Theme 4: Cardiovascular Biology During Stress and Disease

Structural: • Abnormalities in the development of body parts • Not amenable to treatment, but may be correctable by surgery Functional: • Abnormalities in the systems that run the body • Vary in severity from inconsequential (hammer toe) to life-threatening (heart defects) • Includes metabolic disorders (phenylketonuria) and degenerative diseases (muscular dystrophy) • May be treatable in some cases

• Heart defects are the most common class of structural birth defects • CHD affects ~1% of all live births, on average 13 per day in the UK • Despite modern surgery, still the biggest cause of infant mortality and morbidity • May affect up to 10% of still births and spontaneous terminations

• Phenotyping is a full investigation of the nature and severity of defects • This is done via 2D and 3D ultrasound from 20 weeks of pregnancy • After birth, phenotyping may continue using Magnetic Resonance Imaging (MRI) or X-Ray/CT scan

The most common is a bicuspid aortic valve, which is not usually a problem until later life when there is a higher risk of calcification.

About 30%

• Chromosomal abnormalities • Copy number variation (CNV) • Small nucleotide polymorphisms (SNP)

• These can involve duplication or absence of an entire chromosome • Alternatively they can be insertion, deletion, duplication, translocation or inversion of a large portion of a chromosome (many Mb) • The best known example is Down syndrome (trisomy 21) where 40% of patients have CHD • They can be diagnosed by isolating cells from the embryo or placenta and looking at the karyotype, fluorescence in situ hybridization (FISH) or PCR -> The latest techniques enable embryonic cells to be isolated from a sample of the mother’s blood from 9-12 weeks

• These are duplications or deletions of small regions of chromosome, typically 1-18 kb • These can be detected by fluorescence in situ hybridization (FISH), array comparative genomic hybridization (aCGH) or next generation sequencing • Typically cause deletion or duplication of one entire gene

• The human genome has ~3 billion base pairs • The reference genome is derived from the DNA of 13 anonymous donors (USA) • Any particular individual has ~3 million SNPs that vary from the reference genome • Exome sequencing is often used: • Exome sequencing requires exon isolation (hybridisation) followed by next generation sequencing • This is rapid but only covers <90% of the exome, and misses non-coding variation • An exome dataset has ~60k variants, with ~100 “private” or unique to that individual/family • It then remains a task to identify which of these variants is causative of the disease (see table)

• It doesn’t cover ~10% of exons • It misses variation in gene regulatory regions that might be causing defects Whole genome sequencing is the alternative. It is now cheap enough to use clinically (around £1000 per sample), but it generates huge amounts of data, which become difficult to store.

• Infectious diseases (e.g. Rubella and Zika viruses) • Environmental teratogens (e.g. hypoxia, hyperthermia) • Maternal nutritional deficiencies (e.g. Vitamin B3, iron) • Maternal non-communicable diseases (e.g. pre-gestational diabetes) • Maternal genetic conditions (e.g. phenylketonuria) • Teratogenic therapeutic drugs (e.g. Thalidomide, Roaccutane)

• Mouse embryos • However, they do not always respond in the same was as humans (e.g. they do not respond to thalidomide)

Retrospective observational case-control studies

• All the key events of human embryonic heart development occur before week 8 of gestation. Therefore, the mother may not accurately remember her exposure to risk factors when the birth defect is diagnosed. • Likewise, clinical workup of maternal physiological parameters when the birth defect is first detected will not necessarily reflect her conditions during weeks 1-8. • Comprehensive maternal histories often not recorded • Can take decades to satisfactorily test if the association is real (e.g. folic acid) • Can take years before risk factor and/or corrective therapy becomes widely known (Valproate for epilepsy)

Infarction is when the cells die.

• Ischaemia occurs when blood supply to a tissue is inadequate to meet the tissue’s demand. • There are 3 main components: • Hypoxia • Insufficiency of metabolic substrates • Accumulation of metabolic waste

• Angina (stable, unstable) • Chest pain caused by myocardial ischaemia • Usually due to atherosclerosis • Myocardial infarction • Complete occlusion of coronary flow • Plaque rupture with occlusive thrombus

• The gold-standard marker of myocardial injury is blood test (ELISA) for cardiac troponin (cTn) I or T. • This is because troponin is usually found inside cardiac myocytes.

• It is not only an indicator of myocardial infarction, but it also appears to be associated with all-cause mortality • (Chesnaye, 2022): • It has previous been shown that cardiac troponin T (cTnT) is associated with mortality in chronic kidney disease (CKD). • Studied 176 patients with stage 4-5 CKD aged ≥65 years and not on dialysis • Took cTnT measurements over a median follow-up of 2.4 years • Found that 3 factors were associated with all-cause mortality@ • Longitudinally measured cTnT • Slope of the cTnT trajectory • Area under the cTnT trajectory

• Extreme exercise has been shown to lead to increases in troponin T • 2/3rds of individuals after a marathon gave a positive blood troponin test