Poláková H

High Frequency of Alkaptonuria in Slovakia: Evidence for the Appearance of Multiple Mutations in HGO Involving Different Mutational Hot Spots

Alkaptonuria (AKU) is an autosomal recessive disorder caused by the deficiency of homogentisate 1,2 dioxygenase (HGO) activity. AKU shows a very low prevalence (1:100,000-250,000) in most ethnic groups. One notable exception is in Slovakia, where the incidence of AKU rises to 1:19,000. This high incidence is difficult to explain by a classical founder effect, because as many as 10 different AKU mutations have been identified in this relatively small country. We have determined the allelic associations of 11 HGO intragenic polymorphisms for 44 AKU chromosomes from 20 Slovak pedigrees. These data were compared to the HGO haplotype data available in our laboratory for >80 AKU chromosomes from different European and non-European countries. The results show that common European AKU chromosomes have had only a marginal contribution to the Slovak AKU gene pool. Six of the ten Slovak AKU mutations, including the prevalent G152fs, G161R, G270R, and P370fs mutations, most likely originated in Slovakia. Data available for 17 Slovak AKU pedigrees indicate that most of the AKU chromosomes have their origins in a single very small region in the Carpathian mountains, in the northwestern part of the country. Since all six Slovak AKU mutations are associated with HGO mutational hot spots, we suggest that an increased mutation rate at the HGO gene is responsible for the clustering of AKU mutations in such a small geographical region.

Linkage of Autosomal Recessive Primary Congenital Glaucoma to the GLC3A Locus in Roms (Gypsies) from Slovakia

The autosomal recessive form of primary congenital glaucoma (gene symbol GLC3) has been recently mapped to two different loci, GLC3A (at 2p21), and GLC3B (at 1p36), respectively, on families of Turkish and Saudi Arabian provenance. This disorder is known to occur with an extremely high incidence in Roms (Gypsies) in Slovakia. We performed a standard linkage analysis on a sample of 7 Slovak Gypsy families comprising 18 affected members, and found significant linkage with four STR markers from the chromosomal region of 2p21 (D2S1788, D2S1346, D2S2328, and D2S1356), without heterogeneity. This finding demonstrates that in the Rom population of Slovakia, primary congenital glaucoma is due to the locus GLC3A, and consequently, to the mutation(s) in the cytochrome P4501B1 gene, which has been recently identified as the principal cause of the disease. Roms represent the third population, in which the disorder has been mapped to GLC3A.

Rapid detection methods for five HGO gene mutations causing alkaptonuria.

Alkaptonuria (AKU) is an autosomal recessive disorder caused by the deficiency of homogentisate 1,2 dioxygenase (HGO) activity. The disease is characterized by homogentisic aciduria, ochronosis and ochronotic arthritis. AKU shows a very low prevalence (1:250 000), in most ethnic groups. Altogether 43 HGO mutations have been identified in approximately 100 patients. In Slovakia, however, the incidence of this disorder rises up to 1:19 000, and 10 different AKU mutations have been identified in this relatively small country. Here, we report detection methods developed for rapid identification of five HGO mutations. PCR primers were designed enabling detection of mutations IVS5 + 1G→A, R58fs, and V300G by restriction digestion of amplification‐created restriction sites (ACRS). Mutation G152fs is readily identified by heteroduplex analysis, and G161R by amplification refractory mutation system (ARMS) PCR.

GJB2 gene mutations in Slovak hearing-impaired patients of Caucasian origin: spectrum, frequencies and SNP analysis.

To the Editor: In developed countries, due to genetic factors, more than 60% of patients suffer from prelingual, moderate to profound hearing impairment, and more than 70% of hereditary hearing impairment cases are non-syndromic (nonsyndromic hearing impairment, NSHI). Of these, approximately 80% are estimated to be autosomal recessive, with 22 recessive genes identified so far (http://webhost.ua.ac.be/hhh/). Among them, most causative mutations are in the gene GJB2 (1). This gene is located at 13q12 and belongs to the connexin gene family. Connexin genes are simple in organization, composed of two exons. The first exon encodes the 50-untranslated region, while the second exon encodes the complete open reading frame and the 30-untranslated region. This makes connexin genes relatively easy targets for screening of mutations by direct sequencing. Thus far, more than 100 different NSHIcausing mutations and 24 polymorphic variants have been identified worldwide within the GJB2 gene (http://davinci.crg.es/deafness/). Although the majority of mutations are recessive, some of them are dominant [W44C (2); R75W (3)]. As it is the case in many recessive disorders, the mutational spectra often vary at this locus between different populations, with a single mutation being sometimes prevalent and thus specific for a particular population. In Caucasians, the 35delG mutation accounts for up to 85% of the GJB2 mutant alleles (4–6). However, it is less frequent in populations of non-European origin, where other GJB2 mutations prevail. Thus, the mutation 235delC is prevalent in Koreans (7), Japanese (8), Chinese (9) and Taiwanese (10); 167delT prevails in Ashkenazi Jews (11), R143W in Africans (12, 13) and W24X in NSHI patients of Indian origin (14–16). The exact frequency of congenital hearing impairment or deafness in the Slovak population is unknown, but it is estimated to be approximately 3–4 in 1000 newborns with impaired hearing and 1 in 1000 with deafness (personal communication with Dr Zuzana Kabatova, First Department of Otolaryngology, Comenius University Faculty of Medicine). This study is aimed to determine the spectrum and frequencies of GBJ2 gene (coding region) mutations in Slovak NSHI patients of Caucasian origin.

Identification of 11 Novel Homogentisate 1,2 Dioxygenase Variants in Alkaptonuria Patients and Establishment of a Novel LOVD-Based HGD Mutation Database

Enzymatic loss in alkaptonuria (AKU), an autosomal recessive disorder, is caused by mutations in the homogentisate 1,2 dioxygenase (HGD) gene, which decrease or completely inactivate the function of the HGD protein to metabolize homogentisic acid (HGA). AKU shows a very low prevalence (1:100,000-250,000) in most ethnic groups, but there are countries with much higher incidence, such as Slovakia and the Dominican Republic. In this work, we report 11 novel HGD mutations identified during analysis of 36 AKU patients and 41 family members from 27 families originating from 9 different countries, mainly from Slovakia and France. In Slovak patients, we identified two additional mutations, thus a total number of HGD mutations identified in this small country is 12. In order to record AKU-causing mutations and variants of the HGD gene, we have created a HGD mutation database that is open for future submissions and is available online ( http://hgddatabase.cvtisr.sk/ ). It is founded on the Leiden Open (source) Variation Database (LOVD) system and includes data from the original AKU database ( http://www.alkaptonuria.cib.csic.es ) and also all so far reported variants and AKU patients. Where available, HGD-haplotypes associated with the mutations are also presented. Currently, this database contains 148 unique variants, of which 115 are reported pathogenic mutations. It provides a valuable tool for information exchange in AKU research and care fields and certainly presents a useful data source for genotype-phenotype correlations and also for future clinical trials.

PKU in Slovakia: mutation screening and haplotype analysis

The restriction fragment length polymorphism haplotypes and seven common mutations in the phenylalanine hydroxylase gene were analysed in 49 unrelated Slovak phenylketonuria (PKU) families of Caucasian origin. The predominant mutation in this population sample is R408W, with a frequency of 45.9%. In addition, four other mutations have been identified at relatively high frequencies: IVS12nt1, 10.2%; R158Q, 7.1%; R261Q, 7.1%; R252W, 2.0%. The mutation-haplotype associations correspond to those described in other European populations. The high proportion of mutations (72.4%) amenable to simple rapid detection based on the polymerase chain reaction provides a good basis for direct DNA-diagnosis of PKU in the Slovak population.

Comprehensive genetic study of cystic fibrosis in Slovak patients in 25 years of genetic diagnostics

Cystic fibrosis (CF) has one of the longest histories in hereditary disease molecular diagnostics. However, identification of causative mutations in the CFTR gene is complicated by over 2000 currently identified mutations; with more still being discovered. Knowledge of mutation spectrum may improve effective routine diagnostics and is obligatory in mutation‐specific treatment.

Study of the effect of DNA polymorphisms in the mannose-binding lectin gene (MBL2) on disease severity in Slovak cystic fibrosis patients.

Lung infections are the leading cause of morbidity and mortality in cystic fibrosis (CF). Mannose-binding lectin (MBL) is a key factor in innate immunity. We therefore investigated whether MBL2 gene variants are associated with pulmonary function or susceptibility to Pseudomonas aeruginosa and Burkholderia cepacia infection in Slovak patients affected with CF. DNA polymorphisms in exon 1 and the promoter region were typed by single base primer extension assay in 91 patients and 100 healthy controls. The concentrations of MBL protein were determined in 34 patients by a sandwich enzyme-linked immunosorbent assay, and spirometric and microbiological data were collected from medical records. In this study we found that MBL2 genotypes were associated neither with earlier acquisition of P. aeruginosa or B. cepacia nor with reduced pulmonary function among patients. Although MBL2 genotypes were associated with the MBL2 protein serum level, results were statistically significant only for polymorphisms in exon 1, with p = 0.0008. The role of the MBL2 gene in lung disease severity in CF patients represents a very complex phenomenon where both genetic and environmental factors play an important role in addition to that of the MBL2 gene. Understanding this complexity requires further studies based on a broader scale of genetic factors involving both a whole-genome approach and a larger patient cohort.