Recurrent intrauterine fetal loss due to near absence of HERG: clinical and functional characterization of a homozygous nonsense HERG Q1070X mutation.
BACKGROUND
Inherited arrhythmias may underlie intrauterine and neonatal arrhythmias. Resolving the molecular genetic nature of these rare cases provides significant insight into the role of the affected proteins in arrhythmogenesis and (extra-) cardiac development.


OBJECTIVE
The purpose of this study was to perform clinical, molecular, and functional studies of a consanguineous Arabian family with repeated early miscarriages and two intrauterine fetal losses in the early part of the third trimester of pregnancy due to persistent arrhythmias.


METHODS
In-depth clinical investigation was performed in two siblings, both of whom developed severe arrhythmia during the second trimester of pregnancy. Homozygosity mapping with microsatellite repeat polymorphic markers encompassing various cardiac ion channel genes linked to electrical instability of the heart was performed. Screening of the candidate gene in the homozygous locus was performed. Biochemical and electrophysiologic analysis was performed to elucidate the function of the mutated gene.


RESULTS
Screening of the HERG gene in the homozygous locus detected a homozygous nonsense mutation Q1070X in the HERG C-terminus in affected children. Biochemical and functional analysis of the Q1070X mutant showed that although the mutant HERG had the ability to traffic to the plasma membrane and to form functional channels, it was destroyed by the nonsense-mediated decay (NMD) pathway before its translation. NMD leads to near absence of HERG in homozygous Q1070X mutation carriers, causing debilitating arrhythmias (prior to birth) in homozygous carriers but no apparent phenotype in heterozygous carriers.


CONCLUSIONS
Homozygous HERG Q1070X is equivalent to near functional knockout of HERG. Clinical consequences appear early, originating during the early stages of embryonic life. The NMD pathway renders HERG Q1070X functionless before it can form a functional ion channel.
Bhuiyan
Zahurul A
ZA
Department of Clinical Genetics, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands. Z.A.Bhuiyan@amc.uva.nl
Momenah
Tarek S
TS
Gong
Qiuming
Q
Amin
Ahmad S
AS
Ghamdi
Saleh Al
SA
Carvalho
Julene S
JS
Homfray
Tessa
T
Mannens
Marcel M A M
MM
Zhou
Zhengfeng
Z
Wilde
Arthur A M
AA
D000022:Abortion, Spontaneous / Q000209:etiology / Q000235:genetics*; D000328:Adult; D018389:Codon, Nonsense; D003241:Consanguinity; D016757:Death, Sudden, Cardiac; D051638:Ether-A-Go-Go Potassium Channels / Q000235:genetics*; D005260:Female; D005313:Fetal Death / Q000209:etiology*; D005973:Glutamine; D006720:Homozygote; D006801:Humans; D007231:Infant, Newborn; D008133:Long QT Syndrome / Q000150:complications* / Q000235:genetics; D008297:Male; D010375:Pedigree; D010865:Pilot Projects; D011110:Polymorphism, Genetic; D011247:Pregnancy; D011263:Pregnancy Trimester, Third; D012008:Recurrence; D012307:Risk Factors
D018389:Codon, Nonsense; D051638:Ether-A-Go-Go Potassium Channels; C496884:KCNH1 protein, human; D005973:Glutamine