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A family with three children affected with congenital polycystic kidneys, hepatic fibrosis, mental retardation, minor anomalies of the hands, and dysmorphic facial features is reported. All children progressed to chronic renal failure. Linkage to the locus for autosomal recessive polycystic kidney disease was excluded by haplotype analysis. The family is endogamic, and the affected siblings are of both sexes, which is in agreement with an autosomal recessive determination of this syndrome. A similar syndrome was reported in 1990 by Labrune et al. [J Pediatr Gastroenterol Nutr (1990) 10:540-543]. Our report provides further evidence for the etiological heterogeneity of polycystic kidney with hepatic fibrosis. The syndrome reported here should be considered in the differential diagnosis of the early manifestation of polycystic kidneys. Mental retardation and hand anomalies are the hallmarks for the differential diagnosis of this syndrome.

Background: The autosomal recessive Nijmegen breakage syndrome (NBS) is a DNA repair disorder due to a mutation in the NBS1 gene on 8q21. Hyperradiosensitivity and high risk for lymphoreticular malignancy are important reasons for early diagnosis and prevention by avoidance of ionisation. The frequency of NBS heterozygotes of the mutation 657de15, which is predominant in the Slavic population was estimated to be in the range of 1:90-1:314 in different parts of Poland, and 1:128-154 among Czech newborns, born 20 years ago., Methods and Results: Lower prevalence of affected homozygotes born in Czechoslovakia in the period 1969- 1992 (24 among 5.2 million newborns corresponds to 1:271000) than expected on the basis of carrier frequency is explained to be due to underdiagnosing because the rate of prenatal lethality in the NBS families is not increased or it is even lower than in the general population. The underdiagnosing of NBS is emphasized also by the mean age at diagnosis (7.5 years) although severe microcephaly is present at birth. The possibility to offer effective prevention of primary and secondary malignancies becomes the motivation for interdisciplinary collaboration with paediatricians, neurologists, immunologists and clinical geneticists. A decrease of the mean age down to 6 months at diagnosis among the 11 newly recognized patients has been achieved in the previous 4 years. The occurrence of homozygotes was relatively higher in Slovakia with 5 million inhabitants (14 patients in 11 families) than in the Czech Republic with a population of 10 million (21 patients in 14 families), and therefore the frequency of NBS heterozygotes was studied among 2996 newborns born in 2002-2003 in 12 maternity hospitals of west, middle and east Slovakia. Surprisingly, only 3 heterozygotes were found., Conclusions: This discrepancy of heterozygote frequency and the number of homozygotes shows that due to traditional subisolates the population is not in the genetic equilibrium. It explains the high prevalence of alcaptonuria in Slovakia in the middle of last century, which is a rare disorder in other countries.

Genomic imprinting is one of epigenetic factors, which influences expression of genes. It represents specific marking of some chromosome segments depending on the parental origin of the mutation. Imprinted genes are for some time inactive; such period varies in different developmental stage and in different tissues. Such inactivation is manifested as expriming genes and represents an exception to the 3rd Mendel's rule. In the last 10 years, a large group of disorders was recognised, the clinical manifestation of which depends on the parental origin of the mutation, such as Albright's hereditary osteodystrophy, progressive osseous hyperplasia. Curschmann-Steinert myotonic dystrophy, Huntington disease, Beckwith-Wiedemann EMG syndrome, Silver-Russell syndrome, Angelman syndrome, Prader-Willi syndrome. Genomic imprinting contributes to the clarification of mechanisms of the variable expressivity, incomplete penetration, generation anticipation etc.

A novel type of mutation--due to expansion of DNA trinucleotide repeats--has been discovered about 10 years ago. Nowadays 15 genetic syndromes and diseases caused by these mutations are known such as FRA X A syndrome, FRA X E syndrome, Kennedy syndrome spinobulbare muscle atrophy, Curschmann-Steinert syndrome of myotonic dystrophia, Huntington disease, Friedreich ataxia, spinocerebellare ataxias types I., II., III., VI., VII., VIII., XII. and Taylor's oculopharyngeal muscle dystrophy. The mutations of instable trinucleotids represent some exceptions from the regular monogenic transmission such as premutation, genomic imprinting, generation anticipation (acceleration, accentuation), somatic mosaicism. A good understanding of their special properties is necessary for efficient interdisciplinar collaboration of medical teams taking care for these patients and their families.

1) Mosaicism results from the mutation in part of somatic cells after the fertilization, only a few cases occur due to mutation during meiosis. Mosaicism is characterized by genetic or functional difference of two or more cell lines in one individual from one zygote. 2) Phenotypical variety is high and depends on the proportion of cell lines of individual clones. 3) Clinical prognosis of mosaic individuum is better in comparison to the full mutation in all cells. 4) The genetic prognosis of reproduction in relatives of the mosaic individuum is without increased recurrent risk, genetic prognosis of own offspring depends on the moment of mutation occurrence--wheit occurs before day 16 to 20 when gonadal cells are differentiated, it represents high risk of transmission. 5) Diagnosis of mixoploids in some cases requests investigation of different cells (fibroblasts, lymphocytes). 6) Clinical "signal" features of the mosaic are hemihypertrophy, asymmetry, Blaschko lines, pigmentations. 7) Risk of malignant tumor is increased, similarly to other chromosomal aberrations, chromosomal instability or hamartomatoses. 8) Mosaics of gene mutation have usually normal mental development and are manifested by external abnormalities only. 9) Incidence of mosaic phenotypes is high and therefore the diagnosis of mixoploids and gene mosaic is important for the estimation of clinical as well as genetic prognosis.

New high-resolution cytogenetical technique identified an increased number of terminal, interstitial and subtelomeric microdeletion as the etiology of many syndromes of multiple congenital anomalies, mental retardation and facial dysmorphy. A loss of contiguous genes shows a high phenotypical variability and at the same time it is significant for genetic prognosis. 1) Variability of clinical features depends on the size and pathogenetic mechanism of underlying deletion; 2) Dysmorphic face features are of a characteristic type and can be somatoscopically recognized; 3) Heart defects and mental retardation are common features of microdeletion syndromes; 4) New mutations represent the most common etiology of microdeletions; only 1 to 10% of mutations are transmitted from the parental gonadal mosaics, from the balanced translocation or from the same microdeletion in parents; 5) Recurrence risk is low, but it may be as high as 50% in individual cases of inherited mutation; 6) Genetic heterogeneity is high and the responsible genes can be located at different chromosomes (e.g. Di George syndrome due to mutation on 22q or 10q) and can also result from microdeletion or point mutation (in the Shprintzen syndrome 70% represent microdeletion and 30% point mutation at 22q11, in Rubinstein-Taybi syndrome 10% cases result from microdeletions and 90% from point mutations); 7) Population incidence of microdeletions is high (1:4000 to 1:30,000) because their etiologic mechanism is related to the common unequal crossing over; 8) Imprinting plays a role in some cases, e.g. Prader-Willi syndrome results from nullisomy of paternal 15q12 chromosome, Angelman syndrome is related to that of maternal 15q12 chromosome; 9) Prenatal prevention of the high risk familial chromosomal rearrangements is feasible since the 12th gestation week.

Syndromology belongs to diagnostic methods based on the analysis of phenotypic (clinical or anatomical--dysmorphics) features, which occur very often together and have a common etiology (e.g. teratogenic embryopathy, numerical and structural chromosomal aberrations or gene mutations). In the phenotype analysis important appear so-called signal features, which enable to narrow the range of possible disorders for the differential diagnosis of the assumptive diseases.

We refer 55 cases of the chromosomal instability syndromes (SCI), diagnosed in patients of our genetical clinics. Problems of early diagnosis can be documented by a discrepancy between the expected number of patients and their relative advanced age at the time when SCI was ascertained. We have also shown that NBS patients can be diagnosed earlier and the disease sufficiently confirmed on the basis of congenital microcephaly and on the direct detection of 657de15 mutation in NBS1 gene. Genealogical analysis of families with SCI revealed a low risk of prenatal selection of affected homozygotes and high cancer prevalence in relative (in NBS families recognized heterozygotes) at young adult age. Due to severe DNA repair disorder and hyperradiosensitivity of affected homozygotes as well as unaffected heterozygotes, conventional diagnostics and treatment protocols of lymphoreticular malignancies in affected homozygotes are prohibited. The use of Nijmegen treatment protocol improved in our patients dramatically their clinical prognosis, which is documented by 6 NBS patients surviving one or two malignancies. Early diagnose of SCI and information for families and their doctors about consequences of DNA repair disorder and about their hyperradiosensitivity is essential for improving the clinical prognosis of SCI patients.

We report on five independent families with a chromosome instability disorder that earlier had been called the Nijmegen breakage syndrome (NBS). These families, two from the Netherlands and three from Czechoslovakia, had a total of eight patients, five of whom are still alive. The main clinical manifestations were microcephaly, short stature, a "bird-like" face, immunological defects involving both the humoral and cellular system. In four of the five living patients it has been possible to study the chromosomes of cultured lymphocytes. The basic karyotype in these patients were normal, but in 17% to 35% of the metaphases rearrangements were found, preferentially involving chromosomes 7 and/or 14 at the sites 7p13, 7q34, and 14q11. The chromosomes of all five living patients were very sensitive to ionizing radiation. In addition, the DNA synthesis in their cultured lymphocytes and fibroblasts was more resistant to X-rays than in cells from controls. The NBS shares a number of important features with ataxia telangiectasia (AT). Both syndromes are characterized by the occurrence of typical rearrangements of chromosomes 7 and/or 14, cellular and chromosomal hypersensitivity to X-irradiation, radioresistance of DNA replication and immunodeficiency. However, there are also obvious differences: NBS patients have microcephaly but neither ataxia nor telangiectasia, and in contrast to the situation in AT the alpha-fetoprotein level in their serum is normal.

The authors describe on examples from the practice of a genetic clinic seven different genetic syndromes associated with obesity: Laurence-Moon-Biedl, Alström, Weiss, Cohen, Carpenter, Prader-Willi and syndrome of insulin resistance. The autosomal recessive determination of the majority of these syndromes emphasizes their genetic impact with a high risk of repeated occurrence in the family. Visual and hearing defects increase clinical and social importance of these syndromes. When evaluating the genetic prognosis of risk families, the authors consider the possibility of prenatal diagnosis and its forms and the risk of implementation of a preventive method. In some instances obesity is a manifestation of a disorder of insulin receptors.