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Skeletal ciliopathies are a heterogeneous group of autosomal recessive osteochondrodysplasias caused by defects in formation, maintenance and function of the primary cilium. Mutations in the underlying genes affect the molecular motors, intraflagellar transport complexes (IFT), or the basal body. The more severe phenotypes are caused by defects of genes of the dynein-2 complex, where mutations in DYNC2H1, WDR34 and WDR60 have been identified. In a patient with a Jeune-like phenotype we performed exome sequencing and identified compound heterozygous missense and nonsense mutations in DYNC2LI1 segregating with the phenotype. DYNC2LI1 is ubiquitously expressed and interacts with DYNC2H1 to form the dynein-2 complex important for retrograde IFT. Using DYNC2LI1 siRNA knockdown in fibroblasts we identified a significantly reduced cilia length proposed to affect cilia function. In addition, depletion of DYNC2LI1 induced altered cilia morphology with broadened ciliary tips and accumulation of IFT-B complex proteins in accordance with retrograde IFT defects. Our results expand the clinical spectrum of ciliopathies caused by defects of the dynein-2 complex.

Background: Increased frequency of chromosomal aberration in children of mothers aged 35 years and older is very well known and since 1973 it is an indication to investigate the foetal karyotype in cells obtained by invasive method (amniocentesis), because the genetic risk of severe affection is higher than the risk of necessary invasive method. Mutagenic effect of advanced paternal age is known only among geneticists (1-4). The reason is not only low absolute risk of new mutation but particularly a high number of involved genes and last not least the limited spectrum of autosomal dominant disorders without abiotrofic character. Therefore the preventive methods for elimination of this risk are very limited. Only a few of them could be recognized prenatally by noninvasive methods of prenatal diagnostics., Methods: Genealogical, anamnestic and clinical data of 83 patients were studied with clinical suspection on neurocardiofaciocutaneous syndrome (NCFCs) (5-7). The diagnosis has not been confirmed in 29 patients, no mutation was detected in 8 investigated genes (PTPN11, SOS1, HRAS, BRAF, RAF1, MEK1, KRAS, NRAS). In 54 patients with autosomal dominant inherited Noonan syndrome, Costello syndrome and cardiofaciocutaneous syndrome the diagnosis was confirmed on DNA level and the biological fitness was estimated for each disorder. Paternal age at conception was compared in the group of patients with familial and sporadic occurrence of Noonan and NCFC syndromes. The clinical prognosis of this disorder is represented by biological fitness of patients. Coefficient of selection is 0,6 in Noonan and LEOPARD syndromes (29 from 48). All 6 patients with Costello and cardiofaciocutaneous syndromes developed due to a new mutation., Conclusion: Paternal age at birth was studied in 83 children patients with autosomal dominant Neurocardiofaciocutaneous syndrome (Noonan, LEOPARD, Costello, CFC) with a high population incidence and decreased biological fitness. Due to severe congenital heart defects, failure to thrive in infancy, increased risk for malignancy and further health problems the clinical prognosis of patients in the past was not good. Therefore high mutation rate is expected until now. Identification of genes responsible for manifestation of this disorder, enables to confirm the diagnosis and to recognize inherited and de novo mutations. Genealogy and DNA analysis of PTPN11, SOS1, HRAS, BRAF, RAF1, MEK1, KRAS and NRAS were obtained in cohort of 54 patients with NCFC syndromes and their parents. There were 48 patients with Noonan and LEOPARD syndromes, in 29 cases due to mutation de novo, 19 patients inherited the mutation from one of parents. All 6 patients with Costello syndrome and CFC syndrome were affected due to new mutation. DNA analysis revealed 32 mutations in PTPN11 gene, mutation in SOS1 gene was found in 10 patients, RAF1 mutation was present in 3 patients; mutation in MEK1, KRAS and NRAS genes was present in one patient each. In Costello syndrome and CFC syndrome mutations in HRAS (4 patients) and BRAF (2 patients) genes were detected. Genealogic data allow analysing parental age in the group of patients with new mutation and inherited mutation. Paternal age at conception of patients with Noonan syndrome due to new mutation was significantly increased in comparison to the group of fathers of Noonan patients with inherited mutation - 38,4 years and 29,6 years, resp., range 28 to 55 years and 25 to 35 years, resp. Maternal age was slightly increased too, -30,9 and 27,7, resp. and range 24 to 42 years and 21 to 36 years, resp. but not significantly. The results support the mutagenic effect of paternal age, espec. autosomal dominant mutations.

Background: Nijmegen breakage syndrome (NBS) is one of the chromosomal instability syndromes due to DNA repair disorder. The syndrome is autosomal recessive determined, in homozygotes is characterized by many disorders including high predisposition to lymphoreticular malignancy in childhood and adolescence., Methods: Laboratory findings represent low level of immunoglobulins, B and T lymphocytes, increased sensitivity to the mutagens, especially hyperradiosensitivity and increased chromosomal instability. Heterozygotes show also elevated radiosensitivity and have an increased cancer risk in adult age. There is no predilection of the malignancy. Colorectal cancer was found often among the relatives of patients with NBS. Majority of the NBS patients are of the Central and Eastern European origin and carry the common founder mutation 657del5 in the NBN gene. The formation of second malignancy both in homozygotes and heterozygotes can be prevented by excluding any radiation. The aim of study is estimation of frequency of 657del5 heterozygotes among patients with colorectal cancer., Results and Conclusions: Within a group of 161 patients with colorectal cancer 5 heterozygotes with 657del5 mutation were registered, e.g. 5-times higher incidence than expected. The elemental prevention in patients with proved positivity of Slavic mutation in NBN gene is to exclude any radiation.

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 chromosomal instability disorder Nijmegen breakage syndrome (NBS) is associated with increased risk of lymphoid malignancies and other cancers. Cells from NBS patients contain many double-stranded DNA breaks. More than 90% of NBS patients are homozygous for a founder mutation, 657del5, in the NBN gene. We investigated the 657del5 carrier status of cancer patients among blood relatives (i.e., first-, through fourth-degree relatives) of NBS patients in the Czech Republic and Slovakia to test the hypothesis that NBN heterozygotes have an increased cancer risk., Methods: Medical information was compiled from 344 blood relatives of NBS patients in 24 different NBS families from January 1, 1998, through December 31, 2003. The 657del5 carrier status of subjects was unknown at the time of their recruitment but was later determined from blood samples collected at the time of the interview. Medical records and death certificates were used to confirm a diagnosis of cancer. For the relatives with cancer who are not obligate heterozygotes (such as parents and two grandparents in consanguineous families), the observed and expected number of mutation carriers were compared by use of the index-test method, which estimated the risk of cancer associated with carrying the mutation. All P values were two-sided., Results: Thirteen of the 344 blood relatives had confirmed cases of any type of cancer; 11 of these 13 cancer patients carried the NBN 657del5 mutation, compared with 6.0 expected (P = .005). Among the 56 grandparents with complete data from 14 NBS families, 10 of the 28 carriers of 657del5, but only one of the 28 noncarriers, developed cancer (odds ratio = 10.7, 95% CI = 1.4 to 81.5; P<.004)., Conclusions: The NBN 657del5 mutation appears to be associated with an elevated risk of cancer in heterozygotes.

Rubinstein-Taybi syndrome (RSTS) is a well-known autosomal dominant mental retardation syndrome with typical facial and skeletal abnormalities. Previously, we have reported two patients presenting with RSTS and additional clinical features including failure to thrive, seizures, and intractable infections (Bartsch et al. in Eur J Hum Genet 7:748-756, 1999). Recently we identified a third patient with this condition, termed here severe RSTS, or chromosome 16p13.3 deletion syndrome. The three patients died in infancy, and all displayed a specific mutation, a chromosomal microdeletion including the 3'-end of the CREBBP gene. Using fluorescence in situ hybridization and closely spaced DNA probes, we characterized the deletion intervals in these patients and in three individuals with a deletion of CREBBP and typical RSTS. The deleted DNA segments were found to greatly vary in size, spanning from approximately 40 kb to >3 Mb. Four individuals, including the patients with severe RSTS, exhibited deletions containing gene/s in addition to CREBBP. The patients with severe RSTS all had deletions comprising telomeric neighbor genes of CREBBP, including DNASE1, a dominant gene encoding a nuclease that has been associated with systemic lupus erythematodes. Our findings suggest that severe RSTS is distinct from RSTS and represents a novel true contiguous gene syndrome (chromosome 16p13.3 deletion syndrome). Because of the risk of critical infections and high mortality rate, we recommend that the size of the deletion interval should be determined in CREBBP deletion-positive patients with RSTS, especially in young children. Further studies are needed to delineate the clinical spectrum of the new disorder and to clarify the role of DNASE1.

Nijmegen breakage syndrome (NBS) patients and carriers are predisposed to malignancy and are often treated with X-irradiation. In the present study, the single-cell gel electrophoresis (Comet) assay was used to examine radiation-induced DNA damage and repair in peripheral blood mononuclear cells from NBS patients (n=13) and carriers (n=36) of six unrelated families. Cells from apparently healthy donors (n=10) and from breast cancer patients with normal clinical radiosensitivity (n=10) served as controls. Cells were irradiated with 5 Gy of X-rays and assayed for initial DNA damage and for residual DNA damage after 40 min of repair; the kinetics of DNA repair also was estimated. In addition, the nuclear area of unirradiated cells was extracted from the Comet data. The initial radiation-induced DNA fragmentation indicated that cells from members of two out of six NBS families were significantly more sensitive to X-irradiation than cells from the controls. Cells from four NBS families had longer DNA repair half-time values, while cells from five NBS families had significantly increased residual DNA damage following repair. The mean nuclear area of unirradiated cells processed in the Comet assay was 1.3-fold higher in cells from all NBS families than in the controls (P<0.05). Notably, the Comet assay parameters (initial and residual DNA damage and the repair kinetics) of irradiated NBS cells predicted the carrier status of the majority (86%) of blindly tested individuals. The prediction of NBS status was higher if the nuclear area of unirradiated cells was used as the endpoint. The results of this study suggest that the impaired radiation response of NBS cells should be taken into account if radiotherapy of NBS patients and carriers is required., (Copyright (c) 2006 Wiley-Liss, Inc.)

Background: The autosomal recessive chromosomal instability and hyperradiosensitivity Nijmegen breakage syndrome (NBS) in consequence of a mutation in the NBSI gene at 8q21 is associated with high occurrence of lymphoreticular malignancies due to deficient DNA reparation (double strand breaks). In the Slavic population the majority of patients are homozygotes of the so-called "Slavic mutation" 657de15 in exon 6. Increased occurrence of malignant solid tumors (1) in families of NBS patients has been described already prior to the identification of the responsible gene, and the increased risk of malignancies in heterozygotes was thus hypothetical., Methods and Results: The possibility of discerning mutation carriers in families from normal homozygotes enables verification of that hypothesis. Through molecular genetics investigations of grandparents and immediate relatives, we have been successful in determining the genotype in 79 of 112 grandparents in 28 families of our 39 patients and 54 their parents and siblings. A single family had affected children in consequence of compound heterozygosity of the 657de15 and R215W mutations in the same exon of the NBSI gene. The proband's families were investigated genealogically and data on relatives were obtained over four generations. Obtained data were repeatedly supplemented and objectively verified in church books and in healthcare documentation. Seven families have been followed up for 20-30 years, six families for 10-20 years, and 15 families for 1-10 years. Out of 28 families we were successful in examining the genotype of both grandparents in 18 families, there having been revealed one non-paternity; in five families only one of the grandparents has been examined; in five families we were not successful in examining any grandparent. Among 40 grandparents - normal homozygotes, there has appeared a malignancy in three (7.4 %), while among 39 heterozygotes of mutation 657de15 in the NBSI gene malignancies were documented in 15 (38,2 %). Mean age of NBS heterozygotes at manifestation of malignancy was 59.3 year (range 47-72 years), in the group of homozygotes it was 52.6 years (range 44-62 years). Nine grandparents died of malignancy prior to the discovery of the NBSI gene and their genotype has been deduced genealogically in seven on the basis of the genotype in the sponse and children, in two from preserved DNA. Out of that number, from three grandparents that had died of malignancies we were successful in obtaining neoplastic tissue for molecular genetics investigation, aimed at LOH or amplification of the NBS1 gene. In another seven grandparents - heterozygotes, malignancies were manifested after determination of their genotype by DNA analysis, and consequently also from tumor tissue that has been obtained from three of them for molecular genetic investigation., Conclusions: The age distribution and socio-economic status of both groups of grandparents did not differ, the sex ratio was slightly shifted towards females in the group of homozygotic grandparents (22 females and 18 males), and in the group of heterozygotes it was towards males (21 males and 18 females). The sex ratio between heterozygotic grandparents with malignancies was likewise shifted towards the male gender (11 males and 4 females), in the group of homozygotic grandparents malignancy affected one male and two females. As verified in healthcare and church books documentation, the occurrence of malignancies was significantly more frequent among grandparents heterozygotic for NBS1 mutation than in healthy homozygotes. Among sibs of grandparents and great-grandparents was found significant difference in frequency of malignancies in heterozygotes (5/18 = 27,7 %) and healthy homozygotes (2/36 = 5,5 %), too.

Background: Mutations 657del5 and R215W in exon 6 of tumor suppressor gene NBS I are found in 1% Slavic populations. Increased occurrence of cancer was repeatedly reported in adult relatives of patients with Nijmegen breakage syndrome. Among children with oncological problematic, nonsignificantly increased frequency of NBS1 heterozygotes was found, which seems not to play any important role in cancerogenesis in childhood. However, the proportion of NBS heterozygotes among adult patients with malignancies could be significant and their therapy and follow up should respect their hyperradiosensitivity., Methods and Results: Mutations in exon were studied in 706 adult patients with malignancies. We found 5 NBS heterozygotes, which not more than the population prevalence (1:129-165). Increased frequency of NBS heterozygotes was found among patients with colon and rectal cancer (2/101), breast cancer (1/60), skin malignancies (1/98)., Conclusions: Surprisingly only one NBS heterozygote was found among 228 patients with nonHodgkin lymphoma, the malignancy which is a common complication in NBS homozygotes. Other types of malignancies were uncommon and only one R215W heterozygote was found. Comparison frequency of NBS heterozygotes with incidence NBS among person older than 70 years shows significant difference. Prevention of malignancies by avoidance from ionisation could be realized also in relatives of patients after identification of their genotype.

Rubinstein-Taybi syndrome (RSTS) is a distinct dominant disorder characterized by short stature, typical face, broad angulated thumbs and halluces, and mental retardation. The RSTS can be caused by chromosomal microdeletions and molecular mutations in the CREBBP gene; however, relatively few mutations have been reported to date. Here, we aimed to determine the rate of point mutations and other small molecular lesions in true RSTS and possible mild variants, by using genomic DNA sequencing. A consecutive series of patients including 17 patients from our previous study was investigated. We identified 19 causative mutations of CREBBP in a total of 45 patients representing three different diagnostic groups: (a) 17 mutations in 30 patients with unequivocal RSTS (detection rate 56.6%), (b) two mutations in eight patients with features suggestive of RSTS ("moderate or incomplete RSTS", detection rate 25%), and (c) no mutation in seven patients with undiagnosed syndromes and isolated features of RSTS. In general, the mutations were distributed without hot spots and most were unique; however, three recurrent mutations (R370X, R1664H, and N1978S) were identified. Furthermore, we detected 15 different intragenic polymorphisms, including two non-synonymous coding polymorphisms, L551I and Q2208H. We report not only the highest detection rate (56.6%) of CREBBP mutations in patients with RSTS to date, but also the second missense mutation (N1978S) in a patient with moderate or incomplete RSTS. Previous studies have identified cytogenetic deletions in the CREBBP gene in eight to 12% of patients and very recently, Roelfsema et al. reported EP300 gene mutations in three of 92 (3.3%) patients with either true RSTS or different syndromes resembling RSTS. Our 56.6% detection rate of molecular mutations in CREBBP in patients with unequivocal RSTS supports the new concept that RSTS is a genetically heterogeneous disorder and furthermore, indicates that RSTS may be caused by gene/s other than CREBBP in up to 30% of cases.

While growth retardation and short stature are well-known features of patients with classical neurofibromatosis type 1 (NF1), we found advanced height growth and accelerated carpal bone age in patients with an NF1 microdeletion. Our analysis is based on growth data of 21 patients with common 1.4/1.2 Mb microdeletions, including three patients with a Weaver-like appearance. Overgrowth was most evident in preschool children (2-6 years, n=10, P=0.02). We conclude that childhood overgrowth is part of the phenotypic spectrum in patients with the common 1.4/1.2 Mb NF1 microdeletions and assume that the chromosomal region comprised by the microdeletions contains a gene whose haploinsufficiency causes overgrowth.

The Nijmegen breakage syndrome is a rare autosomal recessive chromosomal instability disorder characterized by early growth retardation, congenital microcephaly, immunodeficiency, borderline mental development, and a high tendency to lymphoreticular malignancies. Most Nijmegen breakage syndrome patients are of Slavonic origin, and all of them known so far carry a founder homozygous 5 nucleotide deletion in the NBS1 gene. Microcephaly was present in 100% of Nijmegen breakage syndrome patients in a recent large international cooperative study. The frequency of Nijmegen breakage syndrome among children with primary microcephaly was not known. Early correct diagnosis of the syndrome is crucial for appropriate preventive care and therapy. We tested 67 Czech patients of different ages with simple microcephaly for the presence of the most common mutation in the NBS1 gene. Three new Nijmegen breakage syndrome cases were detected in this cohort, representing 4.5% of the cohort. All these newly diagnosed Nijmegen breakage syndrome patients were younger than 10 months at the time of diagnosis. They were all born within a 2.5-year period. Twenty-three of the 67 children in the cohort were born within this 2.5-year period, representing a 13% incidence of Nijmegen breakage syndrome. Frequency of Nijmegen breakage syndrome heterozygotes among infants in the Czech Republic is 1: 130-158 and the birth rate is 90,000 per year, therefore in the time span of 2.5 years, three new Nijmegen breakage syndrome homozygotes are expected to be born. Therefore we assume that by DNA testing of Czech primary microcephalic children it is possible to detect all Nijmegen breakage syndrome patients to be expected. The age at correct diagnosis was lowered from 7.1 years at the time before DNA testing, to well under 1 year of age. All new Nijmegen breakage syndrome patients could receive appropriate preventive care, which should significantly improve their life expectancy and prognosis.

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.

Mulibrey nanism (for muscle-liver-brain-eye nanism, MUL; MIM 253250) is an autosomal recessive disorder that involves several tissues of mesodermal origin, implying a defect in a highly pleiotropic gene. Characteristic features include severe growth failure of prenatal onset and constrictive pericardium with consequent hepatomegaly. In addition, muscle hypotonia, J-shaped sella turcica, yellowish dots in the ocular fundi, typical dysmorphic features and hypoplasia of various endocrine glands causing hormonal deficiency are common. About 4% of MUL patients develop Wilms' tumour. MUL is enriched in the Finnish population, but is rare elsewhere. We previously assigned MUL to chromosome 17q22-q23 and constructed a physical contig over the critical MUL region. The region has now been further refined by haplotype analysis and new positional candidate genes have been localized. We identified a gene with four independent MUL-associated mutations that all cause a frameshift and predict a truncated protein. MUL is ubiquitously expressed and encodes a new member of the RING-B-box-Coiled-coil (RBCC) family of zinc-finger proteins, whose members are involved in diverse cellular functions such as developmental patterning and oncogenesis.

Female phenotype, sexual infantilism, small stature and stigmatization are typical for patients with Turner's syndrome (TS). The most frequent cardiovascular manifestations in these patients are a bicuspidal aortal valve and coarctation of the aorta. In 5% patients dilatation of the aorta is found which can develop into a dissecting aneurysm. In the submitted case-history the authors describe a 34-year-old patient where the diagnosis of TS was proved only in adult age at the time when a dissecting aneurysm of the aorta was detected. The submitted case-history supports the recommendation of regular echocardiographic check-up examinations of patients with TS.

Nijmegen breakage syndrome (NBS) is an autosomal recessive chromosomal instability syndrome characterized by microcephaly, growth retardation, immunodeficiency, and cancer predisposition. Cells from NBS patients are hypersensitive to ionizing radiation with cytogenetic features indistinguishable from ataxia telangiectasia. We describe the positional cloning of a gene encoding a novel protein, nibrin. It contains two modules found in cell cycle checkpoint proteins, a forkhead-associated domain adjacent to a breast cancer carboxy-terminal domain. A truncating 5 bp deletion was identified in the majority of NBS patients, carrying a conserved marker haplotype. Five further truncating mutations were identified in patients with other distinct haplotypes. The domains found in nibrin and the NBS phenotype suggest that this disorder is caused by defective responses to DNA double-strand breaks.