Prevalence of p.G87V and p.Gln298=Variations in LIPA Gene Within Middle Eastern Population Living Around Los Angeles.

Background: The LIPA gene encodes for lysosomal acid lipase (LAL), which catalyzes the hydrolysis of cholesterol esters and triglycerides. Variations in the LIPA gene impair LAL activity, predisposing patients to a rare metabolic disorder called LAL deficiency (LAL-D). The lack of functioning LAL promotes lipid accumulation and subsequent dyslipidemia, which can increase the likelihood of complications in both infants and adults. Although the worldwide prevalence is 1:500,000 births, the frequency in Mizrahi Jewish populations is projected to be as high as 1 in every 4200 births (Valles-Ayoub et al.) based on the LIPA p.G87V variant frequency among 162 individuals. Materials and Methods: This study was conducted to validate the previously reported prevalence of LAL-D in the Mizrahi Jewish population based on the pathogenic LIPA missense variants in exon 4 (c.260G>T; p.G87V) and exon 8 (c.894G>A; p.Gln298=) using a larger cohort of those with Middle Eastern ancestry living around Los Angeles. Among the 1184 individual samples sequenced, 660 self-reported as Mizrahi Jewish, while the remaining 524 came from other Middle Eastern groups labeled as "non-Jewish." Results: Of the 1184 samples, 22 alleles of the exon 4 variant were identified (1.85%), and 2 alleles of the exon 8 variant were identified (0.16%). For the exon 4 variant, 20 of 22 (90.9%) heterozygotes were Mizrahi Jewish, while 2 of 22 (9.09%) heterozygotes were "non-Jewish." For the exon 8 variant, 2 of 2 (100%) heterozygotes were Mizrahi Jewish. This suggests that the prevalence of LAL-D in this population is 1 in 900, which suggests that LAL-D may be 4.6% higher in the Mizrahi Jewish population in previous reports. Conclusion: These findings show increased prevalence of LIPA gene exon 4 variation p.G87V in the Middle East population when compared to the general population, indicating the need for prenatal screening in those of Mizrahi Jewish ancestry.

Targeting GNE Myopathy: A Dual Prodrug Approach for the Delivery of N-Acetylmannosamine 6-Phosphate.

ProTides comprise an important class of prodrugs currently marketed and developed as antiviral and anticancer therapies. The ProTide technology employs phosphate masking groups capable of providing more favorable druglike properties and an intracellular activation mechanism for enzyme-mediated release of a nucleoside monophosphate. Herein, we describe the application of phosphoramidate chemistry to 1,3,4-O-acetylated N-acetylmannosamine (Ac3ManNAc) to deliver ManNAc-6-phosphate (ManNAc-6-P), a critical intermediate in sialic acid biosynthesis. Sialic acid deficiency is a hallmark of GNE myopathy, a rare congenital disorder of glycosylation (CDG) caused by mutations in GNE that limit the production of ManNAc-6-P. Synthetic methods were developed to provide a library of Ac3ManNAc-6-phosphoramidates that were evaluated in a series of studies for their potential as a treatment for GNE myopathy. Prodrug 12b showed rapid activation in a carboxylesterase (CPY) enzymatic assay and favorable ADME properties, while also being more effective than ManNAc at increasing sialic acid levels in GNE-deficient cell lines. These results provide a potential platform to address substrate deficiencies in GNE myopathy and other CDGs.

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.

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.