A mutation in the major autophagy gene, WIPI2, associated with global developmental abnormalities.

We describe a large consanguineous pedigree from a remote area of Northern Pakistan, with a complex developmental disorder associated with wide-ranging symptoms, including mental retardation, speech and language impairment and other neurological, psychiatric, skeletal and cardiac abnormalities. We initially carried out a genetic study using the HumanCytoSNP-12 v2.1 Illumina gene chip on nine family members and identified a single region of homozygosity shared amongst four affected individuals on chromosome 7p22 (positions 3059377-5478971). We performed whole-exome sequencing on two affected individuals from two separate branches of the extended pedigree and identified a novel nonsynonymous homozygous mutation in exon 9 of the WIPI2 (WD-repeat protein interacting with phosphoinositide 2) gene at position 5265458 (c.G745A;pV249M). WIPI2 plays a critical role in autophagy, an evolutionary conserved cellular pathway implicated in a growing number of medical conditions. The mutation is situated in a highly conserved and critically important region of WIPI2, responsible for binding PI(3)P and PI(3,5)P2, an essential requirement for autophagy to proceed. The mutation is absent in all public databases, is predicted to be damaging and segregates with the disease phenotype. We performed functional studies in vitro to determine the potential effects of the mutation on downstream pathways leading to autophagosome assembly. Binding of the V231M mutant of WIPI2b to ATG16L1 (as well as ATG5-12) is significantly reduced in GFP pull-down experiments, and fibroblasts derived from the patients show reduced WIPI2 puncta, reduced LC3 lipidation and reduced autophagic flux.

Identification of Novel Mutation in CNGA3 gene by Whole-Exome Sequencing and In-Silico Analyses for Genotype-Phenotype Assessment with Autosomal Recessive Achromatopsia in Pakistani families.

OBJECTIVE: To identify the underlying genetic anomalies in two consanguineous Pakistani families with autosomal recessive achromatopsia. METHODS: The exploratory study was conducted under the patronage of International Islamic University, Islamabad, Pakistan, and Sungshin Women University, Seoul, South Korea, after two families coded PKCN-02 and PKCN-07 belonging to different ethnic groups were recruited from different areas of Khyber Pakhtunkhawa province of Pakistan in July 2016. The families were originally diagnosed with nystagmus upon medical examination. Exome sequencing was performed to identify the possible causative gene which was found to be cyclic nucleotide-gated channel alpha-3. Sanger sequencing was performed to confirm the mutations. After genetic analysis, clinical analysis was re-evaluated for colour vision using Ishihara 26 plates. Pathogenic potential of these mutations was evaluated using algorithmic mutation prediction tools. In-silico analysis was performed to predict effect of these mutations on protein structure of the gene in question. RESULTS: Exome sequencing revealed a reported missense mutation c .1306C>T (p.R436W) in family PKCN-02 and a novel missense mutation c.1540G>A (p.D514N) in family PKCN-07. After mutational analysis, clinical re-evaluation revealed that both families were segregating autosomal recessive achromatopsia. Further, the topological model of the cyclic nucleotide-gated channel alpha-3 polypeptide describes these missense mutations primarily affecting the C-linker and cyclic guanosine monophosphate-binding sites, respectively. Protein structure modelling of cyclic nucleotide-gated channel alpha-3 protein revealed abnormal structure produced by p.R436W and p.D514N.. CONCLUSIONS: Exome sequencing approach was used to first identify the genetic alteration in families with nystagmus. Two mutations in cyclic nucleotide-gated channel alpha-3gene were uncovered, including one novel mutation. Clinical re-evaluation uncovered that both families had achromatopsia.

Genetics of speech and language disorders.

Vocal communication mediated by speech and language is a uniquely human trait, and has served an important evolutionary role in the development of our species. Deficits in speech and language functions can be of numerous types, including aphasia, stuttering, articulation disorders, verbal dyspraxia, and specific language impairment; language deficits are also related to dyslexia. Most communication disorders are prominent in children, where they are common. A number of these disorders have been shown to cluster in families, suggesting that genetic factors are involved, but their etiology at the molecular level is not well understood. In the past decade, genetic methods have proven to be powerful for understanding these etiologies. Linkage studies and molecular genetic analyses in a large family containing multiple individuals affected with verbal dyspraxia led to the discovery of mutations in the FOXP2 gene. This gene encodes a forkhead domain transcription factor, a finding that has led researchers to a new avenue of investigation into the substrates and mechanisms that underlie human speech development. In studies of stuttering, linkage and candidate gene approaches in consanguineous families identified mutations in the lysosomal enzyme-targeting pathway genes GNPTAB, GNPTG, and NAGPA, revealing a role for inherited defects in cell metabolism in this disorder. In specific language impairment, linkage studies have identified several loci, and candidate gene association studies are making progress in identifying causal variants at these loci. Although only a small fraction of all cases of speech and language disorders can be explained by genetic findings to date, the significant progress made thus far suggests that genetic approaches will continue to provide important avenues for research on this group of disorders.

A functional variant in FCRL3, encoding Fc receptor-like 3, is associated with rheumatoid arthritis and several autoimmunities.

Rheumatoid arthritis is a common autoimmune disease with a complex genetic etiology. Here we identify a SNP in the promoter region of FCRL3, a member of the Fc receptor-like family, that is associated with susceptibility to rheumatoid arthritis (odds ratio = 2.15, P = 0.00000085). This polymorphism alters the binding affinity of nuclear factor-kappaB and regulates FCRL3 expression. We observed high FCRL3 expression on B cells and augmented autoantibody production in individuals with the disease-susceptible genotype. We also found associations between the SNP and susceptibility to autoimmune thyroid disease and systemic lupus erythematosus. FCRL3 may therefore have a pivotal role in autoimmunity.

Characteristics of amylose-lipid complex prepared from pullulanase-treated rice and wheat flour.

This study aimed to evaluate the properties of amylose-lipid complexes in rice and wheat flours utilizing pullulanase as a debranching enzyme. Rice and flour were both treated with pullulanase before being combined with free fatty acids to form compounds denoted as RPF (rice-pullulanase-fatty acid) and FPF (flour-pullulanase-fatty acid), respectively. Our results showed that RPF and FPF had higher complex index and lower hydrolysis values than enzyme-untreated amylose-lipid complexes. Furthermore, RPF and FPF demonstrated lower swelling power and higher water solubility values, indicating changes in the physical properties of the starches. In vivo studies showed that RPF and FPF caused a smaller increase in blood glucose levels than untreated rice and flour, highlighting their potential use as functional food ingredients. These findings provide valuable information for the development of novel rice-and wheat-based foods with improved nutritional and physiological properties. Supplementary Information: The online version contains supplementary material available at 10.1007/s10068-023-01411-0.

Mutations in the lysosomal enzyme-targeting pathway and persistent stuttering.

BACKGROUND: Stuttering is a disorder of unknown cause characterized by repetitions, prolongations, and interruptions in the flow of speech. Genetic factors have been implicated in this disorder, and previous studies of stuttering have identified linkage to markers on chromosome 12. METHODS: We analyzed the chromosome 12q23.3 genomic region in consanguineous Pakistani families, some members of which had nonsyndromic stuttering and in unrelated case and control subjects from Pakistan and North America. RESULTS: We identified a missense mutation in the N-acetylglucosamine-1-phosphate transferase gene (GNPTAB), which encodes the alpha and beta catalytic subunits of GlcNAc-phosphotransferase (GNPT [EC 2.7.8.15]), that was associated with stuttering in a large, consanguineous Pakistani family. This mutation occurred in the affected members of approximately 10% of Pakistani families studied, but it occurred only once in 192 chromosomes from unaffected, unrelated Pakistani control subjects and was not observed in 552 chromosomes from unaffected, unrelated North American control subjects. This and three other mutations in GNPTAB occurred in unrelated subjects with stuttering but not in control subjects. We also identified three mutations in the GNPTG gene, which encodes the gamma subunit of GNPT, in affected subjects of Asian and European descent but not in control subjects. Furthermore, we identified three mutations in the NAGPA gene, which encodes the so-called uncovering enzyme, in other affected subjects but not in control subjects. These genes encode enzymes that generate the mannose-6-phosphate signal, which directs a diverse group of hydrolases to the lysosome. Deficits in this system are associated with the mucolipidoses, rare lysosomal storage disorders that are most commonly associated with bone, connective tissue, and neurologic symptoms. CONCLUSIONS: Susceptibility to nonsyndromic stuttering is associated with variations in genes governing lysosomal metabolism.

Effect of Processing Parameters on Bonding Performance of a Carbon Fiber/Polyetheretherketone Thermoplastic Composite Prepared by Induction Welding.

Among the various welding techniques used to bond thermoplastic composites, induction welding stands out as a fast, clean, and contact-free process that shortens the welding time and prevents the weight increase of mechanical fastening, such as rivets and bolts. In this study, we manufactured polyetheretherketone (PEEK)-resin-based thermoplastic carbon fiber (CF) composite materials at different automated fiber placement laser powers (3569, 4576, and 5034 W) and investigated their bonding and mechanical characteristics after induction welding. The quality of the composite was evaluating using various techniques, including optical microscopy, C-scanning, and mechanical strength measurements, and a thermal imaging camera was used to monitor the surface temperature of the specimen during its processing. The results revealed that the preparation conditions of the polymer/carbon fiber composites, such as the laser power and surface temperature, significantly affect the quality and performance of the induction-welding-bonded composites. A lower laser power during preparation resulted in weaker bonding between components of the composite and yielded samples with a lower shear stress.

Analysis of mannose 6-phosphate uncovering enzyme mutations associated with persistent stuttering.

GlcNAc-1-phosphodiester-N-acetylglucosaminidase ("uncovering enzyme" (UCE); EC 3.1.4.45) is a Golgi enzyme that mediates the second step in the synthesis of the mannose 6-phosphate lysosomal targeting signal on acid hydrolases. Recently, three mutations (two missense and one deletion/frameshift) in the NAGPA gene that encodes UCE have been identified in individuals with persistent stuttering. We now demonstrate that each mutation leads to lower cellular UCE activity. The p.R328C mutation impairs folding in the endoplasmic reticulum, resulting in degradation of a significant portion by the proteasomal system. The p.H84Q mutation also impairs folding and, in addition, decreases the specific activity of the enzyme that folds sufficiently to traffic to the Golgi. The p.F513SfsX113 frameshift mutation adds 113 amino acids to the C terminus of the cytoplasmic tail of the protein, including a VWLL sequence that causes rapid degradation via the proteasomal system. These biochemical findings extend the genetic data implicating mutations in the NAGPA gene in the persistent stuttering phenotype.

A role for inherited metabolic deficits in persistent developmental stuttering.

Stuttering is a common but poorly understood speech disorder. Consistent evidence for the involvement of genetic factors in stuttering has motivated studies aimed at identifying causative genetic variants that could shed light on the underlying molecular and cellular deficits in this disorder. Such studies have begun to identify causative genes. The purpose of this review is to summarize the gene discoveries to date, and to cover the subsequent functional studies that are beginning to provide insights into how these gene mutations might cause stuttering. Surprisingly, the first variant genes to be associated with stuttering are those encoding the lysosomal targeting system, GNPTAB, GNPTG, and NAGPA. Although mutations in NAGPA have not been associated with a disorder in humans, mutations in GNPTAB and GNPTG cause mucolipidosis types II and III, which are rare autosomal recessive lysosomal storage disorders, associated with pathology of bone, connective tissue, liver, spleen, and brain. Analysis of mutations in these genes has so far identified predominantly missense mutations in stuttering, in contrast to the truncating and other mutations that result in very low GNPTAB/G enzyme activity and are historically associated with mucolipidosis. Genetic evidence for the role of lysosomal targeting mutations in stuttering has now been buttressed by biochemical studies of the mutant enzymes found in this disorder. While data on the GlcNAc-phosphotransferase encoded by GNPTAB/G remains limited and only suggestive, a study of the enzyme encoded by NAGPA has shown that the mutations found in stuttering reduce the overall cellular activity of this enzyme by about half, and that they result in deficits in intracellular processing and trafficking that lead to a reduced cellular half life. How these deficits result in the presumed speech-specific neuropathology associated with stuttering is not yet known. However these findings have opened several new lines of inquiry, including studies in mice carrying human stuttering mutations, that represent promising approaches to this disorder.

Manufacturing of Carbon Fibers/Polyphenylene Sulfide Composites via Induction-Heating Molding: Morphology, Mechanical Properties, and Flammability.

Conventional thermosetting composites exhibit advantageous mechanical properties owing to the use of an autoclave; however, their wide usage is limited by high production costs and long molding times. In contrast, the fabrication of thermoplastic composites involves out-of-autoclave processes that use press equipment. In particular, induction-heating molding facilitates a quicker thermal cycle, reduced processing time, and improved durability of the thermoplastic polymers; thus, the process cost and production time can be reduced. In this study, carbon fiber/polyphenylene sulfide thermoplastic composites were manufactured using induction-heating molding, and the relationships among the process, structure, and mechanical properties were investigated. The composites were characterized using optical and scanning electron microscopy, an ultrasonic C-scan, and X-ray computed tomography. In addition, the composites were subjected to flammability tests. This study provides novel insights into the optimization of thermoplastic composite manufacturing and thermoset composite curing processes.

Characterization of a mutation commonly associated with persistent stuttering: evidence for a founder mutation.

Stuttering is a disorder that affects the fluency of speech. It has been shown to have high heritability and has recently been linked to mutations in the GNPTAB gene. One such mutation, Glu1200Lys, has been repeatedly observed in unrelated families and individual cases. Eight unrelated individuals carrying this mutation were analyzed in an effort to distinguish whether these arise from repeated mutation at the same site, or whether they represent a founder mutation with a single origin. Results show that all 12 chromosomes carrying this mutation share a common haplotype in this region, indicating that it is a founder mutation. Further analysis estimated the age of this allele to be ∼ 572 generations. Construction of a cladogram tracing the mutation through our study sample also supports the founder mutation hypothesis.

Two missense mutations in GPNMB cause autosomal recessive amyloidosis cutis dyschromica in the consanguineous pakistani families.

BACKGROUND: Amyloidosis cutis dyschromica (ACD) is a rare variant of cutaneous amyloidosis. This disorder often clusters in families, and it has been suggested that genetic factors might be involved in its development. OBJECTIVE: To identify the genetic causes of ACD, we recruited a consanguineous Pakistani family with multiple cases of ACD that display a recessive mode of inheritance. METHODS: We performed whole-exome sequencing of samples from 7 members of this family, followed by bioinformatic and in silico analyses to identify the causative variant. For the replication study, we recruited a British family with Pakistani ancestry, and sequenced all exons of glycoprotein non-metastatic melanoma protein b (GPNMB) to identify mutations. We also investigated effects of the mutations on the stability of the GPNMB protein using the I-TASSER three-dimensional modeling tool. RESULTS: We found a novel homozygous mutation, p.Gly363Val (c.1088 G>T), in GPNMB in all affected cases. In a replication study, another homozygous missense mutation in GPNMB, pIle174Met (c.522 C>G), was carried by the affected son. The two mutations were not observed in our in-house data set comprising 217 healthy Pakistani individuals or in The Genome Aggregation Database. Our structural modeling of GPNMB suggested that p.Gly363Val enhanced its stability, whereas p.Ile174Met caused instability. CONCLUSIONS: This study reports two novel missense mutations in two Pakistani families that cause ACD. The mutations appear to influence GPNMB stability, as revealed by protein modeling.

Biallelic inheritance in a single Pakistani family with intellectual disability implicates new candidate gene RDH14.

In a multi-branch family from Pakistan, individuals presenting with palmoplantar keratoderma segregate in autosomal dominant fashion, and individuals with intellectual disability (ID) segregate in apparent autosomal recessive fashion. Initial attempts to identify the ID locus using homozygosity-by-descent (HBD) mapping were unsuccessful. However, following an assumption of locus heterogeneity, a reiterative HBD approach in concert with whole exome sequencing (WES) was employed. We identified a known disease-linked mutation in the polymicrogyria gene, ADGRG1, in two affected members. In the remaining two (living) affected members, HBD mapping cross-referenced with WES data identified a single biallelic frameshifting variant in the gene encoding retinol dehydrogenase 14 (RDH14). Transcription data indicate that RDH14 is expressed in brain, but not in retina. Magnetic resonance imaging for the individuals with this RDH14 mutation show no signs of polymicrogyria, however cerebellar atrophy was a notable feature. RDH14 in HEK293 cells localized mainly in the nucleoplasm. Co-immunoprecipitation studies confirmed binding to the proton-activated chloride channel 1 (PACC1/TMEM206), which is greatly diminished by the mutation. Our studies suggest RDH14 as a candidate for autosomal recessive ID and cerebellar atrophy, implicating either disrupted retinoic acid signaling, or, through PACC1, disrupted chloride ion homeostasis in the brain as a putative disease mechanism.

Whole-exome sequencing analysis reveals co-segregation of a COL20A1 missense mutation in a Pakistani family with striate palmoplantar keratoderma.

Palmoplantar keratoderma (PPK) is a rare group of excessive skin disorder characterized by thickness over the palms and soles. The striate palmoplantar keratoderma (PPKS) is a form in which hyperkeratotic lesions are restricted to the pressure regions extending longitudinally in the length of each finger to the palm. Dominantly inherited mutations in genes including desmoglein 1, desmoplakin and keratin 1 have been suggested as genetic causes of PPKS. In this study, we investigated a three-generation Pakistani family segregating PPKS phenotype in autosomal dominant fashion to identify genetic cause in this family. We have performed whole-exome and Sanger sequencing followed by in silico bioinformatics analysis to pinpoint candidate mutation associated with PPK. Revealed a novel heterozygous mutation (NM_020882.2, COL20A1 c. 392C > G; p.Ser131Cys) in the loop region close to fibronectin type III-1 domain of the c ollagen 20 α1. This variant was not found in our in-house 219 ethnically matched Pakistani unaffected controls and showed minor allele frequency of 3.4 × 10-5 in Exome Aggregation Consortium database containing exome data of 59,464 worldwide individuals. It was assigned as "pathogenic" by in silico prediction tools. Previously, association of mutation in the COL14A1, one of the paralogous gene of COL20A1, with PPK was reported in the study with a Chinese family. Our study proposes COL20A1 gene as another potential candidate gene for PPKS which expand the spectrum of collagen proteins in the pathogenicity of PPK.

One-step noninvasive prenatal testing (NIPT) for autosomal recessive homozygous point mutations using digital PCR.

Previously, we introduced a noninvasive prenatal testing (NIPT) protocol for diagnosing compound heterozygous autosomal recessive point mutations via maternal plasma DNA and simulated control genomic DNA sampling based on fetal DNA fraction. In our present study, we have improved our NIPT protocol to make it possible to diagnose homozygous autosomal recessive point mutations without the need to acquire fetal DNA fraction. Moreover, chi-squared test and empirical statistical range based on the proportion of mutant allele reads among the total reads served as the gatekeeping method. If this method yielded inconclusive results, then the Bayesian method was performed; final conclusion was drawn from the results of both methods. This protocol was applied to three families co-segregating congenital sensorineural hearing loss with monogenic homozygous mutations in prevalent deafness genes. This protocol successfully predicted the fetal genotypes from all families without the information about fetal DNA fraction using one-step dPCR reactions at least for these three families. Furthermore, we suspect that confirmatory diagnosis under this protocol is possible, not only by using picodroplet dPCR, but also by using the more readily available chip-based dPCR, making our NIPT protocol more useful in the diagnosis of autosomal recessive point mutations in the future.

Genetic polymorphisms of selected DNA repair genes, estrogen and progesterone receptor status, and breast cancer risk.

PURPOSE: Genetic polymorphisms of DNA repair genes seem to determine the DNA repair capacity, which in turn may affect the risk of breast cancer. To evaluate the role of genetic polymorphisms of DNA repair genes in breast cancer, we conducted a hospital-based case-control study of Korean women. EXPERIMENTAL DESIGN: We included 872 incident breast cancer cases and 671 controls recruited from several teaching hospitals in Seoul from 1995 to 2002. Twelve loci of selected DNA repair genes were genotyped by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (XRCC2 Arg188His, XRCC4 921G > T, XRCC6 1796G > T, LIG4 1977T/C, RAD51 135G > C, 172G > T, RAD52 2259C > T, LIG1 551A > C, ERCC1 8092A > C, 354C > T, hMLH1 -93G > A, and Ile219Val). RESULTS: We found that the RAD52 2259 CT or TT, hMLH1 -93 GG, and ERCC1 8092 AA genotypes were associated with breast cancer risk after adjustment for known risk factors [odds ratio (OR), 1.33; 95% confidence interval (95% CI), 1.02-1.75; OR, 1.31; 95% CI, 0.99-1.74; and OR, 0.58; 95% CI, 0.38-0.89, respectively]. When Bonferroni's method was used to correct for multiple comparisons for nine polymorphisms with P = 0.005, all of these associations were not significant. However, the effects of RAD52 2259 CT or TT and ERCC1 354 CT or TT genotypes were more evident for the estrogen/progesterone receptor-negative cases (OR, 2.03; 95% CI, 1.24-3.34 and OR, 1.99; 95% CI, 1.35-2.94, respectively). CONCLUSION: Our findings suggest that genetic polymorphisms of RAD52, ERCC1, and hMLH1 may be associated with breast cancer risk in Korean women.

A novel homozygous PTH1R variant identified through whole-exome sequencing further expands the clinical spectrum of primary failure of tooth eruption in a consanguineous Saudi family.

OBJECTIVES: The present study aimed to identify the genetic cause of non-syndromic primary failure of tooth eruption in a five-generation consanguineous Saudi family using whole-exome sequencing (WES) analysis. DESIGN: The family pedigree and phenotype were obtained from patient medical records. WES of all four affected family members was performed using the 51 Mb SureSelect V4 library kit and then sequenced using the Illumina HiSeq2000 sequencing system. Sequence alignment, variant calling, and the annotation of single nucleotide polymorphisms and indels were performed using standard bioinformatics pipelines. The genotype of candidate variants was confirmed in all available family members by Sanger sequencing. RESULTS: Pedigree analysis suggested that the inheritance was autosomal recessive. WES of all affected individuals identified a novel homozygous variant in exon 8 of the parathyroid hormone 1 receptor gene (PTH1R) (NM_000316: c.611T>A: p.Val204Glu). CONCLUSION: To the best of our knowledge, this is the first report of primary failure of eruption caused by a homozygous mutation in PTH1R. Our findings prove the application of WES as an efficient molecular diagnostics tool for this rare phenotype and further broaden the clinical spectrum of PTH1R pathogenicity.

Development of novel noninvasive prenatal testing protocol for whole autosomal recessive disease using picodroplet digital PCR.

We developed a protocol of noninvasive prenatal testing (NIPT), employing a higher-resolution picodroplet digital PCR, to detect genetic imbalance in maternal plasma DNA (mpDNA) caused by cell-free fetal DNA (cffDNA). In the present study, this approach was applied to four families with autosomal recessive (AR) congenital sensorineural hearing loss. First, a fraction of the fetal DNA in mpDNA was calculated. Then, we made artificial DNA mixtures (positive and negative controls) to simulate mpDNA containing the fraction of cffDNA with or without mutations. Next, a fraction of mutant cluster signals over the total signals was measured from mpDNA, positive controls, and negative controls. We determined whether fetal DNA carried any paternal or maternal mutations by calculating and comparing the sum of the log-likelihood of the study samples. Of the four families, we made a successful prediction of the complete fetal genotype in two cases where a distinct cluster was identified for each genotype and the fraction of cffDNA in mpDNA was at least 6.4%. Genotyping of only paternal mutation was possible in one of the other two families. This is the first NIPT protocol potentially applicable to any AR monogenic disease with various genotypes, including point mutations.

Mucolipidosis types II and III and non-syndromic stuttering are associated with different variants in the same genes.

Homozygous mutations in GNPTAB and GNPTG are classically associated with mucolipidosis II (ML II) alpha/beta and mucolipidosis III (ML III) alpha/beta/gamma, which are rare lysosomal storage disorders characterized by multiple pathologies. Recently, variants in GNPTAB, GNPTG, and the functionally related NAGPA gene have been associated with non-syndromic persistent stuttering. In a worldwide sample of 1013 unrelated individuals with non-syndromic persistent stuttering we found 164 individuals who carried a rare non-synonymous coding variant in one of these three genes. We compared the frequency of these variants with those in population-matched controls and genomic databases, and their location with those reported in mucolipidosis. Stuttering subjects displayed an excess of non-synonymous coding variants compared to controls and individuals in the 1000 Genomes and Exome Sequencing Project databases. We identified a total of 81 different variants in our stuttering cases. Virtually all of these were missense substitutions, only one of which has been previously reported in mucolipidosis, a disease frequently associated with complete loss-of-function mutations. We hypothesize that rare non-synonymous coding variants in GNPTAB, GNPTG, and NAGPA may account for as much as 16% of persistent stuttering cases, and that variants in GNPTAB and GNPTG are at different sites and may in general, cause less severe effects on protein function than those in ML II alpha/beta and ML III alpha/beta/gamma.