Stuttering associated with a pathogenic variant in the chaperone protein cyclophilin 40.

Stuttering is a common speech disorder that interrupts speech fluency and tends to cluster in families. Typically, stuttering is characterized by speech sounds, words or syllables which may be repeated or prolonged and speech that may be further interrupted by hesitations or 'blocks'. Rare variants in a small number of genes encoding lysosomal pathway proteins have been linked to stuttering. We studied a large four-generation family in which persistent stuttering was inherited in an autosomal dominant manner with disruption of the cortico-basal-ganglia-thalamo-cortical network found on imaging. Exome sequencing of three affected family members revealed the PPID c.808C>T (p.Pro270Ser) variant that segregated with stuttering in the family. We generated a Ppid p.Pro270Ser knock-in mouse model and performed ex vivo imaging to assess for brain changes. Diffusion-weighted MRI in the mouse revealed significant microstructural changes in the left corticospinal tract, as previously implicated in stuttering. Quantitative susceptibility mapping also detected changes in cortico-striatal-thalamo-cortical loop tissue composition, consistent with findings in affected family members. This is the first report to implicate a chaperone protein in the pathogenesis of stuttering. The humanized Ppid murine model recapitulates network findings observed in affected family members.

Increased incidence of eosinophilic esophagitis among the child population of Zaragoza. An emergent disease.

Eosinophilic esophagitis is a chronic inflammatory disease characterized by esophageal dysfunction and progression to fibrosis. Its incidence is increasing in our setting with deep regional variations. To corroborate this hypothesis, a longitudinal, retrospective, multicenter observational study was carried out of patients who received a diagnosis of eosinophilic esophagitis from 2008 to 2022 at public hospitals in the province of Zaragoza. The annual incidence rates and mean incidence rate were calculated using the data for the reference population. A total of 104 patients were included. The mean incidence rate was 5.1 cases per 100,000 inhabitants < 15 years old/year (0.75-11.2). In the first five-year period (2008-2012) the rate was 1.2 cases per 100,000 inhabitants/year, compared with a rate of 6 cases per 100,000 inhabitants/year in the second 5-year period (2013-2017), [OR 5,68 (IC 95% 2,55 - 12,67, p < 0,05]; and 8.1 cases per 100,000 inhabitants/year in the third five-year period (2018-2022), [OR 7,74 (IC 95% 3,52 - 16,99, p < 0,05] It is concluded that eosinophilic esophagitis incidence has increased among the child population of Zaragoza over the past 15 years, with a 7-fold higher risk of having the condition in the third five-year period compared with the first one.

Evaluation of liver function tests in the paediatric patient.

INTRODUCTION: Although changes in liver function tests can be non-specific in numerous clinical conditions, they can be the first sign of a potentially serious disease in an asymptomatic patient. MATERIAL AND METHODS: Retrospective cohort study, performed by reviewing the records of children of a reference hospital central laboratory with alanine aminotransferase enzyme (ALT) elevation during a 6-month aleatory period. RESULTS: 572 blood tests with serum ALT elevation corresponding to 403 patients have been assessed during the period studied. 98 patients were excluded for presenting abnormal liver test before the study period of comorbidity that could produce ALT elevation. The remaining 305 patients, 22.6% were diagnosed with a medical condition during the first blood test that explained the ALT elevation, although only 33.3% of them were followed up until verifying their normalisation. Final study sample consists of 236 patients with abnormal liver test without apparent liver disease. Adequate follow-up was found only in 29% of them. From this group, 9 patients (13%) were diagnosed with liver disease. The rest of the samples were not properly monitored. In patients with higher serum ALT levels, follow-up was early and more appropriate. CONCLUSIONS: In our area, most children without apparent liver disease are no properly monitored. Therefore, an opportunity to diagnosis and treat a potential liver disease was lost in a great number of children. All children with unexplained hypertransaminasaemia must be studied.

Artritis como debut de enfermedad inflamatoria intestinal en pediatría / Arthritis as clinical presentation of inflammatory bowel disease in children

La incidencia de enfermedad inflamatoria intestinal en la edad pediátrica se ha incrementado mundialmente en las últimas décadas. La forma de presentación puede ser diversa y, hasta en un 6-35 %, las manifestaciones extraintestinales pueden ser el debut; la artritis periférica es la más frecuente de estas. Una presentación atípica implica un retraso diagnóstico y, asociado a que el fenotipo de enfermedad inflamatoria intestinal es más grave en los niños, conlleva un incremento de las complicaciones intestinales y secuelas asociadas. Se presentan dos casos clínicos de enfermedad de Crohn cuya clínica inicial fue la claudicación de la marcha por una artritis periférica y una entesitis, respectivamente.

Inflammatory bowel disease in children has increased worldwide during the last decades. Clinical presentations are diverse and extraintestinal manifestations are the presenting sign in 6-35 % of patients, the most common of them being peripheral arthritis. An atypical clinical presentation results in diagnosis delay and, added to the greater seriousness of inflammatory bowel disease phenotypes in children, it entails more intestinal complications and sequelae. We describe two cases of inflammatory bowel disease with an initial symptom of lameness due to peripheral arthritis and enthesitis, respectively.

[Arthritis as clinical presentation of inflammatory bowel disease in children]. / Artritis como debut de enfermedad inflamatoria intestinal en pediatría.

Inflammatory bowel disease in children has increased worldwide during the last decades. Clinical presentations are diverse and extraintestinal manifestations are the presenting sign in 6-35 % of patients, the most common of them being peripheral arthritis. An atypical clinical presentation results in diagnosis delay and, added to the greater seriousness of inflammatory bowel disease phenotypes in children, it entails more intestinal complications and sequelae. We describe two cases of inflammatory bowel disease with an initial symptom of lameness due to peripheral arthritis and enthesitis, respectively.

La incidencia de enfermedad inflamatoria intestinal en la edad pediátrica se ha incrementado mundialmente en las últimas décadas. La forma de presentación puede ser diversa y, hasta en un 6-35 %, las manifestaciones extraintestinales pueden ser el debut; la artritis periférica es la más frecuente de estas. Una presentación atípica implica un retraso diagnóstico y, asociado a que el fenotipo de enfermedad inflamatoria intestinal es más grave en los niños, conlleva un incremento de las complicaciones intestinales y secuelas asociadas. Se presentan dos casos clínicos de enfermedad de Crohn cuya clínica inicial fue la claudicación de la marcha por una artritis periférica y una entesitis, respectivamente.

Genetic factors and therapy outcomes in persistent developmental stuttering.

PURPOSE: We investigated whether outcomes of therapy for persistent developmental stuttering differ in individuals who carry a mutation in one of the known genes associated with stuttering compared to individuals without such mutations. METHOD: We studied outcomes of an intensive fluency shaping-based therapy program in individuals with persistent developmental stuttering. We evaluated a cohort of 51 stuttering individuals with who carried a mutation in either the GNPTAB, GNPTG, NAGPA, or AP4E1 gene. We compared therapy outcomes in these individuals with outcomes in 51 individuals matched for age, gender, and ethnicity, who stutter and underwent the same therapy program, and did not carry a mutation in any of these genes. Fluency pre- and post-therapy was evaluated using blinded observer-based quantitative stuttering dysfluency measures (Dysfluent Words Score, DWS), and by subjects' self-reported measures of struggle, avoidance and expectancy behavior associated with speaking (Perceptions of Stuttering Inventory, PSI). The difference between pre- and post-therapy fluency scores was taken as the measure of near-term therapy efficacy. RESULTS: Comparison of fluency measures showed a strong effect of therapy overall. Mutation carriers achieved significantly less resolution in PSI following therapy, with PSI scores showing significantly less improvement in individuals who carry a mutation (p = 0.0157, RR = 1.75, OR = 2.92) while the group difference in DWS between carriers and non-carriers was statistically not significant in the present study, the trend observed in the results warrants further research focused on this important issue. CONCLUSIONS: These results suggest stuttering is more resistant to therapy in individuals who carry a mutation in one of the genes known to be associated with stuttering.

An African-specific haplotype in MRGPRX4 is associated with menthol cigarette smoking.

In the U.S., more than 80% of African-American smokers use mentholated cigarettes, compared to less than 30% of Caucasian smokers. The reasons for these differences are not well understood. To determine if genetic variation contributes to mentholated cigarette smoking, we performed an exome-wide association analysis in a multiethnic population-based sample from Dallas, TX (N = 561). Findings were replicated in an independent cohort of African Americans from Washington, DC (N = 741). We identified a haplotype of MRGPRX4 (composed of rs7102322[G], encoding N245S, and rs61733596[G], T43T), that was associated with a 5-to-8 fold increase in the odds of menthol cigarette smoking. The variants are present solely in persons of African ancestry. Functional studies indicated that the variant G protein-coupled receptor encoded by MRGPRX4 displays reduced agonism in both arrestin-based and G protein-based assays, and alteration of agonism by menthol. These data indicate that genetic variation in MRGPRX4 contributes to inter-individual and inter-ethnic differences in the preference for mentholated cigarettes, and that the existence of genetic factors predisposing vulnerable populations to mentholated cigarette smoking can inform tobacco control and public health policies.

[Implementation of a low FODMAP diet for functional abdominal pain]. / Implantación de la dieta baja en FODMAP para el dolor abdominal funcional.

INTRODUCTION: The low FODMAP diet (fermentable oligosaccharides, monosaccharides, disaccharides, and polyols) has shown to be effective in adult patients with irritable bowel syndrome, but there are few studies on paediatric patients. The aim of this study is to assess the implementation and the outcomes of a low FODMAP diet in the treatment of functional abdominal pain in children from a Mediterranean area. MATERIAL AND METHODS: A table was designed in which foods were classified according to their FODMAP content, as well as a 'Symptoms and Stools Diary'. A prospective study was conducted on children with functional abdominal pain in our Paediatric Gastroenterology Unit. RESULTS: A total of 22 patients were enrolled in the trial, and 20 completed it. Data were collected of the abdominal pain features over a period of 3 days, and then patients followed a two-week low FODMAP diet. Afterwards, information about abdominal pain features was collected again. After the diet, they showed fewer daily abdominal pain episodes compared to baseline (1.16 [IQR: 0.41-3.33] versus 2 [IQR: 1.33-6.33] daily episodes, P=.024), less pain severity compared to baseline (1.41cm [IQR: 0.32-5.23] versus 4.63cm [IQR: 2.51-6.39] measured by 10-cm Visual Analogue Scale, P=.035), less interference with daily activities, and less gastrointestinal symptoms. Only 15% of patients found it difficult to follow the diet. CONCLUSIONS: The implementation of a low FODMAP diet for 2 weeks in a Mediterranean paediatric population diagnosed with functional abdominal pain is possible with adapted diets. It was highly valued by patients, and they showed an improvement in abdominal pain symptoms assessed by objective methods.

Antimicrobial Properties of Extracellular Matrix Scaffolds for Tissue Engineering.

The necessity to manufacture graft materials with superior biocompatibility capabilities and biodegradability characteristics for tissue regeneration has led to the production of extracellular matrix- (ECM-) based scaffolds. Among their advantages are better capacity to allow cell colonization, which enables its successful integration into the tissue surrounding the area to be repaired. In addition, it has been shown that some of these scaffolds have antimicrobial activity, preventing possible infections; therefore, it could be used as an alternative to control surgical infection and decrease the use of antimicrobial agents. The purpose of this review is to collect the existing information about antimicrobial activity of the ECM and their components.

Taste Perception of Antidesma bunius Fruit and Its Relationships to Bitter Taste Receptor Gene Haplotypes.

It was shown more than 40 years ago that the ability to perceive the bitterness of the fruit of the Antidesma bunius tree is inversely correlated with the ability to perceive the well-studied bitter tastant phenylthiocarbamide (PTC). To determine if variants of the TAS2R38 gene, which encodes the PTC taste receptor, or variants in any of the other TAS2R bitter or TAS1R sweet receptor genes account for Antidesma taste perception, we recruited an independent subject sample and examined associations between these taste receptor gene haplotypes and Antidesma perception. Consistent with previous findings, almost none of our subjects who reported Antidesma juice as bitter was a PTC "responder" by previous definitions (i.e. a PTC taster). In our study, of the 132 individuals who perceived PTC as bitter, 15 perceived Antidesma as bitter, although these 15 subjects had very weak bitterness perception scores. Examination of TAS2R38 gene haplotypes showed that, of the subjects who perceive Antidesma as bitter, all carried at least one copy of the TAS2R38 AVI (PTC non-taster) haplotype. However, 86 subjects carried at least one AVI haplotype and failed to perceive Antidesma as bitter. No other TAS2R or TAS1R gene variants showed an association with Antidesma bitter, sweet, or sour perception. Our results show that TAS2R38 haplotypes are associated with differential perception of Antidesma berry juice bitterness, and that all those who perceive this bitterness carry at least one AVI haplotype. This indicates that the AVI haplotype is necessary for this perception, but that additional variable factors are involved.

Evaluation of decellularized matrix and ß-tricalcium phosphate as biomaterials for bone neoformation: in vivo study / Evaluación de la matriz descelularizada y ß-fosfato tricálcico como biomateriales para neoformación ósea: estudio in vivo

The aim of this study was to evaluate histologically the effect of two biomaterials, a biomaterial derived from porcine Urinary submucosa Bladder Matrix (UBM) and beta-TriCalcium Phosphate (ß-TCP), on bone defects. Twenty male New Zealand rabbits were used; the models were divided in two groups: the UBM group; the ß-TCP group, and a Negative Control (NC) group. Five-mm defects were created in the femur of each model and then the different biomaterials were set in place depending on each group. At 4 and 8 weeks, the animals in the models were sacrificed and samples of the defect site were collected to perform a Hematoxylin and Eosin stain (H&E). Histologically, ß-TCP group at 4 and 8 weeks presented neoformation of bone-like and cartilage-like tissue, with the presence of inflammatory infiltrate; at 4 and 8 weeks, the UBM group presented neoformation of bone-like and cartilage-like tissue with a low presence of inflammatory infiltrate, and the NC group presented the formation of connective tissue and, in a low proportion, neoformation of bone tissue and cartilage. Both biomaterials, UBM and ß-TCP, exhibited the capacity to promote bone neoformation; however, the UBM-based biomaterial produced a better-organized tissue with a lower inflammatory response compared with the ß-TCP group.

El objetivo de este estudio fue evaluar histológicamente el efecto de dos biomateriales: derivado de matriz de submucosa de vejiga urinaria porcina (UBM) y b-fosfato tricálcico (ß-TCP) en defectos óseos. Veinte conejos macho de raza Nueva Zelanda fueron empleados para este estudio; los modelos fueron divididos en dos grupos: UBM, ß-TCP y un grupo control negativo. Se crearon defectos de 5 mm en el fémur de cada uno de los modelos y posteriormente se colocó el biomaterial correspondiente de acuerdo a cada uno de los grupos. A las 4 y 8 semanas los modelos fueron sacrificados y se tomaron muestras del sitio del defecto óseo para realizar una tinción de Hematoxilina y Eosina. Histológicamente el grupo de ß-TCP tanto a las 4 como a las 8 semanas mostró neoformación de tejido óseo y tejido cartilaginoso con presencia de infiltrado inflamatorio; el grupo de UBM a las 4 y 8 semanas presentó neoformación de tejido óseo, tejido cartilaginoso y un bajo infiltrado inflamatorio; el grupo control negativo presentó formación de tejido conectivo y en baja proporción neoformación de tejido óseo y cartílago. Ambos biomateriales, UBM y ß-TCP mostraron la capacidad de promover la neoformación de tejido óseo; sin embargo, el biomaterial basado en UBM produjo un tejido mejor organizado y un menor infiltrado inflamatorio en comparación con el ß-TCP.

Probing the Evolutionary History of Human Bitter Taste Receptor Pseudogenes by Restoring Their Function.

Lineage-specific gene losses can be driven by selection or environmental adaptations. However, a lack of studies on the original function of species-specific pseudogenes leaves a gap in our understanding of their role in evolutionary histories. Pseudogenes are of particular relevance for taste perception genes, which encode for receptors that confer the ability to both identify nutritionally valuable substances and avoid potentially harmful substances. To explore the role of bitter taste pseudogenization events in human origins, we restored the open reading frames of the three human-specific pseudogenes and synthesized the reconstructed functional hTAS2R2, hTAS2R62 and hTAS2R64 receptors. We have identified ligands that differentially activate the human and chimpanzee forms of these receptors and several other human functional TAS2Rs. We show that these receptors are narrowly tuned, suggesting that bitter-taste sensitivities evolved independently in different species, and that these pseudogenization events occurred because of functional redundancy. The restoration of function of lineage-specific pseudogenes can aid in the reconstruction of their evolutionary history, and in understanding the forces that led to their pseudogenization.

Genetic Variation in the TAS2R38 Bitter Taste Receptor and Smoking Behaviors.

Common TAS2R38 taste receptor gene variants specify the ability to taste phenylthiocarbamide (PTC), 6-n-propylthiouracil (PROP) and structurally related compounds. Tobacco smoke contains a complex mixture of chemical substances of varying structure and functionality, some of which activate different taste receptors. Accordingly, it has been suggested that non-taster individuals may be more likely to smoke because of their inability to taste bitter compounds present in tobacco smoke, but results to date have been conflicting. We studied three cohorts: 237 European-Americans from the state of Georgia, 1,353 European-Americans and 2,363 African-Americans from the Dallas Heart Study (DHS), and 4,973 African-Americans from the Dallas Biobank. Tobacco use data was collected and TAS2R38 polymorphisms were genotyped for all participants, and PTC taste sensitivity was assessed in the Georgia population. In the Georgia group, PTC tasters were less common among those who smoke: 71.5% of smokers were PTC tasters while 82.5% of non-smokers were PTC tasters (P = 0.03). The frequency of the TAS2R38 PAV taster haplotype showed a trend toward being lower in smokers (38.4%) than in non-smokers (43.1%), although this was not statistically significant (P = 0.31). In the DHS European-Americans, the taster haplotype was less common in smokers (37.0% vs. 44.0% in non-smokers, P = 0.003), and conversely the frequency of the non-taster haplotype was more common in smokers (58.7% vs. 51.5% in non-smokers, P = 0.002). No difference in the frequency of these haplotypes was observed in African Americans in either the Dallas Heart Study or the Dallas Biobank. We conclude that TAS2R38 haplotypes are associated with smoking status in European-Americans but not in African-American populations. PTC taster status may play a role in protecting individuals from cigarette smoking in specific populations.

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.

Association between Rare Variants in AP4E1, a Component of Intracellular Trafficking, and Persistent Stuttering.

Stuttering is a common, highly heritable neurodevelopmental disorder characterized by deficits in the volitional control of speech. Whole-exome sequencing identified two heterozygous AP4E1 coding variants, c.1549G>A (p.Val517Ile) and c.2401G>A (p.Glu801Lys), that co-segregate with persistent developmental stuttering in a large Cameroonian family, and we observed the same two variants in unrelated Cameroonians with persistent stuttering. We found 23 other rare variants, including predicted loss-of-function variants, in AP4E1 in unrelated stuttering individuals in Cameroon, Pakistan, and North America. The rate of rare variants in AP4E1 was significantly higher in unrelated Pakistani and Cameroonian stuttering individuals than in population-matched control individuals, and coding variants in this gene are exceptionally rare in the general sub-Saharan West African, South Asian, and North American populations. Clinical examination of the Cameroonian family members failed to identify any symptoms previously reported in rare individuals carrying homozygous loss-of-function mutations in this gene. AP4E1 encodes the ε subunit of the heterotetrameric (ε-ß4-µ4-σ4) AP-4 complex, involved in protein sorting at the trans-Golgi network. We found that the µ4 subunit of AP-4 interacts with NAGPA, an enzyme involved in the synthesis of the mannose 6-phosphate signal that targets acid hydrolases to the lysosome and the product of a gene previously associated with stuttering. These findings implicate deficits in intracellular trafficking in persistent stuttering.

Quantification of DNA in urinary porcine bladder matrix using the ACTB gene.

Extracellular matrix (ECM) is a rich network of proteins and proteoglycans that has proved to be very useful in tissue regeneration. Porcine ECM has been proposed as a biological scaffold, and urinary bladder matrix (UBM) has demonstrated superior biological properties; however, its use in human treatment requires ensuring that it is DNA free. Several protocols have been used for decellularization and to demonstrate the absence of DNA, but until now, a porcine housekeeping gene for quantifying DNA by real-time quantitative PCR (qPCR) has been limiting. The aim of this study was to propose a protocol to quantify the DNA content of decellularized UBM by qPCR for the beta-actin gene (ACTB). A total of 20 porcine bladders were used, and each bladder was divided into three pieces: one as a control and the others decellularized with either SDS or Triton X-100 detergent. The presence of DNA was assessed by histology, spectrophotometry, conventional PCR, and qPCR for the ACTB. Histological analysis demonstrated the absence of nuclei using both protocols. Spectrophotometrical evaluation resulted in DNA concentrations of 1561.4 ± 357.1 and 1211.9 ± 635.2 ng of DNA/mg dry weight after the SDS and Triton X-100 protocols, respectively. DNA was not detected in any protocol by conventional PCR. In contrast, using qPCR, we found 3.9 ± 2.8 ng of DNA/mg dry weight in the Triton X-100 protocol. Therefore, the use of qPCR is a reliable method to quantify residual DNA content after decellularization procedures.

A study of the role of the FOXP2 and CNTNAP2 genes in persistent developmental stuttering.

A number of speech disorders including stuttering have been shown to have important genetic contributions, as indicated by high heritability estimates from twin and other studies. We studied the potential contribution to stuttering from variants in the FOXP2 gene, which have previously been associated with developmental verbal dyspraxia, and from variants in the CNTNAP2 gene, which have been associated with specific language impairment (SLI). DNA sequence analysis of these two genes in a group of 602 unrelated cases, all with familial persistent developmental stuttering, revealed no excess of potentially deleterious coding sequence variants in the cases compared to a matched group of 487 well characterized neurologically normal controls. This was compared to the distribution of variants in the GNPTAB, GNPTG, and NAGPA genes which have previously been associated with persistent stuttering. Using an expanded subject data set, we again found that NAGPA showed significantly different mutation frequencies in North Americans of European descent (p=0.0091) and a significant difference existed in the mutation frequency of GNPTAB in Brazilians (p=0.00050). No significant differences in mutation frequency in the FOXP2 and CNTNAP2 genes were observed between cases and controls. To examine the pattern of expression of these five genes in the human brain, real time quantitative reverse transcription PCR was performed on RNA purified from 27 different human brain regions. The expression patterns of FOXP2 and CNTNAP2 were generally different from those of GNPTAB, GNPTG and NAPGA in terms of relatively lower expression in the cerebellum. This study provides an improved estimate of the contribution of mutations in GNPTAB, GNPTG and NAGPA to persistent stuttering, and suggests that variants in FOXP2 and CNTNAP2 are not involved in the genesis of familial persistent stuttering. This, together with the different brain expression patterns of GNPTAB, GNPTG, and NAGPA compared to that of FOXP2 and CNTNAP2, suggests that the genetic neuropathological origins of stuttering differ from those of verbal dyspraxia and SLI.

The G-protein coupling properties of the human sweet and amino acid taste receptors.

The human T1R taste receptors are family C G-protein-coupled receptors (GPCRs) that act as heterodimers to mediate sweet (hT1R2 + hT1R3) and umami (hT1R1 + hT1R3) taste modalities. Each T1R has a large extracellular ligand-binding domain linked to a seven transmembrane-spanning core domain (7TMD). We demonstrate that the 7TMDs of hT1R1 and hT1R2 display robust ligand-independent constitutive activity, efficiently catalyzing the exchange of GDP for GTP on Galpha subunits. In contrast, relative to the 7TMDs of hT1R1 and hT1R2, the 7TMD of hT1R3 couples poorly to G-proteins, suggesting that in vivo signaling may proceed primarily through hT1R1 and hT1R2. In addition, we provide direct evidence that the hT1Rs selectively signal through Galpha(i/o) pathways, coupling to multiple Galpha(i/o) subunits as well as the taste cell specific Gbeta(1)gamma(13) dimer.