly positive), diffuse thickening of facial skin with loss of eyebrows, and bilateral thickened greater auricular nerves. Nerve conduction studies show symmetric sensory loss. Slit-skin smear from the left arm shows a bacillary index (BI) of +5. Skin biopsy of the arm lesion shows dense sheets of foamy macrophages (Virchow cells) packed with AFB; lymphocytes are scanty. What does this pattern indicate about the patient's immune status and the grade of disease?
A
Strong Th1 response; tuberculoid pole (TT); high bacterial killing; the extensive nerve involvement is due to excessive granuloma formation
B
Weak Th1 response with predominant Th2/anti-inflammatory polarisation; lepromatous pole (LL); failure to form granulomas → unrestricted bacillary multiplication in macrophages
✓
C
Borderline state (BB); mixed histology with both granulomas and foamy macrophages; immunologically unstable; may upgrade toward TT with treatment
D
Pure neural leprosy; absence of skin lesions despite AFB-positive smear indicates the bacteria is confined to nerves without skin tropism
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A 52-year-old diabetic man is admitted to the ICU with severe COVID-19 pneumonia (SpO₂ 82% on room air) and is intubated. On day 7 he dies. Autopsy would MOST characteristically show which pulmonary pathological sequence leading to the ARDS pattern seen in fatal COVID-19?
A
Lobar consolidation with neutrophilic exudate in alveoli (hepatisation) → pleural fibrinopurulent exudate → resolution or organisation; no hyaline membranes
B
Diffuse alveolar damage (DAD): alveolar epithelial necrosis → protein-rich exudate → hyaline membrane formation lining alveolar walls (exudative phase) → followed by type II pneumocyte hyperplasia and fibroblast proliferation (organising phase)
✓
C
Granulomatous pneumonitis with Langhans giant cells and central caseous necrosis surrounded by epithelioid macrophages — identical to Mycobacterium tuberculosis
D
Interstitial pneumonia with lymphocytic infiltrates only, no hyaline membranes, no exudate, and preserved alveolar architecture — identical to CMV pneumonitis
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A 3-year-old boy is referred after his parents notice he 'looks different from his siblings.' Physical exam: upward-slanting palpebral fissures, single palmar crease, flat nasal bridge, and generalised hypotonia. ECHO shows a large atrioventricular septal defect (AVSD). His karyotype is 47,XY,+21. His mother is 22 years old. Which statement MOST accurately explains the mechanism AND risk pattern of this child's chromosomal abnormality?
A
The extra chromosome 21 results from mitotic non-disjunction after fertilisation, producing mosaicism in only some cell lines; risk does not increase with maternal age
B
Non-disjunction during maternal meiosis I is the most common mechanism (~75%); the resulting trisomy 21 risk increases exponentially with maternal age; in young mothers, de novo meiotic error is still possible but recurrence risk is approximately 1% above age-related background
✓
C
Robertsonian translocation (21;14) is the mechanism in the majority of Down syndrome cases; maternal age is not a risk factor; recurrence risk in siblings is up to 10-15% if the mother is a balanced carrier
D
The trisomy 21 is inherited from an autosomal dominant mutation in the DYRK1A gene; all children of an affected individual have a 50% chance of inheriting the same mutation
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A 2-year-old girl is brought to the emergency department with an acute episode of stridor, drooling, and inability to swallow. Her parents report progressive difficulty feeding, frequent chest infections, and a hoarse cry since birth. Examination reveals coarse facial features, cloudy corneas, a palpable liver 4 cm below the costal margin, and a non-tender abdominal mass in the right flank. MRI brain shows dilated ventricles with periventricular white matter T2 signal abnormality. Which diagnosis BEST integrates all findings?
A
Gaucher disease type 1 (non-neuronopathic): glucocerebrosidase deficiency; hepatosplenomegaly without CNS involvement
B
Hunter syndrome (MPS II): X-linked recessive iduronate-2-sulfatase deficiency; coarse facies, hepatosplenomegaly, clear corneas, CNS involvement in severe form — but cloudy corneas argue against this
C
Hurler syndrome (MPS I): autosomal recessive α-L-iduronidase deficiency; coarse facies, corneal clouding, hepatosplenomegaly, airway involvement (macroglossia, tracheal narrowing), skeletal dysostosis, CNS neurodegeneration
✓
D
Niemann-Pick disease type A: sphingomyelinase deficiency; hepatosplenomegaly, neurodegeneration with cherry-red spot; corneal clouding is not a feature
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A 5-year-old boy presents with abdominal distension and a firm, non-tender mass in the right flank that does not cross the midline. CT abdomen shows a 9 cm intrarenal heterogeneous mass with areas of necrosis, displacing but not invading the aorta or IVC. Biopsy shows triphasic histology: primitive blastemal cells, tubular epithelium, and stromal elements. Cytogenetics reveals deletion of WT1 gene on chromosome 11p13. His parents report he was born with hemihypertrophy and aniridia. Which statement about the molecular mechanism and additional surveillance recommendation is MOST appropriate?
A
WT1 deletion causes constitutive activation of the Wnt pathway; since only one hit is needed (haploinsufficiency), all carriers develop Wilms tumour
B
WT1 is a tumour suppressor; in germline WT1 mutation (first hit), somatic loss of the second allele (second hit) in nephrogenic progenitors is required for tumorigenesis; hemihypertrophy and aniridia indicate WAGR syndrome, warranting bilateral renal ultrasound surveillance every 3-4 months until age 8
✓
C
WT1 encodes a proto-oncogene; gain-of-function mutation drives uncontrolled blastemal proliferation; the tumour is therefore inherited in an autosomal dominant pattern with 100% penetrance
D
Hemihypertrophy and aniridia are coincidental findings unrelated to WT1 deletion; contralateral surveillance is not indicated because Wilms tumour is overwhelmingly unilateral
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A 45-year-old male coal miner with 25 years of underground work presents with progressive exertional dyspnoea and a productive cough. Chest X-ray shows multiple bilateral upper-lobe nodular opacities (2-5 mm) with bilateral hilar calcification in an 'eggshell' pattern. Spirometry shows a mixed obstructive-restrictive pattern. Which pathological process drives the pulmonary disability in this patient?
A
Coal dust directly triggers type I hypersensitivity via IgE → mast cell degranulation → bronchoconstriction (occupational asthma mechanism)
B
Alveolar macrophages phagocytose coal/silica particles → fail to degrade crystalline silica → NLRP3 inflammasome activation → IL-1β/IL-18 release → macrophage death and particle release → chronic cycle of inflammation → collagen deposition (hyalinised fibrosis) → silicotic nodules
✓
C
Coal dust directly mutates the EGFR gene in bronchial epithelium → squamous cell carcinoma → paraneoplastic COPD
D
Inhalation of coal dust → systemic absorption via alveolar capillaries → hepatic accumulation → fibrosis → hepatopulmonary syndrome with gas exchange failure
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A 5-year-old child from a drought-affected region presents with bilateral pitting pedal oedema, a protuberant abdomen, and skin rash (peeling, 'flaky-paint' appearance). His weight-for-height Z-score is -2.8. Serum albumin is 1.2 g/dL; haemoglobin is 8.4 g/dL. He is alert, communicates in sentences, and his subcutaneous fat appears preserved. Which specific biochemical cascade BEST explains the oedema, and how does it differ from marasmus?
A
Total caloric deficit → adipose and muscle wasting → reduced plasma volume → tissue hypoperfusion → oedema from reduced cardiac output; in marasmus the same mechanism occurs but with greater adipose loss
B
Selective protein deficiency → reduced hepatic albumin synthesis → hypoalbuminaemia → reduced oncotic pressure → fluid shifts from intravascular to interstitial compartment; marasmus involves total caloric deficit with relative protein sparing and normal albumin due to muscle catabolism maintaining amino acid supply
✓
C
Protein deficiency → lymphocyte depletion → impaired lymphatic drainage → lymphoedema; marasmus causes cachexia but does not impair lymphatics
D
Vitamin D deficiency from malnutrition → hypocalcaemia → increased capillary permeability → calcium-dependent tight junction failure → oedema; in marasmus vitamin D is sufficient from skin synthesis
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A 40-year-old man with a BMI of 37 kg/m² attends a metabolic clinic. He has a waist circumference of 102 cm and has been taking anti-hypertensive medication for 2 years. Fasting labs: plasma glucose 7.1 mmol/L, triglycerides 2.6 mmol/L, HDL cholesterol 0.88 mmol/L, LDL cholesterol 3.8 mmol/L. He smokes 10 cigarettes/day. On which adipokine axis does visceral obesity PRIMARILY act to drive insulin resistance and atherogenesis in this patient?
A
Reduced leptin → decreased satiety → increased caloric intake → hyperinsulinaemia → secondary insulin resistance via receptor downregulation
B
Visceral adipocytes → ↑TNF-α, IL-6, resistin + ↓adiponectin → IRS-1 serine phosphorylation → impaired PI3K/Akt insulin signalling → hepatic insulin resistance (gluconeogenesis ↑) + skeletal muscle glucose uptake ↓ + pro-atherogenic dyslipidaemia
✓
C
Visceral fat releases free fatty acids → direct mitochondrial uncoupling in pancreatic β-cells → β-cell apoptosis → primary insulin deficiency (type 1–like mechanism)
D
Visceral fat produces excess cortisol via HSD11B1 (11β-hydroxysteroid dehydrogenase type 1) → systemic hypercortisolism → all features of metabolic syndrome via glucocorticoid receptor activation alone
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A 16-year-old girl is referred for primary amenorrhoea and short stature (height 142 cm). Examination: webbed neck, widely spaced nipples, low posterior hairline, and shield-shaped chest. Breasts are Tanner stage 1; pubic hair is Tanner stage 2. Echocardiography shows a bicuspid aortic valve. Pelvic ultrasound shows streak gonads bilaterally. Serum FSH is markedly elevated; LH is elevated; serum oestradiol is very low. Which combination of karyotype and pathophysiological mechanism BEST explains the streak gonads?
A
46,XY karyotype; androgen insensitivity syndrome (AIS) → testes present but non-functional; Müllerian structures absent; high testosterone but inactive due to receptor defect
B
45,X karyotype; absence of second sex chromosome → abnormal meiosis in primary oocytes → accelerated follicular atresia in utero → streak gonads (fibrous ovarian remnants) by birth; no oestrogen → no negative feedback → high FSH/LH
✓
C
47,XXX karyotype; triple X syndrome → premature ovarian failure via X-chromosome dosage; streak gonads develop in adolescence after a brief period of ovarian function
D
46,XX karyotype; Mayer-Rokitansky syndrome → Müllerian aplasia → absent uterus and upper vagina; ovaries are normal (functional) but pelvic ultrasound fails to image them correctly
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A 9-month-old boy presents with increasing abdominal girth, progressive neurological decline (loss of head control, inability to sit), and hypotonia. He had normal development until 4 months of age. Examination shows hepatosplenomegaly and a cherry-red macular spot on fundoscopy. Serum acid sphingomyelinase activity is undetectable. Bone marrow biopsy shows large, pale 'foam cells' with a 'sea-blue' histiocyte appearance. Which storage material accumulates, and what is the mode of inheritance?
A
Glucocerebroside accumulates in macrophages (Gaucher cells with 'wrinkled tissue paper' cytoplasm); autosomal recessive inheritance; neurological involvement indicates type 2 (acute neuronopathic)
B
Sphingomyelin accumulates in macrophages and neurons; autosomal recessive inheritance (acid sphingomyelinase, SMPD1 gene); Niemann-Pick type A with severe neurodegeneration in infancy
✓
C
GM2 ganglioside accumulates in neurons (Tay-Sachs disease); autosomal recessive (HEXA gene); cherry-red spot present but NO hepatosplenomegaly because GM2 accumulates only in neurons
D
Ceramide accumulates in all tissues; autosomal recessive (Farber disease); presents with periarticular nodules, hoarse cry, and hepatosplenomegaly — cherry-red spot is not a feature
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