Comparison of mtDNA haplogroups in Hungarians with four other European populations: a small incidence of descents with Asian origin.

Hungarians are unique among the other European populations because according to history, the ancient Magyars had come from the eastern side of the Ural Mountains and settled down in the Carpathian basin in the 9th century AD. Since variations in the human mitochondrial genome (mtDNA) are routinely used to infer the histories of different populations, we examined the distribution of restriction fragment length polymorphism (RFLP) sites of the mtDNA in apparently healthy, unrelated Hungarian subjects in order to collect data on the genetic origin of the Hungarian population. Among the 55 samples analyzed, the large majority belonged to haplogroups common in other European populations, however, three samples fulfilled the requirements of haplogroup M. Since haplogroup M is classified as a haplogroup characteristic mainly for Asian populations, the presence of haplogroup M found in approximately 5% of the total suggests that an Asian matrilineal ancestry, even if in a small incidence, can be detected among modern Hungarians.

[Indirect genotype analysis as a diagnostic procedure in Marfan syndrome]. / Die indirekte Genotypanalyse als diagnostisches Verfahren beim Marfan-Syndrom.

Marfan syndrome (MFS) is an autosomal dominant disorder of connective tissue characterized by skeletal, ocular and cardiovascular manifestations. The disease is caused by mutations in the FBN1 gene, encoding fibrillin, an important component of elastic fibers. Diagnosis of Marfan syndrome is currently based on detailed clinical examination and/or mutation analysis in the fibrillin gene. Clinical expression varies widely both among and within families, rendering clinical diagnosis extremely difficult. In this study, we performed segregation analysis of allelic DNA polymorphisms to support diagnosis of Marfan syndrome. This type of genotype analysis is a useful, additional diagnostic tool for families with Marfan syndrome and provides incremental information of diagnosis or exclusion of Marfan syndrome based on clinical findings.

Genetics and phenotypes of RPE65 mutations in inherited retinal degeneration.

PURPOSE: To characterize the spectrum of RPE65 mutations present in 453 patients with retinal dystrophy with an interest in understanding the range of functional deficits attributable to sequence variants in this gene. METHODS: The 14 exons of RPE65 were amplified by polymerase chain reaction (PCR) from patients' DNA and analyzed for sequence changes by single-strand conformation polymorphism (SSCP) and direct sequencing. Haplotype analysis was performed using RPE65 intragenic polymorphisms. Patients were examined clinically and with visual function tests. RESULTS: Twenty-one different disease-associated DNA sequence changes predicting missense or nonsense point mutations, insertions, deletions, and splice site defects in RPE65 were identified in 20 patients in homozygous or compound heterozygous form. In one patient, paternal uniparental isodisomy (UPD) of chromosome 1 resulted in homozygosity for a probable functional null allele. Eight of the disease-associated mutations (Y79H, E95Q, E102X, D167Y, 669delCA, IVS7+4a-->g, G436V, and G528V) and one mutation likely to be associated with disease (IVS6+5g-->a) have not been reported previously. The most commonly occurring sequence variant identified in the patients studied was the IVS1+5g-->a mutation, accounting for 9 of 40 (22.5%) total disease alleles. This splice site mutation, as well as R91W, the most common missense mutation, exists on at least two different genetic backgrounds. The phenotype resulting from RPE65 mutations appears to be relatively uniform and independent of mutation class, suggesting that most missense mutations (15 of 40 disease alleles [37.5%]) result in loss of function. At young ages, this group of patients has somewhat better subjective visual capacity than is typically associated with Leber congenital amaurosis (LCA) type I, with a number of patients retaining some useful visual function beyond the second decade of life. CONCLUSIONS: RPE65 mutations account for a significant percentage (11.4%) of disease alleles in patients with early-onset retinal degeneration. The identification and characterization of patients with RPE65 mutations is likely to represent an important resource for future trials of rational therapies for retinal degeneration.

Early-onset severe rod-cone dystrophy in young children with RPE65 mutations.

PURPOSE: To describe the ocular phenotype of patients with RPE65 mutations in infancy and young childhood. METHODS: Four children from three families with severe early-onset visual impairment related to electrophysiologically detectable retinal dystrophy were screened for mutations in the RPE65 gene. Visual function from infancy to the age of 10 years was assessed with age-adapted methods. Clinical examinations and electroretinograms (ERGs) were also performed on the six parents. RESULTS: In all three families, patients were compound heterozygous for mutations of the RPE65 gene (ins144T/IVS1+5G-->A, R91W/Y368H, 1114delA+T457N/IVS1+5G-->A). Visual acuity was measurable in all patients at the age of 6 to 10 years, despite severe visual impairment noted during infancy and congenital nystagmus in three of the four patients. Photophobia was not a feature. Funduscopic changes were discrete, the most prominent finding being increased granularity in the macula and the periphery. Peripheral vision was well preserved, measured by Goldmann perimetry. Rod ERGs were not recordable, whereas cone ERGs were detectable in early childhood. All features taken together suggest a specific form of Leber congenital amaurosis (LCA) distinguishable on clinical grounds. ERGs were normal in five of the six parents. One father had an ERG compatible with congenital stationary night blindness unrelated to his heterozygous state for the RPE65 mutation. CONCLUSIONS: RPE65 mutations on both alleles may be associated with early-onset severe rod-cone dystrophy. Visual functions of the four patients were better than is usually seen in LCA, in particular in cases associated with retGC1 mutations. RPE65 mutations should be suspected in infants who appear to be blind in dim surroundings but react to objects in bright illumination and have nonrecordable rod ERGs and residual cone ERGs.

Distribution of Q188R and N314D mutations in the Hungarian galactosemic population.

The most common causes of galactosemia are mutations of the gene coding galactose-1-phosphate uridyltransferase. Since genotype may correlate with the outcome of the disease, and probably not all of the naturally occurring disease associated mutations are described, characterization of the genotypes in different galactosemic populations are in progress. So far the most extensively examined mutations are the Q188R and the N314D. The first one is associated with the classical galactosemia producing a severe clinical picture with an early onset in homozygous patients. The N314D mutation is associated with the Duarte phenotype, which means a milder form of the disease with a later onset of the symptoms. We studied these mutations in the whole Hungarian galactosemic population by PCR and restriction analysis. We have found the frequency of the Q188R mutation at 33.3%, and the N314D mutation at 11.1%. These results differ from other published data in any other populations. Since the incidence of the disease is the same in Hungary as in other European countries, our study suggests that it is worth to investigate for other mutations in the Hungarian population, of which frequency should be consequently higher.

Trinucleotide repeat polymorphism at five disease loci in mixed Hungarian population.

In apparently healthy, unrelated Hungarians we examined triplet repeat length polymorphism at Huntington disease (HD), spinal and bulbar muscular atrophy (SBMA), spinocerebellar ataxia type 1 (SCA-1), dentatorubral-pallidoluysian atrophy (DRPLA), and myotonic dystrophy (MD) loci. The distribution of alleles of the SCA-1 locus was markedly different compared with Asians and Caucasian samples examined by Watkins WS, Bamshad M, and Jorde LB [1995: Hum Mol Genet 4:1485-1491]. The unimodal distribution of peaks was shifted towards the shorter repeats on the average with 4-5 repeats. Alleles under 21 repeats at the SBMA locus were significantly less frequent in Hungarians than in Asians and Caucasians. We also found significant difference in the distribution of DRPLA allele size at repeat length over 15 repeats; these alleles were less frequent in Hungarians compared with Asians and Caucasians. No significant differences were found in alleles at the MD and also at the HD loci compared with the other groups. These findings suggest that these trinucleotide sites in combination with other markers are particularly useful for determination of the genetic origin of a population, if they can be compared with similar subset of data of other populations. The present results could not confirm the large genetic distance between Hungarian and Oriental races and the relatively short distance between Hungarian and other European populations suggested in earlier reports [Czeizel A, Benkmann H-G, Goedde HW, editors. 1991: Genetics of the Hungarian population. Budapest: Akadémiai Kiadó. p 82-334].

Deletion patterns of dystrophin gene in Hungarian patients with Duchenne/Becker muscular dystrophies.

Deletion pattern analysis of the dystrophin gene was performed in 159 Hungarian patients with Duchenne/Becker muscular dystrophy. In 116 cases (73% of total patients), exon deletions were detected by PCR amplification. In 37 patients (31.9% of patients with a deletion) one exon was deleted, while five or more exons were missing in 40 children (34.4%). With respect to the proximal-distal distribution of the deletions, 90 children (77.6%) had deletions exclusively at the 3' end of the gene, 21 deletions (18.1%) affected only the 5' end, and in five patients (4.3%) large-scale deletions were detected, which affected both regions. Analysis of the breakpoint distribution pattern in the dystrophin gene showed that, similarly to that observed in several Western European populations, intron 44 was involved most frequently (n = 35, 15.1%) as a starting breakpoint. In the Hungarian population introns 50 and 52 were the second (n = 30, 12.9%) and third (n = 29, 12.5%) most frequently observed hot spots at the 3' end; these seem to be characteristic for the Hungarian patients. At the 5' end the breakpoint peak (n = 6, 2.58%) was in intron two. As it was proposed by previous national studies, our findings also suggest that certain intronic sequences, characteristic for a population, probably determine the development of a preferential breakpoint profile in this disease.