Double heterozygosity with mutations involving both the GJB2 and GJB6 genes is a possible, but very rare, cause of congenital deafness in the Czech population.

Mutations in the GJB2 gene are the most common cause of prelingual, autosomal recessive, sensorineural hearing loss worldwide. Nevertheless, 10% to 50% of patients with prelingual nonsyndromic deafness only carry one mutation in the GJB2 gene. Recently a large 342 kb deletion named Delta(GJB6-D13S1830) involving the GJB6 gene was reported in Spanish and French deafness patients, either in a homozygous state or in combination with a monoallelic GJB2 mutation. No data have been reported about the frequency of this mutation in central Europe. Thirteen Czech patients with prelingual nonsyndromic sensorineural deafness carrying only one pathogenic mutation in the GJB2 gene were tested for the presence of the Delta(GJB6-D13S1830) mutation. One patient with a GJB2 mutation (313del14) also carried the Delta(GJB6-D13S1830). This is the first reported Czech case, and probably also the first central European case, of prelingual deafness due to mutations involving both the GJB2 and GJB6 genes. In addition, the Delta(GJB6-D13S1830) was not detected in 600 control chromosomes from Czech individuals with normal hearing. We show that in the Czech Republic the Delta(GJB6-D13S1830) is not the second most common causal factor in deafness patients heterozygous for a single GJB2 mutation, and that Delta(GJB6-D13S1830) is very rare in central Europe compared to reports from Spain, France and Israel.

Spectrum and frequencies of mutations in the GJB2 (Cx26) gene among 156 Czech patients with pre-lingual deafness.

Mutations in the gene gap junction beta 2 (GJB2), the gene for the connexin 26, are the most common cause of pre-lingual deafness worldwide. The mutation 35delG within GJB2 is prevalent in Europe. To date, there are no data about GJB2 mutation spectrum and frequencies from the Czech population. We investigated and report here the spectrum and frequencies of mutations in the GJB2 gene among 156 unrelated, congenital deafness Czech patients. Allele-specific polymerase chain reaction, together with fluorescent fragment analysis, were used for the detection of the 35delG mutation. The entire coding region of the GJB2 was directly sequenced in all patients who were not homozygous for the 35delG. No pathogenic mutation was detected in 51.9% of patients. At least one pathogenic mutation was found in 48.1% of patients, and both pathogenic mutations were detected in 37.8% of patients. Single mutations in a heterozygous state were detected in 10.3% of patients. The mutation 35delG accounts for 82.8% of detected disease mutations, Trp24stop accounts for 9.7% of pathogenic alleles and was found in patients with gypsy heritage. Mutation 313del14 accounts for 3.7% of pathogenic alleles. The frequency of 35delG heterozygotes in the Czech Republic is 1 : 29.6. Testing for only the three most common mutations would detect over 96% of all pathogenic alleles in the Czech Republic.

The use of a killer factor in the selection of hybrid yeast strains.

A new selection method of yeast cell hybrids, based on the application of yeast killer factors, has been developed in the model system of induced protoplast fusion of Saccharomyces cerevisiae superkiller strain T158C (alpha, his-) and different sensitive strains. The method is comparable in its efficiency to the currently used selection techniques based on the auxotrophy or respiration deficiency of the parental cells. Selection by means of a killer factor, when compared to other methods, has the following advantages: (1) Sensitivity to a killer factor is a current natural property of most of the yeast strains. (2) Killer strains of different species of yeast are available and the killer character can be easily transmitted from strain to strain. (3) Hybrid cells produce a killer factor (K+) and are resistant to it (R+). Both these properties are easily and independently testable. (4) Hybrid cells can be cured of the "killer character" by growth at elevated temperatures. Therefore the killer character can also serve as a temporary marker for the purposes of selection of hybrid cells and can be eliminated when no longer desired. On an example of interspecific fusion of strain T158C of S. cerevisiae and strain P9 of S. uvarum the procedure has been shown to be advantageous particularly for the construction of new industrial yeast strains because mutagenesis of the original industrial strain is not required.