Human Diseases

Single gene disorders

mutations in single genes (often causing loss of function). Use Mendelian principals. can affect structural proteins, enzymes, receptors, transcription factors.

Multifactorial disorders

Variants in genes causing alteration of function, enviornment has role too.
One organ system affected.

Chromosome disorders

Chromosomal imbalance causes alteration in gene dosage. Many genes may be involved
- multiple organ systems affected at multiple stages in gestation.
- usually spontaneous (de novo) trisomies, deletions, duplications
- in rare cases, can be inherited (translocations)

Down’s syndrome

Disorder caused by additional chromosome at no.21.

Can be detected in pregnancy with ultrasound: short femurs, nuchal translucency, echogenic bowel, choroid plexus cyst, sandal gap, single palmar
crease.

Symptoms: round face, protruding tongue, upslanting palpebral fissures, epicanthic folds, developmental delay.

Screen pregnant women >35y.o as higher risk of Down’s & families with syndrome.

Patau syndrome

Known as Trisomy 13. Caused by error in meiosis - causing midline malformations.

Symptoms: high infant death rate, severe intellectual disability (ID), incomplete brain lobe, cleft lip, congential heart disease.

Meiosis

Meiosis is a type of cell division that reduces the chromosome number by half, resulting in the formation of four non-identical daughter cells.

Stage 1 - occurs in ovulation Stage 2 - occurs at fertilisation

Meiosis errors

Damage to repair mechanisms of the primary oocyte increases the chance of non-disjunction → errors in chromosome alignment.

Causes two copies (disomy) instead of one and other cells to have no copies (nullisomy).

Microdeletions

chromosomal region is lost - too small to be observed microscopically. Identified by use of specific molecular cytogenetic techniques.

Numerical chromosome abnormalities

Gain or loss of entire chromosome. serious, often lethal consequences (particularly autosomal anomalies) e.g. multiple congenital anomalies/mental retardation (MCA/MR) syndromes

DiGeorge Syndrome

Syndrome caused by 22q11.2 microdeletion. Symptoms: congenital heart defects, small mouth, prominent nose.

Huntington’s disease

Mutation in HHT gene → neurodegeneration of white matter in brain (nerve cells)

Symptoms: mood changes, cognitive impairment, dementia, coordination issues…

Cystic Fibrosis

Mutation in CFTR gene → causes thick mucus secretions and limited lung function.

Duchenne muscular dystrophy

Mutation in DMD gene - causes muscle fibre weakness and progressive damage. X-linked recessive disorder.

Phenylketonuria

Mutation causing defect in Phenlyalanine metabolism. Symptoms: ID, epilepsy, Parkinson’s in severe cases, hypopigmentation of eyes, musty smell, impaired melanin synthesis.

Familial hypercholesterolaemia (FH)

Mutation to LDLR gene causes disorder of cholesterol metabolism → atherosclerosis. Detected by high LDL levels. Causes high risk of cardiovascular disease (CVD), Tendinous xanthomas, Arcus cornealis and xanthelasmata.

Treated with cholesterol decreasing drugs (statins).

Hypertension

Mutations in genes related to renal salt balance - ENaC, mineralocorticoid receptor gene. Causes high blood pressure.

Diabtetes

Mutations to glucokinase transcription factors. Causes defects in development & function of pancreatic Beta cells

Epilepsy

Mutation to GABARD gene encoding ion channels. Causing seizures and CNS disorders.

Karotyping

Arrangement of the chromosomes in descending order of size. Physically distinguishing chromosomes to observe cytogenetic characteristics. Abnormalities can be in structure or number (aneuploidy).

Must use actively dividing cells to observe - sample amniotic fluid, choronic villus sampling. Viewed with Giemsa strain.

Idiogram - chromosome banding patterns. Chromosomes characterised by topography.

Fluorescence in situ hybridization (FISH)

Chromosomal analysis at DNA/gene resolution. Performed on cells in metaphase/interphase to identify structual abnormalities - repetitive sequences, DNA segments covering whole chomosome, previously known regions.

Williams syndrome

Syndrome caused by microdeletion >q11.23. Detected using FISH.

Symptoms:

bright eyes, stellate irides
wide mouth, upturned nose, long
philtrum, flattened nasal bridge
heart defects

Oligonucleotide ligation assay (OLA)

Assay to detect point mutaions/SNPs - as primers can’t ligate and bind if nucleotide not perfect.

Sanger sequencing

chain termination sequencing uses the synthesis of new DNA strands which are complementary to a single-stranded template. Strand synthesis would normally proceed indefinitely until the end of the template is reached.

Neonatal screening

new-born blood spot (heel prick) testing from Guthrie cards, congenital hypothyroidism, cystic fibrosis, hemoglobinopathies (sickle cell anaemia)
other inborn errors of metabolism - test using mass spectometry.

Tay Sach’s disease

Disease caused by metabolic disorder → accumulation of gangliosides, so can’t form glycosidic bonds. Symptoms: severe ID, seizures, death.

Test for using hexosaminidase A activity in plasma/WBCs.

Hallmarks of cancer

Sustaining prolieration signals, Evade growth suppressors, activate invasion + metastasis, replicative immortality, induce angiogenesis, resist death.

Blood vessel structure

Endothelium on outside, then ECM, smooth muscle, nervous connections, other cells, hollw. ECM allows communication between cells/non-cells.

Vasculogenesis

De novo blood vessel formation:

haemangioblasts congregate (vascular stem cells) → new networks form

Intussusception - inward sprouting

Angiogenesis

Outward sprouting of new vessels. Driven by endothelial based proliferation, migration, movement. New sprouts divided into endothelial cell types.

Endothelial cells

Cells that are essential tubular blocks. Functions:

Cell adhesion - Intracellular barrier, move molecules/cells, barrier in angiogenesis/vasculogenesis.

growth factor response, interact with migrating cells, balanced quiescence (dormancy), proliferation, death.

Endothelial cell production

Primary vasculature stimmed by VEGF → Unstable immature → +VEGF1/2 + ANG1 +EphrinB2 + Tie ½ → stable mature → remodelled vasculature.

Metastasis

Spread of cancer cells around the body via blood/lymph systems. Stages: Intravasation (enter vessel)→ spread → extravasation (exit vessel) → tumour growth & tissue disruption

Neovascularisation

Innervation of tumour with leaky blood vessels → allows tumour growth with nutrients & spread via blood.

Tumour angiogenesis

Stages:

Hypoxia - HIF-1a induces VEGF-A when O2 <1%

Proteolytic degradation - as enzymes + GFs gained

Tip cell migration - along angio factor gradient

Tube formation - ECs → Stalk cells

Regulation of size - VEGF→DLL4→Notch-1Rs→VEGFR decreased → decrease proliferation.

Tumour vascularisation - PDGFB decreases VEGF sensitivity

HIF1/2a

Functions:

Cell survival - prolif/apoptosis/autophagy, Stem cell maintencance, tumour vascularisation, NT & meutrophil secretion, Invasion + metastasis, Metabolic switch, radioresistance.

Warburg effect

Normally cells have low glycolysis rate (anaerobic) for ATP synthesis. But cancer cells make more ATP by increasing glycolysis & lactate production. Increasing growth.

Metformin

AMPK activator - used for glucose & ATP control - so can be used to decrease tumour growth.

Tumour growth promotion

Deregulate cell energetics, Avoid immune destruction, Genome instability, Tumours promoting inflammation

Cancer therapy targets

Angiogenesis via VEGF, Growth receptors, RAF/P13/AKT kinase, Apoptosis, Ubiquitin proteasome, mTOR/AKT.

Atherosclerosis

Lipid plaque/lesion accumulates in artery wall. Can form non-calcified (soft) or calcified (hard) plaques.

Symptoms: CHD, heart failure, stroke, pulmonary blockage, peripheral arterial disease.

Atherosclerosis development

Fatty streak forms initially - intracellular accumulation → Fibrous plaque forms → Complicated lesion - has extracellular lipid cores → Destablilisation (Fiberatheroma) many lipid cores & layers. Causes surface defects, thrombosis (blood clot formation), hematoma, haemorrhage & rupture

Low density lipoprotein (LDL)

Lipid particle made of cholesterol, cholesterol esters, apopproteins & triglycerides. Used to carry cholesterol to arteries.

LDL accumulation

Lipid that accumulates in macrophages & smooth muscle cells → forming foam cells → buildup develops into streak → coronary artery block = cardiac disease / brain blood clot → stroke

Increased LDL = Increased OxLDL = Increased AS

Cholesterol

Lipid particle that functions as: membrane component, Vitamin D/hormone precursor, bile synthesis & repair processes. Addition of fatty acid tail = cholesterol ester. Needs lipoproteins to sheild itself from aqeous plasma.

Its levels regulate LDLR transcription

Hypercholesterolaemia

High blood choplesterol levels, caused by lipid metabolism mutations (mainly LDL) → fatty deposits form in blood vessels.

Foam cells

Accumulation of LDL in macrophages. Can rupture and induce pro-inflammatory response → increasing leukocyte recruitment & adhesion.

OxLDL

Created when when LDL interacts with free radicals. triggers inflammation, promotes plaque formation, and increases the risk of atherosclerosis.

Trans-Endothelial migration (TEM)

Where leukocyte moves between ECM, disrupting EC-EC connections temporarily. Thethering & rolling in lumen of vessel → activation & adhesion → transmigration

Platelets

Cells that interact with vasculature via cell surface receptors. Use Fibrinogen + WWF to bind to clots. Made by megakaryocytes.

Endothelial nitric oxide synthetase (eNOS)

Enzyme to make endothelial NO. Which has role in vascular muscle relaxation, blocks leukocyte adhesion & platelet aggregation.

Vascular Smooth Muscle Cells

Cells that contribut to blood pressure regulation & plaque formation - via apoptosis & remodelling damage.

Atherosclerosis risk factors

Smoking - induces SNPs, Cardiometabolic disorders - causing fat depositions in liver/muscle.

Angiogenesis in atherosclerosis

Process can be good: sprout new vessels to avoid clots/plaque (collaterals), or destabilise them to decrease blood pressure, can stimulate repair, can regulate cells

Bad: Destabilising stable plaque can rupture it, trigger clot formation & platelet attraction.

Peripheral Arterial Disease (PAD)

Disease with peripheral (leg) artery blockage → decreasing blood flow → creating sores → risk of gangrene infection. Amputation may be necessary.

Treatments:

Remove blockage surgically, add stent, vein bypass graft, inject VEGF-A to induce angiogenesis.

Pre-eclampsia

Disease where increased soluble Flt-1 → sequesters VEGF-A & removes it from ECs → forms non-productive signalling complexes that’re soluble & membrane bound.

Causes increased blood pressure during pregnancy.

Treated with: Increasing CO expression with HO-1, to decrease SFlt-1 expression. Stimulate BV into bulirubin to decrease SFlt-1 expression. Statins to decrease blood pressure & stim HO-1 increase & inhibit soluble endoglin.

Cyclopamine

Poison from Veratum californium, disrupts sonic hedgehog pathway → causing cyclopia in babies.

Sonic hedgehog pathway (SHH)

Pathway is a critical signaling mechanism that regulates embryonic development, cellular differentiation, tissue growth/repair & homeostasis. Has implications in cancer. Occurs in primary cilia.

On: Hh + CDO/BOC binding to patched → triggers exocytosis. Smoothened (SMO) activates displacement of GLI → Inducing expression of target genes.

GLI

Protein within SHH pathway that allows for gene repression/activation. Activated by phosphorylation.

3 forms:

1 - inducible activator. 2 - constiuitive activator. 3 - constituitive repressor

When inactive is bound to SUFU. When active binds to nuclear GLI-Rs to change gene expression.

7-TM protein family

Protein family that act as: endogenous agonists of cholesterol/oxysterols, have G-protein coupling capacity & constituitive signalling (ligand).

Includes: rhodopsin, glutamate, pheromones, CAMPRs.

Smoothened protein (SMO)

Protein that selectively activates heterotrimeric G proteins of Gi family. When inhibited it resides in cytosol. Activated by cholesterol.

SHH dysfunction

Patched mutations - prevent it from inhibiting SMO - cancer in pancreas, stomach, breast, prostate etc…

SMO mutations - Can cause persistent SHH signalling without ligands - basal cell/medulla cancer.

GLI mutation - can alter tumour gene expression - glioblastoma

SHH activation

• Different levels of HH protein cause different intracellular signalling responses.

• Canonical Activation – This occurs when SHH binds to its receptor Patched (PTCH1), relieving inhibition on Smoothened (SMO), which then triggers downstream signaling and gene expression.

• Non-Canonical Activation – SHH signaling can bypass the traditional pathway, influencing cellular processes through alternative mechanisms, such as direct interactions with other signaling pathways.

• Ligand-Dependent Activation – SHH proteins are secreted and bind to receptors on target cells, initiating signaling cascades.

• Ligand-Independent Activation – Mutations in PTCH1 or SMO can lead to constitutive activation of the pathway, even in the absence of SHH ligand.

• SHH Modulators – Certain molecules, including agonists and antagonists, can enhance or inhibit SHH signaling, affecting cell differentiation and proliferation.

Medullablastoma

Commonly malignant CNS cancer in children. Mechanism - cerbrrellar neuronal progenitors proliferate in late embryonal/neo-natal period in response to SHH path.

Treated with SMO inhibitor to reduce growth. Linked with increased cholesterol production - as more SMO activated - so can be treated with statins.

Indian Hedgehog Pathway (IHH)

Pathway that regulates long bone growth in childhood. Dysfunction = dwarfism

Gorlin syndrome

Genetic disorder caused by mutations in the PTCH1 gene, leading to abnormal Hedgehog pathway activation. Symptoms: skeletal abnormalities & increased risk of medullablastoma & BCC.

Basal cell carcinoma (BCC)

Common sporadic (by chance) tumour, linked with UV exposure - typically beneign. Mutations in SHH, causing constant activation, linked with this cancer as it drives tumour growth.

Advanced form vulnerable to SMO inhibitors.

Patched protein (PTCH)

Protein in SHH pathway that functions to: Suppress SMO activity when Hedgehog is absent. Bind Hedgehog ligands, relieving inhibition on SMO and activating downstream signaling. Regulate cell differentiation, growth, and tissue patterning.

RAS proteins

Small G-proteins that are involved in signal transduction, signalling intermediate for many GF-RTKs. Activates MAPK (proliferation) & P13/Akt (survival) pathways.

RAS activation

Guanine exhange factors (GEF) facilitate the exchange of GDP for GTP, inducing conformational change for RAS to bind to downstream effectors.

Oncogenic RAS mutations

Common mutations: G12/13 & Q61. Mutations decrease GTPase activity, but requires upstream SOS activation.

RAS inhibition

Methods: effector lobe blockage, covalent inhibitors, bind endogenous proteins, or degraders (PROTACs - proteolysis targeting chimeras).

RASopathies

Systemic diseases linked to germline mutations causing moderate activation of the Ras-MAPK pathway. Lead to malformations & increased risk of cancer. e.g. Costello, Noonan, CBL syndromes… Especially leukaemias: uvenile Jmyelomonocytic leukemia (JMML), Myeloproliferative disorder.

Noonan syndrome

Multiple causes that increase Ras-MAPK signalling. e.g PTPN11/SHP2 & SOS1 mutations.

Symptoms: heart & pulmonary defects, ID, hearing loss, higher risk of leukaemia.

NS-Ml

Noonan syndrome variant with multiple lentigenes (small melanomas/freckles). Caused by decreased GAP affinity for NF1 + RAF>MAPK affinity.

Symptoms: ID, deafness, Electrocardiographic conduction anomalies, hypertension.

Neurofibromatosis Type I (NF1)

Schwann cell tumours form in spinal, peripheral & cranial nerves. Causing freckles over body & iris, scoliosis, tibial bowing & external tumours.

Mechanism: Tumour suppressor gene that stops RAS activation. Biallelic expression is necessary to control RAS
activation. Mutations can also induce actin stress fiber production → more mobile tumour cells.

Neurofibromatosis Type II (NF2)

Bilateral acustic/vestibular neurofibrilomas, affecting auditory nerves. Mutations can lead to truncation/frameshifts → negative regulation of proliferation pathways.

DNA damage causes

Can be caused by: ionising radiation, cancer drugs, replicative stress, random mutation, UV, alcohol/smoking, viruses.

DNA damage responses

Apoptosis, repair, chromatin remodelling - nucelosome, cell cycle checkpoints, transcription levels, replication fork stalling.

Types of DNA damge

Alkylation → 6-O-Methylguanine. Oxidation → 8-oxo-dG. Hydrolysis - deamination/depurination (leaves abasic site). UV damage → pyrimidine dimer (C=T). Toxic chemicals → inert/intra crosslinks. Replication error → Base pair mismatch.

Backbone damage

SSB → DSB if replication fork collapses. DSB → lose DNA structural connectivity. Crosslinking damage - caused by nucelotide covalent bonding on same strand. Interstrand → Strand separation → DNA breakage & Chromosome rearrangement.

Consequences of DNA damage

Cell cycle can be blocked; Inhibit transcripton → apoptosis → death; Mutations/chromosomal abberations → cancer, ageing & disease.

Diagnosing DNA damage

Functional assays to detect: shortened telomere length, immunodeficiency, chromosome breakage, genetic testing (sequencing), family tracing.

DNA damage & cancer

Genome instability + mutations, Non-mutational epigenetic reprogramming, DNA repair dysfunction.

Neurodegeneration

DNA damage (SSBs) or O2 metabolism can induce transcriptional interferrence. leading to: tumours, microcephaly, Az, PD.

Microcephaly

Disorder characterised by smaller brain size & limited head growth. Occurs from DNA repair mechanism mutations.

Class switching

Leads to change in Ig types, occurs via DNA change - can lead to repair deficiency → immunodeficiency.

Xermadosa pigmentosum

Disorder causing incresed sensitivity to UV DNA damage. Symptoms: sunburns, blistering, eye sensitivity, neurodegeneratiuon & hearing loss.

Caused by mutations affecting NER pathway.

Nuclear excision repair (NER) pathway

UV damage → crosslinks - pyrimidine dimer (=) → creates bulky adducts. Helicases (XPB) unwind DNA, nucleases (XPG/XPF) cut out damage. DNApol fills gap, DNA ligase zips backbone

Mutations to pathway lead to increase in risk of cancer.

Transcription coupled NER (TCNER)

RNA pol detects lesions and stalls ribosome, during transcription. CSA/CSB recruit NER complex proteins to perform repair.

global genome NER (GGNER)

Whole genome examined for distorted helices, that are disturbed by base pair mutations. XPC detects alterered nucleotides in all DNA.

Ataxia–telangiectasia

Syndrome characterised by poor muscle & eye control, and dilated blood vessels, impaired immune system & risk of cancer. Progression occurs with neurodegeneration. Caused by mutation to PIKK enzyme (ATM) - mediates protein binding to damage sites.

Fanconi anaemia (FA)

Syndrome characterised by decrease in blood cell production (~90%). Symptoms: bone marrow failure, ID, risk of cancer, skeletal issues. Caused by LOF mutation to FA pathway → increases crosslinks, some break → reduction in cell cycle checkpoint function.

FA pathway

Cooperates in signal transduction that monitors gene integrity in cell cycle.

Actin

1/2-outer domain. 3-4-inner domain. D-loop for actin-actin filament interactions. 2 actins form 2 helical filaments (asymmetrical). Pointed (-) and barbed (+) end. + grows quick, - slow. Actin monomer & ATP bind to + end. ADP leaves at - end.

Myosin

Protein that binds to actin at + end. Structure: Light chain - binds to lever. 2 Heavy chains dimerise into coil + 2 globular heads to make thick filament (are antiparallel & central region is parallel).

Contractin

Myosin heads & crossbridges pull on actin filaments towards sarcomere.

Actin-Myosin organisation

• Myosin thick filaments - run in the middle.

• Actin thin filaments - surround the myosin filaments, attaching to the Z-discs at the ends of the sarcomere.

Contraction

Myosin heads bind to actin and pull the actin filaments towards the centre of the sarcomere, causing the sarcomere to shorten and the muscle to contract.

Sarcomere

The basic contractile unit of muscle, defined by the region between two Z-discs.

Each sarcomere – small movement Sums (sarcomeres work in series) up to a large movement – at the ends of the muscle – (tendons) In striated muscle only.

Proteins organising actin

Cap-Z - caps barbed end of actin in Z-disc.

a-actin - crosslinksactin in Z-disc

Tropomodulin - caps actin - end towards M-line

Nebulette (Cardiac) Nebulin: (Skeletal)
thin filament stabilisers

Tropomyosin: along the length of actin