Non-GNE Quadriceps Sparing Distal Myopathy in an Iranian Jewish Patient.

GNE myopathy is an autosomal-recessive distal myopathy. It is caused by a hypomorphic GNE gene, encoding the rate-limiting enzyme in sialic acid synthesis. This myopathy is prevalent in the Iranian Jewish (IJ) descendants because of a founder mutation GNE: p. M712T. We report a 52-year-old IJ woman who presented with a 20-year history of progressive distal muscle weakness. Physical examination and magnetic resonance imaging revealed lower-extremity weakness and atrophy. Electromyography confirmed myopathy. Genetic testing showed no mutations on the GNE gene. Muscle histochemistry demonstrated no rimmed vacuoles. The analysis of polysialylated neural cell adhesion molecule Western blot pattern was negative. Non-GNE myopathy with quadriceps sparing presentation has been previously described in a few cases of non-IJ descents. To the best of our knowledge, this is the first case of an IJ patient, presenting with quadriceps sparing myopathy, without associated GNE mutations and/or tubule-filamentous inclusions.

Novel GNE mutations in autosomal recessive hereditary inclusion body myopathy patients.

Hereditary Inclusion Body Myopathy (HIBM, IBM2, MIM:600737) is an autosomal recessive adult onset progressive muscle wasting disorder. It is associated with the degeneration of distal and proximal muscles, while often sparing the quadriceps. The bifunctional enzyme UDP-GlcNAc 2-epimerase/ManNAc kinase (GNE/MNK), encoded by the GNE gene, catalyzes the first two committed, rate-limiting steps in the biosynthesis of N-acetylneunaminic acid (sialic acid). Affected individuals have been identified with mutations in the GNE gene. In the present study, the GNE coding region of 136 symptomatic patients were sequenced. A total of 41 patients were found to have GNE mutations. Eight novel mutations were discovered among seven patients. Of the eight novel mutations, seven were missense (p.I150V, p.Y186C, p.M265T, p.V315T, p.N317D, p.G669R, and p.S699L) and one was nonsense (p.W495X), all of which span the epimerase, kinase, and allosteric domains of GNE. In one patient, one novel mutation was found in the allosteric region and kinase domain of the GNE gene. Mutations in the allosteric region lead to a different disease, sialuria; however, this particular mutation has not been described in patients with sialuria. The pathological significance of this variation with GNE function remains unknown and further studies are needed to identify its connection with HIBM. These findings further expand the clinical and genetic spectrum of HIBM.

The Gne M712T mouse as a model for human glomerulopathy.

Pathological glomerular hyposialylation has been implicated in certain unexplained glomerulopathies, including minimal change nephrosis, membranous glomerulonephritis, and IgA nephropathy. We studied our previously established mouse model carrying a homozygous mutation in the key enzyme of sialic acid biosynthesis, N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase. Mutant mice died before postnatal day 3 (P3) from severe glomerulopathy with podocyte effacement and segmental glomerular basement membrane splitting due to hyposialylation. Administration of the sialic acid precursor N-acetylmannosamine (ManNAc) led to improved sialylation and survival of mutant pups beyond P3. We determined the onset of the glomerulopathy in the embryonic stage. A lectin panel, distinguishing normally sialylated from hyposialylated glycans, used WGA, SNA, PNA, Jacalin, HPA, and VVA, indicating glomerular hyposialylation of predominantly O-linked glycoproteins in mutant mice. The glomerular glycoproteins nephrin and podocalyxin were hyposialylated in this unique murine model. ManNAc treatment appeared to ameliorate the hyposialylation status of mutant mice, indicated by a lectin histochemistry pattern similar to that of wild-type mice, with improved sialylation of both nephrin and podocalyxin, as well as reduced albuminuria compared with untreated mutant mice. These findings suggest application of our lectin panel for categorizing human kidney specimens based on glomerular sialylation status. Moreover, the partial restoration of glomerular architecture in ManNAc-treated mice highlights ManNAc as a potential treatment for humans affected with disorders of glomerular hyposialylation.

Serum neural cell adhesion molecule is hyposialylated in hereditary inclusion body myopathy.

Hereditary inclusion body myopathy (HIBM) is a young-adult onset autosomal recessive disorder caused by a hypomorphic rate limiting enzyme of sialic acid biosynthesis. The enzyme is UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase, and is encoded by the GNE gene. HIBM causes slowly progressive muscle weakness and atrophy. Patients are typically diagnosed at 20-30 years of age, and most patients are incapacitated and wheelchair-confined by 30-50 years of age. Some sialic acid containing glycoproteins, including neural cell adhesion molecule (NCAM), are hyposialylated in HIBM muscle biopsy samples. We developed a method to allow detection of serum NCAM sialylation using Western blot, and tested serum samples from several patients and a HIBM mouse model. Preliminary results showed a clear difference in polysialylated and hyposialylated forms of NCAM extracted from serum, and showed NCAM is hyposialylated in HIBM serum samples. This initial finding may prove useful in reducing the need for serial muscle biopsies in HIBM treatment trials. Additional studies are underway to further validate this finding and to evaluate the specificity, reliability, and robustness of this potential serum biomarker for HIBM.

Wolman disease (LIPA p.G87V) genotype frequency in people of Iranian-Jewish ancestry.

Wolman disease (WD) is a rare inherited condition caused by lysosomal acid lipase (LAL) deficiency first described in Iranian-Jewish (IJ) children. Newborns with WD are healthy and active, but soon the infant develops symptoms of severe malnutrition in the first few months of life, and often dies before the age of 1 year. Harmful amounts of lipids accumulate in the spleen, liver, bone marrow, intestine, adrenal glands, and lymph nodes. Although worldwide incidence is estimated at 1/350,000 newborns, WD occurs at higher than expected frequency in the IJ community of the Los Angeles area. As a validation study, we analyzed 162 DNA specimens of IJ origin by automated sequencing. For LIPA p.G87V (ggc>gtc, alternative numbering p.G66V), a heterozygous frequency of 5/162 (3.086%) was discovered. Thus, we estimate that as high as 1 in 4200 newborns of IJ couples may be at risk. Additional studies are required to confirm and further validate the higher frequencies seen in our sample pool, and to determine if people of IJ and even possibly Middle Eastern descent are at a higher risk for WD.

Novel GNE mutations in hereditary inclusion body myopathy patients of non-Middle Eastern descent.

Autosomal recessive hereditary inclusion body myopathy (HIBM or IBM2) is a progressive adult onset muscle wasting disorder characterized by sparing of the quadriceps. IBM2 is also known as distal myopathy with rimmed vacuoles or nonaka myopathy. IBM2 is associated with mutations in the UDP-GlcNAc 2-Epimerase/ManNAc Kinase gene (GNE). GNE is the rate-limiting enzyme of N-Acetylneuraminate (Neu5Ac, Sialic acid) biosynthesis. The GNE coding region of 64 symptomatic patients were sequenced. Twenty-eight patients were found to bear GNE mutations. Ten novel mutations were identified among nine patients, including four nonsense (p.R8X, p.W204X, p.Q436X, and p.S615X) and five missense (p.R71W, p.I142T, p.I298T, p.L556S, and p.E2G) variations spanning both the epimerase and kinase domains of GNE. Additionally, a synonymous variation (p.Y591Y, codon tac > tat) was seen in a patient bearing compound heterozygous nonsynonymous mutations (p.S615X and p.Y675H). Six of the nine are Caucasian, one patient is Taiwanese, one patient is Asian Indian, and one patient is of European descent. These findings further expand the clinical and genetic spectrum of IBM2.

MTHFR C677T genotype frequency in patients of Middle Eastern descent as determined by real-time PCR and melting curve analysis.

The 5,10-methylenetetrahydrofolate reductase gene (MTHFR) 677C>T polymorphism produces an elevation in plasma homocysteine concentrations when present in the homozygous state. Increased homocysteine levels have been associated with a greater risk for vascular diseases, including cardiovascular disease and ischemic stroke. In this study, we genotyped 42 nucleic acid samples for the C677T allele from our database of Middle Eastern patients as routine validation of the MTHFR 677C>T assay. Our study is the first to evaluate MTHFR C677T genotype frequency in a population of Middle Eastern patients residing in the United States. Among the patients, 47.6% were wild type, 40.5% were heterozygous, and 11.9% were homozygous for the C677T variant. Although C677T genotype frequency in our patient population is slightly higher than that reported by Golbahar et al. (2005), statistical analysis showed no statistically significant difference beyond chance in genotype profiles (chi(2) = 1.54, df = 2, p = 0.1675). However, our findings implicate the need for a larger sample size to explore the need to implement standard clinical screening of MTHFR 677C>T. We also highlight the robust, reliable, and reproducible assay afforded by the use of anchor and sensor hybridization probes within the LightCycler platform to perform amplification and melting curve analysis protocols. Melting curve profiles that are produced display distinct and robust T(m) peaks based on the degree of anchor and sensor hybridization to amplicons produced from template DNA that is either wild-type, heterozygous, or a homozygous variant at the MTHFR 677C>T locus. A 10 degrees C gap between T(m) peaks allows for rapid and accurate qualitative identification of genotype.

Validation of GNE:p.M712T identification by melting curve analysis.

Hereditary inclusion body myopathy/distal myopathy with rimmed vacuoles is an adult onset autosomal recessive muscle-wasting disease common in people of Iranian-Jewish descent, due to the founder allelic variant GNE:p.M712T. High correlation of disease susceptibility with GNE:p.M712T allows its use as a molecular marker for diagnosis. In this study, we applied and validated the use of melting curve analysis using SimpleProbe technology for detection of this mutation using specimens obtained by mouthwash, buccal swab, and whole blood. The assay was then applied to 43 clinical specimens, and results were validated by additional methods. A probe spanning this mutation in exon 12 accurately discerns two Tm corresponding to its hybridization to wild-type and M712T-derived amplicons. A 10 degrees C divergence in Tm allowed rapid single-tube genotyping of reference and patient samples with 100% accuracy. Distal myopathy constitutes a large heterogeneous group of pathologies with similar physiological manifestations and little molecular markers for distinguishing subtypes. Application of SimpleProbes for detection of GNE:p.M712T on genomic DNA obtained from buccal epithelial cells allows accurate, rapid, and cost-effective identification of this allele in individuals at risk. This procedure is amenable to automated high-throughput applications and can be extended to both clinical and research applications.

Preclinical assessment of wt GNE gene plasmid for management of hereditary inclusion body myopathy 2 (HIBM2).

Hereditary Inclusion Body Myopathy (HIBM2) is a chronic progressive skeletal muscle wasting disorder which generally leads to complete disability before the age of 50 years. There is currently no effective therapeutic treatment for HIBM2. Development of this disease is related to expression in family members of an autosomal recessive mutation of the GNE gene, which encodes the bifunctional enzyme UDP-GlcNAc 2-epimerase/ManNAc kinase (GNE/MNK). This is the rate limiting bifunctional enzyme that catalyzes the first 2 steps of sialic acid biosynthesis. Decreased sialic acid production, consequently leads to decreased sialyation of a variety of glycoproteins including the critical muscle protein alpha-dystroglycan (alpha-DG). This in turn severely cripples muscle function and leads to the onset of the syndrome. We hypothesize that replacing the mutated GNE gene with the wildtype gene may restore functional capacity of GNE/MNK and therefore production of sialic acid, allowing for improvement in muscle function and/or delay in rate of muscle deterioration. We have constructed three GNE gene/CMV promoter plasmids (encoding the wildtype, HIBM2, and Sialuria forms of GNE) and demonstrated enhanced GNE gene activity following delivery to GNE-deficient CHO-Lec3 cells. GNE/MNK enzyme function was significantly increased and subsequent induction of sialic acid production was demonstrated after transfection into Lec3 cells with the wild type or R266Q mutant GNE vector. These data form the foundation for future preclinical and clinical studies for GNE gene transfer to treat HIBM2 patients.

Mutation in the key enzyme of sialic acid biosynthesis causes severe glomerular proteinuria and is rescued by N-acetylmannosamine.

Mutations in the key enzyme of sialic acid biosynthesis, uridine diphospho-N-acetylglucosamine 2-epimerase/N-acetylmannosamine (ManNAc) kinase (GNE/MNK), result in hereditary inclusion body myopathy (HIBM), an adult-onset, progressive neuromuscular disorder. We created knockin mice harboring the M712T Gne/Mnk mutation. Homozygous mutant (Gne(M712T/M712T)) mice did not survive beyond P3. At P2, significantly decreased Gne-epimerase activity was observed in Gne(M712T/M712T) muscle, but no myopathic features were apparent. Rather, homozygous mutant mice had glomerular hematuria, proteinuria, and podocytopathy. Renal findings included segmental splitting of the glomerular basement membrane, effacement of podocyte foot processes, and reduced sialylation of the major podocyte sialoprotein, podocalyxin. ManNAc administration yielded survival beyond P3 in 43% of the Gne(M712T/M712T) pups. Survivors exhibited improved renal histology, increased sialylation of podocalyxin, and increased Gne/Mnk protein expression and Gne-epimerase activities. These findings establish this Gne(M712T/M712T) knockin mouse as what we believe to be the first genetic model of podocyte injury and segmental glomerular basement membrane splitting due to hyposialylation. The results also support evaluation of ManNAc as a treatment not only for HIBM but also for renal disorders involving proteinuria and hematuria due to podocytopathy and/or segmental splitting of the glomerular basement membrane.

Limb-girdle muscular dystrophy in the United States.

Limb-girdle muscular dystrophy (LGMD) has been linked to 15 chromosomal loci, 7 autosomal-dominant (LGMD1A to E) and 10 autosomal-recessive (LGMD2A to J). To determine the distribution of subtypes among patients in the United States, 6 medical centers evaluated patients with a referral diagnosis of LGMD. Muscle biopsies provided histopathology and immunodiagnostic testing, and their protein abnormalities along with clinical parameters directed mutation screening. The diagnosis in 23 patients was a disorder other than LGMD. Of the remaining 289 unrelated patients, 266 had muscle biopsies sufficient for complete microscopic evaluation; 121 also underwent Western blotting. From this combined evaluation, the distribution of immunophenotypes is 12% calpainopathy, 18% dysferlinopathy, 15% sarcoglycanopathy, 15% dystroglycanopathy, and 1.5% caveolinopathy. Genotypes distributed among 2 dominant and 7 recessive subtypes have been determined for 83 patients. This study of a large racially and ethnically diverse population of patients with LGMD indicates that establishing a putative subtype is possible more than half the time using available diagnostic testing. An efficient approach to genotypic diagnosis is muscle biopsy immunophenotyping followed by directed mutational analysis. The most common LGMDs in the United States are calpainopathies, dysferlinopathies, sarcoglycanopathies, and dystroglycanopathies.

A case of hereditary inclusion body myopathy: 1 patient, 2 novel mutations.

Hereditary inclusion body myopathy is an autosomal recessive disorder that presents in early adulthood with slowly progressive weakness sparing the quadriceps. Muscle histopathology reveals rimmed vacuoles without inflammation. The disorder is caused by a mutation in the gene for UDP-N-acetylglucosamine 2-epimerase-N-acetylmannosamine kinase (GNE), a bifunctional enzyme involved in protein glycosylation. Over 40 mutations have been described to date. We present a case of a young woman with progressive lower extremity weakness. Clinical presentation, laboratory evaluation, electrodiagnostic testing, muscle pathology, and genetic sequencing are described. The patient was found to have heterozygous mutations in the GNE gene, confirming the diagnosis of hereditary inclusion body myopathy. The mutations she carried have not been described previously. We briefly review the clinical, histopathologic, and molecular genetic findings of this disorder.

Single nucleotide polymorphisms in the dystroglycan gene do not correlate with disease severity in hereditary inclusion body myopathy.

Aberrant glycosylation of dystroglycan occurs in certain muscular dystrophies, including hereditary inclusion body myopathy (HIBM). HIBM harbors a widely varying clinical severity and age of onset, which raised the suspicion of the presence of disease modifier genes. We considered the highly polymorphic dystroglycan gene (DAG1) as a feasible candidate modifier gene. DAG1 genomic DNA was sequenced for 32 HIBM patients, mainly of Persian-Jewish descent. Five novel DAG1 single nucleotide polymorphisms (SNPs) were identified, bringing the total number of SNPs to 19. However, no direct correlation between DAG1 SNPs and clinical severity of HIBM could be detected. Several identified SNPs substitute an amino acid and might modulate dystroglycan function or glycosylation status, and deserve further research. These data are valuable for future studies on the role of DAG1 in HIBM and other muscular dystrophies, especially those dystrophies that involve abnormal glycosylation of dystroglycan.

Inclusion body myopathy associated with Paget disease of bone and frontotemporal dementia is caused by mutant valosin-containing protein.

Inclusion body myopathy associated with Paget disease of bone and frontotemporal dementia (IBMPFD) is a dominant progressive disorder that maps to chromosome 9p21.1-p12. We investigated 13 families with IBMPFD linked to chromosome 9 using a candidate-gene approach. We found six missense mutations in the gene encoding valosin-containing protein (VCP, a member of the AAA-ATPase superfamily) exclusively in all 61 affected individuals. Haplotype analysis indicated that descent from two founders in two separate North American kindreds accounted for IBMPFD in approximately 50% of affected families. VCP is associated with a variety of cellular activities, including cell cycle control, membrane fusion and the ubiquitin-proteasome degradation pathway. Identification of VCP as causing IBMPFD has important implications for other inclusion-body diseases, including myopathies, dementias and Paget disease of bone (PDB), as it may define a new common pathological ubiquitin-based pathway.