Haploinsufficiency in combination with aging causes SCN5A-linked hereditary Lenègre disease.
OBJECTIVE
The goal of this study was to investigate the genotype-to-phenotype relationship between SCN5A gene mutation and progressive cardiac conduction defect in order to gain insights into the pathophysiologic mechanisms of the disease.


BACKGROUND
Progressive cardiac conduction defect is a frequent disease commonly attributed to degeneration and fibrosis of the His bundle and its branches. In a French family, we have identified a splicing mutation in the SCN5A gene leading to hereditary progressive cardiac conduction defect.


METHODS
We have extended the size of the pedigree and phenotyped and genotyped all family members, and also investigated in vitro the functional consequences of the mutation.


RESULTS
Among 65 potentially affected members, 25 individuals were carriers of the IVS.22+2 T-->C SCN5A mutation. In relation to aging, gene carriers exhibit various types of conduction defects. P-wave, PR, and QRS duration increased progressively with age in gene carriers and in noncarriers. Whatever the age, conduction parameters were longer in gene carriers. The widening in the QRS complex with aging was more pronounced in gene carriers older than 40 years. Functional studies show that the IVS.22+2 T-->C SCN5A mutation lead to exon 22 skipping and to a complete loss of function of the affected allele, but to a normal trafficking of the mutated gene product.


CONCLUSIONS
Our findings demonstrate that hereditary Lenègre disease is caused by a haploinsufficiency mechanism, which in combination with aging leads to progressive alteration in conduction velocity.
Probst
Vincent
V
Cardiology Department, Hôpital G&R Laennec, Nantes, France.
Kyndt
Florence
F
Potet
Franck
F
Trochu
Jean-Noel
JN
Mialet
Guy
G
Demolombe
Sophie
S
Schott
Jean-Jacques
JJ
Baró
Isabelle
I
Escande
Denis
D
Le Marec
Hervé
H
D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D002648:Child; D005260:Female; D005838:Genotype; D006238:Haploidy; D006327:Heart Block / Q000209:etiology / Q000235:genetics* / Q000503:physiopathology*; D006329:Heart Conduction System / Q000503:physiopathology*; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D008875:Middle Aged; D009154:Mutation / Q000235:genetics*; D062554:NAV1.5 Voltage-Gated Sodium Channel; D010375:Pedigree; D010641:Phenotype; D015222:Sodium Channels / Q000235:genetics*
D062554:NAV1.5 Voltage-Gated Sodium Channel; C568320:SCN5A protein, human; D015222:Sodium Channels