Phenotype, origin and estimated prevalence of a common long QT syndrome mutation: a clinical, genealogical and molecular genetics study including Swedish R518X/KCNQ1families

Table 1 Clinical characteristics of the Swedish R518X/ KCNQ1 study population

	JLNS^a,b	LQTS^a
Cases	15	86
Females	8 (53)	54 (63)
Age at last follow-up, years	29 ± 23, 28	34 ± 21, 37
Non-medicated follow-up, years	16 ± 20, 9	31 ± 21, 33
Experience of first cardiac event	12 (80)	15 (17)
Age at onset, years	2 ± 1, 3	18 ± 15, 12
Experience of ACA/SCD	7 (47)	1 (1)
Number of events	9	1
Non-medicated life-years, n	241	2466
Annual incidence rate before therapy,%^c	4	0.04
Triggers of symptoms,%
Exercise/Swimming/Emotions/Other	46/ 12/ 2/ 20	44/ 2/ 22/ 32
ECG (% recorded off therapy)	11^d (27)	81 (73)
QTc, ms^e	576 ± 61, 560	462 ± 34, 459
<440 ms	0 (0)	20 (25)
≥500 ms	10 (91)	13 (17)
Heart rate, bpm	77 ± 23, 75	73 ± 20, 69
Beta-blocker therapy	11^f (73)	37 (43)
Age at therapy start, years	8 ± 15, 2^g	25 ± 19, 17

Abbreviations: JLNS- Jervell and Lange-Nielsen syndrome, LQTS- long QT syndrome, ACA- aborted cardiac arrest requiring resuscitation (not including device therapy), SCD- sudden cardiac death.
^a Values are expressed as number of patients (percentage of total), or as mean ± standard deviation, followed by median, if not otherwise specified.
^b Clinical data on JLNS cases have been previously described together with all identified Swedish JLNS cases, by our group [4]. JLNS cases in family JLN5 have been described previously by others, [14] our study is based on contact with the proband in 2010.
^c Calculated as number of life-threatening events/sum of non-medicated life years (×100).
^d Electrocardiograms were not available from the four deceased JLNS cases in family JLN5.
^e Intra-observer measurement error 0.4 ± 5.7 ms between repeated measurements, coefficient of variation 0.1%.
^f All now living JLNS cases were on beta-blocker therapy.
^g Among JLNS cases born from 1980 and onwards (n=8), 3 received beta-blockers during the first year of life and the remaining 5 received beta-blockers during the first 3 years of life.

ISSN: 1471-2261