Download One familial III degree atrioventricular block and its gene detection

Cardiology Plus Dec 2016, Vol 1. No 4
14
Research
RESEARCH ARTICLES
One familial III degree atrioventricular block and its
gene detection
Jin-chun Zhang, Damin Huang, Zhaoxia Wang, XiaohanLuo, Jian Ji, Lei Song, Zhihua Li,
Shuxin Hou, Caiwen Wei, Zengyan Zhao, Yingmin Lu *
Department of Cardiology, Chongming branch of Shanghai Xinhua Hospital, ShangHai, 200072, China
Abstract
Objective: To investigate the genetic basis of a Chinese familial third degree atrioventricular
block. Methods: The clinical data of all family members were collected, including physical
examination, electrocardiogram and echocardiography. Exome sequencing was performed for all
patients. Results: This family contains 22 members of which 6 are patients. Cardiac symptoms
appeared at forty years of age, starting with second degree atrioventricular block eventually developing
into third degree atrioventricular block. These 6 patients received permanent pacemaker implantation.
The genetic pedigree suggested that the autosomal disorder may not be completely dominant. Compared
with normal subjects, 24 different genes were detected in patients with familial atrioventricular block.
Conclusion: This family is unambiguously affected by familial atrioventricular block caused by
incomplete dominant inheritance of euchromosome, and another genetic mutations that may contribute
to it.
Key Words: Cardiology; Atrioventricular block; Arrhythmia; Family study; Gene mutation
Complete atrioventricular block (AVB), also known as third-
relatively rare and mainly related to gene mutations. Currently,
degree AVB, is complete atrioventricular dissociation caused by
two types of familial AVB have been proposed: a congenital type
abnormally decreased conduction ability in the atrioventricular
and an adult-onset type, both of which are autosomal dominant
conduction system. In this condition, the impulse generated in
genetic disorders. The former is relatively uncommon and can
the atrium of the heart cannot propagate to the ventricles. AVB
be seen at birth or during infancy. It is associated with very poor
is more common in patients over 50 years old and can have
prognosis and may be caused by maternal ribonucleoprotein
multiple causes, most of which are secondary. Familial AVB is
autoantibodies
[1]
. The latter has an onset in patients 30 to
50 years of age and is associated with various heart block
phenotypes with symptoms ranging in severity. Adult-onset
familial AVB is an incomplete autosomal dominant disease and
can result in syncope or sudden death [2]. In this study, a pedigree
Corresponding author : LU Yingmin. Department of Cardiology,
investigation was conducted for a patient with familial AVB.
chongming branch of shanghai xiahua hospital;
Preliminary genetic detection studies were performed for the
Email: [email protected]
pedigree and the results are reported.
Zhang et al III AVB block and gene detection
15
1 Data and Methods
1.1 Pedigree Investigation
The family members and spouse of the proband were included.
Medical histories were collected for the included respondents
and examinations including physical examination of
conventional systems, conventional 12-lead electrocardiogram
(24-h ambulatory electrocardiogram if necessary) and cardiac
ultrasound were performed. A family genetic map was generated
(see Figure 1). Blood samples were collected from each included
respondent into anticoagulant tubes, and the DNA was extracted
for genetic studies. All procedures were agreed upon by pedigree
investigators and all respondents signed informed consent forms.
The investigation was discussed and justified by the medical
ethics committee of Xinhua Hospital affiliated with the Shanghai
Jiao Tong University School of Medicine.
Figure 1 Family pedigree for familial atrioventricular block
1.2 Genetic Detection
1.2.1 Sample Collection
electrocardiogram suggested second-degree atrioventricular
5 mL of venous blood was collected and transferred into
block (AVB) and pre-excitation syndrome. The ambulatory
anticoagulant tubes. The tubes were placed in a horizontal
electrocardiogram also showed second-degree AVB and third-
centrifuge and centrifuged at 3000 RPM for 20 minutes. After
degree AVB in particular. Results of the heart echocardiography
centrifugation, the mononuclear cell layer between the plasma
indicated that measurement values for the four chambers of heart
and erythrocytes was obtained and DNA extraction from
were within the normal range, thickening of interventricular
the mononuclear cells was performed. Blood genomic DNA
septum (14 mm), a left ventricular ejection fraction of 67% and
isolation kits (TRIzol® Reagent, Life Technologies) were used
decreased left ventricular diastolic compliance. After admission,
for DNA extraction according to the manufacturer’s instructions.
the patient was given Xinbao pills and Salbutamol Sulfate to
1.2.2 Exome Sequencing
increase heart rate, however no improvement was observed. A
Through hybridization and enrichment of exon sequences,
single chamber pacemaker (VVI) implantation was performed in
low-quality reads were removed and the quantity of reads and
our hospital and the pacemaker was later replaced in 2011 due to
sequencing quality were summarized with quality control (QC).
battery charge depletion.
Short sequences were rapidly mapped to the genome, redundant
Family history of the patient was further inquired and other
reads from PCR amplification were removed by the rmdup tool,
members in the family had similar diseases. Therefore, other
multiple local sequence alignment was re-conducted and false
members in the family were also investigated. Six members
positives around indel were eliminated.
in the family had the disease, which is shown in the family
1.2.3 Mutation Analysis
pedigree (see Figure 1). The father of the proband received a
The base qualities were re-graded and the bases were screened.
VVI in Changhai Hospital, Shanghai in 1995 that was replaced
Possible pathogenic gene mutations screened were verified by
in our hospital in 2003. The younger brother of the proband
real-time PCR.
received a dual chamber pacemaker (DDD) in Renji Hospital,
Shanghai in 2005. The elder brother of his father received a
2 Results
VVI in our hospital in 2000. The younger male cousin received
2.1 Clinical Data
had a prior medical history of bradycardia (unknown medical
The 42-year-old male proband was admitted to the hospital
history) and had received a pacemaker for treatment.
a DDD in our hospital in 2003. The grandfather of the proband
due to “chest tightness and palpitations for 3 days”. He had
experienced these symptoms with occasional syncope in his
2.2 Mutant Gene Detection
30s without special treatment. After admission in 2003, the
The mutant genes of patients in the family were detected by
Cardiology Plus Dec 2016, Vol 1. No 4
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exome sequencing and the alignment with the healthy Asian
not have the disease, or are currently too young for its potential
population was performed. 24 differential genes were found,
onset.
including KDELC2, SEC14L2, SEC31A, DNAH9, EPB41L2,
Previous studies have reported that associated morbidity
RFX8, KBTBD12, KLHL29, LRRC59, LRP5, MUC6,
had a trend of familial aggregation, which suggested a gene
OLFML2B, PLXNA3, KCNH6, SALL1, ARMCX4, SLC22A16,
mutation. Possible causative genes (SCN5A, NKX2.5 and
STON2, TTF1, TMEM159, UNC13B, ZNF628, ZNF699 and
LMNA) were found in the proband and his family members.
ZRANB2.
Functional expression was performed for the gene mutation and
3 Discussion
[4-8]
a pathogenic electrophysiological mechanism was uncovered
. Many studies focus on the SCN 5A gene, which encodes
the voltage-gated sodium channel type V alpha subunit and is
Atrioventricular block (AVB) is mainly diagnosed according to
located on 3p21-24. This gene plays an important role in rapid
electrocardiogram findings and clinical manifestations include
depolarization, conduction and maintenance of the cardiac
symptoms such as palpitations, weariness, asthenia, dizziness
action potential. Mutations in this gene can alter sodium
and angina pectoris. Cerebral hypoperfusion as a result of AVB
channel function and reduce sodium inflow current, slowing
can cause symptoms including syncope and confusion. In severe
action potential firing and reducing their peak amplitude in the
cases heart failure and stroke can occur. The most effective
depolarization phase. Therefore, excitability and conductibility
treatment is permanent pacemaker implantation. AVB can be
of myocardial cells are reduced, impairing cardiac conduction
caused by a variety of factors with the most common being
velocity [9].
myocardial inflammation resulting from rheumatic and viral
DNA extraction from the patients in the family was performed
myocarditis as well as other infections, vagal excitation, adverse
for gene sequencing to detect mutant genes. No SCN5A mutant
drug reactions, organic heart diseases, trauma and surgery.
genes were found, suggesting that familial atrioventricular block
These causes were excluded by the pedigree investigation. For
might be caused by other gene mutations. Compared with the
the 6 patients with this disease in the pedigree investigation,
normal population, the patients in the family were found to have
electrocardiograms suggested pre-excitation syndrome with
24 abnormal genes including KDELC2, SEC14L2, SEC31A,
AVB. Initially, it was second-degree AVB that gradually
DNAH9, EPB41L2, RFX8, KBTBD12, KLHL29, LRRC59,
developed into third-degree AVB, constituting the family
LRP5, MUC6, OLFML2B, PLXNA3, KCNH6, SALL1,
pedigree of hereditary AVB. From the pedigree analysis,
ARMCX4, SLC22A16, STON2, TTF1, TMEM159, UNC13B,
hereditary transmission was continuous in the family with
ZNF628, ZNF699 and ZRANB2. Although these genes have
patients in 3 continuous generations. The patients in the family
different sequences compared to the normal population, not
were adult males, suggesting an incomplete autosomal dominant
all are necessarily related to the onset of AVB and need further
disease in the family.
characterization by cytology experiments. Among these genes,
Familial AVB is very rare clinically and occurs once patients
KCNH6, a gene encoding a potassium channel, can potentially
reach middle age. There is currently no treatment other than
be related to the onset of the disease in the family. Its mutation
pacemaker implantation to increase heart rate and this therapy
can increase the resting membrane potential and threshold
is generally recognized around the world [3], thus the quality
value and decrease the excitability and conductibility of the
of life for patients with this disease is greatly reduced. Defining
atrioventricular node or bundle branch.
the pathogenesis and causes of familial AVB plays a key role
Currently, there are only a small number of reports on familial
in prophylaxis and treatment. A total of 6 patients in the family
AVB in China [10-12] and its genetic basis requires further research.
presented with chest tightness and palpitations with syncope and
Although most studies focus on SCN5A gene mutation, onset
had heart rates of approximately 40 bpm before reaching the age
of the disease in this family was unrelated to the SCN5A gene.
of 40. Ambulatory electrocardiograms suggested bradycardia
In recent years, molecular biological techniques combined with
and AVB. In the family, I1, II2, II3, III2, III3 and III7 all
the use of patch-clamp electrophysiology further elucidate the
received permanent pacemaker implantation. IV1 and IV2 have
role of mutations in familial AVB. Such studies can contribute
no clinical manifestations of the disease. Electrocardiograms
to the early diagnosis of high-risk populations with hereditary
suggested pre-excitation syndrome, but no atrioventricular block,
susceptibility, making it possible to formulate reasonable
delayed interval or lost waves were found. These individuals
measures of prevention and treatment.
may require continued monitoring to determine if they indeed do
Zhang et al III AVB block and gene detection
References
1.
congenital heart block, integration of clinical and research
NKX2-5[J]. Science, 1998, 281(5373): 108-11 .
Benson DW. Genetics of atrioventricular conduction disease
cardiomyopathy and conduction-system disease[J]. N Engl J
in humans [J].Anat Rec A Discov Mol Cell Evol Biol, 2004,
Med, 1999, 341(23): 1715-1724.
9.
Wang DW, Viswanathan PC,Balser JR, et al.Clinical,
EpsteinAE, Dimarco JP, Ellenbogen KA, et al. ACC/
genetic, and biophysical characterization of SCN5A
AHA/HRS 2008 guidelines for Device-Based Therapy of
mutations associated with atrioventricular conduction block
Cardiac Rhythm Abnormalities:executive summary[J].
[J]. Circulation, 2002, 105(3):341.
10. LiBing,Zeng xuezhai,Yang jiefu,A familial atrioventricular
Schott JJ, ic AI, Kynd TF, et al. Cardiac conduction defects
block [J].Chinese journal of cardiology, 2003, 31(10): 775-5.
associate with mutations in SCN- 5A[J]. Nature Genet,
11. Yang chunmei,Huangjun ,Ma wenzhu,Familialy cardiac
Tan HL, Bink-Boelkens MT, Bezzina CR, et al. A sodiumchannel mutation causes isolated cardiac conduction
disease[J]. Nature, 2001, 409(6823): 1043-1047.
6.
Fatkin D, Macrae C, Sasaki T, et al. Missense mutations in
the rod domain of the lamin A/C gene as causes of dilated
1999, 23(1): 20-21.
5.
8.
[J].J Intern Med, 2009, 265(6): 653.
HeartRhythm, 2008, 5(6):934-55
4.
Jean-Jacques S, Woodrow BD, Basson CT, et al. Congenital
heart disease caused bymutations in the transcription factor
280(2): 934.
3.
7.
Buyon JP, Clancy RM, Friend DM.Autoimmune associate
clues in the management of the maternal/foetal dyad at risk
2.
17
Royer A, van Veen TA, Le Bouter S, et al. Mouse model
of SCN5A-linked hereditary Lenègre's disease:age-related
conduction slowing and myocardial fibrosis[J]. Circulation,
2005, 111(14): 1738-46.
conduction block and the cause,[J]. Chinese journal of
cardiology, 2000, 28(6): 476-7.
12. Qu haixia,Yanlu,Familialy atrioventricular block a follow-up
Practical electrocardiology magazine , 2006, 15(2): 126-7