Rare Compound Heterozygous Mutations Research Articles

A case of a 6-year-old girl with a rare compound heterozygous mutation of KCTD7 presenting with progressive myoclonic epilepsy

BackgroundProgressive myoclonic epilepsy is a clinically and genetically heterogeneous group of diseases characterized by myoclonic seizures, drug-resistant epilepsy and neurodevelopmental regression. The disease is attributed to mutations in KCTD7 (a member of the potassium channel tetramerization domain).Case presentationWe report the case of a 6-year-old girl with compound heterozygous mutation in KCTD7. Whole-exome sequencing was carried out to detect the mutations followed by Sanger sequencing of the patient in addition to the unaffected parents which confirmed the diagnosis. The first mutation [c. 202A > G (p.Thr68Ala)] was inherited from mother and the second one [c. 458G > A (p.Arg153His)] was inherited from father.ConclusionsTo our knowledge, this is the first report of compound heterozygousKCTD7-related progressive myoclonic epilepsy in Iran with c.202A > G in particular as a novel mutation. Our findings widen the scope of our knowledge of the underlying genetic etiology of the aforementioned disease which can further help us in the genetic diagnosis of these patients.

A Rare Compound Heterozygous Mutation of TRPM6 Gene in Hereditary Hypomagnesemia with Secondary Hypocalcemia: A Cause of Refractory Seizures in an Infant

Background: Hypomagnesemia is an important cause of refractory hypocalcemic seizures. Among the causes of hypomagnesemia, genetic defects are rare. Clinical Description: A 20-month-old boy presented with a history of repeated hypocalcemic convulsions since 1 month of age. Besides seizures, the infant was thriving well and otherwise asymptomatic. Management and Outcome: On investigation, he had low serum calcium, normal vitamin D, low parathormone, and very low serum magnesium (0.5 mg/dl) levels, with normal sodium, potassium levels, and renal functions. The child was initiated on parenteral magnesium supplementation and subsequently discharged on high-dose oral magnesium supplementation. As further investigations ruled out common causes of hypomagnesemia, clinical exome sequencing was done, which revealed a compound heterozygous state with two variants in the TRPM6 gene NM_017662.5, one being a missense variant (chr9: c.5614T>C, [p.Trp1872Arg]/Heterozygous) and the other being a frameshift deletion (chr9: c.1939_1946delGCAATGGC, [p.Ala647Profs*2]/Heterozygous). The child maintained normal serum magnesium levels at follow-up and was seizure-free. Conclusion: Hereditary hypomagnesemia with secondary hypocalcemia is a rare cause of refractory seizures with onset since early infancy. Here, a compound heterozygous variant of the TRPM6 gene was identified as the cause of this condition.

Clinical and functional characterization of rare compound heterozygous mutations in the SERPINC1 gene causing severe thrombophilia

IntroductionHereditary antithrombin (AT) deficiency is a rare autosomal dominant disorder with significant clinical heterogeneity. In the study, we identified a patient with AT deficiency caused by compound heterozygous mutations in the SERPINC1 gene. MethodsA total of 9 individuals from three generations were investigated. The mutations were identified by direct sequencing of SERPINC1. Multiple in silico tools were programmed to predict the conservation of mutations and the effect on the AT structure. The coagulation state was evaluated by the thrombin generation assay. Recombinant AT was overexpressed in HEK293T cells; the mRNA level was determined using RT-qPCR. Western blotting, ELISA, and immunocytofluorescence were applied to characterize the recombinant AT protein. ResultsThe proband was a 26-year-old male who experienced recurrent venous thrombosis. He presented the type I deficiency with 33 % AT activity and a synchronized decrease in AT antigen. Genetic screening revealed that he carried a heterozygous c.318_319insT (p.Asn107*) in exon 2 and a heterozygous c.922G > T (p.Gly308Cys) in exon 5, both of which were completely conserved in homologous species and resulted in enhanced thrombin generation capability. Hydrophobicity analysis suggested that the p.Gly308Cys mutation may interfere with the hydrophobic state of residues 307–313. In vitro expression studies indicated that the levels of the recombinant protein AT-G308C decreased to 46.98 % ± 2.94 % and 41.35 % ± 1.48 % in transfected cell lysates and media, respectively. After treatment with a proteasome inhibitor (MG132), the quantity of AT-G308C protein in the cytoplasm was replenished to a level comparable to that of the wild type. The mRNA level of AT-N107* was significantly reduced and the recombinant protein AT-N107* was not detected in either the lysate or the culture media. ConclusionThese two mutations were responsible for the AT defects and clinical phenotypes of the proband. The p.Gly308Cys mutation could lead to proteasome-dependent degradation of the AT protein in the cytoplasm by altering local residue hydrophobicity. The c.318_319insT could eliminate aberrant transcripts by triggering nonsense-mediated mRNA degradation. Both mutations resulted in type I AT deficiency.

Description of a Rare Compound Heterozygous Transthyretin Mutation Val30Met/Val122Ile Conferring Early Onset Hereditary Amyloidosis with Severe Features (P14-8.009)

<h3>Objective:</h3> To describe a case of hereditary amyloidosis with a rare compound heterozygous mutation that is not described in the literature. <h3>Background:</h3> Hereditary amyloidosis is a rare disease characterized by accumulation of amyloid deposits in tissue, causing end-organ failure. Most common manifestations include cardiomyopathy, nephropathy, and neuropathy. The transthyretin (TTR) is encoded on chromosome 18 and functions to transport thyroxine and retinol through blood and CSF. Mutations in TTR increase the amyloidogenic potential of the protein. TTR is inherited in an autosomal dominant fashion, and thus mutagenic carriers often have a strong family history of the associated diseases. There are over 100 characterized mutations of this gene. The vast majority of genetically proven cases are associated with missense mutations in a single codon. Compound heterozygotes are rarely reported in the literature. <h3>Design/Methods:</h3> N/A <h3>Results:</h3> A 40-year-old male with history of chronic diarrhea and anemia presents with two years of pedal edema, weight loss, dyspnea on exertion, and progressive limb weakness resulting in multiple falls. On cardiac evaluation he was found to have severe cardiomyopathy with increase LV thickness and evidence of amyloidosis on cardiac MRI. EMG demonstrated a severe sensorimotor polyneuropathy. Exam was notable for absent joint position sense resulting in gait dysfunction necessitating use of a cane. Subsequent endomyocardial biopsy revealed ATTR type amyloid deposition. Genetic evaluation demonstrated two separate pathogenic variants in TTR (Val30Met/Val122Ile). He was started on therapy with tafamidis and later transitioned to patisiran infusions with some symptomatic improvement. Genetic testing of family members was suggested however not yet completed. <h3>Conclusions:</h3> Compound heterozygous mutations in TTR are exceedingly rare, and this report presents a perhaps never before described case of an individual with both Val30Met and Val122Ile mutations resulting in early onset severe hereditary amyloidosis with multisystem involvement. <b>Disclosure:</b> Dr. Nardin has nothing to disclose. Dr. Traub has received personal compensation in the range of $500-$4,999 for serving on a Scientific Advisory or Data Safety Monitoring board for Alnylam. Dr. Traub has received personal compensation in the range of $500-$4,999 for serving on a Scientific Advisory or Data Safety Monitoring board for Argenx. The institution of Dr. Traub has received research support from Alnylam Pharmaceuticals. The institution of Dr. Traub has received research support from Alexion. The institution of Dr. Traub has received research support from Muscular Dystrophy Association (MDA). The institution of Dr. Traub has received research support from Ionis.

A rare compound heterozygous EIF2AK4 mutation in pulmonary veno-occlusive disease

BackgroundPulmonary veno-occlusive disease (PVOD) is a rare, progressive, and oft-fatal condition of pulmonary arterial hypertension that is typically difficult to diagnose and treat. However, with the development of next-generation sequencing technology, an increasing number of patients with PVOD are being diagnosed.MethodsInitially, we used whole exome sequencing (WES) to identify the proband as a rare compound heterozygous mutation of EIF2AK4 in PVOD. Subsequently, the parents of patient underwent EIF2AK4 screening by Sanger sequencing.ResultsIn this study, we describe the family tree of a patient with PVOD with a rare compound heterozygous EIF2AK4 mutation. Moreover, we identified a new EIF2AK4 mutation, c.2236_2237insAAGTCCTTCT, in exon 12 of the proband and his mother. This frameshift mutation led to premature termination of the coding protein sequence and widespread loss of protein function, which promoted the development of PVOD.ConclusionsOur results expand our understanding of the EIF2AK4 mutation spectrum in patients with PVOD, as well as highlight the clinical applicability of WES.

Whole-exome sequencing identifies rare compound heterozygous mutations in the MSTO1 gene associated with cerebellar ataxia and myopathy

Human MSTO1 is involved in the regulation of mitochondrial distribution and morphology and its unregulated expression leads to mitochondrial disorder. Despite its significance for mitochondrial functions, human MSTO1 gene is rarely studied before 2017. As of late, MSTO1 mutations have been reported to cause clinical manifestations such as myopathy, cerebellar atrophy and ataxia, motor developmental delay, and pigmentary retinopathy. Here we have performed a whole-exome sequencing in a family which includes two brothers showing cerebellar atrophy and ataxia, intellectual disability, and myopathy. As a result, two mutations were identified. One of these mutations has been identified as a missense mutation, c.836G > A; p. (Arg279His) and a novel frameshift variant, c.1259delG; p. (Gly420ValfsTer2). So, the two brothers both had compound heterozygous mutations with a combination of protein-truncation mutation and missense mutation. These findings suggested an association of MSTO1 mutations with the early onset of symptoms and revealed the genotype-phenotype correlation between different mutation cases. In this case, the two brothers both have pes planus which is not reported in other cases. This might suggest that the novel mutation is responsible for dysmorphia. Thus, the recessive and novel MSTO1 mutations enriches genetic information on the pathogenicity of MSTO1 in humans.

Recessive multiple epiphyseal dysplasia – Clinical characteristics caused by rare compound heterozygous SLC26A2 genotypes

Pathogenic sequence variants in the solute carrier family 26 member 2 (SLC26A2) gene result in lethal (achondrogenesis Ib and atelosteogenesis II) and non-lethal (diastrophic dysplasia and recessive multiple epiphyseal dysplasia, rMED) chondrodysplasias. We report on two new patients with rMED and very rare compound heterozygous mutation combinations in non-consanguineous families. Patient I presented in childhood with waddling gait and joint stiffness. Radiographs showed epiphyseal changes, bilateral coxa plana–deformity and knee valgus deformity, for which he underwent surgeries. At present 33 years his height is 165 cm. Patient II presented with cleft palate, small jaw, short limbs, underdeveloped thumbs and on radiographs, cervical kyphosis with an underdeveloped C4. He also developed severe scoliosis but has grown at −2.9 SD curve. Molecular analysis revealed that patient I is heterozygous for two known pathogenic variants in SLC26A2, a splice site variant c.-26+2T > C and a missense variant c.1957T > A (p.Cys653Ser), while patient II is compound heterozygous for missense variants c.835C > T (p.Arg279Trp) and c.1535C > A (p.Thr512Lys). These patients further elucidate the variability of the phenotypic and genetic presentations of rMED.

Whole-exome sequencing identifies rare compound heterozygous mutations in the MYBPC3 gene associated with severe familial hypertrophic cardiomyopathy

Most patients with hypertrophic cardiomyopathy have single-gene autosomal dominant mutations in loci that encode for sarcomeric proteins. The aim of this study was to determine whether pathogenic mutations were present by whole-exome sequencing (WES) in two families with hypertrophic cardiomyopathy (HCM) that presented during adolescence. Blood samples and clinical data were collected from individuals in two families with HCM. DNA was extracted. Mutations were identified using whole-exome sequencing (WES), and the genotypes of family members were identified using Sanger sequencing. Compound heterozygous mutations in the MYBPC3 gene (c.659A > G, p.Tyr220Cys; c.772G > A, p.Glu258Lys,NM_000256, Family 1), (c.873delG, p. Ile292PhefsTer8; c.3G > A, p.Met1?, NM_000256, Family 2) were identified by WES. Patient 1 carried the maternally inherited c.659A > G mutation and the paternally inherited c.772G > A mutation. Patient 2 carried the maternally inherited frameshift mutation c.873delG and the paternally inherited mutation c.3G > A. Two families with HCM presenting during adolescence (age of onset is about 11 years old) demonstrated compound heterozygous mutations in the MYBPC3 gene. These findings suggested an association of MYBPC3 mutations with the early onset of symptoms and worsened prognoses. Our study highlights the importance of genetic screening of all family members in cases of HCM.

Case report of unexpected gastrointestinal involvement in type 1 Gaucher disease: comparison of eliglustat tartrate treatment and enzyme replacement therapy

BackgroundGastrointestinal involvement in Gaucher disease is very rare, and appears to be unresponsive to enzyme replacement therapy (ERT).Case presentationHere, we describe identical twin, splenectomized, non-neuronopathic Gaucher patients on long-term ERT for 9 years, who complained of epigastric discomfort due to Gaucher cell infiltration of the gastroduodenal mucosa. Rare compound heterozygous mutations (p.Arg48Trp and p.Arg257Gln) of the GBA gene were found in both. Improvement in the gastroduodenal infiltration and reduced chitotriosidase levels were observed in one who switched to eliglustat tartrate for 1 year, whereas the other one who maintained ERT showed no improvement of chitotriosidase level and persistent duodenal lesions.ConclusionThis shows that eliglustat might be an effective treatment for Gaucher disease patients having lesions resistant to ERT.

The Characteristics and Long-Term Course of Epilepsy in Lipoid Proteinosis: A Spectrum From Mild to Severe Seizures in Relation toECM1Mutations

Lipoid proteinosis (LP) is a rare autosomal recessive disease characterized by deposition of hyaline material in skin and mucosae. Epilepsy, as an extracutaneous manifestation associated with typical mesial temporal calcifications, has already been identified, but its characteristics and long-term prognosis have not been thoroughly investigated. We included 7 consecutive patients with LP with typical intracranial calcifications out of 16 patients with ECM1 mutations and investigated the semiologic features, ictal and interictal EEG findings, and long-term prognosis of epilepsy in this genodermatosis. Four of them had seizures (57.1%), and focal seizures with motionless staring were the most common seizure phenotype, originating from bilateral mesial temporal areas, but interictal spikes were scant. Auras were observed in three patients, mostly as epigastric sensation and déjà vu, which indicated mesial temporal lobe origin. Three patients with homozygous mutations in sixth and seventh exons of the ECM1 gene had a drug-resistant course at the end of long-term follow-up. Molecular genetic testing showed a rare compound heterozygous mutation in one patient, which was also associated with seizures but without drug-resistance. Our findings indicated a spectrum for epilepsy with a desperate drug-resistant course for decades in most patients with LP, which is still an underrecognized disease by neurologists.

Probing the Effect of Two Heterozygous Mutations in Codon 723 of SLC26A4 on Deafness Phenotype Based on Molecular Dynamics Simulations.

A Chinese family was identified with clinical features of enlarged vestibular aqueduct syndrome (EVAS). The mutational analysis showed that the proband (III-2) had EVAS with bilateral sensorineural hearing loss and carried a rare compound heterozygous mutation of SLC26A4 (IVS7-2A>G, c.2167C>G), which was inherited from the same mutant alleles of IVS7-2A>G heterozygous father and c.2167C>G heterozygous mother. Compared with another confirmed pathogenic biallelic mutation in SLC26A4 (IVS7-2A>G, c.2168A>G), these two biallelic mutations shared one common mutant allele and the same codon of the other mutant allele, but led to different changes of amino acid (p.H723D, p.H723R) and both resulted in the deafness phenotype. Structure-modeling indicated that these two mutant alleles changed the shape of pendrin protein encoded by SLC26A4 with increasing randomness in conformation, and might impair pendrin’s ability as an anion transporter. The molecular dynamics simulations also revealed that the stability of mutant pendrins was reduced with increased flexibility of backbone atoms, which was consistent with the structure-modeling results. These evidences indicated that codon 723 was a hot-spot region in SLC26A4 with a significant impact on the structure and function of pendrin, and acted as one of the genetic factors responsible for the development of hearing loss.

Hereditary protein C deficiency caused by compound heterozygous mutants in two independent Chinese families

We report two compound heterozygous mutants that caused severe type I protein C (PC) deficiency in two independent Chinese families.PC antigen was determined by enzyme-linked immunosorbent assay (ELISA), and PC activity was measured by chromogenic assay. Genetic mutations were screened with polymerase chain reaction (PCR) followed by direct sequencing. PC mutants were transiently expressed in COS-7 cells for the evaluation of PC secretory activity and function. The subcellular location was visualised by immunofluorescence assay. The structural analysis of mutation was performed as well.Compound heterozygous mutations of Arg178Trp and Asp255His with reduced PC activity and antigen levels were identified in Proband 1, a 28-year-old male with deep vein thrombosis (DVT) and pulmonary embolism. The other mutations of Leu-34Pro and Thr295Ile with reduced PC activity and antigen levels were identified in Proband 2, a 19-year-old male with DVT. The PC activities with Arg178Trp, Asp255His, Leu-34Pro and Thr295Ile mutations decreased significantly. Immunofluorescence assay demonstrated that only trace amount of PC with novel Thr295Ile mutation was transported to the Golgi apparatus. Subsequent structural analysis indicated severe impairments of intracellular folding and secretion.The two rare compound heterozygous mutations could cause type I PC deficiency via impairment of secretory activity of PC.

Mutations in TMEM231 cause Joubert syndrome in French Canadians

BackgroundJoubert syndrome (JBTS) is a predominantly autosomal recessive disorder characterised by a distinctive midhindbrain malformation, oculomotor apraxia, breathing abnormalities and developmental delay. JBTS is genetically heterogeneous, involving genes required for...

Mutations in C5ORF42 Cause Joubert Syndrome in the French Canadian Population

Joubert syndrome (JBTS) is an autosomal-recessive disorder characterized by a distinctive mid-hindbrain malformation, developmental delay with hypotonia, ocular-motor apraxia, and breathing abnormalities. Although JBTS was first described more than 40 years ago in French Canadian siblings, the causal mutations have not yet been identified in this family nor in most French Canadian individuals subsequently described. We ascertained a cluster of 16 JBTS-affected individuals from 11 families living in the Lower St. Lawrence region. SNP genotyping excluded the presence of a common homozygous mutation that would explain the clustering of these individuals. Exome sequencing performed on 15 subjects showed that nine affected individuals from seven families (including the original JBTS family) carried rare compound-heterozygous mutations in C5ORF42. Two missense variants (c.4006C>T [p.Arg1336Trp] and c.4690G>A [p.Ala1564Thr]) and a splicing mutation (c.7400+1G>A), which causes exon skipping, were found in multiple subjects that were not known to be related, whereas three other truncating mutations (c.6407del [p.Pro2136Hisfs*31], c.4804C>T [p.Arg1602*], and c.7477C>T [p.Arg2493*]) were identified in single individuals. None of the unaffected first-degree relatives were compound heterozygous for these mutations. Moreover, none of the six putative mutations were detected among 477 French Canadian controls. Our data suggest that mutations in C5ORF42 explain a large portion of French Canadian individuals with JBTS.

Classical familial homocystinuria in an adult presenting as an isolated lens subluxation

To report a case of late diagnosis of a classical familial homocystinuria based on an ophthalmologic examination. A 35-year-old male with Marfan-like phenotype complained of a progressive increase of myopia during the previous 2years. Ophthalmologic exploration showed a bilateral subluxation of the lens with inferior and nasal displacement. Biochemical study detected a profile of increased amino acid levels (homocysteinemia) consistent with suspected homocystinuria. Vascular and skeletal studies ruled out Marfan syndrome. Response to treatment demonstrated B(6)-non-responsive homocystinuria. Molecular study showed compound heterozygous T353N and D444N mutations of the cystathionine beta-synthase (CBS) gene, and also a C667T homozygous mutation of the methylenetetrahydrofolate-reductase (MTHFR) gene. Family study showed classical homocystinuria in his father and sister, although they did not present any systemic or ocular features of the disease. Homocystinuria is a metabolic disease usually presenting at an early age as vascular, skeletal and neuropsychiatric abnormalities, as well as ectopia lentis. Our case is atypical because of the absence of thromboembolism and the mild phenotype, in spite of being B(6)-non-responsive, and the association of a rare compound heterozygous mutation of the CBS gene and also an homozygous mutation of the MTHFR gene. It is necessary to rule out homocystinuria in patients with ectopia lentis, even in the absence of systemic symptoms.

Infarctus cérébral et iridodonésis révélant une homocystinurie par mutation hétérozygote composite de la cystathionine bêta-synthase

Iridodonesis or tremulous iris is a clinical sign of ectopia lentis which is frequently associated with homocystinuria. We present a forty-two-year-old woman victim of a left middle cerebral artery ischemic stroke. The clinical examination found bilateral iridodonesis and laboratory tests showed an increased level of serum homocysteine and homocystinuria. Homocystinuria was caused by a compound heterozygous I278T and D444N mutation of cystathionine beta-synthase (CBS) gene and also a C667T heterozygous polymorphism of methylene-tetrahydrofolate-reductase gene. This case was atypical because of the incomplete phenotype, development of complications in adulthood and the association of a rare compound heterozygous mutation of the CBS gene.