Deoxypodophyllotoxin 6-hydroxylase, a cytochrome P450 monooxygenase from cell cultures of Linum flavum involved in the biosynthesis of cytotoxic lignans

Cell-suspension cultures of Linum flavum L. (Linaceae) synthesize and accumulate aryltetrahydronaphthalene lignans with 6-methoxypodophyllotoxin as the main component. The experimental data indicate that the biosynthesis of 6-methoxypodophyllotoxin occurs via deoxypodophyllotoxin, beta-peltatin, and beta-peltatin-A methyl ether. The enzyme catalyzing the introduction of the hydroxyl group in position 6 is deoxypodophyllotoxin 6-hydroxylase (DOP6H). The enzyme was shown to be a cytochrome P450-dependent monooxygenase by blue-light reversion of carbon monoxide inhibition and inhibition by cytochrome c. DOP6H is a membrane-bound microsomal enzyme with a pH optimum of 7.6 and a temperature optimum of 26 degrees C. Deoxypodophyllotoxin is specifically accepted with an apparent Km of 20 microM and a saturation concentration of 200 microM; 4'-demethyldeoxypodophyllotoxin is the only other tested substrate accepted for hydroxylation. DOP6H predominantly accepts NADPH as electron donor; NADH can only sustain low hydroxylation activities. A synergistic effect of NADPH and NADH is not observed. The enzyme is saturated around 250 microM NADPH; the apparent Km for this substrate is 36 microM.

Level set approach to reversible epitaxial growth

We generalize the level set approach to model epitaxial growth to include thermal detachment of atoms from island edges. This means that islands do not always grow and island dissociation can occur. We make no assumptions about a critical nucleus. Excellent quantitative agreement is obtained with kinetic Monte Carlo simulations for island densities and island size distributions in the submonolayer regime.

Induction of bile ducts in embryonic liver by mesenchyme: a new perspective for the treatment of biliary atresia?

Presently only those forms of Extrahepatic Biliary Atresia (EHBA) with minimal or no intrahepatic manifestations can be treated successfully by extensive hepatoportoenterostomy. Intraoperative macro- and microscopic observations show that the typical pathogenetic manifestations in EHBA are most prominent at the porta hepatis. We therefore postulate that EHBA is the result of a defective embryonic development of the porta hepatis. In rat embryos hepatic bile duct formation is initiated at the porta hepatis and in this context mesenchyme from the periportal region seems to play a major inductive role. In order to demonstrate the role of invading periportal mesenchyme for the process of bile duct rudiment formation we established an organ culture model of the embryonic porta hepatis by recombining periportal mesenchyme with peripheral liver fragments from 15 days old rat embryos (Carnegie Stage 21). The degree of mesenchyme invasion as well as the formation of mesenchyme-surrounded liver cell clusters, rosettes or vesicles (bile duct rudiments) were assessed. Mesenchyme from the porta hepatis invaded the peripheral liver fragments and induced the formation of mesenchyme-surrounded liver cell clusters and rosettes with the beginning of lumen formation. Kidney mesenchyme recombined with liver fragments as a mesenchymal alternative showed almost the same effect, lung mesenchyme showed only a very weak inductive effect. To assess the effect of a diffusible factor versus direct cell contact, a millipore filter with and without paraffin coating was interposed between mesenchyme containing tissue and peripheral liver tissue fragments. Without direct cell contact to mesenchyme no hepatoblast cluster or rosette formation could be observed. Comparing this result to the normal development of the liver in rats our investigations suggest that the embryogenesis of the porta hepatis is probably defined by the following two developmental steps: First, differentiation of the intrahepatic bile duct system which is induced by invading mesenchyme originating from the extrahepatic periportal region and realized by epithelium mesenchyme interaction. Second, fusion of extra- and intrahepatic bile duct systems at the level of the later porta hepatis. Disturbances of this complex process can possibly lead to biliary atresia. Further investigations regarding details of the role of the mesenchyme, its inductive factors and the kidney mesenchyme's inductive potential in liver development may provide a new perspective for future treatment of biliary atresia.

No evidence for bradykinin B1 receptors in rat dorsal root ganglion neurons

Bradykinin receptors are believed to contribute to hyperalgesia under conditions of neuropathic pain. Using calcium imaging we investigated responses to B1 and B2 agonists on isolated rat dorsal root ganglion neurons. No response to the B1 agonist was detected, whereas 12% of neurons responded to the B2 agonist. Northern blot analysis confirmed the lack of B1 receptor expression in dorsal root ganglia, as B1 mRNA was neither detected under normal conditions nor after nerve injury. In the calcium imaging experiments, agonists were applied with an elevated superfusion flow rate to avoid tachyphylaxis to the drug. Normal external solution applied at this flow rate constituted a mechanical stimulus causing a response in some neurons. Thus, in comparable set-ups mechanosensitivity has first to be tested to avoid masking effects.

Missense mutations in the N-terminal domain of human phenylalanine hydroxylase interfere with binding of regulatory phenylalanine

Hyperphenylalaninemia due to a deficiency of phenylalanine hydroxylase (PAH) is an autosomal recessive disorder caused by >400 mutations in the PAH gene. Recent work has suggested that the majority of PAH missense mutations impair enzyme activity by causing increased protein instability and aggregation. In this study, we describe an alternative mechanism by which some PAH mutations may render PAH defective. Database searches were used to identify regions in the N-terminal domain of PAH with homology to the regulatory domain of prephenate dehydratase (PDH), the rate-limiting enzyme in the bacterial phenylalanine biosynthesis pathway. Naturally occurring N-terminal PAH mutations are distributed in a nonrandom pattern and cluster within residues 46-48 (GAL) and 65-69 (IESRP), two motifs highly conserved in PDH. To examine whether N-terminal PAH mutations affect the ability of PAH to bind phenylalanine at the regulatory domain, wild-type and five mutant (G46S, A47V, T63P/H64N, I65T, and R68S) forms of the N-terminal domain (residues 2-120) of human PAH were expressed as fusion proteins in Escherichia coli. Binding studies showed that the wild-type form of this domain specifically binds phenylalanine, whereas all mutations abolished or significantly reduced this phenylalanine-binding capacity. Our data suggest that impairment of phenylalanine-mediated activation of PAH may be an important disease-causing mechanism of some N-terminal PAH mutations, which may explain some well-documented genotype-phenotype discrepancies in PAH deficiency.

Erosion of root epidermal cell walls by Rhizobium polysaccharide-degrading enzymes as related to primary host infection in the Rhizobium-legume symbiosis

A central event of the infection process in the Rhizobium-legume symbiosis is the modification of the host cell wall barrier to form a portal of entry large enough for bacterial penetration. Transmission electron microscopy (TEM) indicates that rhizobia enter the legume root hair through a completely eroded hole that is slightly larger than the bacterial cell and is presumably created by localized enzymatic hydrolysis of the host cell wall. In this study, we have used microscopy and enzymology to further clarify how rhizobia modify root epidermal cell walls to shed new light on the mechanism of primary host infection in the Rhizobium-legume symbiosis. Quantitative scanning electron microscopy indicated that the incidence of highly localized, partially eroded pits on legume root epidermal walls that follow the contour of the rhizobial cell was higher in host than in nonhost legume combinations, was inhibited by high nitrate supply, and was not induced by immobilized wild-type chitolipooligosaccharide Nod factors reversibly adsorbed to latex beads. TEM examination of these partially eroded, epidermal pits indicated that the amorphous, noncrystalline portions of the wall were disrupted, whereas the crystalline portions remained ultrastructurally intact. Further studies using phase-contrast and polarized light microscopy indicated that (i) the structural integrity of clover root hair walls is dependent on wall polymers that are valid substrates for cell-bound polysaccharide-degrading enzymes from rhizobia, (ii) the major site where these rhizobial enzymes can completely erode the root hair wall is highly localized at the isotropic, noncrystalline apex of the root hair tip, and (iii) the degradability of clover root hair walls by rhizobial polysaccharide-degrading enzymes is enhanced by modifications induced during growth in the presence of chitolipooligosaccharide Nod factors from wild-type clover rhizobia. The results suggest a complementary role of rhizobial cell-bound glycanases and chitolipooligosaccharides in creating the localized portals of entry for successful primary host infection.

Prevalence and risk factors of tendinitis and related disorders of the distal upper extremity among U.S. workers: comparison to carpal tunnel syndrome

BACKGROUND

National estimates of tendinitis and related disorders of the distal upper extremity among U.S. workers have not been available with the exception of carpal tunnel syndrome.

METHODS

The Occupational Health Supplement Data of the 1988 National Health Interview Survey were analyzed for tendinitis and related disorders of the hand/wrist and elbow (distal upper extremity) using the Survey Data Analysis (SUDAAN) software.

RESULTS

Among the 30,074 respondents (statistically weighted population of 127 million) who had worked anytime during the previous 12 months, 0.46% (95% CI: 0.36, 0.56) reported that they experienced a "prolonged" hand discomfort which was called tendinitis, synovitis, tenosynovitis, deQuervain's disease, epicondylitis, ganglion cyst, or trigger finger, by a medical person. This corresponds to 588,000 persons (95% CI: 457,000; 712,000) reporting one of these disorders, 28% (or 164,000) of which were thought to be work-related by the medical person. Among various risk factors examined by multiple logistic regression analysis, bending/twisting of the hands/wrists at work and female gender were significantly associated with reporting of these disorders.

CONCLUSIONS

By combining these cases with the previously reported cases of work-related carpal tunnel syndrome, we estimate that there were approximately 520,000 cases of work-related musculoskeletal disorders of the distal upper extremity among US workers in 1988.

Synthesis and NMR-analysis of tricyclic nucleosides

Two anomeric tricyclic nucleosides have been synthesised from diacetone-D-glucose using oxidation, stereoselective Grignard-addition of a vinyl-group, a stereoselective dihydroxylation followed by a tandem ring closing reaction, and finally a nucleobase coupling. The main beta-configured product was examined and its configuration confirmed using NMR-spectroscopy in connection to ab initio calculations. The preferred conformation of this tricyclic nucleoside was described.

LNA (locked nucleic acid) and the diastereoisomeric alpha-L-LNA: conformational tuning and high-affinity recognition of DNA/RNA targets

The remarkable binding properties of LNA (Locked Nucleic Acid) and alpha-L-LNA (the alpha-L-ribo configured diastereoisomer of LNA) are summarized, and hybridization results for LNA/2'-O-Me-RNA chimera and LNAs with a "dangling" nucleotide are introduced. In addition, results from NMR investigations on the furanose conformations of the individual nucleotide monomers in different duplexes are presented. All these data are discussed with focus on the importance of conformational steering of unmodified nucleotides in partly modified LNA and alpha-L-LNA sequences in relation to the unprecedented binding properties of LNA and alpha-L-LNA.

Classification of wheat varieties: Use of two-dimensional gel electrophoresis for varieties that can not be classified by matrix assisted laser desorption/ionization-time of flight-mass spectrometry and an artificial neural network

Analyzing a gliadin extract by matrix assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS) combined with an artificial neural network (ANN) is a suitable method for identification of wheat varieties. However, the ANN can not distinguish between all different wheat varieties. Two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) was applied to three pairs of wheat varieties, which can not be classified correctly by ANN. By 2-D PAGE the varieties in the three pairs can be discriminated and these six wheat varieties can be separated from each other, which could not be separated by MALDI-TOF-MS and NN.

Prevalence and risk factors of tendinitis and related disorders of the distal upper extremity among U.S. workers: comparison to carpal tunnel syndrome

BACKGROUND

National estimates of tendinitis and related disorders of the distal upper extremity among U.S. workers have not been available with the exception of carpal tunnel syndrome.

METHODS

The Occupational Health Supplement Data of the 1988 National Health Interview Survey were analyzed for tendinitis and related disorders of the hand/wrist and elbow (distal upper extremity) using the Survey Data Analysis (SUDAAN) software.

RESULTS

Among the 30,074 respondents (statistically weighted population of 127 million) who had worked anytime during the previous 12 months, 0.46% (95% CI: 0.36, 0.56) reported that they experienced a "prolonged" hand discomfort which was called tendinitis, synovitis, tenosynovitis, deQuervain's disease, epicondylitis, ganglion cyst, or trigger finger, by a medical person. This corresponds to 588,000 persons (95% CI: 457,000; 712,000) reporting one of these disorders, 28% (or 164,000) of which were thought to be work-related by the medical person. Among various risk factors examined by multiple logistic regression analysis, bending/twisting of the hands/wrists at work and female gender were significantly associated with reporting of these disorders.

CONCLUSIONS

By combining these cases with the previously reported cases of work-related carpal tunnel syndrome, we estimate that there were approximately 520,000 cases of work-related musculoskeletal disorders of the distal upper extremity among US workers in 1988.

The production of cytotoxic lignans by plant cell cultures

Cytotoxic lignans derived from podophyllotoxin are currently used in cancer chemotherapy. Podophyllotoxin for semi-synthetic derivatization is isolated from the rhizomes of Podophyllum plants growing wild, some of which are counted as endangered species. An alternative source for podophyllotoxin or related lignans may in future be cell cultures derived from different plant species, such as Podophyllum spp or Linum spp. These cell cultures were shown to accumulate considerable amounts of podophyllotoxin or 5-methoxypodophyllotoxin. Optimization of the cell cultivation regime might lead to a renewable source of cytotoxic lignans for medicinal uses. This Mini-Review summarizes the attempts to establish plant cell cultures for the production of podophyllotoxin and related lignans and their optimization towards high levels of these target compounds. It also summarizes the results of studies on the biosynthesis of podophyllotoxin and 5-methoxypodophyllotoxin.

In vitro expression of 34 naturally occurring mutant variants of phenylalanine hydroxylase: correlation with metabolic phenotypes and susceptibility toward protein aggregation

Phenylalanine hydroxylase (PAH) is a homotetrameric enzyme that catalyzes the conversion of phenylalanine to tyrosine, the rate-limiting step of phenylalanine disposal in humans. Primary dysfunction of PAH caused by mutations in the PAH gene results in hyperphenylalaninemia, which may impair cognitive development unless corrected by dietary restriction of phenylalanine. The mechanism(s) by which PAH missense mutations cause enzyme impairment has been studied in detail only in a small number of cases, but existing evidence points to a major role of enhanced proteolytic degradation due to aberrant folding of mutant polypeptides. We have used two heterologous in vitro expression systems (a mammalian cell-free transcription-translation system and the pET system of Escherichia coli) to examine 34 mutations that have been associated with PAH deficiency in the Danish population. These mutations represent a broad range of amino acid substitutions, functional enzyme domains, and metabolic phenotypes. In both systems, residual in vitro activities correlated broadly with metabolic phenotypes, however, with significant discrepancies. Analysis of E. coli extracts by nondenaturing polyacrylamide gel electrophoresis and storage experiments showed that (i) in general, mutations in the N-terminal regulatory domain are associated with relatively stable proteins compared to most mutations in the central catalytic domain, and (ii) for mutations in the catalytic domain, high levels of protein aggregation do not always correspond with a severe phenotype. Our data support and extend previous evidence that PAH mutations exert their pathogenic effects by several distinct mechanisms that may operate individually or in concert.

Identification of barley and rye varieties using matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry with neural networks

Cereal varieties are normally identified using time-consuming methods such as visual examination of either the intact grain or one-dimensional electrophoretic patterns of the grain storage proteins. A fast method for identification of wheat (Triticum aestivum L.) varieties has previously been developed, which combines analysis of alcohol-soluble wheat proteins (gliadins) using matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry with neural networks. Here we have applied the same method for the identification of both barley (Hordeum vulgare L.) and rye (Secale cereale L.) varieties. For barley, 95% of the mass spectra were correctly classified. This is an encouraging result, since in earlier experiments only a grouping into subsets of varieties was possible. However, the method was not useful in the classification of rye, due to the strong similarity between mass spectra of different varieties.

Arabidopsis map kinase 4 negatively regulates systemic acquired resistance

Transposon inactivation of Arabidopsis MAP kinase 4 produced the mpk4 mutant exhibiting constitutive systemic acquired resistance (SAR) including elevated salicylic acid (SA) levels, increased resistance to virulent pathogens, and constitutive pathogenesis-related gene expression shown by Northern and microarray hybridizations. MPK4 kinase activity is required to repress SAR, as an inactive MPK4 form failed to complement mpk4. Analysis of mpk4 expressing the SA hydroxylase NahG and of mpk4/npr1 double mutants indicated that SAR expression in mpk4 is dependent upon elevated SA levels but is independent of NPR1. PDF1.2 and THI2.1 gene induction by jasmonate was blocked in mpk4 expressing NahG, suggesting that MPK4 is required for jasmonic acid-responsive gene expression.

Cardioinhibition during tilt testing identifies patients who may benefit from pacing

This study examined whether the various hemodynamic collapse patterns observed during tilt testing in patients with suspected neurocardiogenic syncope are relevant when planning therapy, particularly whether a predominantly cardioinhibitory response predicts a beneficial response from pacing.

METHODS

The effects of temporary atrioventricular (A-V) sequential pacing were studied during tilt testing in 34 patients 48.2 +/- 18.5 years of age. The patient population was divided into a cardioinhibitory group (VASIS classes 2A and 2B) or mixed group (VASIS classes 1 and 3) according to their response to baseline tilt testing. The test was then repeated during A-V pacing with rate hysteresis. A positive response to A-V pacing was defined as a > or = 30-second increase between onset of symptoms and syncope, or mitigation of symptoms compared with the baseline tilt test.

RESULTS

The study protocol was not successfully completed in three patients. Among the remaining 31 patients, a baseline cardioinhibitory response was observed in 17, and a mixed response in 14 patients. A-V sequential pacing was successful in 13 of 17 patients with a cardioinhibitory response versus 5 of 14 patients with a mixed response (P = 0.024).

CONCLUSION

The presence of a predominantly cardioinhibitory collapse pattern (VASIS 2A and 2B) during baseline tilt testing doubled the likelihood of successful temporary A-V sequential pacing, and may identify patients with neurocardiogenic syncope most likely to benefit from permanent dual chamber pacing.

Low-threshold heat response antagonized by capsazepine in chick sensory neurons, which are capsaicin-insensitive

The heat-transducing receptor VR1 cloned from rat sensory neurons can be activated by both noxious heat and capsaicin. As the response of sensory neurons to capsaicin is species dependent, it is conceivable that the responses to noxious heat and to capsaicin are transduced by distinct receptors across different species. Therefore, we investigated responses to noxious heat from a capsaicin-insensitive (chick) and a capsaicin-sensitive (rat) species. In chick, whole-cell patch-clamp experiments in isolated dorsal root ganglion neurons revealed two populations of neurons with different thresholds to noxious heat, activated at approximately 43 degrees C and approximately 53 degrees C. In cobalt uptake experiments, the proportion of neurons showing a heat-induced response increased with increasing heat stimuli. Application of capsaicin (1-10 microM) did not result in inward currents or cobalt uptake. Rat neurons yielded comparable results in heat experiments, but were capsaicin-sensitive. Although chick neurons are insensitive to capsaicin, the competitive capsaicin antagonist capsazepine (1-10 microM) was effective in blocking heat-induced responses, verified by patch-clamp and cobalt uptake methods. The noncompetitive capsaicin antagonist ruthenium red (10 microM) reduced to almost nil the proportion of heat-responsive neurons identified with the cobalt uptake method. These findings suggest that chick DRG neurons express a low-threshold heat-transducing receptor with a pharmacological profile distinct from the low-threshold heat receptor VR1 cloned from rat DRG neurons. The data support the idea that there might be heat receptor subtypes with differences in the capsaicin binding site.

Arabidopsis ATP A2 peroxidase. Expression and high-resolution structure of a plant peroxidase with implications for lignification

Lignins are phenolic biopolymers synthesized by terrestrial, vascular plants for mechanical support and in response to pathogen attack. Peroxidases have been proposed to catalyse the dehydrogenative polymerization of monolignols into lignins, although no specific isoenzyme has been shown to be involved in lignin biosynthesis. Recently we isolated an extracellular anionic peroxidase, ATP A2, from rapidly lignifying Arabidopsis cell suspension culture and cloned its cDNA. Here we show that the Atp A2 promoter directs GUS reporter gene expression in lignified tissues of transgenic plants. Moreover, an Arabidopsis mutant with increased lignin levels compared to wild type shows increased levels of ATP A2 mRNA and of a mRNA encoding an enzyme upstream in the lignin biosynthetic pathway. The substrate specificity of ATP A2 was analysed by X-ray crystallography and docking of lignin precursors. The structure of ATP A2 was solved to 1.45 A resolution at 100 K. Docking of p-coumaryl, coniferyl and sinapyl alcohol in the substrate binding site of ATP A2 were analysed on the basis of the crystal structure of a horseradish peroxidase C-CN-ferulic acid complex. The analysis indicates that the precursors p-coumaryl and coniferyl alcohols are preferred by ATP A2, while the oxidation of sinapyl alcohol will be sterically hindered in ATP A2 as well as in all other plant peroxidases due to an overlap with the conserved Pro-139. We suggest ATP A2 is involved in a complex regulation of the covalent cross-linking in the plant cell wall.

Structural studies of LNA:RNA duplexes by NMR: conformations and implications for RNase H activity

We have used NMR and CD spectroscopy to study the conformations of modified oligonucleotides (locked nucleic acid, LNA) containing a conformationally restricted nucleotide (T(L)) with a 2'-O,4'-C-methylene bridge. We have investigated two LNA:RNA duplexes, d(CTGAT(L)ATGC):r(GCAUAUCAG) and d(CT(L)GAT(L)AT(L)GC):r(GCAUAUCAG), along with the unmodified DNA:RNA reference duplex. Increases in the melting temperatures of +9.6 degrees C and +8.1 degrees C per modification relative to the unmodified duplex were observed for these two LNA:RNA sequences. The three duplexes all adopt right-handed helix conformations and form normal Watson-Crick base pairs with all the bases in the anti conformation. Sugar conformations were determined from measurements of scalar coupling constants in the sugar rings and distance information derived from 1H-1H NOE measurements; all the sugars in the RNA strands of the three duplexes adopt an N-type conformation (A-type structure), whereas the sugars in the DNA strands change from an equilibrium between S- and N-type conformations in the unmodified duplex towards more of the N-type conformation when modified nucleotides are introduced. The presence of three modified T(L) nucleotides induces drastic conformational shifts of the remaining unmodified nucleotides of the DNA strand, changing all the sugar conformations except those of the terminal sugars to the N type. The CD spectra of the three duplexes confirm the structural changes described above. On the basis of the results reported herein, we suggest that the observed conformational changes can be used to tune LNA:RNA duplexes into substrates for RNase H: Partly modified LNA:RNA duplexes may adopt a duplex structure between the standard A and B types, thereby making the RNA strand amenable to RNase H-mediated degradation.

The siaA gene involved in capsule polysaccharide biosynthesis of Neisseria meningitidis B codes for N-acylglucosamine-6-phosphate 2-epimerase activity

The capsule polysaccharide of Neisseria meningitidis serogroup B is composed of a homopolymer of alpha-2-->8 linked N-acetyl-neuraminic acid (sialic acid). The enzymes required for sialic acid biosynthesis and polymerization are encoded in region A of the capsule gene complex. We here describe the enzymatic activity of the siaA gene product as determined by biochemical analysis. siaA was overexpressed in Escherichia coli and the SiaA protein was purified to homogeneity. Enzymatic assays revealed that SiaA did not accept N-acetyl-glucosamine as substrate, but only N-acetyl-glucosamine-6-phosphate (EC 5.1.3.9). SiaA catalyzes the isomerization of N-acetyl-glucosamine-6-phosphate to form N-acetyl-mannosamine-6-phosphate. This reaction represents the first step in capsule biosynthesis of N. meningitidis B.

High carrier frequency of the 35delG deafness mutation in European populations. Genetic Analysis Consortium of GJB2 35delG

Congenital deafness accounts for about 1 in 1000 infants and approximately 80% of cases are inherited as an autosomal recessive trait. Recently, it has been demonstrated that connexin 26 (GJB2) gene is a major gene for congenital sensorineural deafness. A single mutation (named 35delG) was found in most recessive families and sporadic cases of congenital deafness, among Caucasoids, with relative frequencies ranging from 28% to 63%. We present here the analysis of the 35delG mutation in 3270 random controls from 17 European countries. We have detected a carrier frequency for 35delG of 1 in 35 in southern Europe and 1 in 79 in central and northern Europe. In addition, 35delG was detected in five out of 376 Jewish subjects of different origin, but was absent in other non-European populations. The study suggests either a single origin for 35delG somewhere in Europe or in the Middle East, and the possible presence of a carrier advantage together with a founder effect. The 35delG carrier frequency of 1 in 51 in the overall European population clearly indicates that this genetic alteration is a major mutation for autosomal recessive deafness in Caucasoids. This finding should facilitate diagnosis of congenital deafness and allow early treatment of the affected subjects.