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NSWBiologyQuick questions
Module 8: Non-infectious Disease and Disorders
Quick questions on Genetic disorders: cystic fibrosis, sickle cell, Huntington's: HSC Biology Module 8
11short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is cystic fibrosis (autosomal recessive)?Show answer
Gene and mutation. CFTR (cystic fibrosis transmembrane conductance regulator), chromosome 7. The most common mutation is $\Delta F508$, a three-base-pair deletion that removes phenylalanine at position 508 of the CFTR protein.
What is sickle cell anaemia (autosomal recessive)?Show answer
Gene and mutation. HBB (beta-globin) on chromosome 11. A single point mutation (GAG to GTG) changes glutamate to valine at position 6 of the beta-globin chain (the HbS allele).
What is huntington's disease (autosomal dominant)?Show answer
Gene and mutation. HTT (huntingtin), chromosome 4. The mutation is an expanded CAG trinucleotide repeat in exon 1. Fewer than 27 repeats is normal; 36 or more causes disease. The expanded repeat encodes a long polyglutamine tract that makes the huntingtin protein toxic to neurons.
What is pedigree analysis for these conditions?Show answer
Autosomal recessive pedigree (cystic fibrosis, sickle cell).
What is gene and mutation?Show answer
CFTR (cystic fibrosis transmembrane conductance regulator), chromosome 7. The most common mutation is $\Delta F508$, a three-base-pair deletion that removes phenylalanine at position 508 of the CFTR protein.
What is inheritance?Show answer
Autosomal recessive. Two unaffected carrier parents ($Cc \times Cc$) have a 25 percent chance of an affected child. Carrier frequency in Australians of Northern European ancestry is approximately 1 in 25.
What is pathophysiology?Show answer
CFTR is a chloride channel in the apical membrane of epithelial cells. Loss of function reduces chloride and water secretion onto epithelial surfaces, producing thick viscous mucus. The mucus obstructs:
What is treatment?Show answer
Airway clearance physiotherapy, inhaled antibiotics, pancreatic enzyme replacement, high-calorie diet, and CFTR modulator drugs (e.g. ivacaftor for G551D, elexacaftor/tezacaftor/ivacaftor for $\Delta F508$). Lung transplant for end-stage disease.
What is options?Show answer
Preimplantation genetic diagnosis (PGD), prenatal testing by chorionic villus sampling, or natural conception with neonatal screening. Genetic counselling is essential.
What is confusing carriers and affected individuals?Show answer
Carriers of recessive disease (CF, sickle cell) are heterozygous and unaffected. Dominant disease (HD) has no carriers in this sense; heterozygotes are affected.
What is forgetting heterozygote advantage in sickle cell?Show answer
The HbS allele frequency is high in malarial regions because $Ss$ carriers resist Plasmodium falciparum.