Lecture 7

Question 1

what are even more rare than rare diseases?

Answer 1

undiagnosed disease

Question 2

what are even more rare than rare diseases?

Answer 2

undiagnosed disease

Question 3

what is the definition of rare based on?

Answer 3

the frequency of the disease → 1:10,000, 1:5000 is quite rare

Question 4

why is a rare disease better than an undiagnosed disease?

Answer 4

because we have at least some knowledge of the phenotype, symptoms, and characteristics

Question 5

what program did the US put into place 10 years ago to manage unnamed conditions?

Answer 5

Undiagnosed Disease Program (UDP)

Question 6

what does the UDP deal with?

Answer 6

new syndromes, rare disease, and unusual presentations of known disease

Question 7

what is the aim of the UDN?

Answer 7

to provide wider access to cross-disciplinary expertise and to leverage specific advantages of the collaborative network such as deep subtypes of expertise, as well as to evaluate clinical cases that have an unclear or never described phenotype →collaborative network

Question 8

what does the UDN do with the information they gain?

Answer 8

report the results of their evaluation from a clinical and genetic point of view → the sharing of this information is important and fundamental for other clinics as well all over the world to classify patients with the same or similar phenotype in order to increase the diagnosis of other patients with unnamed disorders

Question 9

how does the UDN work?

Answer 9

cases are submitted by the patients themselves or the clinician, which are all discussed weekly at Harvard, and evaluated based on information provided and chosen for analysis

Question 10

what is the main goal of the UDN?

Answer 10

to share the findings in order to improve the diagnosis of other cases with similar phenotypes

Question 11

what is an important tool that is used to better characterize the phenotype considering all the symptoms?

Answer 11

Human Phenotype Ontology (HPO) → a list of codes associated with all human symptoms considering all the phenotypes that are described and known

Question 12

what does the use of the HPO allow for?

Answer 12

possible to standardize the clinical characteristics of a specific phenotype

Question 13

what does the UDN use to analyze patents and perform sequencing?

Answer 13

Illumina platform → after the paired end sequencing (read 1 and read 2) they complete the primary, secondary, and tertiary analysis and at the end of the process it is necessary to filter out all the variants that are probably not associated with that phenotype

Question 14

what criteria does the UDN use?

Answer 14

uses the American College of Medical Genetic’s guidelines

Question 15

what is the program analogous to the UDN in Italy?

Answer 15

an undiagnosed diseased program granted by Telethon performed in TIGEM (Naples) → idea is the same: collect all the genetic cases in which the clinical description is not clear

Question 16

what age does long QT syndrome usually effect?

Answer 16

affect mainly males during their adolescence or adulthood

Question 17

what is the inheritance pattern of long QT?

Answer 17

characterized by an autosomal dominant inheritance

Question 18

why was the two year old boy who experienced sudden cardiac arrest and a very aggressive phenotype not typical with long QT syndrome with which he was diagnosed?

Answer 18

• he was a young child (usually in adolescence or adults)
• most likely a recessive inheritance (disease is typically autosomal dominant)
• he was treated with beta blockers and they drug was completely ineffective
• he presented with malignant ventricular fibrillation and LQT does not have this symptom

Question 19

what type of sequencing was performed for the two year old with sudden cardiac arrest?

Answer 19

trio whole exon sequencing → both him and his parents were sequenced in order to prioritize variants that are expressed in all three individuals (de novo and x-linked genes can be excluded)

Question 20

the trio sequencing was performed on the two year old and his parents, what was discovered?

Answer 20

there were three variants shared between the three, and the proband was the only one who carried the homozygous variant → gene of interest was TRDN

Question 21

what does TRDN encode for?

Answer 21

Triadin - expressed in the heart

Question 22

what is the function of Triadin?

Answer 22

protein that is localized on the sarcoplasmic reticulum and is important for the Ca2+ release complex → regulates the RYR (ryanodine receptor) and the flux of calcium during the excitation - contraction coupling - expressed in the heart ad skeletal muscle

Question 23

what occurs in the TRDN missence mutation?

Answer 23

substitution of a Leu with a Pro

Question 24

describe the structure of Triadin:

Answer 24

has a trans-membrane domain with an alpha-helix domain in the TM region - it is known that the proline in the TM region is a helix-breaker

Question 25

what other disease is Triadin a causitive gene in?

Answer 25

CPVT - catecholaminergic polymorphic ventricular tachycardia (another arrhythmogenic form that affects young boys and leads to cardiac arrest)

Question 26

why is the clinical characterization so important?

Answer 26

the pattern of the ventricular tachycardia was not polymorphic as the CPVT but showed typical patterns of the long QT - very strange presentation of long QT

Question 27

if we have a mutation in the TRDN gene, what do we see?

Answer 27

an alteration in the muscle fibers and localization of Triadin

Question 28

when there is a mutation in the TRDN gene, we see a higher mobility - what might this influence?

Answer 28

may influence the link with the Ryanodine Receptor complex (the physiological function of the calcium release complex is reduced)

Question 29

what is the main mechanism caused by the TRDN mutation?

Answer 29

the reduction of Ca2+ flow may stop the feedback inhibition of that calcium channel and we have a final increase in Ca2+ concentration in the cytosol → increase in Ca2+ concentration leads to the arrhythmic phenotype

Question 30

currently, how many cases of Triadin KO syndrome have been reported?

Answer 30

22

Question 31

what is the best animal model for an in vivo approach to study cardiac disorders?

Answer 31

zebrafish

Question 32

what is the definition of morpholinos?

Answer 32

a widely adopted method to transiently modify the expression of a gene of interest by its injection into the zebrafish embryo at the developmental state of 1-cell

Question 33

what is the main limitation of the zebrafish animal model?

Answer 33

limited action of the gene knockdown

Question 34

why is a mouse not a good model for cardiac studies?

Answer 34

the structure of the heart is much different and it has a high resting bpm

Question 35

what makes the zebrafish a good experimental model for cardiac studies?

Answer 35

it is more structurally similar, has a similar bpm, and they are easy to investigate because they are small and able to be observed with an optic microscope → in this case TRDN is present and has a good homology between fish and humans

Question 36

how was the function of TRDN studied in this case to be applied to the TRDN KO syndrome?

Answer 36

the mopholino strategy was used to identify a spatiotemporal expression of Triadin → the conditions were set up and morpholine efficacy and the depend assays were evaluated to exclude the negative effects that are associated with the doses of moropholino and not related to the KO of the triadin

Question 37

what is the phenotypic effect of Triadin KO in zebrafish?

Answer 37

they exhibited an alteration at the skeletal level as well as edema, so we can say that Triadin KO can be associated with ventricular tachycardia → showed there is an alteration in conduction between the atrium and ventricles

Question 38

how are patients currently treated for TRDN KO syndrome?

Answer 38

patients are implanted with a defibrillator to prevent ventricular tachycardia but there is not a therapeutic treatment