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PubMed2000

AXR2 encodes a member of the Aux/IAA protein family.

The dominant gain-of-function axr2-1 mutation of Arabidopsis causes agravitropic root and shoot growth, a short hypocotyl and stem, and auxin-resistant root growth. We have cloned the AXR2 gene using a map-based approach, and find that it is the same as IAA7, a member of the IAA (indole-3-acetic acid) family of auxin-inducible genes. The axr2-1 mutation changes a single amino acid in conserved domain II of AXR2/IAA7. We isolated loss-of-function mutations in AXR2/IAA7 as intragenic suppressors of axr2-1 or in a screen for insertion mutations in IAA genes. A null mutant has a slightly longer hypocotyl than wild-type plants, indicating that AXR2/IAA7 controls development in light-grown seedlings, perhaps in concert with other gene products. Dark-grown axr2-1 mutant plants have short hypocotyls and make leaves, suggesting that activation of AXR2/IAA7 is sufficient to induce morphological responses normally elicited by light. Previously described semidominant mutations in two other Arabidopsis IAA genes cause some of the same phenotypes as axr2-1, but also cause distinct phenotypes. These results illustrate functional differences among members of the Arabidopsis IAA gene family.

Arabidopsis↗
PubMed2004

ABCG2 mediates differential resistance to SN-38 (7-ethyl-10-hydroxycamptothecin) and homocamptothecins.

One activity potentially limiting the efficacy of camptothecin anticancer agents is their cellular efflux by the ATP-binding cassette half-transporter, ABCG2. Homocamptothecins are novel anticancer drugs that inhibit topoisomerase 1 with a greater potency than camptothecins. Homocamptothecins differ from camptothecins by their E-ring, which is seven-membered instead of the six-membered ring of camptothecins. We report herein that, like camptothecins, homocamptothecin and its difluoro derivative BN80915 are substrates for ABCG2. However, the resistance of three selected cell lines overexpressing wild-type or mutant ABCG2 to homocamptothecin or BN80915 was less than resistance to SN-38 (7-ethyl-10-hydroxycamptothecin), indicating that both the seven-membered E-ring present in homocamptothecin and the A- and B-ring modifications present in SN-38 are involved in substrate recognition by ABCG2. HEK-293 cells transfected with vectors encoding wild-type or mutant ABCG2 were found to be less resistant to both homocamptothecins than to SN-38. However, transfectants overexpressing mutant ABCG2 had relative resistance values for homocamptothecin and BN80915 4- to 14-fold higher than cells expressing wild-type ABCG2, suggesting that the gain of function resulting from mutation at amino acid 482, although not affecting SN-38, extends to the homocamptothecins. Resistance was reversed by the ABCG2 inhibitor fumitremorgin C. BN80915 was 17-fold more potent than SN-38 in wild-type ABCG2-transfected cells, suggesting that BN80915 has the potential to overcome ABCG2-related resistance to SN-38, the active metabolite of CPT-11 (irinotecan).

ATP Binding Cassette Transporter, Subfamily G, Mem↗
PubMed1996

Genetic analysis of tyrosine kinase function in B cell development.

B lymphopoiesis is regulated by multiple signals from stromal cell contact, soluble cytokines, antigen, and T helper cells. In vitro and biochemical experiments have implicated tyrosine kinases as key components of many of these signaling pathways. Genetic analysis of the role of these tyrosine kinases has been facilitated by recent advance in transgenic and gene targeting technology as well as by the identification of the genetic basis of several human and murine immune deficiencies. This review discusses the effect of gain and loss of function mutations of selected tyrosine kinases and their regulators and substrates on B cell development and function.

Animals↗
PubMed2025

Bidirectional shifts in Pm20d1 expression impact thermogenesis and metabolism.

BACKGROUND: Peptidase M20 domain containing 1 (PM20D1) is a secreted N-fatty acyl amino synthase and hydrolase that controls tissue and blood levels of N-fatty acyl amino acids. In brown adipocytes, N-fatty acyl amino acids bind to mitochondria and act as uncouplers of mitochondria, independent of UCP1. Interventions aimed at increasing or inhibiting PM20D1 expression considerably impact energy balance and metabolism; however, little is known about naturally occurring variants of the PM20D1/Pm20d1 gene and their impact on phenotype. METHODS: In vivo, gene expression of Pm20d1 in BALB/c, C57BL/6, and Ucp1 KO in brown adipose tissue and other metabolic tissues was measured. In vitro, transcriptional activity of Pm20d1 and brown adipocytes' oxygen consumption in primary culture were assessed. Human PM20D1 circulating levels were quantified. In silico analysis of the Pm20d1 gene sequencing and human polymorphisms associated with PM20D1 was performed. RESULTS: Here, we identified a gain-of-function variant in the Pm20d1 promoter region present in BALB/c mice and absent in C57BL/6 mice. The presence of this variant is accompanied by increased expression of Pm20d1 in brown and white adipose tissues, muscle, liver, and hypothalamus; moreover, it leads to increased cold tolerance and UCP1-independent brown adipose tissue mitochondrial respiration. Inhibition of Pm20d1 in brown adipose tissue results in defective cold tolerance in BALB/c, whereas the brown adipose tissue overexpression of Pm20d1 results in increased cold tolerance in C57BL/6 mice. In humans, variants of the PM20D1 gene are associated with changes in body mass index, whereas at least one variant in the promoter region is associated with increased body mass index and metabolic syndrome. CONCLUSION: Thus, PM20D1 plays a bidirectional role in regulating thermogenesis and body mass, and, at least in part, variants in the promoter region can partially explain the differences in PM20D1 expression and its impact on the metabolic phenotype.

Thermogenesis↗
PubMed2006

Muscle Na+ channelopathies: MRI detects intracellular 23Na accumulation during episodic weakness.

BACKGROUND: Muscle channelopathies such as paramyotonia, hyperkalemic periodic paralysis, and potassium-aggravated myotonia are caused by gain-of-function Na+ channel mutations. METHODS: Methods: Implementation of a three-dimensional radial 23Na magnetic resonance (MR) sequence with ultra-short echo times allowed the authors to quantify changes in the total muscular 23Na signal intensity. By this technique and T2-weighted 1H MRI, the authors studied whether the affected muscles take up Na+ and water during episodes of myotonic stiffness or of cold- or exercise-induced weakness. RESULTS: A 22% increase in the 23Na signal intensity and edema-like changes on T2-weighted 1H MR images were associated with cold-induced weakness in all 10 paramyotonia patients; signal increase and weakness disappeared within 1 day. A 10% increase in 23Na, but no increase in the T2-weighted 1H signal, occurred during cold- or exercise-induced weakness in seven hyperkalemic periodic paralysis patients, and no MR changes were observed in controls or exercise-induced stiffness in six potassium-aggravated myotonia patients. Measurements on native muscle fibers revealed provocation-induced, intracellular Na+ accumulation and membrane depolarization by -41 mV for paramyotonia, by -30 mV for hyperkalemic periodic paralysis, and by -20 mV for potassium-aggravated myotonia. The combined in vivo and in vitro approach showed a close correlation between the increase in 23Na MR signal intensity and the membrane depolarization (r = 0.92). CONCLUSIONS: The increase in the total 23Na signal intensity reflects intracellular changes, the cold-induced Na+ shifts are greatest and osmotically relevant in paramyotonia patients, and even osmotically irrelevant Na+ shifts can be detected by the implemented 23Na MR technique.

Adult↗
PubMed2004

Convergent, RIC-8-dependent Galpha signaling pathways in the Caenorhabditis elegans synaptic signaling network.

We used gain-of-function and null synaptic signaling network mutants to investigate the relationship of the G alpha(q) and G alpha(s) pathways to synaptic vesicle priming and to each other. Genetic epistasis studies using G alpha(q) gain-of-function and null mutations, along with a mutation that blocks synaptic vesicle priming and the synaptic vesicle priming stimulator phorbol ester, suggest that the G alpha(q) pathway generates the core, obligatory signals for synaptic vesicle priming. In contrast, the G alpha(s) pathway is not required for the core priming function, because steady-state levels of neurotransmitter release are not significantly altered in animals lacking a neuronal G alpha(s) pathway, even though these animals are strongly paralyzed as a result of functional (nondevelopmental) defects. However, our genetic analysis indicates that these two functionally distinct pathways converge and that they do so downstream of DAG production. Further linking the two pathways, our epistasis analysis of a ric-8 null mutant suggests that RIC-8 (a receptor-independent G alpha guanine nucleotide exchange factor) is required to maintain both the G alpha(q) vesicle priming pathway and the neuronal G alpha(s) pathway in a functional state. We propose that the neuronal G alpha(s) pathway transduces critical positional information onto the core G alpha(q) pathway to stabilize the priming of selected synapses that are optimal for locomotion.

Animals↗
PubMed2006

The molecular pathogenesis of gastrointestinal stromal tumors.

Gastrointestinal stromal tumors (GISTs) are clinically diagnosed by positive immunohistochemical staining of KIT, a type III receptor tyrosine kinase. Most GISTs contain gain-of-function, ie, oncogenic mutations in c-KIT or in platelet-derived growth factor receptor-alpha (PDGFR-alpha), which appears to be the major initiating event that drives the pathogenesis for GIST. Furthermore, mutations in either of these genes appear to be required for tumor growth and progression. This scenario can be thought of as "oncogenic addiction" and is one of the major reasons why some GISTs respond significantly to therapies that target these mutant receptors. In addition to mutations in c-KIT or PDGFR-alpha, genomic alterations contribute to disease progression. Moreover, GISTs that harbor different c-KIT or PDGFR-alpha mutations have different molecular signatures at the level of gene expression, which further contributes to the complexity of GIST biology and variable responses to treatment. This article will discuss the molecular basis of pathogenesis and genetic and genomic alterations that contribute to GIST tumorigenesis and disease progression as well as the heterogeneity of this disease.

Antineoplastic Agents↗
PubMed2003

Pubertal development in patients with McCune-Albright syndrome or pseudohypoparathyroidism.

Gain or loss of function mutations of the GNAS1 gene lead to McCune-Albright syndrome (MAS) or pseudohypoparathyroidism Ia (PHP-Ia), respectively. Patients with MAS, caused by a post-zygotic missense mutation leading to constitutive activation of Gs alpha, suffer from gonadotropin-independent precocious puberty, and delayed or incomplete sexual development and reproductive dysfunction is found in women with PHP-Ia, an inherited disorder caused by deficient expression or function of the Gs alpha protein. In females with MAS, 50% developed precocious puberty by the age of 4 years, the remaining between 4 and 8 years. Peripheral precocious puberty is often atypical and characterized by alternate periods of rapid progression and regression of pubertal development; menstrual bleeding may occur before breast development. Ovarian cyst growth and regression is often described as a sign of ovarian follicle hyperactivation. Notwithstanding this clinical heterogeneity, a subset of patients with MAS develop relentlessly progressive precocious puberty ultimately resulting in premature epiphyseal fusion and reduced adult stature. Long-term information on reproductive function has been obtained in females: some patients had regular menses without ovarian cysts on pelvic US scan, whereas others were oligomenorrheic and showed recurrent ovarian cysts. In males with MAS, precocious puberty occurred in three patients between 4 and 9 years of age. In one patient, long-term follow-up demonstrated normal plasma testosterone and gonadotropin values at the age of 17 years. On testicular sonography, multiple hyperechogeneic spots were found in both testicles (snow-storm appearance). Female patients with PHP-Ia were oligomenorrheic or amenorrheic; more than half had delayed or incomplete sexual development, They were mildly hypoestrogenic with normal to slightly elevated serum gonadotropin levels. These clinical and biochemical findings indicate partial resistance of the theca and granulosa cells of the ovary to gonadotropins due to deficient Gs alpha activity. Responsiveness might be sufficient to promote some degree of follicular development and steroid secretion, but insufficient to induce ovulation

Amenorrhea↗
PubMed1997

Transduction of envelope stress in Escherichia coli by the Cpx two-component system.

Disruption of normal protein trafficking in the Escherichia coli cell envelope (inner membrane, periplasm, outer membrane) can activate two parallel, but distinct, signal transduction pathways. This activation stimulates the expression of a number of genes whose products function to fold or degrade the mislocalized proteins. One of these signal transduction pathways is a two-component regulatory system comprised of the histidine kinase CpxA and the response regulator, CpxR. In this study we characterized gain-of-function Cpx* mutants in order to learn more about Cpx signal transduction. Sequencing demonstrated that the cpx* mutations cluster in either the periplasmic, the transmembrane, or the H-box domain of CpxA. Intriguingly, most of the periplasmic cpx* gain-of-function mutations cluster in the central region of this domain, and one encodes a deletion of 32 amino acids. Strains harboring these mutations are rendered insensitive to a normally activating signal. In vivo and in vitro characterization of maltose-binding-protein fusions between the wild-type CpxA and a representative cpx* mutant, CpxA101, showed that the mutant CpxA is altered in phosphotransfer reactions with CpxR. Specifically, while both CpxA and CpxA101 function as autokinases and CpxR kinases, CpxA101 is devoid of a CpxR-P phosphatase activity normally present in the wild-type protein. Taken together, the data support a model for Cpx-mediated signal transduction in which the kinase/phosphatase ratio is elevated by stress. Further, the sequence and phenotypes of periplasmic cpx* mutations suggest that interactions with a periplasmic signaling molecule may normally dictate a decreased kinase/phosphatase ratio under nonstress conditions.

ATP-Binding Cassette Transporters↗
PubMed2002

Association of calnexin with mutant peripheral myelin protein-22 ex vivo: a basis for "gain-of-function" ER diseases.

Schwann cell-derived peripheral myelin protein-22 (PMP-22) when mutated or overexpressed causes heritable neuropathies with a previously unexplained "gain-of-function" endoplasmic reticulum (ER) retention phenotype. In wild-type sciatic nerves, PMP-22 associates in a specific, transient (t(1/2 ) approximately equal to 11 min), and oligosaccharide processing-dependent manner with the lectin chaperone calnexin (CNX), but not calreticulin nor BiP. In Trembler-J (Tr-J) sciatic nerves, prolonged association of mutant PMP-22 with CNX is found (t(1/2) > 60 min). In 293A cells overexpressing PMP-22(Tr-J), CNX and PMP-22 colocalize in large intracellular structures identified at the electron microscopy level as myelin-like figures with CNX localization in the structures dependent on PMP-22 glucosylation. Similar intracellular myelin-like figures were also present in Schwann cells of sciatic nerves from homozygous Trembler-J mice with no detectable activation of the stress response pathway as deduced from BiP and CHOP expression. Sequestration of CNX in intracellular myelin-like figures may be relevant to the autosomal dominant Charcot-Marie-Tooth-related neuropathies.

Animals↗
PubMed2005

Functional analysis of p53 gene and the prognostic impact of dominant-negative p53 mutation in endometrial cancer.

In addition to the loss of function, mutant p53 can possess a dominant-negative effect on wild-type p53 and may also exert gain-of-function activity. It is not clear whether the functional status of p53 mutation contributes to differences in outcome in endometrial cancer. We collected a total of 92 RNA samples of high quality from endometrial cancer tissues, and the samples were subjected to yeast functional assay and sequencing for p53 mutations. The detected mutant p53 genes were further investigated for their dominant-negative activity using a yeast-based transdominance assay. p53 mutation was found in 24 out of 92 (26.1%) tumors, of which 10 exhibited no dominant-negative activity (recessive mutation) and 14 showed dominant-negative activity. Dominant-negative p53 mutation was related to advanced stages (p = 0.01), nonendometrioid type tumors (p = 0.01) and grade 3 tumors (p = 0.04). The patients with dominant-negative mutation had significantly shorter survival than patients with no mutation (p < 0.0001) and those with a recessive mutation (p = 0.01) in the p53 gene. No difference in survival was found between the patients with tumors harboring a recessive p53 mutation and those with tumors harboring a wild-type p53. Multivariate analysis revealed that dominant-negative p53 mutation (p = 0.019), FIGO stage (p = 0.0037) and histologic subtype (p = 0.014) were independently related to patient survival. Dominant-negative p53 mutation was the most important prognostic factor for stage III/IV endometrial cancer (p = 0.0023). In conclusion, dominant-negative p53 mutation is often found in advanced stages and aggressive histologic subtypes of endometrial cancer and it is a strong predictor of survival of patients with advanced endometrial cancer. To elucidate further the role of p53 mutation in endometrial cancer, it is necessary to investigate gain-of-function activity involving dominant-negative p53 mutant proteins.

Biological Assay↗
PubMed2007

The folate metabolic enzyme ALDH1L1 is restricted to the midline of the early CNS, suggesting a role in human neural tube defects.

Folate supplementation prevents up to 70% of human neural tube defects (NTDs), although the precise cellular and metabolic sites of action remain undefined. One possibility is that folate modulates the function of metabolic enzymes expressed in cellular populations involved in neural tube closure. Here we show that the folate metabolic enzyme ALDH1L1 is cell-specifically expressed in PAX3-negative radial glia at the midline of the neural tube during early murine embryogenesis. Midline restriction is not a general property of this branch of folate metabolism, as MTHFD1 displays broad and apparently ubiquitous expression throughout the neural tube. Consistent with previous work showing antiproliferative effects in vitro, ALDH1L1 upregulation during central nervous system (CNS) development correlates with reduced proliferation and most midline ALDH1L1(+) cells are quiescent. These data provide the first evidence for localized differences in folate metabolism within the early neural tube and suggest that folate might modulate proliferation via effects on midline Aldh1l1(+) cells. To begin addressing its role in neurulation, we analyzed a microdeletion mouse strain lacking Aldh1l1 and observed neither increased failure of neural tube closure nor detectable proliferation defects. Although these results indicate that loss-of-function Aldh1l1 mutations do not impair these processes in mice, the specific midline expression of ALDH1L1 and its ability to dominantly suppress proliferation in a folate responsive manner may suggest that mutations contributing to disease are gain-of-function, rather than loss-of-function. Moreover, a role for loss-of-function mutations in human NTDs remains possible, as Mthfr null mice do not develop NTDs even though MTHFR mutations increase human NTD risk.

Aldehyde Dehydrogenase↗
PubMed2005

NOD2 mutation and mice: no Crohn's disease but many lessons to learn.

Many patients with ileal Crohn's disease, a chronic intestinal inflammation, carry mutations in the gene encoding NOD2 (CARD15), but the mechanistic details of how this mutation leads to disease are not fully understood. NOD2 is expressed in antigen-presenting cells and Paneth cells, which are secretory epithelial cells of the small intestine. Two complementary studies using genetically engineered murine models help to explain the association of NOD2 malfunction and mucosal disease. One study observes a dysregulation of proinflammatory responses, suggesting that the most common NOD2 mutation in humans results in a gain of function. The other study determined that NOD2-null mutations impair the Paneth-cell antimicrobial response, which is consistent with recent findings in humans. Together, these studies fuel optimism that new therapeutic directions might emerge to better treat this severe mucosal disease.

Animals↗
PubMed1993

Dosage-dependent dominance over wild-type p53 of a mutant p53 isolated from nasopharyngeal carcinoma.

Mutational inactivation of p53, a tumor suppressor gene, is the most common genetic alteration found in human cancer. Most mutated p53s either lose tumor suppressor function or gain oncogenic activity. We recently reported the detection of a heterozygous point mutation of p53 at codon 280 in nasopharyngeal carcinoma (NPC) (1), a high-incidence malignancy in southern China and southeast Asia. Given its heterozygous state, in which both wild-type and mutated p53 gene were expressed, p53-thr280 should function dominantly in the presence of the wild-type form if it is to play a role in nasopharynx carcinogenesis. We tested this dominance hypothesis in the cells of two model systems: 1) human Saos-2 cells lacking endogenous p53, and 2) mouse JB6 tumor promotion-resistant cells (P-) expressing endogenous wild-type p53. The results showed dosage-dependent dominance of p53-thr280 in controlling WT p53-driven transcriptional activity; in governing cell growth; and in progressing P- phenotype to tumor promotion-sensitive (P+) phenotype. This dominant negative effect was seen at a 1:1 (WT:MU) ratio and was more striking at a ratio of 1:3. A model is proposed to explain the dominant negative effect of mutant p53. We conclude from this study that p53-thr280 is likely to be dominant in the heterozygous state found in NPC and that this dominant-negative mutated p53 may contribute to the genesis of NPC or of other carcinomas in which both mutant and wild-type p53 are expressed.

Animals↗
PubMed2006

The metastasis-associated gene S100A4 is a novel target of beta-catenin/T-cell factor signaling in colon cancer.

BACKGROUND & AIMS: Activation of the Wnt/beta-catenin pathway is frequently observed in colorectal cancers. Our aim was to elucidate the impact of gain-of-function beta-catenin on the metastasis-associated gene S100A4 in human colon cancer cell lines and tumors. METHODS: We analyzed cell lines heterozygous for gain-of-function and wild-type beta-catenin, and variants homozygous for gain- or loss-of-function mutation in beta-catenin, for S100A4 expression, cell motility, and in vivo metastasis. beta-catenin-mediated S100A4 promoter activation was tested by reporter assays. For human colon carcinomas, S100A4 expression, beta-catenin genotype, and metachronous metastasis were correlated. RESULTS: We identified S100A4 as the most regulated gene by gain-of-function beta-catenin using a 10K microarray. Cell lines with gain-of-function beta-catenin expressed up to 60-fold elevated S100A4 levels, displayed strongly increased migration and invasion in vitro, and induced metastasis in mice. S100A4 small interfering RNA, beta-catenin small interfering RNA, or dominant negative T-cell factor (TCF) knocked down S100A4 and blocked biological effects. S100A4 complementary DNA transfection increased migration and invasion. We identified a TCF binding site within the S100A4 promoter and demonstrated the direct binding of heterodimeric beta-catenin/TCF complexes. Reporter assays confirmed the beta-catenin-induced S100A4 promoter activity. Furthermore, S100A4 mRNA expression was increased in primary colon cancers, which later developed distant metastases, compared to non-metastasizing tumors. Colon tumors heterozygous for gain-of-function beta-catenin showed concomitant nuclear beta-catenin localization, high S100A4 expression, and metastases. CONCLUSIONS: S100A4 is a direct beta-catenin/TCF target, induces migration and invasion in vitro and metastasis in vivo, and has value for prognosis of metastasis formation in colon cancer patients.

Cell Movement↗
PubMed2026

Rare variant analysis of whole genome sequenced juvenile idiopathic arthritis multiplex pedigrees identifies rare variants in NOD2 and ACVR1.

Juvenile idiopathic arthritis is a complex rheumatic disease that is influenced by environmental and genetic factors. Linkage and genome-wide association studies have identified genes that contribute to the risk of developing juvenile idiopathic arthritis but are limited in their ability to identify disease-risk variants of large effect. Penetrant, heritable risk variants can be detected in high-risk families, but such cases are uncommon due to the low prevalence of juvenile idiopathic arthritis. This study utilizes whole-genome sequencing of 23 multiplex families, the largest such cohort to date, to discover variants and genes relevant to JIA pathogenesis. Pathogenic variants in NOD2 associated with Blau syndrome, an ultra-rare Mendelian inflammatory disorder, are the most recurrent variants in the cohort, consistent with previous reports that milder presentations of Blau syndrome are oftentimes misdiagnosed as juvenile idiopathic arthritis. For the first time, however, rare variants in ACVR1 and SMAD6, integral components of the Bone Morphogenic Protein pathway, are found to be associated with juvenile idiopathic arthritis. Identified ACVR1 variants map to critical protein domains. AlphaFold modeling predicts that the ACVR1 interaction with its inhibitor OGT is disrupted by these variants, indicating that the patient-mutated protein has a gain-of-function phenotype. Drosophila melanogaster expressing either a wild-type or patient-mutated version of ACVR1 exhibit embryonic lethality, with the mutant exhibiting 1.4-fold greater lethality than wild-type. The combination of family-based cohorts for gene discovery, AI-based computational tools, and animal model studies for tests of variant function underscores shared disease pathogenesis between JIA and monogenic disorders of immunity and connective tissue.

Arthritis, Juvenile↗
PubMed2004

Mutation in the AChR ion channel gate underlies a fast channel congenital myasthenic syndrome.

BACKGROUND: Most congenital myasthenic syndromes (CMS) have postsynaptic defects from mutations within the muscle acetylcholine receptor (AChR). Mutations underlying the slow channel syndrome cause a "gain of function" and usually show dominant inheritance, whereas mutations underlying AChR deficiency or the fast channel syndrome cause a "loss of function" and show recessive inheritance. OBJECTIVE: To characterize the disease mechanism underlying an apparently dominantly inherited CMS that responds to IV edrophonium. METHODS: DNA from CMS patients was analyzed for mutations by single-strand conformation polymorphism analysis, DNA sequence analysis, and restriction endonuclease digestion. Functional analysis of mutations was by alpha-bungarotoxin binding studies and by patch clamp analysis of mutant AChR expressed in human embryonic kidney cells. RESULTS: Analysis of muscle biopsies from father and son in an affected kinship showed normal endplate morphology and AChR number but severely reduced miniature endplate potentials. DNA analysis revealed that each harbors a single missense mutation in the AChR alpha-subunit gene, alphaF256L. Expression studies demonstrate this mutation underlies a fast channel phenotype with fewer and shorter ion channel activations. The major effect of alphaF256L, located within the M2 transmembrane domain, is on channel gating, both reducing the opening and increasing the closure rate. CONCLUSIONS: Mutation alphaF256L results in fast channel kinetics. Expression studies suggest a dominant-negative effect within the AChR pentamer, severely compromising receptor function.

Adolescent↗