Array comparative genomic hybridization identifies a heterozygous deletion of the entire KCNJ2 gene as a cause of sudden cardiac death

A novel complex genomic rearrangement affecting the KCNJ2 regulatory region causes a variant of Cooks syndrome

Cooks syndrome (CS) is an ultrarare limb malformation due to in tandem microduplications involving KCNJ2 and extending to the 5' regulatory element of SOX9. To date, six CS families were resolved at the molecular level. Subsequent studies explored the evolutionary and pathological complexities of the SOX9-KCNJ2/Sox9-Kcnj2 locus, and suggested a key role for the formation of novel topologically associating domain (TAD) by inter-TAD duplications in causing CS. Here, we report a unique case of CS associated with a de novo 1;17 translocation affecting the KCNJ2 locus. On chromosome 17, the breakpoint mapped between KCNJ16 and KCNJ2, and combined with a ~ 5 kb deletion in the 5' of KCNJ2. Based on available capture Hi-C data, the breakpoint on chromosome 17 separated KCNJ2 from a putative enhancer. Gene expression analysis demonstrated downregulation of KCNJ2 in both patient's blood cells and cultured skin fibroblasts. Our findings suggest that a complex rearrangement falling in the 5' of KCNJ2 may mimic the developmental consequences of in tandem duplications affecting the SOX9-KCNJ2/Sox9-Kcnj2 locus. This finding adds weight to the notion of an intricate role of gene regulatory regions and, presumably, the related three-dimensional chromatin structure in normal and abnormal human morphology.

Andersen-Tawil Syndrome: A Comprehensive Review

Andersen-Tawil syndrome (ATS) is a very rare orphan genetic multisystem channelopathy without structural heart disease (with rare exceptions). ATS type 1 is inherited in an autosomal dominant fashion and is caused by mutations in the KCNJ2 gene, which encodes the α subunit of the K+ channel protein Kir2.1 (in ≈ 50-60% of cases). ATS type 2 is in turn linked to a rare mutation in the KCNJ5-GIRK4 gene that encodes the G protein-sensitive-activated inwardly rectifying K+ channel Kir3.4 (15%), which carries the acetylcholine-induced potassium current. About 30% of cases are de novo/sporadic, suggesting that additional as-yet unidentified genes also cause the disorder. A triad of periodic muscle paralysis, repolarization changes in the electrocardiogram, and structural body changes characterize ATS. The typical muscular change is episodic flaccid muscle weakness. Prolongation of the QU/QUc intervals and normal or minimally prolonged QT/QTc intervals with a tendency to ventricular arrhythmias are typical repolarization changes. Bidirectional ventricular tachycardia is the hallmark ventricular arrhythmia, but also premature ventricular contractions, and rarely, polymorphic ventricular tachycardia of torsade de pointes type may be present. Patients with ATS have characteristic physical developmental dysmorphisms that affect the face, skull, limbs, thorax, and stature. Mild learning difficulties and a distinct neurocognitive phenotype (deficits in executive function and abstract reasoning) have been described. About 60% of affected individuals have all features of the major triad. The purpose of this review is to present historical aspects, nomenclature (observations/criticisms), epidemiology, genetics, electrocardiography, arrhythmias, electrophysiological mechanisms, diagnostic criteria/clues of periodic paralysis, prognosis, and management of ATS.

Long QT molecular autopsy in sudden unexplained death in the young (1-40 years old): Lessons learnt from an eight year experience in New Zealand

BACKGROUND

To review long QT syndrome molecular autopsy results in sudden unexplained death in young (SUDY) between 2006 and 2013 in New Zealand.

METHODS

Audit of the LQTS molecular autopsy results, cardiac investigations and family screening data from gene-positive families.

RESULTS

During the study period, 365 SUDY cases were referred for molecular autopsy. 128 cases (35%) underwent LQTS genetic testing. 31 likely pathogenic variants were identified in 27 cases (21%); SCN5A (14/31, 45%), KCNH2 (7/31, 22%), KCNQ1 (4/31, 13%), KCNE2 (3/31, 10%), KCNE1 (2/31, 7%), KCNJ2 (1/31, 3%). Thirteen variants (13/128, 10%) were ultimately classified as pathogenic. Most deaths (63%) occurred during sleep. Gene variant carriage was more likely with a positive medical history (mostly seizures, 63% vs 36%, p = 0.01), amongst females (36% vs 12%, p = 0.001) and whites more than Maori (31% vs 0, p = 0.0009). Children 1-12 years were more likely to be gene-positive (33% vs 14%, p = 0.02). Family screening identified 42 gene-positive relatives, 18 with definitive phenotypic expression of LQTS/Brugada. 76% of the variants were maternally inherited (p = 0.007). Further family investigations and research now support pathogenicity of the variant in 13/27 (48%) of gene-positive cases.

CONCLUSION

In New Zealand, variants in SCN5A and KCNH2, with maternal inheritance, predominate. A rare variant in LQTS genes is more likely in whites rather than Maori, females, children 1-12 years and those with a positive personal and family history of seizures, syncope or SUDY. Family screening supported the diagnosis in a third of the cases. The changing classification of variants creates a significant challenge.

Genetic variations involved in sudden cardiac death and their associations and interactions

Although the mechanism of sudden cardiac death (SCD) in heart failure is not completely known, genetic variations are known to play key roles in this process. Increasing numbers of mutations and variants are being discovered through genome-wide association studies. The genetic variations involved in the mechanisms of SCD have aroused widespread concern. Comprehensive understanding of the genetic variations involved in SCD may help prevent it. To this end, we briefly reviewed the genetic variations involved in SCD and their associations and interactions, and observed that cardiac ion channels are the core molecules involved in this process. Genetic variations involved in cardiac structure, cardiogenesis and development, cell division and differentiation, and DNA replication and transcription are all speculated to be loci involved in SCD. Additionally, the systems involved in neurohumoral regulation as well as substance and energy metabolism are also potentially responsible for susceptibility to SCD. They form an elaborate network and mutually interact with each other to govern the fate of SCD-susceptible individuals.

Variability in a three-generation family with Pierre Robin sequence, acampomelic campomelic dysplasia, and intellectual disability due to a novel ∼1 Mb deletion upstream of SOX9, and including KCNJ2 and KCNJ16

BACKGROUND

Campomelic dysplasia and acampomelic campomelic dysplasia (ACD) are allelic disorders due to heterozygous mutations in or around SOX9. Translocations and deletions involving the SOX9 5' regulatory region are rare causes of these disorders, as well as Pierre Robin sequence (PRS) and 46,XY gonadal dysgenesis. Genotype-phenotype correlations are not straightforward due to the complex epigenetic regulation of SOX9 expression during development.

METHODS

We report a three-generation pedigree with a novel ∼1 Mb deletion upstream of SOX9 and including KCNJ2 and KCNJ16, and ascertained for dominant transmission of PRS.

RESULTS

Further characterization of the family identified subtle appendicular anomalies and a variable constellation of axial skeletal features evocative of ACD in several members. Affected males showed learning disability.

CONCLUSION

The identified deletion was smaller than all other chromosome rearrangements associated with ACD. Comparison with other reported translocations and deletions involving this region allowed further refining of genotype-phenotype correlations and an update of the smallest regions of overlap associated with the different phenotypes. Intrafamilial variability in this pedigree suggests a phenotypic continuity between ACD and PRS in patients carrying mutations in the SOX9 5' regulatory region.

Array comparative genomic hybridization identifies a heterozygous deletion of exon 3 of the RYR2 gene

BACKGROUND

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a heritable cardiac disorder characterized by life-threatening ventricular tachycardia caused by exercise or acute emotional stress. The standard diagnostic screening involves Sanger-based sequencing of 45 of the 105 translated exons of the RYR2 gene, and copy number changes of a limited number of exons that are detected using multiplex ligation-dependent probe amplification (MLPA).

METHODS

In the current study, a previously validated bespoke array comparative genomic hybridization (aCGH) technique was used to detect copy number changes in the RYR2 gene in a 43-year-old woman clinically diagnosed with CPVT.

RESULTS

The CGH array detected a 1.1 kb deletion encompassing exon 3 of the RYR2 gene. This is the first report using the aCGH technique to screen for mutations causing CPVT.

CONCLUSIONS

The aCGH method offers significant advantages over MLPA in genetic screening for heritable cardiac disorders.