Biomedical subjects

R Heine

Publications and source records attributed to R Heine.

At least 19 recordsLinked to original sources

PubMed1999

Ethanol oxidation and acetaldehyde production in vitro by human intestinal strains of Escherichia coli under aerobic, microaerobic, and anaerobic conditions.

BACKGROUND: Many human colonic facultative anaerobic and aerobic bacteria are capable of alcohol dehydrogenase (ADH)-mediated ethanol oxidation. In this bacteriocolonic pathway for ethanol oxidation intracolonic ethanol is first oxidized by bacterial ADHs to acetaldehyde, which is further oxidized by either colonic mucosal or bacterial aldehyde dehydrogenases to acetate. The produced acetaldehyde is a highly toxic and carcinogenic agent. This study was aimed to investigate the ethanol oxidation capability and acetaldehyde formation of Escherichia coli IH 50546 and IH 50817. These intestinal E. coli strains expressed either high (IH 50546) or low (IH 50817) ADH activity. METHODS: Strains were cultured for 48 h on agar plates supplemented with ethanol under aerobic, microaerobic (6% O2), and anaerobic conditions. RESULTS: Under aerobic conditions both E. coli strains oxidized ethanol. The ethanol consumption rates (ECR) were 1.046+/-0.025 mM/h and 0.367+/-0.148 mM/h with IH 50546 and IH 50817, respectively. In the case of IH 50546 this was associated with significant acetaldehyde production (418+/-13 microM), suggesting ADH-mediated ethanol oxidation. Under microaerobic conditions only IH 50546 was able to oxidize ethanol (ECR, 0.498+/-0.074 mM/h) and to produce acetaldehyde (up to 440+/-76 microM) to significant extents. Under anaerobic conditions both strains fermented glucose to ethanol. CONCLUSIONS: This study experimentally shows the potential of certain bacteria representing normal human colonic flora to produce acetaldehyde under various atmospheric conditions that may prevail in different parts of the GI tract. This bacterial adaptation may be an essential feature of the bacteriocolonic pathway to produce toxic and carcinogenic acetaldehyde from either endogenous or exogenous ethanol.

Acetaldehyde↗

PubMed1999

Staging of lymph nodes with FDG dual-headed PET in patients with non-small-cell lung cancer.

Accurate assessment of mediastinal lymph node involvement in patients with non-small-cell lung cancer (NSCLC) is necessary to select patients for direct surgical treatment. The aims of the present study were to assess the feasibility of staging NSCLC with FDG using a dual-headed positron emission tomographic (PET) camera and to compare this non-invasive technique with computed tomography (CT) and lymph node sampling, since both modalities are currently used for staging NSCLC. Thirty-three patients (29 men and 4 women, mean age 60 years) with newly diagnosed NSCLC were studied. In all patients, CT, FDG dual-headed PET and mediastinoscopy were performed within 4 weeks. The results of mediastinoscopy were used to select patients for thoracotomy. For both the assessment of individual lymph node involvement and the patient-based classification, the results of FDG dual-headed PET and CT were compared using the McNemar test. Thirty-one of 187 lymph nodes studied contained tumour metastases. FDG dual-headed PET showed a significantly higher sensitivity (P < 0.001) and specificity (P < 0.001) than CT. FDG dual-headed PET and CT correctly staged 27 and 20 patients, respectively. Due to the significantly higher negative predictive value of FDG dual-headed PET versus CT (P = 0.012), it was a better non-invasive diagnostic tool for selecting patients for surgery. In seven of eight patients, additional intrapulmonary sites of increased uptake were found, which revealed malignancy on histological examination. CT was false-negative in three of these patients. In one patients, increased FDG uptake was caused by an infection. In conclusion, it is possible to stage mediastinal lymph nodes in patients with NSCLC using a dual-headed PET camera. The high negative predictive value of FDG dual-headed PET suggests that mediastinoscopy may be omitted in patients with NSCLC.

Aged↗

PubMed1998

Role of catalase in in vitro acetaldehyde formation by human colonic contents.

Ingested ethanol is transported to the colon via blood circulation, and intracolonic ethanol levels are equal to those of the blood ethanol levels. In the large intestine, ethanol is oxidized by colonic bacteria, and this can lead to extraordinarily high acetaldehyde levels that might be responsible, in part, for ethanol-associated carcinogenicity and gastrointestinal symptoms. It is believed that bacterial acetaldehyde formation is mediated via microbial alcohol dehydrogenases (ADHs). However, almost all cytochrome-containing aerobic and facultative anaerobic bacteria possess catalase activity, and catalase can, in the presence of hydrogen peroxide (H2O2), use several alcohols (e.g., ethanol) as substrates and convert them to their corresponding aldehydes. In this study we demonstrate acetaldehyde production from ethanol in vitro by colonic contents in a reaction catalyzed by both bacterial ADH and catalase. The amount of acetaldehyde produced by the human colonic contents was proportional to the ethanol concentration, the amount of colonic contents, and the length of incubation time, even in the absence of added nicotinamide adenine dinucleotide or H2O2. The catalase inhibitors sodium azide and 3-amino-1,2,4-triazole (3-AT) markedly reduced the amount of acetaldehyde produced from 22 mM ethanol in a concentration dependent manner compared with the control samples (0.1 mM sodium azide to 73% and 10 mM 3-AT to 67% of control). H2O2 generating system [beta-D(+)-glucose + glucose oxidase] and nicotinamide adenine dinucleotide induced acetaldehyde formation up to 6- and 5-fold, respectively, and together these increased acetaldehyde formation up to 11-fold. The mean supernatant catalase activity was 0.53+/-0.1 micromol/min/mg protein after the addition of 10 mM H2O2, and there was a significant (p < 0.05) correlation between catalase activity and acetaldehyde production after the addition of the hydrogen peroxide generating system. Our results demonstrate that colonic contents possess catalase activity, which probably is of bacterial origin, and indicate that in addition to ADH, part of the acetaldehyde produced in the large intestine during ethanol metabolism can be catalase dependent.

Acetaldehyde↗

PubMed1997

Inhibition of bacteriocolonic pathway for ethanol oxidation by ciprofloxacin in rats.

Many colonic bacteria possess marked alcohol dehydrogenase (ADH) activity and are capable of oxidizing ethanol to acetaldehyde both in vitro and in vivo. We have recently shown that part of ingested ethanol is metabolized to acetaldehyde in the colon during normal alcohol metabolism. To assess the contribution of this bacteriocolonic pathway for ethanol oxidation to total ethanol metabolism, the elimination rate of ethanol, faecal aerobic flora and faecal ADH activity were determined in rats before and after the treatment with ciprofloxacin (200 mg/kg/day) for four days. Ciprofloxacin treatment decreased ethanol elimination rate from 310+/-9 to 282+/-13 mg/kg/h (mean+/-SE; p<0.02), markedly reduced faecal aerobic flora, and also lowered faecal ADH activity from 63+/-17 to 17+/-7 nmol/min/mg faeces (p<0.05). Neither hepatic ADH nor microsomal ethanol oxidizing system activities were affected by the ciprofloxacin treatment. On the contrary, an acute intraperitoneal dose of ciprofloxacin had no effect on the rate of ethanol elimination. These results support the significant role of the bacteriocolonic pathway in total ethanol elimination, and open a new, microbiological, perspective for studies on ethanol metabolism and pathogenesis of alcohol related organ damages.

Alcohol Dehydrogenase↗

PubMed1997

Detection of a novel mutation at amino acid position 614 in the ryanodine receptor in malignant hyperthermia.

Malignant hyperthermia (MH) is a potentially fatal autosomal dominant disorder of skeletal muscle and is triggered in susceptible people by all commonly used inhalation anaesthetics and depolarizing neuromuscular blocking agents. To date, eight mutations in the skeletal muscle ryanodine receptor gene (RYR1) have been identified in malignant hyperthermia susceptible (MHS) and central core disease (CCD) cases. We have screened the RYR1 gene in affected individuals for novel MHS mutations by single stranded conformational polymorphism (SSCP) analysis and have identified a G to T transition mutation which results in the replacement of a conserved arginine (Arg) at position 614 with a leucine (Leu). The Arg614Leu mutation was present in three unrelated MHS individuals of 151 investigated. The mutation was not detected in 148 normal chromosomes and segregated precisely with MHS in family members from one of the probands where DNA was available for analysis. This mutation occurs at the same position as the previously identified Arg to Cys mutation reported in all cases of porcine MH and in approximately 5% of human MH. A comparison of the phenotypes of the Arg614Leu and Arg614Cys probands is presented.

Amino Acid Sequence↗

PubMed1997

High acetaldehyde levels in saliva after ethanol consumption: methodological aspects and pathogenetic implications.

Chronic ethanol ingestion leads to an enhanced risk of upper gastrointestinal tract cancer. Although many hypotheses for the tumor promoting effect of alcohol exist, the pathogenetic mechanisms remain unclear since alcohol in itself is not carcinogenic. Acetaldehyde, the first metabolite of ethanol, has been shown to have multiple mutagenic effects and to be carcinogenic to animals. Previous research has revealed that acetaldehyde can be formed from ethanol via microbial alcohol dehydrogenase. Thus, at least part of the proposed tumorigenic effect of ethanol may be linked to local production of acetaldehyde from ethanol by oral microflora. In this study we demonstrate the production of marked amounts of acetaldehyde in saliva after ingestion of moderate amounts of ethanol. Considerable inter individual variation in acetaldehyde production capacity is also shown. In vivo acetaldehyde production is significantly reduced after a 3-day use of an antiseptic mouthwash (chlorhexidine). In vitro acetaldehyde production was shown to be linear in time, inhibited by 4-methylpyrazole and it could not be saturated under ethanol conditions that are relevant in vivo. There was a significant positive correlation between salivary acetaldehyde production in vitro and in vivo. We conclude, that the microbial formation of acetaldehyde in saliva could be one explanation for the tumor promoting effect of ethanol on the upper gastrointestinal tract. Moreover, this may support the epidemiological finding, that poor oral hygiene is an independent risk factor for oral cavity cancer.

Acetaldehyde↗

PubMed1997

A novel sodium channel mutation causing a hyperkalemic paralytic and paramyotonic syndrome with variable clinical expressivity.

A point mutation A4078G predicting the amino acid exchange Met1360Val in segment IV/S1 of the human muscle sodium channel alpha-subunit was identified in a family presenting features of hyperkalemic periodic paralysis and paramyotonia congenita with sex-related modification of expression. In this family, only one male member is clinically affected, presenting episodes of flaccid weakness as well as paradoxical myotonia and cold-induced weakness. Three female family members who have the same mutation show only myotonic bursts on EMG. We studied the functional defect caused by this mutation by investigating recombinant wild type (WT) and mutant sodium channels expressed in a mammalian cell line (HEK293) using the patch-clamp technique. With mutant channels, the decay of the sodium currents was two times slower than with WT, the steady-state inactivation curve was shifted by -13 mV, and recovery from inactivation was 1.5 times faster. High extracellular potassium (9 mM) did not affect channel gating. Single-channel measurements revealed prolonged mean open times and an increased number of channel reopenings. The results are remarkable with respect to the lack of complete penetrance usually seen with sodium channelopathies and the site of mutation that was formerly not thought to be involved in channel inactivation.

Amino Acid Sequence↗

PubMed1997

Characteristics of alcohol dehydrogenases of certain aerobic bacteria representing human colonic flora.

We have recently proposed the existence of a bacteriocolonic pathway for ethanol oxidation [i.e., ethanol is oxidized by alcohol dehydrogenases (ADHs) of intestinal bacteria resulting in high intracolonic levels of reactive and toxic acetaldehyde]. The aim of this in vitro study was to characterize further ADH activity of some aerobic bacteria, representing the normal human colonic flora. These bacteria were earlier shown to possess high cytosolic ADH activities (Escherichia coli IH 133369, Klebsiella pneumoniae IH 35385, Klebsiella oxytoca IH 35339, Pseudomonas aeruginosa IH 35342, and Hafnia alvei IH 53227). ADHs of the tested bacteria strongly preferred NAD as a cofactor. Marked ADH activities were found in all bacteria, even at low ethanol concentrations (1.5 mM) that may occur in the colon due to bacterial fermentation. The Km for ethanol varied from 29.9 mM for K. pneumoniae to 0.06 mM for Hafnia alvei. The inhibition of ADH by 4-methylpyrazole was found to be of the competitive type in 4 of 5 bacteria, and Ki varied from 18.26 +/- 3.3 mM for Escherichia coli to 0.47 +/- 0.13 mM for K. pneumoniae. At pH 7.4, ADH activity was significantly lower than at pH 9.6 in four bacterial strains. ADH of K. oxytoca, however, showed almost equal activities at neutral pH and at 9.6. In conclusion, NAD-linked alcohol dehydrogenases of aerobic colonic bacteria possess low apparent Km's for ethanol. Accordingly, they may oxidize moderate amounts of ethanol ingested during social drinking with nearly maximal velocity. This may result in the marked production of intracolonic acetaldehyde. Kinetic characteristics of the bacterial enzymes may enable some of them to produce acetaldehyde even from endogenous ethanol formed by other bacteria via alcoholic fermentation. The microbial ADHs were inhibited by 4-methylpyrazole by the same competitive inhibition as hepatic ADH, however, with nearly 1000 times lower susceptibility. Individual variations in human colonic flora may thus contribute to the risk of alcohol-related gastrointestinal morbidity, such as diarrhea, colon polyps and cancer, and liver injury.

Acetaldehyde↗

PubMed1996

Role in fast inactivation of conserved amino acids in the IV/S4-S5 loop of the human muscle Na+ channel.

Since it has been shown that point mutations in the S4-S5 loop of the Shaker K+ channel may disrupt fast inactivation, we investigated the role of three conserved amino acids in IV/S4-S5 of the adult human muscle Na+ channel (L1471, S1478, L1482). In contrast to the K+ channel mutations, the analogous substitutions in the Na+ channel (S1478A/C, L1482A) did not substantially affect fast inactivation. Nevertheless, the mutations S1478A/C/Q shifted the voltage dependence of steady-state inactivation; L1471Q and S1478C slowed recovery from inactivation. In contrast, a novel non-conserved IV/S4-S5 mutation causing paramyotonia congenita (F1473S) slowed fast inactivation 2-fold and accelerated recovery from inactivation 5-fold. The results indicate involvement of the IV/ S4-S5 loop of the human muscle Na+ channel in fast inactivation, but different roles for conserved amino acids among Na+ and K+ channels.

Amino Acid Sequence↗

PubMed1996

Aldehyde dehydrogenase activity and acetate production by aerobic bacteria representing the normal flora of human large intestine.

We have recently proposed the existence of a bacteriological pathway for ethanol oxidation, i.e. ethanol is oxidized by alcohol dehydrogenase of intestinal bacteria resulting in high intracolonic levels of reactive and toxic acetaldehyde. This study was aimed to examine aldehyde dehydrogenase (ALDH) activity, acetaldehyde consumption and production of acetate by aerobic bacteria (n = 27), representing the normal human colonic flora. Most bacterial strains did not show any membrane-associated aldehyde dehydrogenase, but possessed marked cytosolic NADP(+) - and NAD(+) - dependent aldehyde dehydrogenase activity, ranging from 155 nmol of NAD(P)H produced/min/mg of protein to zero with acetaldehyde as substrate. NADP(+)-linked ALDH activity was significantly higher than NAD(+)-linked activity in most of the tested bacteria. In addition, aerobic bacteria metabolized acetaldehyde effectively in vitro and this could be inhibited by cyanamide in nearly half of the tested strains. Production of acetate from acetaldehyde ranged from 2420 nmol/10(9) colony-forming units to almost negligible. In conclusion, many human aerobic colonic bacteria possess significant aldehyde dehydrogenase activity and can, consequently, produce acetate from acetaldehyde in vitro at least under the partially aerobic conditions proposed to prevail on the colonic mucosal surface. Individual variation in the capability of colonic flora to remove toxic acetaldehyde may be one factor regulating intracolonic acetaldehyde levels, as well as the rate of bacteriocolonic pathway for ethanol oxidation.

Acetaldehyde↗

PubMed1996

In vitro alcohol dehydrogenase-mediated acetaldehyde production by aerobic bacteria representing the normal colonic flora in man.

Excessive ethanol consumption has been related with the development of liver cirrhosis, as well as with rapid intestinal transit time and diarrhea. Moreover, heavy drinking is associated with an increased incidence of cancer of the oropharynx, larynx, esophagus, and colorectum. Acetaldehyde of microbial origin has recently been suggested as a possible pathogenic factor behind this alcohol-associated gastrointestinal morbidity. The present in vitro study was aimed to investigate alcohol dehydrogenase activity and acetaldehyde formation capacity of some major aerobic bacteria representing the normal colonic flora in man. Cytosolic alcohol dehydrogenase activity and cytosolic protein concentration were determined spectrophotometrically. Alcohol dehydrogenase activity was then calculated as nmoles of reduced substrate produced by milligrams of protein per minute. The ability of different bacteria to produce acetaldehyde was determined by incubating the intact bacterial suspension in closed vials containing ethanol (final concentration 22 mM) for 1 hr at 37 degrees C. The acetaldehyde formed during the incubation was analyzed by headspace gas chromatography. Marked differences in the alcohol dehydrogenase activity and acetaldehyde forming capacity were found among the strains tested. The alcohol dehydrogenase activity varied from 606 +/- 91 nmol/min/mg protein (Escherichia coli IH 50546) to 1 +/- 0.2 nmol/min/mg protein (E. coli IH 50817), and acetaldehyde formation varied from 1,717 +/- 2 nmol acetaldehyde/10(9) colony-forming units (Klebsiella oxytoca IH 35403) to 5 +/- 2 nmol acetaldehyde/10(9) colony-forming units (Pseudomonas aeruginosa ATCC 27853). There was a statistically significant correlation (r = 0.77; p < 0.001) between alcohol dehydrogenase activity and acetaldehyde production from ethanol, strongly suggesting the catalytic role of bacterial alcohol dehydrogenase in this reaction.

Acetaldehyde↗

PubMed1996

Novel muscle chloride channel mutations and their effects on heterozygous carriers.

Mutations within CLCN1, the gene encoding the major skeletal muscle chloride channel, cause either dominant Thomsen disease or recessive Becker-type myotonia, which are sometimes difficult to discriminate, because of reduced penetrance or lower clinical expressivity in females. We screened DNA of six unrelated Becker patients and found four novel CLCN1 mutations (Gln-74-Stop, Tyr-150-Cys, Tyr-261-Cys, and Ala-415-Val) and a previously reported 14-bp deletion. Five patients were homozygous for the changes (Gln-74-Stop, Ala-415-Val, and 14-bp deletion), four of them due to parental consanguinity. The sixth patient revealed compound heterozygosity for Tyr-150-Cys and Tyr-261-Cys. Heterozygous carriers of the Becker mutations did not display any clinical symptoms of myotonia. However, all heterozygous males, but none of the heterozygous females, exhibited myotonic discharges in the electromyogram suggesting (i) a gene dosage effect of the mutations on the chloride conductance and (ii) male predominance of subclinical myotonia. Furthermore, we report a novel Gly-200-Arg mutation resulting in a dominant phenotype in a male and a partially dominant phenotype in his mother. We discuss potential causes of the gender preference and the molecular mechanisms that may determine the mode of inheritance.

Amino Acid Sequence↗

PubMed1995

Myotonia levior is a chloride channel disorder.

The group of dominant non-dystrophic myotonias, comprising disorders characterized by clinically similar forms of myogenic muscle stiffness, is genetically inhomogeneous. Dominant myotonia congenita (Thomsen's disease) is linked to CLCN1, the gene encoding the major muscle chloride channel, localized on chromosome 7q35. In contrast, dominant myotonias sensitive to potassium are caused by point mutations in SCN4A on chromosome 17q, the gene for the alpha subunit of the adult skeletal muscle sodium channel. No linkage or molecular genetic data are as yet available on 'myotonia levior' characterized by milder symptoms and later onset of myotonia than in Thomsen's disease, and absence of muscle hypertrophy. We report a CLCN1 Gln-552-Arg substitution for a family with dominant inheritance previously diagnosed to have myotonia levior. Thus, this disorder appears as a variant of Thomsen's disease due to mutations leading to low clinical expressivity. In addition, we report a novel Ile-290-Met CLCN1 mutation for a typical Thomsen pedigree. In another family previously diagnosed as having Thomsen's disease, we unexpectedly found a CLCN1 14 bp deletion known to cause recessive myotonia, and a rare Trp-118-Gly polymorphism.

Adult↗

PubMed1995

Altered calcium currents in human hypokalemic periodic paralysis myotubes expressing mutant L-type calcium channels.

In a genome-wide search, linkage of hypokalemic periodic paralysis (HypoPP), a muscle disease with autosomal dominant inheritance, to chromosome 1q31-32 and cosegregation with the gene encoding the L-type calcium channel/DHP receptor alpha 1 subunit has been reported (Fontaine et al., 1994). Here we show the extended haplotypes of a large HypoPP family who made the detection of the gene product possible. Sequencing of cDNA synthesized from RNA isolated from muscle specimens of two affected family members revealed a G-to-A transition of nucleotide 3716. This base exchange predicts a substitution of histidine for arginine 1239 located in segment IVS4 of the channel protein. By restriction fragment analysis, the mutation was detected in the genomic DNA of all affected family members. Myotubes cultured from the muscle specimens also revealed the mutation suggesting the expression of mutant L-type calcium channel/DHP receptors. Whole-cell recordings of 20 such myotubes showed a strong reduction of the DHP sensitive, slowly activating and inactivating L-type current density to 30% of the current in normal controls. A rapidly activating and inactivating current component (third-type), which is distinct from the also occurring T-type current, was increased. We conclude that HypoPP is a disease of the skeletal muscle DHP receptor. The point mutation in repeat IV of the protein may have a similar effect as drugs which downregulate the channel activity by binding to this domain.

Calcium Channels↗

PubMed1994

K(+)-aggravated myotonia: destabilization of the inactivated state of the human muscle Na+ channel by the V1589M mutation.

1. Wild type (WT) and V1589M channels were expressed in human embryonic kidney (HEK293) cells for the study of the pathophysiology of the V1589M muscle Na+ channel mutation leading to K(+)-aggravated myotonia. 2. In comparison to WT, whole-cell recordings with V1589M channels showed an increased Na+ steady-state to peak current ratio (Iss/Ipeak) (3.15 +/- 0.70 vs. 0.87 +/- 0.10%, at -15 mV) and a significantly faster recovery from inactivation. The recovery time constants, tau r1 and tau r2, were decreased from 1.28 +/- 0.12 to 0.92 +/- 0.08 ms and from 4.74 +/- 0.94 to 2.66 +/- 0.51 ms for the WT and mutant channels, respectively. 3. Single-channel recordings with mutant channels showed higher probability of short isolated late openings (0.40 +/- 0.09 vs. 0.06 +/- 0.02, at -30 mV) and bursts of late openings (0.011 +/- 0.003 vs. 0.003 +/- 0.001, at -30 mV) compared to WT. 4. These results suggest that the mutation increases the probabilities for channel transitions from the inactivated to the closed and the opened states. 5. Increased extracellular concentrations of K+ had no effects on either V1589M or WT currents in HEK293 cells. The aggravation of myotonia seen in patients during increased serum K+ may arise from the associated membrane depolarization which favours the occurrence of late openings in the mutant channel.

Cell Line↗

PubMed1994

Myotonia fluctuans. A third type of muscle sodium channel disease.

OBJECTIVES: To define a new type of dominant myotonic muscle disorder and to identify the gene lesion. DESIGN: Case series, clinical examination and electromyography, measurements of grip force and relaxation time, and DNA analysis to probe for mutation in the gene for the skeletal muscle sodium channel. SETTING: Outpatient clinic and home. PATIENTS: Three families studied; all together, 17 affected and nine unaffected individuals. RESULTS: The findings in these three families confirm the existence of myotonia fluctuans as we described it previously in another family. Myotonia (prolongation of relaxation time) developed 20 to 40 minutes after exercise. Potassium caused generalized myotonia. Cooling had no major effect on muscle function. Three families had a common mutation in exon 22 and one family had a mutation in exon 14 of the gene for the sodium channel alpha subunit. CONCLUSIONS: Myotonia fluctuans is a disorder of the muscle sodium channel. There are at present two other distinct clinical muscle disorders associated with mutations in the sodium channel: hyperkalemic periodic paralysis and paramyotonia congenita. The findings in the present report indicate that myotonia fluctuans belongs to a third type of sodium channel disorder. Further work is needed to understand the complex genotype-phenotype correlations in sodium channel disorders.

Base Sequence↗

PubMed1994

Mapping of the hypokalaemic periodic paralysis (HypoPP) locus to chromosome 1q31-32 in three European families.

Hypokalaemic periodic paralysis (HypoPP) is an autosomal dominant muscle disease thought to arise from an abnormal function of ion channels. Performing a genome-wide search using polymorphic dinucleotide repeats, we have localized the HypoPP locus in three families of different geographic origin to chromosome 1q31-32, by linkage analysis. Using an intragenic microsatellite, we also demonstrate that the gene encoding the muscle DHP-sensitive calcium channel alpha 1 subunit (CACNL1A3) maps to the same region, sharing a 5 centiMorgan (cM) interval with the HypoPP locus. Moreover, CACNL1A3 co-segregates with HypoPP without recombinants in the two informative families, and is therefore a good candidate for the HypoPP gene.

Calcium Channels↗

PubMed1994

Proof of a non-functional muscle chloride channel in recessive myotonia congenita (Becker) by detection of a 4 base pair deletion.

Recessive myotonia congenita (Becker) is genetically linked to HUMCLC, the gene encoding the muscular chloride channel, localized on chromosome 7q35. Three point mutations have so far been reported in HUMCLC, one causing recessive Becker-type myotonia, the others causing the clinically similar Thomsen-type myotonia, which is inherited as a dominant trait. We report a homozygous patient having a 4 base pair deletion in HUMCLC that shifts the reading frame and causes early stop codons, thus destroying the gene's coding potential for several membrane-spanning domains. In addition, we report a patient homozygous for a novel point mutation located at the extracellular side of the first membrane-spanning domain that causes removal of a negative charge (aspartic acid-136-glycine). Both mutations lead to the recessive type of myotonia congenita. Since the patient having the deletion presents less severe clinical myotonia than the patient carrying the missense mutation, it seems that the absence or truncation of the channel protein may disturb muscle fibre function less than the substitution of a single amino acid.

Amino Acid Sequence↗