First description of germline mosaicism in familial hypertrophic cardiomyopathy

Low-frequency maternal novel MYH7 mosaicism mutation in recurrent fetal-onset severe left ventricular noncompaction: a case report

Background

Left ventricular noncompaction (LVNC) is a rare inherited cardiomyopathy with a broad phenotypic spectrum. The genotype-phenotype correlations in fetal-onset LVNC have not yet been fully elucidated. In this report, we present the first case of severe fetal-onset LVNC caused by maternal low-frequency somatic mosaicism of the novel myosin heavy chain 7 (MYH7) mutation.

Case presentation

A 35-year-old pregnant Japanese woman, gravida 4, para 2, with no significant medical or family history of genetic disorders, presented to our hospital. In her previous pregnancy at 33 years of age, she delivered a male neonate at 30 weeks of gestation with cardiogenic hydrops fetalis. Fetal echocardiography confirmed LVNC prenatally. The neonate died shortly after birth. In the current pregnancy, she again delivered a male neonate with cardiogenic hydrops fetalis caused by LVNC at 32 weeks of gestation. The neonate died shortly after birth. Genetic screening of cardiac disorder-related genes by next-generation sequencing (NGS) was performed which revealed a novel heterozygous missense MYH7 variant, NM_000257.3: c.2729A > T, p.Lys910Ile. After targeted and deep sequencing by NGS, the same MYH7 variant (NM_000257.3: c.2729A > T, p.Lys910Ile) was detected in 6% of the variant allele fraction in the maternal sequence but not in the paternal sequence. The MYH7 variant was not detected by conventional direct sequencing (Sanger sequencing) in either parent.

Conclusions

This case demonstrates that maternal low-frequency somatic mosaicism of an MYH7 mutation can cause fetal-onset severe LVNC in the offspring. To differentiate hereditary MYH7 mutations from de novo MYH7 mutations, parental targeted and deep sequencing by NGS should be considered in addition to Sanger sequencing.

Sperm mosaicism: implications for genomic diversity and disease

While sperm mosaicism has few consequences for men, the offspring and future generations are unwitting recipients of gonadal cell mutations, often yielding severe disease. Recent studies, fueled by emergent technologies, show that sperm mosaicism is a common source of de novo mutations (DNMs) that underlie severe pediatric disease as well as human genetic diversity. Sperm mosaicism can be divided into three types: Type I arises during sperm meiosis and is non-age dependent; Type II arises in spermatogonia and increases as men age; and Type III arises during paternal embryogenesis, spreads throughout the body, and contributes stably to sperm throughout life. Where Types I and II confer little risk of recurrence, Type III may confer identifiable risk to future offspring. These mutations are likely to be the single largest contributor to human genetic diversity. New sequencing approaches may leverage this framework to evaluate and reduce disease risk for future generations.

Investigation of de novo variation in pediatric cardiomyopathy

Pediatric cardiomyopathies can be caused by variants in genes encoding the sarcomere and cytoskeleton in cardiomyocytes. Variants are typically inherited in an autosomal dominant manner with variable expressivity. De novo variants have been reported, however their overall frequency is largely unknown. We sought to determine the rate of de novo, pathogenic and likely pathogenic (P/LP) variants in children with a diagnosis of hypertrophic, dilated, or restrictive cardiomyopathy (HCM, DCM, or RCM), and to compare disease outcomes between individuals with and without a de novo variant. A retrospective record review identified 126 individuals with HCM (55%), DCM (37%), or RCM (8%) ≤18 years of age who had genetic testing. Overall, 50 (40%) had positive genetic testing and 18% of P/LP variants occurred de novo. The rate of de novo variation in those with RCM (80%) was higher than in those with HCM (9%) or DCM (20%). There was evidence of germline mosaicism in one family with RCM. Individuals with de novo variants were more likely than those without to have a history of arrhythmia (p = .049), sudden cardiac arrest (p = .024), hospitalization (p = .041), and cardiac transplantation (p = .030). The likelihood of de novo variation and impact on family risk and screening should be integrated into genetic counseling.

Arrhythmogenic Right Ventricular Cardiomyopathy-Associated Desmosomal Variants Are Rarely De Novo

BACKGROUND

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is associated with pathogenic/likely pathogenic (P/LP) variants in genes encoding the cardiac desmosomal proteins. Origin of these variants, including de novo mutation rate and extent of founder versus recurrent variants has implications for variant adjudication and clinical care, yet this has never been systematically investigated.

METHODS

We identified arrhythmogenic right ventricular cardiomyopathy probands who met 2010 Task Force Criteria and had undergone genotyping that included sequencing of the desmosomal genes (PKP2, DSP, DSG2, DSC2, and JUP) from 3 arrhythmogenic right ventricular cardiomyopathy registries in America and Europe. We classified the desmosomal variants, defined the contribution of unique versus nonunique (ie, not family-specific) P/LP variants, and identified the frequency and characteristics of de novo variants. Next, we haplotyped nonunique variants to determine how often they likely represent a single mutation event in a common ancestor (implied by shared haplotypes) versus multiple mutation events at the same genetic location.

RESULTS

Of 501 arrhythmogenic right ventricular cardiomyopathy probands, 322 (64.3%) carried 327 desmosomal P/LP variants. Most variants (n=247, 75.6%, in 245 patients) were identified in more than one proband and, therefore, considered nonunique. For 212/327 variants (64.8%) genetic cascade screening was performed extensively enough to identify the parental origin of the P/LP variant. Only 3 variants were de novo, 2 of which were whole gene deletions. For 24 nonunique P/LP PKP2 variants, haplotyping was conducted in 183 available families. For all 24 variants, multiple seemingly unrelated families sharing identical haplotypes were identified, suggesting that these variants originate from common founders.

CONCLUSIONS

Most desmosomal P/LP variants are inherited, nonunique, and originate from ancient founders. Two of 3 de novo variants were large deletions. These observations inform genetic testing, cascade screening, and variant adjudication.

A novel TAZ gene mutation and mosaicism in a Polish family with Barth syndrome

Barth syndrome (BTHS) is an X-linked recessive disease primarily affecting males. Clinically, the disease is characterized by hypertrophic or dilated cardiomyopathy, skeletal myopathy, chronic/cyclic neutropenia, 3-methylglutaconic aciduria, growth retardation and respiratory chain dysfunction. It is caused by mutations in the TAZ gene coding for the tafazzin protein which is responsible for cardiolipin remodeling. In this work, we present a novel pathogenic TAZ mutation c.83T>A, p.Val28Glu, found in mosaic form in almost all female members of a Polish family. Sanger sequencing of DNA from peripheral blood and from epithelial cells showed female mosaicism in three generations. This appears to be a new mechanism of inheritance and further research is required in order to understand the mechanism of this mosaicism. We conclude that BTHS genetic testing should include two or more tissues for women that appear to be noncarriers when blood DNA is initially tested. The results of our study should not only be applicable to BTHS families, but also to families with other X-linked diseases.

Mosaic KCNJ2 mutation in Andersen-Tawil syndrome: targeted deep sequencing is useful for the detection of mosaicism

Andersen-Tawil syndrome (ATS) is an inherited disease characterized by ventricular arrhythmias, periodic paralysis, and dysmorphic features. It results from a heterozygous mutation of KCNJ2, but little is known about mosaicism in ATS. We performed genetic analysis of KCNJ2 in 32 ATS probands and their family members and identified KCNJ2 mutations in 25 probands, 20 families who underwent extensive genetic testing. These tests revealed that seven probands carried de novo mutations while 13 carried inherited mutations from their parents. We then specifically assessed a single proband and the respective family. The proband was a 9 year old girl who fulfilled the ATS triad and carried an insertion mutation (p.75_76insThr). We determined that the proband's mother carried a somatic mosaicism and that the proband's younger brother also carried the ATS phenotype with the same insertion mutation. The mother, who exhibited mosaicism, was asymptomatic, although she exhibited Q(T)U prolongation. Mutant allele frequency was 11% as per TA cloning and 17.3% as per targeted deep sequencing. Our observations suggest that targeted deep sequencing is useful for the detection of mosaicism and that the detection of mosaic mutations in parents of apparently sporadic ATS patients can help in the process of genetic counseling.

Molecular genetics in hypertrophic cardiomyopathy: towards individualized management of the disease

Hypertrophic cardiomyopathy is a relatively common genetic disease, affecting one person per 500 in the general population, and is clinically defined by the presence of unexplained left ventricular hypertrophy. Although recognized as the most common cause of sudden death in the young (especially in athletes), the cardiac expression of the disease is highly variable with respect to age at onset, degree of symptoms and risk of cardiac death. As a consequence, therapeutic strategies are diverse and must be adapted to the specific features of an individual. Recently, the molecular bases of the disease have been unraveled with the identification of a large number of mutations in genes encoding sarcomeric proteins. This review focuses on the impact of the molecular data on the understanding of the disease, and considers the emerging issues regarding the impact of molecular testing on the management of patients (or relatives) in clinical practice.

Founder mutations in hypertrophic cardiomyopathy patients in the Netherlands

In this part of a series on cardiogenetic founder mutations in the Netherlands, we review the Dutch founder mutations in hypertrophic cardiomyopathy (HCM) patients. HCM is a common autosomal dominant genetic disease affecting at least one in 500 persons in the general population. Worldwide, most mutations in HCM patients are identified in genes encoding sarcomeric proteins, mainly in the myosin-binding protein C gene (MYBPC3, OMIM #600958) and the beta myosin heavy chain gene (MYH7, OMIM #160760). In the Netherlands, the great majority of mutations occur in the MYBPC3, involving mainly three Dutch founder mutations in the MYBPC3 gene, the c.2373_2374insG, the c.2864_2865delCT and the c.2827C>T mutation. In this review, we describe the genetics of HCM, the genotype-phenotype relation of Dutch founder MYBPC3 gene mutations, the prevalence and the geographic distribution of the Dutch founder mutations, and the consequences for genetic counselling and testing. (Neth Heart J 2010;18:248-54.).

Cardiac troponin mutations and restrictive cardiomyopathy

Mutations in sarcomeric proteins have recently been established as heritable causes of Restrictive Cardiomyopathy (RCM). RCM is clinically characterized as a defect in cardiac diastolic function, such as, impaired ventricular relaxation, reduced diastolic volume and increased end-diastolic pressure. To date, mutations have been identified in the cardiac genes for desmin, α-actin, troponin I and troponin T. Functional studies in skinned muscle fibers reconstituted with troponin mutants have established phenotypes consistent with the clinical findings which include an increase in myofilament Ca²⁺ sensitivity and basal force. Moreover, when RCM mutants are incorporated into reconstituted myofilaments, the ability to inhibit the ATPase activity is reduced. A majority of the mutations cluster in specific regions of cardiac troponin and appear to be mutational “hot spots”. This paper highlights the functional and clinical characteristics of RCM linked mutations within the troponin complex.

Gonadal mosaicism of a TAZ (G4.5) mutation in a Japanese family with Barth syndrome and left ventricular noncompaction

TAZ (G4.5) was initially identified as the gene associated with Barth syndrome and left ventricular noncompaction (LVNC). The purpose of this study was to investigate patients with LVNC for disease-causing mutations in TAZ. In 124 Japanese patients, including 50 families, mutation analysis of TAZ was performed using DNA sequencing. A splice donor mutation was identified in two brothers with Barth syndrome and LVNC, and a sister who was asymptomatic. However, the variant was not identified in either parent or the maternal grandparents, all of whom were asymptomatic. Due to the recurrent inheritance of this variant by each of the children we concluded that this was evidence of gonadal mosaicism in the obligate carrier mother, the first reported occurrence of this in Barth syndrome.

A clinico-genetic study of renal coloboma syndrome in children

Renal coloboma syndrome (RCS) is an autosomal dominant disorder caused by PAX2 gene mutations and characterized by renal hypoplasia and optic disc coloboma. The clinical findings were retrospectively reviewed, and all coding regions of the PAX2 gene were sequenced, in six children with RCS. A c.619_620insG mutation was detected in five patients, including two siblings, and a novel p.Arg104X mutation was detected in one patient. All the patients had progressive renal dysfunction and bilateral hypoplastic kidneys without vesicoureteral reflux (VUR), but the rate of progression to end-stage renal disease showed some diversity. The ocular manifestations showed wide variability, ranging from subtle optic disc anomalies to microphthalmia. In one family with two affected siblings, maternal germline mosaicism was suggested by an intragenic microsatellite marker study. In conclusion, there are variable renal and ocular manifestations in RCS without significant phenotype-genotype correlations. VUR is not a cardinal renal manifestation of RCS. The possibility of germline mosaicism should be considered during molecular diagnosis and genetic counseling for PAX2 mutations.

The pathology of hypertrophic cardiomyopathy

Sudden cardiac death (SCD) is devastating at any age, but even more so when the individual affected is young and asymptomatic, and the death is entirely unexpected. SCD is a catastrophic complication of hypertrophic cardiomyopathy (HCM) and may be the first manifestation of this disease. HCM is an inherited intrinsic disease of the myocardium characterized by left ventricular hypertrophy without chamber dilatation, in the absence of either a systemic or other cardiac disease, which may cause a similar magnitude of hypertrophy. HCM may be a clinically silent disease. Indeed, the pathologist may be the first to encounter a case of HCM at autopsy. HCM has wide-ranging implications for affected families, who will require cardiac screening and genetic counselling even if mutations are not known. Therefore, prompt and accurate diagnosis of HCM is vital. This review article will focus on the pathological diagnosis of HCM, recent advances in the genetics of this disease, and common pitfalls which may arise, leading to diagnostic uncertainty.

Permanent neonatal diabetes due to paternal germline mosaicism for an activating mutation of the KCNJ11 Gene encoding the Kir6.2 subunit of the beta-cell potassium adenosine triphosphate channel

Activating mutations in the KCNJ11 gene encoding for the Kir6.2 subunit of the beta-cell ATP-sensitive potassium channel have recently been shown to be a common cause of permanent neonatal diabetes. In 80% of probands, these are isolated cases resulting from de novo mutations. We describe a family in which two affected paternal half-siblings were found to be heterozygous for the previously reported R201C mutation. Direct sequencing of leukocyte DNA showed that their clinically unaffected mothers and father were genotypically normal. Quantitative real-time PCR analysis of the father's leukocyte DNA detected no trace of mutant DNA. These results are consistent with the father being a mosaic for the mutation, which is restricted to his germline. This is the first report of germline mosaicism in any form of monogenic diabetes. The high percentage of permanent neonatal diabetes cases due to de novo KCNJ11 mutations suggests that germline mosaicism may be common. The possibility of germline mosaicism should be considered when counseling recurrence risks for the parents of a child with an apparently de novo KCNJ11 activating mutation.

Recurrent Third-Trimester Fetal Loss and Maternal Mosaicism for Long-QT Syndrome

Background— The importance of germ-line mosaicism in genetic disease is probably underestimated, even though recent studies indicate that it may be involved in 10% to 20% of apparently de novo cases of several dominantly inherited genetic diseases.

Methods and Results— We describe here a case of repeated germ-line transmission of a severe form of long-QT syndrome (LQTS) from an asymptomatic mother with mosaicism for a mutation in the cardiac sodium channel, SCN5A . A male infant was diagnosed with ventricular arrhythmias and cardiac decompensation in utero at 28 weeks and with LQTS after birth, ultimately requiring cardiac transplantation for control of ventricular tachycardia. The mother had no ECG abnormalities, but her only previous pregnancy had ended in stillbirth with evidence of cardiac decompensation at 7 months’ gestation. A third pregnancy also ended in stillbirth at 7 months, again with nonimmune fetal hydrops. The surviving infant was found to have a heterozygous mutation in SCN5A ( R1623Q ), previously reported as a de novo mutation causing neonatal ventricular arrhythmia and LQTS. Initial studies of the mother detected no genetic abnormality, but a sensitive restriction enzyme-based assay identified a small (8% to 10%) percentage of cells harboring the mutation in her blood, skin, and buccal mucosa. Cord blood from the third fetus also harbored the mutant allele, suggesting that all 3 cases of late-term fetal distress resulted from germ-line transfer of the LQTS-associated mutation.

Conclusions— Recurrent late-term fetal loss or sudden infant death can result from unsuspected parental mosaicism for LQTS-associated mutations, with important implications for genetic counseling.

Somatic and germinal mosaicism for the steroid sulfatase gene deletion in a steroid sulfatase deficiency carrier

Steroid sulfatase deficiency results in X-linked ichthyosis, an inborn error of metabolism in which the principal molecular defect is the complete deletion of the steroid sulfatase gene and flanking markers. Mosaicism for the steroid sulfatase gene has not yet been reported in X-linked ichthyosis. In this study we describe an X-linked ichthyosis patient with complete deletion of the steroid sulfatase gene and his mother with somatic and germinal mosaicism for this molecular defect. The family (X-linked ichthyosis patient, grandmother, mother, and sister) was analyzed through steroid sulfatase enzyme assay, polymerase chain reaction, DNA markers, and fluorescence in situ hybridization of the steroid sulfatase gene. Steroid sulfatase activity was undetectable in the X-linked ichthyosis patient, very low in the mother, and normal in the grandmother and sister. The X-linked ichthyosis patient showed a 2 Mb deletion of the steroid sulfatase gene and flanking regions from 5'DXS1139 to 3'DXF22S1. The mother showed one copy of the steroid sulfatase gene in 98.5% of oral cells and in 80% of leukocytes. The grandmother and sister showed two copies of the steroid sulfatase gene. The origin of the X chromosome with the deletion of the steroid sulfatase gene corresponded to the grandfather of the proband. We report the first case of somatic and germinal mosaicism of the steroid sulfatase gene in an X-linked ichthyosis carrier and propose DNA slippage as the most plausible mechanism in the genesis of this mosaicism.

Human germline mutation in the factor IX gene

The molecular epidemiology of factor IX germline mutations in patients with hemophilia B has been studied in detail because it is an advantageous model for analyzing recent germline mutations in humans. It is estimated that mutations have been defined in the majority of nucleotides that are the target for mutation. The likelihood that a factor IX missense mutation will cause disease correlates with the degree of evolutionary conservation of the amino acid. Mutation rates per base-pair have been estimated after careful consideration and correction for biases, predicting about 76 de novo mutations per generation per individual resulting in 0.3 deleterious changes. The male-to-female sex ratio of mutation varies with the type of mutation. There is evidence for a maternal age effect and an excess of non-CpG G:C to A:T transitions. The factor IX mutation pattern is similar among geographically, racially and ethnically diverse human populations. The data support primarily endogenous mechanisms of germline mutation in the factor IX gene. Mutations at splice junctions are compatible with simple rules for predicting disease causing mutations.

Suspected gonadal mosaicism for isochromosomes 18p and 18q unsubstantiated by fluorescence in situ hybridization analysis of sperm

PURPOSE

A father had two children, one with isochromosome 18p, and another with isochromosome 18q. The father was counseled that he might have gonadal mosaicism for isochromosomes 18p and 18q, which could confer a high recurrence risk.

METHODS

A sperm sample from the father was analyzed with fluorescence in situ hybridization probes for 18p and 18q.

RESULTS

More than 1,000 sperm were scored and none were found with two 18p or 18q signals. There were no differences in the father's specimen compared to a control.

CONCLUSIONS

There was no evidence for gonadal mosaicism. It is important to confirm clinical hypotheses whenever possible.

Homozygotes for a R869G mutation in the beta -myosin heavy chain gene have a severe form of familial hypertrophic cardiomyopathy

Familial Hypertrophic Cardiomyopathy (FHC) is an autosomal dominant disease characterised by ventricular hypertrophy, with predominant involvement of the interventricular septum. It is a monogenic disease with a high level of genetic heterogeneity (nine genes and more than 110 mutations reported so far). We describe a family with a new R869G mutation in the beta -myosin heavy chain gene (MYH7). This mutation was found in the heterozygous status in both parents and in the homozygous status in the two children. A haplotype analysis on the MYH7 locus with microsatellite markers showed that the same haplotype is transmitted within the family, suggesting a founder effect. Clinically, the father was asymptomatic with mild left ventricular hypertrophy on echocardiography. The mother had a mild form of hypertrophic cardiomyopathy and remained asymptomatic until 60 years old when an atrial fibrillation occurred. For the two children, clinical diagnosis was performed at 12 and 8 years and atrial fibrillation occurred at 17 years. For both children, the evolution was characterized by left ventricle (LV) systolic dysfunction and a severe dilatation of the left atrium before 40 years of age.

CONCLUSIONS

In this family, a new R869G mutation in the MYH7 gene was found. Interestingly, a mutation was found at the homozygous status for the first time in FHC. This finding suggests that this particular mutation is compatible with life, but for homozygous subjects, age at onset of symptoms was earlier and the disease much more severe than in the heterozygous subjects, suggesting a gene-dose effect.