Nemaline myopathy and distal arthrogryposis associated with an autosomal recessive TNNT3 splice variant

A male neonate presented with severe weakness, hypotonia, contractures and congenital scoliosis. Skeletal muscle specimens showed marked atrophy and degeneration of fast fibers with striking nemaline rods and hypertrophy of slow fibers that were ultrastructurally normal. A neuromuscular gene panel identified a homozygous essential splice variant in TNNT3 (chr11:1956150G > A, NM_006757.3:c.681+1G > A). TNNT3 encodes skeletal troponin‐T_fast and is associated with autosomal dominant distal arthrogryposis. TNNT3 has not previously been associated with nemaline myopathy (NM), a rare congenital myopathy linked to defects in proteins associated with thin filament structure and regulation. cDNA studies confirmed pathogenic consequences of the splice variant, eliciting exon‐skipping and intron retention events leading to a frameshift. Western blot showed deficiency of troponin‐T_fast protein with secondary loss of troponin‐I_fast. We establish a homozygous splice variant in TNNT3 as the likely cause of severe congenital NM with distal arthrogryposis, characterized by specific involvement of Type‐2 fibers and deficiency of troponin‐T_fast.     

Nebulin (NEB) mutations in a childhood onset distal myopathy with rods and cores uncovered by next generation sequencing

Recessive nebulin (NEB) mutations are a common cause of nemaline myopathy (NM), typically characterized by generalized weakness of early-onset and nemaline rods on muscle biopsy. Exceptional adult cases with additional cores and an isolated distal weakness have been reported. The large NEB gene with 183 exons has been an obstacle for the genetic work-up. Here we report a childhood-onset case with distal weakness and a core-rod myopathy, associated with recessive NEB mutations identified by next generation sequencing (NGS). This 6-year-old boy presented with a history of gross-motor difficulties following a normal early development. He had distal leg weakness with bilateral foot drop, as well as axial muscle weakness, scoliosis and spinal rigidity; additionally he required nocturnal respiratory support. Muscle magnetic resonance (MR) imaging showed distal involvement in the medial and anterior compartment of the lower leg. A muscle biopsy featured both rods and cores. Initial targeted testing identified a heterozygous Nebulin exon 55 deletion. Further analysis using NGS revealed a frameshifting 4 bp duplication, c.24372_24375dup (P.Val8126fs), on the opposite allele. This case illustrates that NEB mutations can cause childhood onset distal NM, with additional cores on muscle biopsy and proves the diagnostic utility of NGS for myopathies, particularly when large genes are implicated.     

A complex phenotype of peripheral neuropathy, myopathy, hoarseness, and hearing loss is linked to an autosomal dominant mutation in MYH14

Both peripheral neuropathy and distal myopathy are well-established inherited neuromuscular disorders characterized by progressive weakness and atrophy of the distal limb muscles. A complex phenotype of peripheral neuropathy, myopathy, hoarseness, and hearing loss was diagnosed in a large autosomal dominant Korean family. A high density single nucleotide polymorphism (SNP)-based linkage study mapped the underlying gene to a region on chromosome 19q13.3. The maximum multipoint LOD score was 3.794. Sequencing of 34 positional candidate genes in the segregating haplotype revealed a novel c.2822G>T (p.Arg941Leu) mutation in the gene MYH14, which encodes the nonmuscle myosin heavy chain 14. Clinically we observed a sequential pattern of the onset of muscle weakness starting from the anterior to the posterior leg muscle compartments followed by involvement of intrinsic hand and proximal muscles. The hearing loss and hoarseness followed the onset of distal muscle weakness. Histopathologic and electrodiagnostic studies revealed both chronic neuropathic and myopathic features in the affected patients. Although mutations in MYH14 have been shown to cause nonsyndromic autosomal dominant hearing loss (DFNA4), the peripheral neuropathy, myopathy, and hoarseness have not been associated with MYH14. Therefore, we suggest that the identified mutation in MYH14 significantly expands the phenotypic spectrum of this gene.     

Nonaka myopathy is caused by mutations in the UDP-N-acetylglucosamine-2-epimerase/N-acetylmannosamine kinase gene (GNE)

This is the first report on mutations of the UDP-N-acetylglucosamine-2-epimerase/N-acetylmannosamine kinase gene (GNE) in Nonaka myopathy or distal myopathy with rimmed vacuoles (OMIM 605820), an autosomal recessive neuromuscular disorder. Sequence and haplotype analyses of GNE in two siblings with Nonaka myopathy from a Japanese family revealed that both patients were compound heterozygotes for a C→T transition (A460V) in exon 8 and a G→C transition (V572L) in exon 10. Their parents and a normal elder brother were all carriers for one or the other of the mutations. GNE mutations are known to cause two other disorders: sialuria (OMIM #269921) and autosomal recessive inclusion body myopathy (IBM2, OMIM #600737). Mutations associated with sialuria are located in the epimerase domain, and those associated with IBM2 are in the epimerase or the kinase domain or both, whereas the mutations we observed in the Nonaka myopathy patients were located in the sugar kinase domain of the gene. Thus, Nonaka myopathy is the third disease known to be caused by GNE mutations. Received: October 12, 2001 / Accepted: November 9, 2001     

Prenatal diagnosis of Fukuyama type congenital muscular dystrophy in eight Japanese families by haplotype analysis using new markers closest to the gene

We conducted prenatal diagnosis by haplotype analysis, using newly developed microsatellite markers, in eight Fukuyama type congenital muscular dystrophy (FCMD) families. In addition to six new families, two previously reported families were re-examined by haplotype analysis including detection of an ancestral founder haplotype (138–183–301) for 3 microsatellite markers closest to the FCMD gene, designated D9S2105–D9S2107–D9S172, the distances of which from the FCMD gene are presumed to be ∼140, ∼20, and ∼280 kb, respectively. Five fetuses from five families were diagnosed as nonaffected, and were subsequently confirmed to be healthy. Three fetuses of the other three families were diagnosed as having a high probability of being affected by FCMD. In the prenatal diagnosis conducted for these eight families, the ancestral founder allele was observed in 13 of 16 (81%) FCMD-bearing chromosomes. Detection of the ancestral haplotype facilitated achieving accurate prenatal diagnosis of FCMD. The brains of all three fetuses prenatally diagnosed as FCMD-affected showed the initial stage of cortical dysplasia, strong evidence of FCMD. Am. J. Med. Genet. 77:310–316, 1998. © 1998 Wiley-Liss, Inc.     

A linkage disequilibrium at the candidate gene locus for 16q-linked autosomal dominant cerebellar ataxia type III in Japan

We previously mapped the gene responsible for autosomal dominant cerebellar ataxia (ADCA) type III to a 10.9-cM interval between D16S3089 and D16S515 on chromosome 16q. This region, however, was identical to the candidate locus of spinocerebellar ataxia type 4 (SCA4). In this study, we extended our research to refine the gene locus of the disease by applying linkage disequilibrium with 20 microsatellite DNA markers. With 9 markers flanked by D16S3031 and D16S3107, we found that the affected individuals in six families had a common haplotype on their disease chromosomes. Furthermore, linkage disequilibrium was demonstrated with 5 informative markers: D16S3019 (P = 0.013), D16S3067 (P = 0.008), D16S3141 (P = 0.011), D16S496 (P = 0.032), and D16S3107 (P = 0.000). These results indicate that the disease could have originated from a common ancestor harboring a mutation within a less than 3-cM region between D16S3043 and D16S3095. The founder alleles were also observed in other patients with ADCA type III unrelated to the six families. Received: October 25, 2000 / Accepted: January 5, 2001     

Mapping of a new locus for autosomal recessive non-syndromic mental retardation in the chromosomal region 19p13.12-p13.2: further genetic heterogeneity

Objective: To identify and clinically evaluate four consanguineous families of Israeli Arab origin with non-syndromic mental retardation (NSMR), comprising a total of 10 affected and 24 unaffected individuals.

Participants and methods: All the families originated from the same small village and had the same family name. Association of the condition in these families with the two known autosomal recessive NSMR loci on chromosomes 3p25-pter and 4q24 (neurotrypsin gene) was excluded.

Results: Linkage of the disease gene to chromosome 19p13.12-p13.2(Zmax = 7.06 at theta = 0.00) for the marker D19S840 was established. All the affected individuals were found to be homozygous for a common haplotype for the markers cen-RFX1-D19S840-D19S558-D19S221-tel.

Conclusions: The results suggest that the disease is caused by a single mutation derived from a single ancestral founder in all the families. Recombination events and a common disease bearing haplotype defined a critical region of 2.4 Mb, between the loci D19S547 proximally and D19S1165 distally.

     

Spanish MYH7 founder mutation of Italian ancestry causing a large cluster of Laing myopathy patients

Laing myopathy is a distal myopathy caused by mutations in the tail of the slow beta-myosin heavy chain gene MYH7. A large cluster of patients belonging to different families, with Laing myopathy due to p.K1729del mutation, was found in the Safor region, Spain. The same mutation was previously reported in an American family with Italian ancestry. The possibility that p.K1729del in MYH7 might be a founder mutation in the Safor patients and the chance of a common origin with the Italian-American family mutation was investigated by haplotype analyses, mutation data origin estimation and historical inquiry. Our results show that the p.K1729del in MYH7 harboured by patients from the Safor indeed is a founder mutation. A common ancestral origin of this mutation in the Spanish and Italian families is also suggested because they all share a core SNP haplotype at locus MYH7. Data estimation yields the origin of the mutation in the Safor at the beginning of the XVII century, when the Moorish were spelt and the region was resettled with Italian families.     

Hereditary inclusion body myopathy maps to chromosome 9p1-q1

Hereditary inclusion body myopathy (HIBM) is a unique disorder of unknown etiology that typically occurs in individuals of Persian Jewish descent. Distinguishing features of the disorder from other limb girdle myopathies include elderly age of onset, ethnic predisposition, and sparing of the quadriceps despite severe involvement of all other proximal leg muscles. Involved muscles demonstrate fibers with rimmed vacuoles and filamentous cytoplasmic and nuclear inclusions. Additional histological features are accumulations of beta-amyloid protein and the absence of inflammatory cells. To identify the chromosomal location of the gene responsible for HIBM, nine Persian Jewish families with HIBM were evaluated. Genomewide linkage analyses identified the recessive IBM locus on chromosome 9 band p1-q1 (maximum lod score at D9S166 = 5.32, theta = 0.0). This region contains the Friedreich's Ataxia gene, raising the possibility that HIBM may be a related neurogenic disorder.      

Mutation analysis of the GNE gene in Korean patients with distal myopathy with rimmed vacuoles

Distal myopathy with rimmed vacuoles (DMRV; MIM 605820) is an autosomal recessive neuromuscular disorder characterized by weakness of the anterior compartment of the lower limbs, sparing the quadriceps muscles. Recently, mutations in the UDP-N-acetylglucosamine-2-epimerase/N-acetylmannosamine kinase (GNE) gene have been identified as the genetic basis of DMRV. To investigate the mutation spectrum of the GNE gene in Korean patients with DMRV, we performed clinical and genetic analysis of nine unrelated patients suspected to have DMRV. Direct sequencing analysis revealed that eight out of nine patients (88.9%) were either homozygous or compound heterozygous for GNE gene mutations, including three known (C13S, R129Q, and V572L) and two novel mutations (M29T and A591P). The allelic frequencies of the V572L and C13S mutations were 68.8% (11/16) and 12.5% (2/16), respectively. These results suggest that screening for GNE gene mutations in patients suspected to have DMRV would be helpful for molecular diagnosis of DMRV in the Korean population. An erratum to this article can be found at     

Familial hypomagnesemia maps to chromosome 9q, not to the X chromosome: genetic linkage mapping and analysis of a balanced translocation breakpoint

Familial hypomagnesemia with secondary hypocalcemia (HSH) (MIM 307600) was studied in three inbred Bedouin kindreds from Israel. The three kindreds, one extended and two nuclear families, contained 13 affected individuals, 11 males and two females. Assuming that the individuals affected with hypomagnesemia shared a chromosomal region inherited from a common ancestor, we used a DNA pooling strategy in a genome-wide search for loci which show homozygosity for shared alleles in affected individuals. DNA samples from affected individuals within a single kindred were pooled and used as the template for PCR amplification of short tandem repeat polymorphic markers (STRPs). Pooled DNA from unaffected siblings and parents were used as controls. A shift towards homozygosity was observed in the affected DNA pool compared with the control pools with D9S301 (GATA7D12). Genotyping of individual DNA samples with D9S301 and several flanking markers confirmed linkage to chromosome 9 with maximum LOD scores of 3.4 (theta = 0.05), 3.7 (theta = 0) and 2.3 (theta = 0) for the three families. We have identified a 14 cM interval on chromosome 9 (9q12-9q22.2), flanked by proximal marker D9S1874 and distal marker D9S1807, within which all affected individuals from the three kindreds are homozygous for a shared haplotype. The disease segregates with a common affected haplotype in the three families, suggesting that hypomagnesemia is caused by a common ancestral mutation in these families. Although HSH has been previously reported to be X linked, these linkage data demonstrate that the disorder is an autosomal recessive disease in these kindreds. Mapping of a chromosomal breakpoint in a somatic cell line established from a patient with HSH and a balanced X;9 translocation placed the chromosomal breakpoint in a 500 kb region flanked by D9S1844 and D9S273. Identification of the gene responsible for hypomagnesemia will provide insight into the regulation of this essential cation.      

Recombinant mapping of the familial hyperinsulinism gene to an 0.8 cM region on chromosome 11p15.1 and demonstration of a founder effect in Ashkenazi Jews

A gene for autosomal recessive familial hyperinsulinism (HI)(OMIM: 256450 [OMIM] ), a neonatal metabolic disease characterized byinappropriate insulin secretion In the presence of severe hypoglycemia,was recently mapped to a 6.6 cM interval between the markersD11S926 and D11S928 on chromosome lip In 15 families (1). inthe current study we evaluated six additional families and fivenew markers, and further localized the gene between D11S419and D11S131O. Using genotype data from CEPH Version 7 and datagenerated from this study, this region was estimated to be 0.8cM in length. Significant linkage disequilib rium between markersand the HI gene was observed over a region of 10.3 cM (11pter-D11S926-D11S1308-11pcen)for Ashkenazi Jewish chromosomes. Haplotype analysis showedthat 12 of 36 HI chromosomes, versus one of 36 non-HI chromosomes, bore a specific haplotype for D11S419-D11 S902-D11 S921(p<0.0007), strongly suggesting a founder eftect In thisethnic group.     

Strong linkage disequilibrium and haplotype analysis in Japanese pedigrees with Machado-Joseph disease

To identify the markers tightly linked to Machado-Joseph disease (MJD) and to investigate whether a limited number of ancestral chromosomes are shared by Japanese MJD pedigrees, a detailed linkage analysis employing D14S55, D14S48, D14S67, D14S291, D14S280, AFM343vf1, D14S81, D14S265, D14S62, and D14S65 was performed. The results of multipoint linkage analysis as well as detection of critical recombination events indicate that the gene for MJD is localized in a 4-cM region between D14S280-D14S81. We found strong linkage disequilibria at AFM343vf1 and D14S81, and association of a few common haplotypes with MJD. These results indicate that there is an obvious founder effect in Japanese MJD and suggest the possibility of the existence of predisposing haplotypes which are prone to expansions of CAG repeats. © 1996 Wiley-Liss, Inc.     

Adult onset distal and proximal myopathy with complete ophthalmoplegia associated with a novel de novo p.(Leu1877Pro) mutation in MYH2

An MYH2 mutation p.(Glu706Lys) was originally described in a family with autosomal dominant inheritance, where the affected family members presented with multiple congenital contractures and ophthalmoplegia, progressing to a proximal myopathy in adulthood. Another patient with a dominant mutation p.(Leu1870Pro) was described, presenting as a congenital myopathy with ophthalmoplegia. Here, we present a patient with symptoms beginning at age 16 years, of prominent distal but also proximal weakness, bulbar involvement and ophthalmoplegia. Initially, clinically classified as oculopharyngodistal myopathy, the patient was found to carry a novel, de novo MYH2 mutation c.5630T>C p.(Leu1877Pro). This expands the phenotype of dominant MYH2 myopathies with the clinical phenotype overlapping the oculopharyngodistal myopathy spectrum.     

Clouston hidrotic ectodermal dysplasia (HED): genetic homogeneity, presence of a founder effect in the French Canadian population and fine genetic mapping

HED is an autosomal dominant skin disorder that is particularly common in the French Canadian population of south-west Quebec. We previously mapped the HED gene to the pericentromeric region of chromosome 13q using linkage analysis in eight French Canadian families. In this study, we extend our genetic analysis to include a multiethnic group of 29 families with 10 polymorphic markers spanning 5.1 cM in the candidate region. Two-point linkage analysis strongly suggests absence of genetic heterogeneity in HED in four families of French, Spanish, African and Malaysian origins. Multipoint linkage analysis in all 29 families generated a peak lod score of 53.5 at D13S1835 with a 1 lod unit support interval spanning 1.8 cM. Recombination mapping placed the HED gene in a 2.4 cM region flanked by D13S1828 proximally and D13S1830 distally. We next show evidence for a strong founder effect in families of French Canadian origin thereby representing the first example of a founder disease in the south-west part of the province of Quebec. Significant association was found between HED in these families and all markers analysed (Fisher's exact test, P < 0.001). Complete allelic association was detected at D13S1828, D13S1827, D13S1835, D13S141 and D13S175 (P(excess) = 1) spanning 1.3 cM. A major haplotype including all 10 associated alleles was present on 65% of affected chromosomes. This haplotype most likely represents the founder haplotype that introduced the HED mutation into the French Canadian population. Luria-Delbrück equations and multipoint likelihood linkage disequilibrium analysis positioned the gene at the D13S1828 locus (likely range estimate: 1.75 cM) and 0.58 cM telomeric to this marker (support interval: 3.27 cM) respectively.     

Linkage disequilibrium at the SCA2 locus

Spinocerebellar ataxia type 2 (SCA2) is caused by the expansion of an unstable CAG repeat encoding a polyglutamine tract. Repeats with 32 to 200 CAGs are associated with the disease, whereas normal chromosomes contain 13 to 33 repeats. We tested 220 families of different geographical origins for the SCA2 mutation. Thirty three were positive (15%). Twenty three families with at least two affected subjects were tested for linkage disequilibium (LD) between the SCA2 mutation and three microsatellite markers, two of which (D12S1332-D12S1333) closely flanked the mutation; the other (D12S1672) was intragenic. Many different haplotypes were observed, indicating the occurrence of several ancestral mutations. However, the same haplotype, not observed in controls, was detected in the German, the Serbian, and some of the French families, suggesting a founder effect or recurrent mutations on an at risk haplotype.     

Linkage disequilibrium analysis of childhood-onset spinal muscular atrophy (SMA) in the French -- Canadian population

Spinal muscular atrophy (SMA) is, after Duchenne muscular dystrophy,the most common neuromuscular disorder in childhood. The generesponsible for childhood SMA has been mapped to the q11. 2– q13. 3 region of chromosome 5. We have extended ourlinkage studies of SMA In the French - Canadian population toInclude microsatellite markers at the D5S125, D5S351, D5S435,JK53CA1/ 2 and MAPI B locl. These markers span about 4 cM ofthe SMA candidate region. We observed significant evidence forlinkage between SMA and all the markers tested. The analysisof recombinant chromosomes provide evidence for the followinggenetic order: D5S125-D5S435-MAP1B-3'-JK53CA1/2 and places D5S351proximal to JK53CA1/2. Furthermore, we confirm the current localizationof the SMA gene distal to D5S435. Finally, we provide demonstrationof significant linkage disequilibrium between childhood-onsetSMA and four of the five marker loci, D5S125, D5S435, D5S351and JK53CA1/2. Analysis of SMA-region haplotypes suggests thatthere may be a predominant SMA allele that is present on about17% of SMA chromosomes in this sample of the French - Canadianpopulation. We conclude that the observed linkage disequilibriumis likely due to genetic drift among regions of Quebec, consistentwith this population's early history.