Long QT syndrome, LQTS, is a congenital or acquired cardiac disorder characterized by prolonged cardiac repolarization phase. It is observed as a prolonged QT period in electrocardiodiagraph and can cause life-threatening specific ventricular tachycardia, torsades de pointes. Hundreds of mutations in 15 genes (LQT1-15) are linked to congenital LQTS. Worldwide prevalence of congenital LQTS gene mutations is from 1:2000 to 1:5000. However, the prevalence in Finland is much higher due to four founder mutations that alone occur in one out of 250 individuals. Acquired LQTS is often drug-induced and the most common cause for the withdrawal of drugs on the market. Carriers of LQTS mutations are more susceptible to acquired LQTS than normal population. LQTS-specific cardiomyocytes can thus provide a thorough model for drug cardiotoxicity screening, better insight into disease mechanisms and assist in drug development. This thesis was a part of a bigger project concentrating on validation of LQT2-specific cell lines that could be used for the purposes mentioned above. Induced pluripotent stem (iPS) cell technology enables creation of disease-specific pluripotent stem cell lines, which can be differentiated into any cell type. In this thesis, two LQT2-specific iPS cell lines derived from a clinically symptomatic 44-year-old female were used. She is heterozygous for Finnish founder mutation L552 in KCNH2 gene, which encodes the α-subunit of the cardiac rapidly activating potassium rectifier channel. iPS cells were first verified to express pluripotency markers and to form embryoid bodies containing all germ layers. iPS cells were then differentiated into cardiomyocytes by culturing them with END-2 cells and mechanical beating of the cardiomyocytes was assessed from video recordings. Single LQT2-specific cardiomyocytes showed LQT2-related phenotype in vitro with 43% of single LQT2 cardiomyocytes showing abnormal beating patterns and prolonged contraction time. This phenotype was rescued in LQT2-specific cardiomyocyte clusters. Finally, the expression ratios of wild type and mutated KCNH2 alleles were compared between cardiomyocytes derived from the female and her son, a carrier of the same mutation but with asymptomatic phenotype. Cardiomyocytes from both individuals expressed KCNH2 alleles with the ratio between 1:2 and 1:1 (wt:mut), thus allelic imbalance does not explain differences in the clinical phenotypes. All in all, the results of this thesis suggest that after further validation, mainly electrophysiology studies, these cell lines are most likely suitable to be applied for disease modeling, cardiotoxicity screening and finding new therapies for LQT2.

Abstract Background Long QT syndrome (LQTS) is an inherited cardiac disorder predisposing to sudden cardiac death (SCD). We studied factors affecting the clinical course of genetically confirmed patients, in particular those not receiving β-blocker treatment. In addition, an attempt was made to associate risk of events to specific types of KCNQ1 and KCNH2 mutations. Methods A follow-up study covering a mean of 18.6 ± 6.1 years was conducted in 867 genetically confirmed LQT1 and LQT2 patients and 654 non-carrier relatives aged 18–40 years. Cox regression models were used to evaluate the contribution of clinical and genetic risk factors to cardiac events. Results In mutation carriers, risk factors for cardiac events before initiation of β-blocker included LQT2 genotype (hazard ratio [HR] = 2.1, p = 0.002), female gender (HR = 3.2, p < 0.001), a cardiac event before the age of 18 years (HR = 5.9, p < 0.001), and QTc ≥500 ms (vs < 470 ms, HR = 2.7, p = 0.001). LQT1 patients carrying the KCNQ1 D317N mutation were at higher risk (HR = 3.0–3.9, p < 0.001–0.03) compared to G589D, c.1129-2A > G and other KCNQ1 mutation carriers after adjusting for gender, QTc duration, and cardiac events before age 18. KCNH2 c.453delC, L552S and R176W mutations associated with lower risk (HR = 0.11–0.23, p < 0.001) than other KCNH2 mutations. Conclusions LQT2 (compared to LQT1), female gender, a cardiac event before age 18, and long QT interval increased the risk of cardiac events in LQTS patients aged 18 to 40 years. The nature of the underlying mutation may be associated with risk variation in both LQT1 and LQT2. The identification of high-risk and low-risk mutations may enhance risk stratification.

Genome-wide sequencing may generate secondary findings (SFs). It is recommended that validated, clinically actionable SFs are reported back to patients/research participants. To explore publics’ perspectives on the best ways to do this, we performed a vignette study among Finnish adults. Our aim was to explore how lay people react to different types of hypothetical genomic SFs. Participants received a hypothetical letter revealing a SF predisposing to a severe but actionable disease - cardiovascular disease (familial hypercholesterolemia, long QT syndrome) or cancer (Lynch syndrome, Li–Fraumeni syndrome). Participants (N=29) wrote down their initial reactions, and discussed (N=23) these in focus groups. Data were analyzed using inductive thematic analysis. Reactions to hypothetical SFs varied according to perceived severity and familiarity of the diseases. SFs for cancer were perceived as more threatening than for cardiovascular diseases, but less distressing than risk for psychiatric or neurological disorders, which participants spontaneously brought up. Illness severity in terms of lived experience, availability of treatment, stigma, and individual’s responsibility to control risk were perceived to vary across these disease types. In addition to clinical validity and utility, SF reporting practices need to take into account potential familiarity and lay illness representations of different diseases. Illness representations may influence willingness to receive SFs, and individuals’ reactions to this information.