RESUMO
A novel autosomal recessive disorder characterized by pre- and postnatal growth restriction with microcephaly, distinctive craniofacial features, congenital alopecia, hypoplastic kidneys with renal insufficiency, global developmental delay, severe congenital sensorineural hearing loss, early mortality, hydrocephalus, and genital hypoplasia was observed in 4 children from 3 families of New Mexican Hispanic heritage. Three of the children died before 3 years of age from uremia and/or sepsis. Exome sequencing of the surviving individual identified a homozygous c.587T>C (p.Ile196Thr) mutation in ZPR1 Zinc Finger (ZPR1) that segregated appropriately in her family. In a second family, the identical variant was shown to be heterozygous in the affected individual's parents and not homozygous in any of her unaffected siblings. ZPR1 is a ubiquitously expressed, highly conserved protein postulated to transmit proliferative signals from the cell membrane to the nucleus. Structural modeling reveals that p.Ile196Thr disrupts the hydrophobic core of ZPR1. Patient fibroblast cells showed no detectable levels of ZPR1 and the cells showed a defect in cell cycle progression where a significant number of cells remained arrested in the G1 phase. We provide genetic and molecular evidence that a homozygous missense mutation in ZPR1 is associated with a rare and recognizable multisystem syndrome.
Assuntos
Anormalidades Múltiplas/genética , Alopecia/genética , Fácies , Transtornos do Crescimento/genética , Rim/anormalidades , Proteínas de Membrana Transportadoras/genética , Microcefalia/genética , Mutação , Pré-Escolar , Feminino , Genes Recessivos , Humanos , MasculinoRESUMO
The inherited peripheral neuropathies (IPNs) are characterized by marked clinical and genetic heterogeneity and include relatively frequent presentations such as Charcot-Marie-Tooth disease and hereditary motor neuropathy, as well as more rare conditions where peripheral neuropathy is associated with additional features. There are over 250 genes known to cause IPN-related disorders but it is estimated that in approximately 50% of affected individuals a molecular diagnosis is not achieved. In this study, we examine the diagnostic utility of whole-exome sequencing (WES) in a cohort of 50 families with 1 or more affected individuals with a molecularly undiagnosed IPN with or without additional features. Pathogenic or likely pathogenic variants in genes known to cause IPN were identified in 24% (12/50) of the families. A further 22% (11/50) of families carried sequence variants in IPN genes in which the significance remains unclear. An additional 12% (6/50) of families had variants in novel IPN candidate genes, 3 of which have been published thus far as novel discoveries (KIF1A, TBCK, and MCM3AP). This study highlights the use of WES in the molecular diagnostic approach of highly heterogeneous disorders, such as IPNs, places it in context of other published neuropathy cohorts, while further highlighting associated benefits for discovery.
Assuntos
Doença de Charcot-Marie-Tooth/genética , Sequenciamento do Exoma , Sequenciamento de Nucleotídeos em Larga Escala , Doenças do Sistema Nervoso Periférico/genética , Acetiltransferases/genética , Doença de Charcot-Marie-Tooth/diagnóstico , Doença de Charcot-Marie-Tooth/patologia , Exoma/genética , Feminino , Humanos , Peptídeos e Proteínas de Sinalização Intracelular/genética , Cinesinas/genética , Masculino , Mutação , Doenças do Sistema Nervoso Periférico/diagnóstico , Doenças do Sistema Nervoso Periférico/patologia , Proteínas Serina-Treonina Quinases/genéticaRESUMO
An accurate diagnosis is an integral component of patient care for children with rare genetic disease. Recent advances in sequencing, in particular whole-exome sequencing (WES), are identifying the genetic basis of disease for 25-40% of patients. The diagnostic rate is probably influenced by when in the diagnostic process WES is used. The Finding Of Rare Disease GEnes (FORGE) Canada project was a nation-wide effort to identify mutations for childhood-onset disorders using WES. Most children enrolled in the FORGE project were toward the end of the diagnostic odyssey. The two primary outcomes of FORGE were novel gene discovery and the identification of mutations in genes known to cause disease. In the latter instance, WES identified mutations in known disease genes for 105 of 362 families studied (29%), thereby informing the impact of WES in the setting of the diagnostic odyssey. Our analysis of this dataset showed that these known disease genes were not identified prior to WES enrollment for two key reasons: genetic heterogeneity associated with a clinical diagnosis and atypical presentation of known, clinically recognized diseases. What is becoming increasingly clear is that WES will be paradigm altering for patients and families with rare genetic diseases.
Assuntos
Exoma , Genes , Doenças Genéticas Inatas/diagnóstico , Mutação , Análise de Sequência de DNA , Canadá , Criança , Doenças Genéticas Inatas/genética , Sequenciamento de Nucleotídeos em Larga Escala , HumanosRESUMO
Limb girdle muscular dystrophy (LGMD) is a heterogeneous group of genetic disorders leading to progressive muscle degeneration and often associated with cardiac complications. We present two adult siblings with childhood-onset of weakness progressing to a severe quadriparesis with the additional features of triangular tongues and biventricular cardiac dysfunction. Whole exome sequencing identified compound heterozygous missense mutations that are predicted to be pathogenic in LIMS2. Biopsy of skeletal muscle demonstrated disrupted immunostaining of LIMS2. This is the first report of mutations in LIMS2 and resulting disruption of the integrin linked kinase (ILK)-LIMS-parvin complex associated with LGMD.
Assuntos
Proteínas Adaptadoras de Transdução de Sinal/genética , Cardiomiopatias/genética , Predisposição Genética para Doença/genética , Proteínas com Domínio LIM/genética , Proteínas de Membrana/genética , Distrofia Muscular do Cíngulo dos Membros/genética , Mutação de Sentido Incorreto , Língua/anormalidades , Adulto , Sequência de Bases , Cardiomiopatias/patologia , Exoma/genética , Feminino , Heterozigoto , Humanos , Masculino , Linhagem , Análise de Sequência de DNA , Índice de Gravidade de Doença , IrmãosRESUMO
Whole-exome sequencing (WES) has transformed our ability to detect mutations causing rare diseases. FORGE (Finding Of Rare disease GEnes) and Care4Rare Canada are nation-wide projects focused on identifying disease genes using WES and translating this technology to patient care. Rare forms of epilepsy are well-suited for WES and we retrospectively selected FORGE and Care4Rare families with clinical descriptions that included childhood-onset epilepsy or seizures not part of a recognizable syndrome or an early-onset encephalopathy where standard-of-care investigations were unrevealing. Nine families met these criteria and a diagnosis was made in seven, and potentially eight, of the families. In the eight families we identified mutations in genes associated with known neurological and epilepsy disorders: ASAH1, FOLR1, GRIN2A (two families), SCN8A, SYNGAP1 and SYNJ1. A novel and rare mutation was identified in KCNQ2 and was likely responsible for the benign seizures segregating in the family though additional evidence would be required to be definitive. In retrospect, the clinical presentation of four of the patients was considered atypical, thereby broadening the phenotypic spectrum of these conditions. Given the extensive clinical and genetic heterogeneity associated with epilepsy, our findings suggest that WES may be considered when a specific gene is not immediately suspected as causal.
Assuntos
Epilepsia/genética , Predisposição Genética para Doença , Mutação , Adolescente , Adulto , Encefalopatias/genética , Criança , Pré-Escolar , Análise Mutacional de DNA , Exoma , Feminino , Humanos , Lactente , Recém-Nascido , Masculino , Linhagem , Fenótipo , Estudos RetrospectivosRESUMO
BACKGROUND: This study set out to identify patterns in the causes of waits and wait-related satisfaction. METHODS: We conducted qualitative interviews with urban, semi-urban, and rural patients (n = 60) to explore their perceptions of the waits they experienced in the detection and treatment of their breast, prostate, lung, or colorectal cancer. We asked participants to describe their experiences from the onset of symptoms to the start of treatment at the cancer clinic and their satisfaction with waits at various intervals. Interview transcripts were coded using a thematic approach. RESULTS: Patients identified five groups of wait-time causes: Patient-related (beliefs, preferences, and non-cancer health issues)Treatment-related (natural consequences of treatment)System-related (the organization or functioning of groups, workforce, institution, or infrastructure in the health care system)Physician-related (a single physician responsible for a specific element in the patient's care)Other causes (disruptions to normal operations of a city or community as a whole) With the limited exception of physician-related absences, the nature of the cause was not linked to overall satisfaction or dissatisfaction with waits. CONCLUSIONS: Causes in themselves do not explain wait-related satisfaction. Further work is needed to explore the underlying reasons for wait-related satisfaction or dissatisfaction. Although our findings shed light on patient experiences with the health system and identify where interventions could help to inform the expectations of patients and the public with respect to wait time, more research is needed to understand wait-related satisfaction among cancer patients.
RESUMO
Spinal muscular atrophy with progressive myoclonic epilepsy (SMA-PME) is a recently delineated, autosomal recessive condition caused by rare mutations in the N-acylsphingosine amidohydrolase 1 (acid ceramidase) ASAH1 gene. It is characterized by motor neuron disease followed by progressive myoclonic seizures and eventual death due to respiratory insufficiency. Here we report an adolescent female who presented with atonic and absence seizures and myoclonic jerks and was later diagnosed as having myoclonic-absence seizures. An extensive genetic and metabolic work-up was unable to arrive at a molecular diagnosis. Whole exome sequencing (WES) identified two rare, deleterious mutations in the ASAH1 gene: c.850G>T;p.Gly284X and c.456A>C;p.Lys152Asn. These mutations were confirmed by Sanger sequencing in the patient and her parents. Functional studies in cultured fibroblasts showed that acid ceramidase was reduced in both overall amount and enzymatic activity. Ceramide level was doubled in the patient's fibroblasts as compared to control cells. The results of the WES and the functional studies prompted an electromyography (EMG) study that showed evidence of motor neuron disease despite only mild proximal muscle weakness. These findings expand the phenotypic spectrum of SMA-PME caused by novel mutations in ASAH1 and highlight the clinical utility of WES for rare, intractable forms of epilepsy.
Assuntos
Ceramidase Ácida/genética , Epilepsias Mioclônicas/genética , Atrofia Muscular Espinal/genética , Ceramidase Ácida/metabolismo , Adolescente , Criança , Eletromiografia , Exoma , Feminino , Humanos , Doença dos Neurônios Motores/genética , Doença dos Neurônios Motores/patologia , Atrofia Muscular Espinal/fisiopatologia , MutaçãoRESUMO
We have studied retinal function by electroretinography in five Becker and six Duchenne muscular dystrophy patients. All had abnormal electroretinograms with a markedly reduced amplitude for the b-wave in the dark-adapted state. Using three antisera raised to different domains of dystrophin, we identified dystrophin in the outer plexiform layer of human retina. The retinal dystrophin is present in multiple isoforms as the result of alternative splicing. The localization of dystrophin to the outer plexiform layer coincident with the abnormal b-wave suggests that dystrophin is required for normal retinal electrophysiology.
Assuntos
Distrofina/fisiologia , Eletrorretinografia , Proteínas do Olho/fisiologia , Distrofias Musculares/fisiopatologia , Retina/química , Adolescente , Adulto , Sequência de Bases , Criança , Distrofina/biossíntese , Distrofina/genética , Proteínas do Olho/biossíntese , Proteínas do Olho/genética , Humanos , Dados de Sequência Molecular , Distrofias Musculares/genética , Especificidade de Órgãos , Reação em Cadeia da Polimerase , RNA Mensageiro/análise , Retina/fisiopatologiaRESUMO
The aetiology of multiple sclerosis (MS) is uncertain. There is strong circumstantial evidence to indicate it is an autoimmune complex trait. Risks for first degree relatives are increased some 20 fold over the general population. Twin studies have shown monozygotic concordance rates of 25-30% compared to 4% for dizygotic twins and siblings. Studies of adoptees and half sibs show that familial risk is determined by genes, but environmental factors strongly influence observed geographic differences. Studies of candidate genes have been largely unrewarding. We report a genome search using 257 microsatellite markers with average spacing of 15.2 cM in 100 sibling pairs (Table 1, data set 1 - DS1). A locus of lambda>3 was excluded from 88% of the genome. Five loci with maximum lod scores (MLS) of >1 were identified on chromosomes 2, 3, 5, 11 and X. Two additional data sets containing 44 (Table 1, DS2) and 78 sib pairs (Table 1, DS3) respectively, were used to further evaluate the HLA region on 6p21 and a locus on chromosome 5 with an MLS of 4.24. Markers within 6p21 gave MLS of 0.65 (non-significant, NS). However, D6S461, just outside the HLA region, showed significant evidence for linkage disequilibrium by the transmission disequilibrium test (TDT), in all three data sets (for DS1 chi2 = 10.8, adjusted P < 0.01)(DS2 and DS3 chi2 = 10.9, P < 0.0005), suggesting a modest susceptibility locus in this region. On chromosome 5p results from all three data sets (222 sib pairs) yielded a multipoint MLS of 1.6. The results support genetic epidemiological evidence that several genes interact epistatically to determine heritable susceptibility.
Assuntos
Esclerose Múltipla/genética , Mapeamento Cromossômico , Cromossomos Humanos Par 11 , Cromossomos Humanos Par 2 , Cromossomos Humanos Par 3 , Cromossomos Humanos Par 5 , Cromossomos Humanos Par 6 , Feminino , Humanos , Desequilíbrio de Ligação , Complexo Principal de Histocompatibilidade , Masculino , Linhagem , Cromossomo XRESUMO
BACKGROUND: Mutations in the leucine-rich repeat kinase 2 gene (LRRK2) have become the most common known cause for developing Parkinson's disease. The frequency of mutations described in the literature varies widely depending on the population studied with most reports focusing only on screening for the most common G2019S mutation in exon 41. METHODS: In this study seven exons (19, 24, 25, 31, 35, 38, and 41) in LRRK2 where mutations have been reported were screened in 230 unselected Parkinson's disease patients using denaturing high-performance liquid chromatography. RESULTS: The sequencing of samples with heteroduplex profiles revealed five novel and two known intronic sequence variants. In our cohort, we were unable to detect any of the known mutations in these exons or identify novel mutations within the LRRK2 gene. CONCLUSIONS: Therefore, despite the availability of diagnostic LRRK2 genetic testing it is unlikely to yield a positive result in this population.
Assuntos
Predisposição Genética para Doença/genética , Testes Genéticos/normas , Doença de Parkinson/genética , Proteínas Serina-Treonina Quinases/genética , Adulto , Idade de Início , Idoso , Idoso de 80 Anos ou mais , Sequência de Bases/genética , Canadá/epidemiologia , Cromatografia Líquida de Alta Pressão , Estudos de Coortes , Análise Mutacional de DNA/normas , Análise Mutacional de DNA/tendências , Éxons/genética , Feminino , Testes Genéticos/tendências , Genótipo , Humanos , Íntrons/genética , Serina-Treonina Proteína Quinase-2 com Repetições Ricas em Leucina , Masculino , Pessoa de Meia-Idade , Mutação/genética , Doença de Parkinson/diagnóstico , Doença de Parkinson/epidemiologia , Valor Preditivo dos TestesRESUMO
Missense mutations of the human skeletal muscle voltage-gated Na channel (hSkM1) underlie a variety of diseases, including hyperkalemic periodic paralysis (HyperPP), paramyotonia congenita, and potassium-aggravated myotonia. Another disorder of sarcolemmal excitability, hypokalemic periodic paralysis (HypoPP), which is usually caused by missense mutations of the S4 voltage sensors of the L-type Ca channel, was associated recently in one family with a mutation in the outermost arginine of the IIS4 voltage sensor (R669H) of hSkM1 (Bulman et al., 1999). Intriguingly, an arginine-to-histidine mutation at the homologous position in the L-type Ca(2+) channel (R528H) is a common cause of HypoPP. We have studied the gating properties of the hSkM1-R669H mutant Na channel experimentally in human embryonic kidney cells and found that it has no significant effects on activation or fast inactivation but does cause an enhancement of slow inactivation. R669H channels exhibit an approximately 10 mV hyperpolarized shift in the voltage dependence of slow inactivation and a twofold to fivefold prolongation of recovery after prolonged depolarization. In contrast, slow inactivation is often disrupted in HyperPP-associated Na channel mutants. These results demonstrate that, in R669H-associated HypoPP, enhanced slow inactivation does not preclude, and may contribute to, prolonged attacks of weakness and add support to previous evidence implicating the IIS4 voltage sensor in slow-inactivation gating.
Assuntos
Paralisia Periódica Hipopotassêmica/genética , Músculo Esquelético/metabolismo , Mutação/genética , Bloqueadores dos Canais de Sódio , Canais de Sódio/genética , Substituição de Aminoácidos , Linhagem Celular , Estimulação Elétrica , Eletrofisiologia , Humanos , Paralisia Periódica Hipopotassêmica/metabolismo , Ativação do Canal Iônico/genética , Ativação do Canal Iônico/fisiologia , Técnicas de Patch-Clamp , Canais de Sódio/metabolismo , TransfecçãoRESUMO
BACKGROUND: Recently, a single base pair substitution (G1747A) mutation of the neurofilament M (NF-M) gene was reported in a French-Canadian patient with early onset Parkinson's disease (PD). Three unaffected siblings were found to be heterozygotes for the NF-M Gly336Ser mutation but, to date, no other affected PD individuals have been found with a similar mutation. No other individuals with Parkinson's disease and of similar ethnic background have been screened for this mutation. METHODS: We screened 102 French-Canadian patients with definite PD and 45 French-Canadian controls for this substitution in the NF-M gene using a PCR-restriction enzyme digestion method. RESULTS: None of the patients or controls carried this mutation. CONCLUSION: Our results would indicate that this mutation is not common even in a PD population of similar ethnic background and suggest this change represents a rare variant. However, these results do not exclude the possibility that other mutations in this gene could be present.
Assuntos
Proteínas de Neurofilamentos/genética , Doença de Parkinson/genética , Idoso , Canadá/epidemiologia , Análise Mutacional de DNA , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Mutação , Reação em Cadeia da PolimeraseRESUMO
BACKGROUND: Lafora disease is a progressive myoclonus epilepsy with polyglucosan accumulations and a peculiar neurodegeneration with generalised organellar disintegration. It causes severe seizures, leading to dementia and eventually death in early adulthood. METHODS: One Lafora disease gene, EPM2A, has been identified on chromosome 6q24. Locus heterogeneity led us to search for a second gene using a genome wide linkage scan in French-Canadian families. RESULTS: We mapped a second Lafora disease locus, EPM2B, to a 2.2 Mb region at 6p22, a region known to code for several proteins, including kinesins. Kinesins are microtubule dependent motor proteins that are involved in transporting cellular components. In neurones, they play a major role in axonal and dendritic transport. CONCLUSION: Analysis of the present locus in other non-EPM2A families will reveal whether there is further locus heterogeneity. Identification of the disease gene will be of major importance towards our understanding of the pathogenesis of Lafora disease.
Assuntos
Cromossomos Humanos Par 6/genética , Doença de Lafora/genética , Mapeamento Cromossômico/métodos , Saúde da Família , Feminino , Haplótipos , Humanos , Doença de Lafora/patologia , Escore Lod , Masculino , Repetições de Microssatélites , LinhagemRESUMO
Immunoreactive dystrophin was examined in muscle fibers of quadriceps, extraocular muscles and cardiac ventricular muscles of female heterozygote mdx mice at 10, 35 and 60 days of age, with microscopic immunoperoxidase method and by immunoblots. In quadriceps muscle fibers there was a marked gradual diminution of the dystrophin-negative fiber segments between age 10 and 60 days. We suggest that this was partly due to a spontaneous fusion of dystrophin-competent satellite cells into the dystrophin-negative fiber segments and partly to an expansion of the cytoplasmic domain of dystrophin expression related to the original myonuclei. In cardiac muscle that lacks satellite cells, there was persistence of a large number of dystrophin-negative fiber segments even at age 60 days and probably beyond. The findings of this study have implications for the detection of heterozygote female carriers of Duchenne muscular dystrophy (DMD) and for the possible therapy of DMD muscles by myoblast transfer.
Assuntos
Envelhecimento/metabolismo , Heterozigoto , Camundongos Mutantes Neurológicos/metabolismo , Proteínas Musculares/metabolismo , Músculos/metabolismo , Músculos Papilares/metabolismo , Animais , Distrofina , Feminino , Masculino , Camundongos , Camundongos Mutantes Neurológicos/genética , Músculos Oculomotores/metabolismo , Linhagem , Regeneração/fisiologia , Coxa da Perna , Distribuição TecidualRESUMO
A population-based study of pairs of relatives (siblings, second- and third-degree) concordant for multiple sclerosis did not show an excess of like-sexed pairs. In addition, data on human lymphocyte antigen typing for sibling pairs concordant for multiple sclerosis did not find an increase in haplotype sharing for like-sexed pairs. These data do not support the notion that sex-related factors influence multiple-sclerosis susceptibility in families.
Assuntos
Suscetibilidade a Doenças , Esclerose Múltipla/genética , Sexo , Família , Feminino , Humanos , Masculino , Esclerose Múltipla/fisiopatologiaRESUMO
We identified a premature chain termination mutation in two brothers with Duchenne muscular dystrophy and correlated the mutation in one of the brothers with immunologic detection of dystrophin in skeletal muscle. Southern and polymerase chain reaction (PCR) studies of genomic DNA from the affected boys showed no major gene rearrangements. However, the noted absence of a HindIII Southern fragment containing the proximal portion of exon 48 led to the identification of a point mutation that creates a new HindIII restriction site in that exon. Exon 48 was amplified by PCR from DNA of the patients and other family members and digested with HindIII to show the mutation in the two boys and also in their mother and maternal grandmother. Direct DNA sequencing demonstrated a cytosine-to-thymine transition at nucleotide 7163 of dystrophin that converts a glutamine codon (CAA) to an ochre chain termination codon (UAA). This mutation predicts a truncated dystrophin missing the distal spectrin-like repeat region, the cysteine-rich domain, and the carboxy terminal. Immunohistochemistry of skeletal muscle from one of the affected boys revealed membrane-localized dystrophin in the majority of fibers detected by anti-dystrophin antibodies against (1) the amino terminal and (2) part of the spectrin-like repeat region; both regions would be present in the truncated dystrophin predicted by the chain termination mutation. This suggests that the carboxy terminal may not be an absolute requirement for dystrophin membrane localization. Very few muscle fibers also showed peripheral immunostaining using anti-dystrophin antibodies against the carboxy terminal, suggesting gene reversion, suppression, or read-through in these rare fibers.
Assuntos
Distrofina/genética , Distrofias Musculares/genética , Mutação/genética , Sequência de Aminoácidos , Sequência de Bases , Pré-Escolar , Desoxirribonuclease HindIII , Distrofina/análise , Humanos , Imuno-Histoquímica , Masculino , Dados de Sequência Molecular , Distrofias Musculares/metabolismo , Linhagem , Reação em Cadeia da PolimeraseRESUMO
We compared demographic and clinical features, including outcome defined by a failure time analysis of disability, in 143 patients with a family history of multiple sclerosis (familial MS) compared with 956 patients without such a history (sporadic MS). Patients with familial MS did not differ from those with sporadic MS even when patients with 1st-degree relatives or multiple relatives with MS were considered separately. An intraclass correlation analysis of 13 pairs of affected 1st-degree relatives, both members of which were followed in our clinic, failed to reveal heterogeneity among different families. We were unable to find any support for differences between familial and sporadic MS.
Assuntos
Esclerose Múltipla/genética , Adulto , Fatores Etários , Análise de Variância , Feminino , Humanos , Masculino , Esclerose Múltipla/fisiopatologia , Ontário , Linhagem , Prognóstico , Fatores SexuaisRESUMO
OBJECTIVE: Inherited myoclonus-dystonia (IMD) is a new term for an autosomal dominant disorder characterized by myoclonus and dystonia. Recently, IMD was linked to a region on chromosome 11q23 with two different mutations identified in the D2 dopamine receptor gene and linked to chromosome 7q with five different loss-of-function mutations identified in the epsilon-sarcoglycan gene. METHODS: These two regions and genes were excluded in a large Canadian family with IMD in whom 13 individuals are affected. A 25-cM genome scan of this large family with 32 individuals was performed. RESULTS: Two-point linkage analysis revealed a maximum lod score of 3.5 (recombination fraction 0.00; affected only) for the microsatellite marker GATA185C06-18 and a multipoint lod score of 3.9 across the 18p11 region. Haplotype analysis demonstrates that all the affected individuals shared a common haplotype between markers D18S1132 and D18S843 that defines the disease gene within a span of 16.9 cM. CONCLUSIONS: These findings indicate that a novel IMD gene exists on chromosome 18p11.
Assuntos
Cromossomos Humanos Par 18/genética , Distonia/genética , Ligação Genética/genética , Mioclonia/genética , Criança , Cromossomos Humanos Par 7/genética , Feminino , Humanos , Escore Lod , Masculino , Repetições de Microssatélites/genética , Mutação/genética , Linhagem , Receptores de Dopamina D2/genética , SíndromeRESUMO
OBJECTIVE: To identify the cause of hypokalemic periodic paralysis (HOKPP) in a family whose disease is not caused by a mutation in the dihydropyridine-sensitive (DHP) receptor alpha1-subunit gene (CACNA1S). BACKGROUND: Hypokalemic periodic paralysis is primarily caused by mutations within CACNA1S. Genetic heterogeneity for HOKPP has been reported, but no other locus has been identified. METHODS: Single-stranded conformational polymorphism (SSCP) analysis and PCR direct sequencing were used to screen the skeletal muscle alpha1-sodium channel gene (SCN4A) for a mutation in our family. RESULTS: SSCP analysis showed an abnormally migrating conformer in exon 12. Direct sequencing of the conformer showed a guanine to adenine transition at position 2006 in the cDNA sequence; this results in an amino acid substitution of a highly conserved arginine (Arg) to histidine (His) at position 669. This sequence alteration segregated only with the affected members of the kindred and was not found in a panel of 100 DNA samples from healthy controls. The amino acid substitution alters the outermost positive charge in the membrane spanning segment DII/S4, which is involved in voltage sensing. CONCLUSIONS: The first arginine in DII/S4 and in DIV/S4 within the skeletal muscle sodium channel and the L-type calcium channel genie CACNA1S appear to be critical for normal function. In all four cases, Arg to His mutations result in a disease phenotype. The identification of a mutation within the skeletal muscle sodium channel resulting in hypokalemic periodic paralysis represents a novel finding.