A novel missense mutation in obscurin gene in a Chinese consanguineous family with left ventricular noncompaction

BACKGROUNDLeft ventricular noncompaction (LVNC) is an increasingly recognised cardiomyopathy of which a significant percentage are genetic in origin. The purpose of the present study was to identify potential pathogenic mutation leading to disease in a Chinese LVNC family.METHODSA 3-generation family affected by LVNC was recruited. Clinical assessments were performed on available family members, with clinical examination, ECG, echocardiography and cardiac MRI. The proband (I-2), the proband’s daughter (II-1, affected) and mother (III-1, unaffected) were selected for WGS. Sanger sequencing were performed in all of the 4 surviving family members.RESULTSCombined whole genome sequencing with linkage analysis identified a novel missense mutation in the giant protein obscurin (OBSCN {"type":"entrez-nucleotide","attrs":{"text":"NM_001098623","term_id":"403501445","term_text":"NM_001098623"}}NM_001098623, c.C19063T), as the only plausible disease-causing variant that segregates with disease among the four surviving individuals, with interrogation of the entire genome excluding other potential causes. This c.C19063T missense mutation resulted in p.R6355W in the encoded OBSCN protein. It affected a highly conserved residue in the C terminus of the obscurin-B-like isoform between the PH and STKc domains, which was predicted to affect the function of the protein by different bioinformatics tools. CONCLUSIONSHere we present clinical and genetic evidence implicating the novel R6355W missense mutation in obscurin as the cause of familial LVNC. This expands the spectrum of obscurin’s roles in cardiomyopathies. It furthermore highlights that rare obscurin missense variants, currently often ignored or left uninterpreted, should be considered to be relevant for cardiomyopathies and can be identified by the approach presented here. This study also provided new insights into the molecular basis of OBSCN mutation positive LVNC.

Left ventricular noncompaction (LVNC) is a relatively rare cardiomyopathy, with or without left ventricular dysfunction, that is characterized by excessively prominent trabeculations and associated deep recesses that communicate with the ventricular cavity.^[1] LVNC is one of the unclassified cardiomyopathies according to the genetic cardiomyopathies classified by the American Heart Association.^[2] The prevalence of LVNC was estimated to be 0.014%−1.3% depending on the age of the patients. The phenotypic expression and evolution of isolated LVNC are highly variable, and clinical features can range from asymptomatic to symptomatic, with a relatively stable course over several years or an evolution toward severe complications including congestive heart failure, ventricular arrhythmia and sudden cardiac death, atrial arrhythmias, and systemic embolic events. LVNC is supposed to be related to premature arrest of compaction of the loose myocardial meshwork during fetal embryogenesis, with persistent trabeculated myocardium, but the precise pathophysiology remains poorly understood. The predominant mode of inheritance is autosomal dominant, with some cases with X-linked transmission. Several genes have been identified as causing LVNC disease. The first reported genetic cause of isolated LVNC was the X-linked tafazzin (TAZ) gene, which also causes Barth syndrome.^[3] The sarcomere-encoding genes (MYH7, ACTC1, TNNT2, MYBPC3, TMP1, TNNI3) have been found to account for 17%–30% of LVNC.^[4,5] Other genes such as DTNA (α-dystrobrevin), NKX2.5, Z-line protein-encoding ZASP/LDB3, and lamin A/C (LMNA) have been also associated with LVNC.^[6] A clinical study by Rowland, et al.^[7] identified a possible association between LVNC and variants in the obscurin (OBSCN) gene. However, the pathogenic involvement of OBSCN in LVNC is unclear. Obscurins (molecular weight about 700 to 900 kDa) are very giant sarcomeric proteins that interact with several other binding partners including titin, myomesmin, and obscurin-like-1 to generate a complex important for myofibrillar M-band function. It plays key roles in myofibrillogenesis and cytoskeletal arrangement.^[8,9] A single study in 2007 reported the association of OBSCN mutations with hypertrophic cardiomyopathy (HCM).^[10] OBSCN variants are now considered to be relatively common in inherited cardiomyopathies. For example, Marston, et al.^[11] found five unique OBSCN variants in four hearts from a group of 30 end-stage failing hearts, Xu, et al.^[12] found six unique OBSCN variants in 74 HCM cases, and Rowland, et al.^[7] found four unique OBSCN variants in 335 patients with dilated cardiomyopathy or LVNC, and OBSCN variants were associated with three out of the 11 LVNC cases. Chen, et al.^[13] also identified an OBSCN frameshift mutation in a patient with arrhythmogenic right ventricular cardiomyopathy (ARVC) (Table 1). However, in all of these studies, family members of the probands were unavailable for segregation analysis of the OBSCN variants. Table 1Cardiomyopathy-linked OBSCN mutations based on the Obscurin B sequence {"type":"entrez-protein","attrs":{"text":"NP_001092093","term_id":"403501446","term_text":"NP_001092093"}}NP_001092093.

	Mutation	CM type	Domain	Patient clinical data	Patient sex	Patient age
Arimura, et al.[10]	R4344Q	HCM	Ob58	No avaliable data	Male	19
	A4484T	HCM	Ob59
Marston, et al.[11]	E963K	DCM	Ob9	LVEF10%, NYHA IV; LVEDD 70, VESD 63, FS10%,	Male	43
	V2161D	DCM	Ob21	LVEF20%, LVEDD 73, LVESD 63, FS13%	Male	17
	F2809V	DCM	Ob27
	R4856H	DCM	Ob47	NYHA IV; IDCM plus mild CAD	Male	56
	D5966N	DCM	PH	Lifelong CM from 8 yr, exercise tachycardia	Male	43
Rowland, et al.[7]	T6309R	LVNC	Between Ob66 and Ob67	Dyspnea on exertion; chest pains; NYHA II-III; LVEF21%, LVEDD60mm;	Male	56
	S6990P	LVNC	Between kinase I and Ob69	Shortness of breath; NYHAI-II; LVEF56%, LVEDD43mm;	Female	30
	A6993P	DCM	Between kinase I and Ob69	Shortness of breath; NYHA II-III; LVEF26%, LVEDD70.8mm;	Female	62
	C25367-1G > C	LVNC		Shortness of breath; chest pains; fatigue; NYHA III; LVEF30-33%, LVEDD60mm;	Male	39
Xu, et al. [12]	A996fs	HCM	Ob10	No avaliable data	No avaliable data	No avaliable data
	A1088fs	HCM	Ob11	No avaliable data	No avaliable data	No avaliable data
	A1272fs	HCM	Ob13	No avaliable data	No avaliable data	No avaliable data
	A1640fs	HCM	Ob17	No avaliable data	No avaliable data	No avaliable data
	G7500R	HCM	Ob69	No avaliable data	No avaliable data	No avaliable data
Forleo, et al.[22]	E268X	HCM	Ig domain	No avaliable data	No avaliable data	No avaliable data
	A5660V	DCM	SH3_Obscurin_like	No avaliable data	No avaliable data	No avaliable data
	R6669H	DCM	STKc_obscurin_rpt1	No avaliable data	No avaliable data	No avaliable data
	A5791P	ARVC	RhoGEF	No avaliable data	No avaliable data	No avaliable data

Open in a separate windowIn the present study, we identified a novel OBSCN mutation in a medium-sized Chinese pedigree with LVNC. By performing whole genome sequencing in two family members, filtering against variants seen in normal population cohorts, and using linkage information derived from single nucleotide polymorphism (SNP) arrays of four family members, we identified a missense mutation in OBSCN ({"type":"entrez-nucleotide","attrs":{"text":"NM_001098623","term_id":"403501445","term_text":"NM_001098623"}}NM_001098623: c.C19063T:p.R6355W) as the most plausible cause of LVNC in the family.