UV filters for hair protection

Synopsis Hair damage, caused by sunlight, and the possibility to protect hair against sunlight by means of cosmetic formulations was studied. For this, five UV-filters were tested: benzophenone-3 (UV-A/UV-B); benzophenone-4 (UV-A/UV-B); phenylbenzimidazole sulfonic acid (UV-B); butylmethoxydibenzoylmethane (UV-A); octyl dimethyl PABA (UV-B). The stability of the UV-filters was tested as pure substances as well as in two cosmetic formulations: a setting lotion and a shine spray. The degree of decolouration and stress strain behaviour were determined. The benzophenones had the best protection ability both on colour and on morphology. Stability data and UV-spectra are discussed.

Two Missense Mutations in the Primary Autosomal Recessive Microcephaly Gene MCPH1 Disrupt the Function of the Highly Conserved N-Terminal BRCT Domain of Microcephalin

Primary microcephaly MCPH1 is an extremely rare autosomal recessive disorder associated with congenital microcephaly, mental retardation and a distinctive cellular phenotype of misregulated chromosome condensation. The MCPH1 gene encodes an 835-amino acid protein, microcephalin, which contains 1 N-terminal and 2 C-terminal BRCT (BRCA1 C-terminus) domains. BRCT domains are predominantly found in proteins involved in cell cycle control and DNA repair. Here we describe 1 novel and 1 previously reported MCPH1 missense mutation, p.Trp75Arg and p.Ser72Leu, respectively, in the N-terminal BRCT domain of microcephalin associated with severe congenital microcephaly. Both residues are entirely conserved in the MCPH1 orthologs of all vertebrate species and Drosophila. Proliferating lymphocytes of the patients with p.Trp75Arg and p.Ser72Leu show the unique cellular MCPH1 phenotype of misregulated chromosome condensation, indicating that these missense alterations disrupt the function of the N-terminal BRCT domain of the protein. Interestingly, both residues are strictly conserved in BRCT domains of BRCA1. ClustalW alignments show that the residue p.Ser72 of microcephalin corresponds to p.Ser1715 of the N-terminal BRCT domain of BRCA1, while the microcephalin residue p.Trp75 is analogous to p.Trp1718 in the N-terminal BRCT and to p.Trp1837 in C-terminal BRCT domains of BRCA1. Missense alterations for all 3 corresponding BRCA1 residues were described and are predicted to be deleterious resulting in the destabilization of the BRCA1 protein. Our data on the 2 MCPH1 missense alterations provide further evidence for the functional significance of these residues in BRCT domains.

High prevalence of the NBN gene mutation c.657-661del5 in Southeast Germany

Nijmegen breakage syndrome (NBS), a rare autosomal recessive chromosomal instability disorder, is caused by mutations in the NBN gene. Most patients known so far are of Slavic origin and carry the major founder mutation c.657-661del5. Due to an unexpectedly high incidence of NBS patients (homozygous for the c.657-661del5 mutation) in a Northeast Bavarian region in Southeast Germany, we estimated the prevalence of this mutation in this area and compared it to another German region. We found a high carrier frequency of 1/176 for the c.657-661del5 mutation among newborns in Northeast Bavaria, while the frequency of the mutation in Berlin was 1/990. We further studied families from a Slavic population isolate, the Sorbs, in the Lusatian region in Northeast Saxony, and revealed a prevalence of the c.657-661del5 mutation of 1/34. Whereas the Slavic origin of the Sorbs has been known, we attribute the surprisingly high frequencies of c.657-661del5 mutation in Bavaria (similar to frequencies of this mutation in various Eastern European countries) to a high percentage of people of Slavic origin in Northeast Bavaria.

Age and origin of major Smith-Lemli-Opitz syndrome (SLOS) mutations in European populations

BACKGROUND

Smith-Lemli-Opitz syndrome (SLOS) (MIM 270 400) is an autosomal recessive multiple congenital anomalies/mental retardation syndrome caused by mutations in the Delta7-sterol reductase (DHCR7, E.C.1.3.1.21) gene. The prevalence of SLOS has been estimated to range between 1:15000 and 1:60000 in populations of European origin.

METHODS AND RESULTS

We have analysed the frequency, origin, and age of DHCR7 mutations in European populations. In 263 SLOS patients 10 common alleles (c.964-1G>C, p.Trp151X, p.Thr93Met, p.Val326Leu, p.Arg352Trp, p.Arg404Cys, p.Phe302Leu, p.Leu157Pro, p.Gly410Ser, p.Arg445Gln) were found to constitute approximately 80% of disease-causing mutations. As reported before, the mutational spectra differed significantly between populations, and frequency peaks of common mutations were observed in North-West (c.964-1G>C), North-East (p.Trp151X, p.Val326Leu) and Southern Europe (p.Thr93Met). SLOS was virtually absent from Finland. The analysis of nearly 8000 alleles from 10 different European populations confirmed a geographical distribution of DHCR7 mutations as reported in previous studies. The common Null mutations in Northern Europe (combined ca. 1:70) occurred at a much higher frequency than expected from the reported prevalence of SLOS. In contrast the most common mutation in Mediterranean SLOS patients (p.Thr93Met) had a low population frequency. Haplotypes were constructed for SLOS chromosomes, and for wild-type chromosomes of African and European origins using eight cSNPs in the DHCR7 gene. The DHCR7 orthologue was sequenced in eight chimpanzees (Pan troglodytes) and three microsatellites were analysed in 50 of the SLOS families in order to estimate the age of the three major SLOS-causing mutations.

CONCLUSIONS

The results indicate a time of first appearance of c.964-1G>C and p.Trp151X some 3000 years ago in North-West and North-East Europe, respectively. The p.Thr93Met mutations on the J haplotype has probably first arisen approximately 6000 years ago in the Eastern Mediterranean. Together, it appears that a combination of founder effects, recurrent mutations, and drift have shaped the present frequency distribution of DHCR7 mutations in Europe.

[Mutations in tumor suppressor gene NBS1 in adult patients with malignancies]

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.

[Increased risk of malignancies in heterozygotes in families of patients with Nijmegen breakage syndrome]

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.

Cerebellar hypoplasia and quadrupedal locomotion in humans as a recessive trait mapping to chromosome 17p

BACKGROUND

Congenital hereditary non-progressive hypoplasia of the cerebellum is a rare condition, frequently associated with other neuropathology such as lissencephaly. Clinically, the condition is associated with variable degrees of mental retardation, microcephaly, seizures, and movement disorders due to ataxia. In severe cases, patients are unable to ambulate independently, but nevertheless do use bipedal locomotion.

METHODS AND RESULTS

Here we present a family with seven affected members, five of whom never learned to walk on two legs but have fully adapted to quadrupedal palmigrade locomotion. These subjects show signs of cerebellar ataxia and are mentally retarded. MRI analysis demonstrated hypoplasia of the cerebellum and the cerebellar vermis as well as a small nucleus dentatus and a thin corpus callosum but no other malformations. We show, by a genome-wide linkage scan, that quadrupedal locomotion is a recessive trait linked to chromosome 17p.

CONCLUSIONS

Our findings have implications for understanding the neural mechanism mediating bipedalism, and, perhaps, the evolution of this unique hominid trait.

Nijmegen breakage syndrome (NBS) with neurological abnormalities and without chromosomal instability

BACKGROUND

Nijmegen breakage syndrome (NBS) is an autosomal recessive chromosomal instability disorder with hypersensitivity to ionising radiation. The clinical phenotype is characterised by congenital microcephaly, mild dysmorphic facial appearance, growth retardation, immunodeficiency, and greatly increased risk for lymphoreticular malignancy. Most NBS patients are of Slavic origin and homozygous for the founder mutation 657del5. The frequency of 657del5 heterozygotes in the Czech population is 1:150. Recently, another NBS1 mutation, 643C>T(R215W), with uncertain pathogenicity was found to have higher frequency among tumour patients of Slavic origin than in controls. This alteration results in the substitution of the basic amino acid arginine with the non-polar tryptophan and thus could potentially interfere with the function of the NBS1 protein, nibrin.

METHODS AND RESULTS

Children with congenital microcephaly are routinely tested for the 657del5 mutation in the Czech and Slovak Republics. Here, we describe for the first time a severe form of NBS without chromosomal instability in monozygotic twin brothers with profound congenital microcephaly and developmental delay who are compound heterozygotes for the 657del5 and 643C>T(R215W) NBS1 mutations. Both children showed reduced expression of full length nibrin when compared with a control and a heterozygote for the 657del5 mutation. Radiation response processes such as phosphorylation of ATM and phosphorylation/stabilisation of p53, which are promoted by NBS1, are strongly reduced in cells from these patients.

CONCLUSIONS

Interestingly, the patients are more severely affected than classical NBS patients. Consequently, we postulate that homozygosity for the 643C>T(R215W) mutation will also lead to a, possibly very, severe disease phenotype.

X chromosome painting in Microtus: origin and evolution of the giant sex chromosomes

Sex chromosomes in species of the genus Microtus present some characteristic features that make them a very interesting group to study sex chromosome composition and evolution. M. cabrerae and M. agrestis have enlarged sex chromosomes (known as 'giant sex chromosomes') due to the presence of large heterochromatic blocks. By chromosome microdissection, we have generated probes from the X chromosome of both species and hybridized on chromosomes from six Microtus and one Arvicola species. Our results demonstrated that euchromatic regions of X chromosomes in Microtus are highly conserved, as occurs in other mammalian groups. The sex chromosomes heterochromatic blocks are probably originated by fast amplification of different sequences, each with an independent origin and evolution in each species. For this reason, the sex heterochromatin in Microtus species is highly heterogeneous within species (with different composition for the Y and X heterochromatic regions in M. cabrerae) and between species (as the composition of M. agrestis and M. cabrerae sex heterochromatin is different). In addition, the X chromosome painting results on autosomes of several species suggest that, during karyotypic evolution of the genus Microtus, some rearrangements have probably occurred between sex chromosomes and autosomes.

[Nijmegen breakage syndrome in Slovakia]

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.

Copy and paste: the impact of a new non-L1 retroposon on the gonosomal heterochromatin of Microtus agrestis

Mobile elements are most abundant in the mammalian genome, comprising at least 40-50% of the DNA. They are differentiated into two most prominent families: the LINE elements, which are preferentially located in the G-bands, and SINES, which are clustered in the R-bands. We report here a novel mammalian non-L1-retroposon, which invaded the genome of Microtus agrestis in a very short time from an evolutionary viewpoint. No relevant sequence homology could be demonstrated to known sequences in the NCBI database. However, cross-hybridizing sequences exist in the genomes of all other Microtus species analyzed, but not in Mus musculus, indicating the recent evolutionary origin of this element. This retroposon is enriched in the entire heterochromatin of the X and Y chromosomes, but is also interspersed in autosomal locations in euchromatic portions of the genome. We show that the retroposon is heavily transcribed from the heterochromatin during female meiosis prerequisite for the subsequent retrotransposition. The estimated rate of retrotransposition is at least 1-2 x 10(-2) per generation, which is hundred-fold higher than that of the majority of invertebrate retroposons and also higher than the transposition rate of a murine L1 element, which was calculated to be 3 x 10(-3) per generation.

DNA methyltransferase 3B mutations linked to the ICF syndrome cause dysregulation of lymphogenesis genes

ICF (immunodeficiency, centromeric region instability and facial anomalies) is a recessive disease caused by mutations in the DNA methyltransferase 3B gene (DNMT3B). Patients have immunodeficiency, chromosome 1 (Chr1) and Chr16 pericentromeric anomalies in mitogen-stimulated lymphocytes, a small decrease in overall genomic 5-methylcytosine levels and much hypomethylation of Chr1 and Chr16 juxtacentromeric heterochromatin. Microarray expression analysis was done on B-cell lymphoblastoid cell lines (LCLs) from ICF patients with diverse DNMT3B mutations and on control LCLs using oligonucleotide arrays for approximately 5600 different genes, 510 of which showed a lymphoid lineage-restricted expression pattern among several different lineages tested. A set of 32 genes had consistent and significant ICF-specific changes in RNA levels. Half of these genes play a role in immune function. ICF-specific increases in immunoglobulin (Ig) heavy constant mu and delta RNA and cell surface IgM and IgD and decreases in Ig(gamma) and Ig(alpha) RNA and surface IgG and IgA indicate inhibition of the later steps of lymphocyte maturation. ICF-specific increases were seen in RNA for RGS1, a B-cell specific inhibitor of G-protein signaling implicated in negative regulation of B-cell migration, and in RNA for the pro-apoptotic protein kinase C eta gene. ICF-associated decreases were observed in RNAs encoding proteins involved in activation, migration or survival of lymphoid cells, namely, transcription factor negative regulator ID3, the enhancer-binding MEF2C, the iron regulatory transferrin receptor, integrin beta7, the stress protein heme oxygenase and the lymphocyte-specific tumor necrosis factor receptor family members 7 and 17. No differences in promoter methylation were seen between ICF and normal LCLs for three ICF upregulated genes and one downregulated gene by a quantitative methylation assay [combined bisulfite restriction analysis (COBRA)]. Our data suggest that DNMT3B mutations in the ICF syndrome cause lymphogenesis-associated gene dysregulation by indirect effects on gene expression that interfere with normal lymphocyte signaling, maturation and migration.

Mutations in the Nijmegen Breakage Syndrome gene (NBS1) in childhood acute lymphoblastic leukemia (ALL)

The Nijmegen Breakage Syndrome (NBS) is a rare autosomal recessive disorder associated with immune deficiency, chromosome fragility, and increased susceptibility to lymphoid malignancies. The aim of the present study was to elucidate the potential role of the gene mutated in NBS (NBS1) in the pathogenesis and disease progression of childhood acute lymphoblastic leukemia (ALL). Samples from 47 children with first relapse of ALL were analyzed for mutations in all 16 exons of the NBS1 gene, and in 7 of them (14.9%), four novel amino acid substitutions were identified. Mutations S93L, D95N, and I171V occur in the two known domains of nibrin that are probably involved in protein-protein interactions. Germ-line origin of the I171V mutation was confirmed in three patients, whereas the D95N exchange was present only in leukemic cells. The R215W mutation was observed in one ALL but also in a population-based study and probably represents a rare sequence variant. No additional mutations were found on the second allele in any of these seven patients. The observed NBS1 gene mutations in ALL patients points to its possible involvement in the pathogenesis of this disease.

Differences in the meiotic pairing behavior of gonosomal heterochromatin between female and male Microtus agrestis: implications for the mechanism of heterochromatin amplification on the X and Y

It is generally thought that pairing and recombination between the X and Y chromosome in eutherian mammals is important for the occurrence of normal meiotic division and the production of functional gametes. Microtus agrestis is one of the examples whose giant and heterochromatin-rich sex chromosomes fail to establish a durable association at any stage of the first meiotic division in males. In contrast, in females, synapsis starts in the euchromatic short arm and pairing progresses unidirectionally and continues until both X chromosomes have paired completely, as can be demonstrated by the use of fluorescence in situ hybridization with a sequence confined to the non-centromeric, gonosomal heterochromatin. However, compared with euchromatin, this association is apparently ephemeral and breaks off precociously in the pachytene and metaphase I stages. We demonstrate that a middle repetitive element is localized interspersed in the noncentromeric heterochromatin of both X and Y, except the telomeric region of the Y. No differences could be detected at the molecular level between male and female DNA, indicating that at least the bulk of these elements are organized in the same manner on the X and Y. Our data imply that the loss of synapsis and recombination between the X and Y might have preceded the process of heterochromatin amplification in the course of Microtinae evolution. Since asynapsed elements are particularly susceptible to DNA strand breaks during prophase I, DNA repair of double-strand breaks involving heterochromatic segments of the X and Y could have resulted in translocations of larger segments from the X to the Y or vice versa during the course of chromosome evolution of the gonosomes, explaining the homology at the molecular level between the heterochromatin of the asynaptic X and Y in M. agrestis.

V(D)J rearrangement in Nijmegen breakage syndrome

Repair of DNA double-strand breaks is essential for maintenance of genomic stability, and is specifically required for rearrangement of immunoglobulin (Ig) and T cell receptor (TCR) loci during development of the immune system. Abnormalities in these repair processes also contribute to oncogenic chromosomal rearrangements that underlie many lymphoid malignancies. Nijmegen breakage syndrome (NBS) is a rare autosomal recessive condition characterized by immunodeficiency, radiation sensitivity, and increased predisposition to lymphoid cancers bearing oncogenic Ig and TCR locus translocations. NBS patients fail to produce nibrin, a protein required for the nuclear localization and function of a DNA repair complex that includes Mre11 and Rad50. Mre11 has biochemical properties that suggest a potential role in V(D)J recombination. We studied V(D)J recombination in NBS cells in vitro and in vivo, using cell lines and peripheral blood leukocyte DNA from NBS patients. We found that NBS cells were competent to rejoin signal substrates with normal efficiency and high fidelity. Coding substrates were similarly rejoined efficiently, and coding end structures appeared normal. In B cells from NBS patients, the spectrums of IgH CDR3 regions were diverse and normally distributed. Moreover, the lengths and composition of Igkappa VJ joins and IgH VDJ joins derived from NBS and normal subjects were indistinguishable. Our data indicate that nibrin plays no essential role in V(D)J recombination and is not required for the generation of an apparently diverse B cell repertoire.

Spectrum of mutations in the Fanconi anaemia group G gene, FANCG/XRCC9

FANCG was the third Faconi anaemia gene identified and proved to be identical to the previously cloned XRCC9 gene. We present the pathogenic mutations and sequence variants we have so far identified in a panel of FA-G patients. Mutation screening was performed by PCR, single strand conformational polymorphism analysis and protein truncation tests. Altogether 18 mutations have been determined in 20 families - 97% of all expected mutant alleles. All mutation types have been found, with the exception of large deletions, the large majority is predicted to lead to shortened proteins. One stop codon mutation, E105X, has been found in several German patients and this founder mutation accounts for 44% of the mutant FANCG alleles in German FA-G patients. Comparison of clinical phenotypes shows that patients homozygous for this mutation have an earlier onset of the haematological disorder than most other FA-G patients. The mouse Fancg sequence was established in order to evaluate missense mutations. A putative missense mutation, L71P, in a possible leucine zipper motif may affect FANCG binding of FANCA and seems to be associated with a milder clinical phenotype.

Clinical ascertainment of Nijmegen breakage syndrome (NBS) and prevalence of the major mutation, 657del5, in three Slav populations

Nijmegen breakage syndrome (NBS) is a chromosomal instability disorder, clinically characterised by microcephaly, immunodeficiency, radiosensitivity and a very high predisposition to lymphoid malignancy. Recently, it was demonstrated that mutations in the NBS1 gene are responsible for NBS. Most of the NBS patients known so far are of Slav origin and carry a major founder mutation 657del5 in exon 6 of the NBS1 gene. In this study we estimated the prevalence of the 657del5 mutation in the Czech Republic, Poland and the Ukraine. We found an unexpectedly high carrier frequency of the 657del5 mutation (1/177) in the three Slav populations, a factor that may contribute to cancer frequency in those countries. In addition, we show that NBS patients are often diagnosed late and therefore receive inappropriate therapy.

Beta-heterochromatin in mammals: evidence from studies in Microtus agrestis based on the extensive accumulation of L1 and non-L1 retroposons in the heterochromatin

The heterochromatin of Microtus agrestis contains two retroposons, one L1 and one non-L1, which were cloned and analyzed with respect to their structure and genomic organization. These sequences have accumulated in the heterochromatin and exhibit a complex interspersed organization of relatively recent origin. In contrast, the pericentromeric heterochromatin is composed of simple, repetitive, tandemly organized elements. From the underlying sequences, the dinucleotide frequencies, the sequence organization, and its transcriptional activity, the heterochromatin of M. agrestis strongly resembles the beta-heterochromatin first described by Heitz and well characterized in Drosophila. This is evidence that this class of heterochromatin, presumably with its own distinct physiological and functional role, is indeed also present in the mammalian genome.

Expression pattern of the Nijmegen breakage syndrome gene, Nbs1, during murine development

The Nijmegen breakage syndrome (NBS; MIM 251260), is an autosomal recessive disease characterized by microcephaly, growth retardation, immuno-deficiency and cancer predisposition. NBS cells show spontaneous chromosomal instability and hypersensitivity to ionizing radiation in combination with radioresistant DNA synthesis. At the cellular level, NBS has some features in common with ataxia teleangiectasia. In this study the murine Nbs1 gene was used for an expression study in mouse embryos at different developmental stages as well as in adult mice. A low level of expression is observed in all tissues. Highly specific expression was observed in organs with physiologic DNA double strand breakage (DSB), such as testis, thymus and spleen. Enhanced expression is also found at sites of high proliferative activity. These are the subventricular layer of the telencephalon and the diencephalon, the liver, lung, kidney and gut, as well as striated and smooth muscle cells in various organs. In the adult cerebellum the postmitotic Purkinje cells are marked specifically. These expression patterns suggest that in addition to the role of the Nbs1 gene product as part of a DNA DSB repair complex, the Nbs1 gene product may serve further functions during development.

Proving the authenticity of ancient DNA by comparative genomic hybridization

In PCR-supported amplification of ancient, degraded DNA, contamination with contemporary DNA can lead to false-positive results, which frequently give rise to discussions in which the mere existence of ancient DNA is doubted. Our confirmation of ancient DNA using comparative genome hybridization (CGH) eliminates these doubts. Unlike PCR methods, CGH requires no amplification of the DNA to be analyzed if adequate amounts of specimen DNA is used. Thus, false results traceable to contaminations are practically ruled out. The examples provided here prove the authenticity of ancient DNA for a 250-year-old and a 3,000-year-old sample. At the same time, the CGH of ancient DNA offers the chance to gain insight into the pattern of DNA degradation and to monitor the preservation of certain chromosomal segments.

Nijmegen breakage syndrome: consequences of defective DNA double strand break repair

The autosomal recessive genetic disorder, Nijmegen Breakage Syndrome, is characterised by an excessively high risk for the development of lymphatic tumours and an extreme sensitivity towards ionising radiation. The most likely explanation for these characteristics, a deficiency in the repair of DNA lesions, has been greatly substantiated by the recent cloning of the gene mutated in Nijmegen Breakage Syndrome patients and the analysis of its protein product, nibrin. The direct involvement of this protein in the processing of DNA double strand breaks caused by ionising radiation and those also necessary for normal DNA metabolism can be correlated with many of the cellular and clinical aspects of the disease, including the cancer predisposition of patients and their heterozygous relatives.

Characterization of ATM gene mutations in 66 ataxia telangiectasia families

Ataxia telangiectasia (AT) is an autosomal recessive disease characterized by neurological and immunological symptoms, radiosensitivity and cancer predisposition. The gene mutated in AT, designated the ATM gene, encodes a large protein kinase with a PI-3 kinase-related domain. In this study, we investigated the mutational spectrum of the ATM gene in a cohort of AT patients living in Germany. We amplified and sequenced all 66 exons and the flanking untranslated regions from genomic DNA of 66 unrelated AT patients. We identified 46 different ATM mutations and 26 sequence polymorphisms and variants scattered throughout the gene. A total of 34 mutations have not been described in other populations. Seven mutations occurred in more than one family, but none of these accounted for more than five alleles in our patient group. The majority of the mutations were truncating, confirming that the absence of full-length ATM protein is the most common molecular basis of AT. Transcript analyses demonstrated single exon skipping as the consequence of most splice site substitutions, but a more complex pattern was observed for two mutations. Immunoblot studies of cell lines carrying ATM missense substitutions or in-frame deletions detected residual ATM protein in four cases. One of these mutations, a valine deletion proximal to the kinase domain, resulted in ATM protein levels >20% of normal in an AT lymphoblastoid cell line. In summary, our results survey and characterize a plethora of variations in the ATM gene identified by exon scanning sequencing and indicate a high diversity of mutations giving rise to AT in a non-isolated population.

Identification of mouse crystallins in 2D protein patterns by sequencing and mass spectrometry. Application to cataract mutants

The eye lens proteins of the mouse were separated into 1940 polypeptide spots by two-dimensional electrophoresis in large gels. All 16 crystallins ubiquitous in mammals were identified by protein sequencing and mass spectrometry except for (gamma)-F, which shows an almost identical sequence with (gamma)-E. Two crystallins, (beta)-A2 and (gamma)-S, were shown for the first time to occur in the mouse lens. An investigation of the murine cataract mutant Cat2(nop)((gamma)-B gene) demonstrated that a monogenic mutation might affect a broad spectrum of proteins.

Localisation of a Fanconi anaemia gene to chromosome 9p

Using homozygosity mapping in a large consanguineous family, we have localised to chromosome 9p a further gene for the autosomal recessive, genetically heterogeneous disease Fanconi anaemia (FA). This is the fourth of at least eight FA genes to be localised to a discrete chromosomal region. Previously localised genes are FAA, FAC and FAD. By analysis of assigned families we show that the gene localised to chromosome 9p is FAF, FAG or FAH, or a new FA gene, and refine the localisation to the 21 cM region between markers D9S1678 and D9S175.

[Small abnormality of the middle ear--a genetically-induced defect?]

Conductive and sensorineural hearing losses are of genetic origin in 20% to 60% of cases. In general, genetic abnormalities are more often expressed as a sensorineural hearing loss than as a conductive hearing loss. At present several genes for sensorineural hearing loss have been isolated. The most common genetically transmitted forms for isolated conductive hearing losses are otosclerosis and small malformations of the ossicles. To date no genes responsible for these deformations have been isolated. We present a family with four siblings having conductive hearing losses caused by ossification of the stapedial tendon. This finding is suggestive of an autosomal recessive inheritance. The early diagnosis of an hereditary conductive hearing loss contains the possibility for permitting normal development of speech.

Nibrin, a novel DNA double-strand break repair protein, is mutated in Nijmegen breakage syndrome

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.

Creation of monosomic derivatives of human cultured cell lines

Monosomic mammalian cell lines would be ideal for studying gene dosage effects, including gene imprinting, and for systematic isolation of recessive somatic mutants parallel to the invaluable mutants derived from haploid yeast. But autosomal monosomies are lethal in early development; although monosomies appear in tumors, deriving cell lines from these tumors is difficult and cannot provide several syngenic lines. We have developed a strategy for generating stable monosomic human cells, based on random autosomal integration of the gpt plasmid, partial inhibition of DNA topoisomerase II during mitosis to promote chromatid nondisjunction, and selection against retention of gpt. These are likely to be valuable as a source of otherwise inaccessible mutants. The strategy can also be used to generate partial mammalian monosomies, which are desirable as a source of information on recessive genes and gene imprinting.

Nijmegen breakage syndrome cells fail to induce the p53-mediated DNA damage response following exposure to ionizing radiation

The functionality of the p53-mediated pathway, activated in response to DNA damage, has been assessed in primary fibroblast cell cultures and Epstein-Barr virus-transformed lymphoblastoid cell lines derived from Nijmegen breakage syndrome (NBS) patients. This autosomal recessive disease is characterized by microcephaly, growth and mental retardation, chromosomal instability, radiosensitivity, and high cancer incidence. The recent mapping of the NBS gene to chromosome 8q21 demonstrates that NBS is genetically distinct from ataxia telangiectasia (AT). Changes in p53 protein levels were significantly reduced and delayed in all the NBS fibroblast cell cultures and lymphoblastoid cell lines examined compared to normal cultures over a 4-h period postirradiation (5 Gy). The transcriptional activation of p21(WAF1/CIP1) mRNA was also lower in 12 NBS fibroblast cultures examined. In agreement with an abrogated p53 function, NBS cells exposed to ionizing radiation show an abnormal cell cycle arrest at G1-S and a prolonged accumulation of cells in the G2 phase. In contrast, exposure to the alkylating agent methyl methanesulfonate results in similar increases of p53 and p21(WAF1/CIP1) mRNA in both cell types. The ATM gene transcript was found to be expressed at similar levels in NBS and normal cells, whereas it was strongly reduced in the AT homozygote cells examined. These results suggest that the ATM gene product cannot substitute for that of the NBS gene in the signaling of cellular damage produced by ionizing radiation and that both are involved in the activation of p53. The suboptimal p53-mediated response could contribute to the high cancer risk and radiosensitivity seen in NBS patients.

Different mechanisms and recurrence risks of imprinting defects in Angelman syndrome

Angelman syndrome (AS) is a neurogenetic disorder that appears to be caused by the loss of function of an imprinted gene expressed from maternal chromosome 15 only. Approximately 6% of patients have a paternal imprint on the maternal chromosome. In the few cases, this is due to an inherited microdeletion, in the 15q11-q13 imprinting center (IC), that blocks the paternal-->maternal imprint switch in the maternal germ line. We have determined the segregation of 15q11-q13 haplotypes in nine families with AS and with an imprinting defect. One family, with two affected siblings, has a microdeletion affecting the IC transcript. In the other eight patients, no mutation was found at this locus. In two families, the patient and a healthy sibling share the same maternal alleles. In one of these families and in two others, grandparental DNA samples were available, and the chromosomes with the imprinting defect were found to be of grandmaternal origin. These findings suggest that germ-line mosaicism or de novo mutations account for a significant fraction of imprinting defects, among patients who have an as-yet-undetected mutation in a cis-acting element. Alternatively, these data may indicate that some imprinting defects are caused by a failure to maintain or to reestablish the maternal imprint in the maternal germ line or by a failure to replicate the imprint postzygotically. Depending on the underlying cause of the imprinting defect, different recurrence risks need to be considered.

Noncomplementation of radiation-induced chromosome aberrations in ataxia-telangiectasia/ataxia-telangiectasia-variant heterodikaryons

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Possible association of the allele status of the CS.7/HhaI polymorphism 5' of the CFTR gene with postnatal female survival

Cystic fibrosis (CF) patients show a high degree of linkage disequilibrium between the CF transmembrane conductance regulator (CFTR) gene and polymorphisms 5' of that gene. To determine whether the region 5' of CFTR contains biologically important sequences, the allele frequencies of six CFTR-linked polymorphisms (metH/MspI, XV-2c/TaqI, CS.7/HhaI, KM19/PstI, MP6d9/MspI, J44/XbaI) were determined in 417 randomly selected elderly individuals (over 75 years of age) from the Czech population. The elderly individuals were considered "escapees" of strong selective pressures that had operated during their lifetime, prior to the introduction of modern health care since 1950. The pooled allele frequencies of the analyzed marker polymorphisms in the elderly did not significantly differ from published data. However, when analyzed by ex, the allele frequencies of markers CS.7/HhaI and KM19/PstI differed significantly (P < 0.05) between elderly females and males. The allele frequencies of the six polymorphisms were then determined in 646 newborns and 345 young adults of reproductive age; these individuals were selected in a similar manner and drawn from the same population. In these control groups, the studied marker polymorphisms exhibited no statistically significant differences between sexes and/or between individuals of the same sex, only between different age groups. A gradual relative increase in the frequency of allele "2" of marker CS.7/HhaI was observed from newborn females to elderly women, the overall difference in allele frequencies of this marker polymorphism between newborn females and elderly women reaching statistical significance (P < 0.05). Interestingly, allele "2" is the major constituent of the extended "B-haplotype", which is in strong linkage disequilibrium with common CF alleles. Taken together, our data suggest that the region spanning markers CS.7 and KM19 is associated with a genetic factor that influences postnatal female survival, providing a possible mechanism for increasing the frequency of particular mutations in the adjacent CFTR gene.

The gene for the ataxia-telangiectasia variant, Nijmegen breakage syndrome, maps to a 1-cM interval on chromosome 8q21

Nijmegen breakage syndrome (NBS; Seemanová II syndrome) and Berlin breakage syndrome (BBS), also known as ataxia-telangiectasia variants, are two clinically indistinguishable autosomal recessive familial cancer syndromes that share with ataxia-telangiectasia similar cellular, immunological, and chromosomal but not clinical findings. Classification in NBS and BBS was based on complementation of their hypersensitivity to ionizing radiation in cell-fusion experiments. Recent investigations have questioned the former classification into two different disease entities, suggesting that NBS/BBS is caused by mutations in a single radiosensitivity gene. We now have performed a whole-genome screen in 14 NBS/BBS families and have localized the gene for NBS/BBS to a 1-cM interval on chromosome 8q21, between markers D8S271 and D8S270, with a peak LOD score of 6.86 at D8S1811. This marker also shows strong allelic association to both Slavic NBS and German BBS patients, suggesting the existence of one major mutation of Slavic origin. Since the same allele is seen in both former complementation groups, genetic homogeneity of NBS/BBS can be considered as proved.

Assignment of the chicken MAX gene to chromosome 5p by fluorescence in situ hybridization

It has been shown that the protein encoded by the MAX gene plays an important role in the physiological activity of Myc oncoproteins. In this study, we determined the chromosome location of the chicken MAX gene via fluorescence in situ hybridization. Hybridization of two biotinylated cloned fragments of 5.7 kb and 12.0 kb derived from the chicken MAX locus localized the gene to chromosome 5p. It is the third gene marker to be assigned to this telocentric macrochromosome. Since the MAX sequence is highly conserved both at the nucleotide and at the amino acid level in a wide range of vertebrate species, our data may provide evidence for the existence of a segmental homology between human and chicken chromosomes.

Phenotypic differences in Angelman syndrome patients: imprinting mutations show less frequently microcephaly and hypopigmentation than deletions

Angelman syndrome (AS) is a relatively frequent disorder of psychomotor development caused by loss of function of a gene from chromosome 15q11-q13, a region subject to genomic imprinting. The AS gene(s) is exclusively expressed from the maternal chromosome. Several kinds of mutations have been found to cause AS. More than half of the cases exhibit a deletion of the maternal 15q11-q13 region. Recently, we and others described a new mutation type, the imprinting mutation, characterised by normal, biparental inheritance but aberrant methylation patterns of the entire chromosomal region. In AS, a paternal imprint is found on the maternal chromosome probably leading to functional inactivation of the AS gene(s). We have now compared the phenotype of 9 AS patients with imprinting mutation to that of nine age-matched ones with a maternally derived deletion. Both groups were evaluated for 19 common AS symptoms. All patients, independently of their molecular findings, showed classical AS symptoms such s mental retardation, delayed motor development, and absent speech. In contrast, for two signs, hypopigmentation and microcephaly, a different distribution among both groups was observed. Only one of nine AS patients with an imprinting mutation, but seven of nine in the deletion control group showed either symptom. Our results suggest that imprinting mutations, in contrast to deletions, cause only incomplete loss of gene function or that maternally derived deletions affect also genes not subject to genomic imprinting. We conclude that AS is caused by loss of function of a major gene that is imprinted but that there are also other genes that contribute to the phenotype when in hemizygous condition.

Partial trisomy/monosomy 6q in fetal cells and CVS long-term culture not present in CVS short-term culture

A cytogenetic discrepancy in chorionic villi with implications for prenatal diagnosis is described. Chromosome analysis revealed a normal karyotype in banded metaphases from short-term culture and a chromosome count of 46 in cells of the long-term culture. After the birth of a malformed infant, a structurally aberrant chromosome 6 was found in lymphocytes and skin fibroblasts. Re-analysis of chorionic villi confirmed the result from short-term culture but disclosed the presence of the structural aberration in cells of the long-term culture. This type of inconsistency is reported for the first time and stresses the importance of a numerical and structural analysis of both short-term and long-term culture. The application of three techniques, chromosome banding, comparative genomic hybridization (CGH), and fluorescence in situ hybridization (FISH) analysis, was essential to prove that the derivative chromosome carried a combined partial trisomy/monosomy for 6q. The findings are discussed with respect to the origin of the structural aberration and to the consequences for prenatal diagnosis on chorionic villi and genetic counselling.

Molecular analysis of Fanconi anaemia

The autosomal recessive genetic disease, Fanconi anaemia, is perceived as another manifestation of defective cellular DNA repair, just as in the autosomal recessive disease Xeroderma pigmentosum. The biochemistry and cellular biology of Xeroderma pigmentosum have been convincingly elucidated, but the same has not been true for Fanconi anaemia. In this review we consider the pleiotropic nature of Fanconi anaemia, its clinical and cellular variability and its genetic heterogeneity. We take into account the wealth of experimental findings available and offer a novel hypothesis involving feedback control of DNA replication during S phase of the cell cycle to explain the basic defect in the disease.

Possible autosomal recessive inheritance of progressive hearing loss with stapes fixation

Four sibs with progressive, bilateral conductive hearing loss are presented. Symmetrical hearing loss averaging 30-60 dB (0.125-8 kHz) became apparent between 8 and 24 years of age. Tympanotomy showed a fixed stapes either through ossified stapedius tendon or through ossified stapedius tendon or through a bony bridge from the stapes to the pyramidal eminence in all patients. After surgical removal of the bony tendon hearing was normal. Both parents, four other sibs, and all grandparents had normal hearing. This family and a further published case suggest a possibly recessive inheritance of this form of conductive hearing loss.

Identification of a HeLa mRNA fraction which corrects the mitomycin C sensitivity of irs1 cells

The hamster cell mutant irs1 is defective in its response to DNA lesions caused by a variety of mutagens, particularly cross-linking agents. These cells have been assigned to complementation group 2 of X-ray-sensitive mutants and the mutated gene is called XRCC2(X-ray repair cross complementing). We have identified, by microinjection, a human mRNA fraction which can transiently correct the sensitivity of these cells to cross-linking agents. This fraction contains mRNAs of 3.5 kb (+/- 0.25) including, therefore, the transcript of the XRCC2 gene.

Evolution of the gonosomal heterochromatin of Microtus agrestis: rapid amplification of a large, multimeric, repeat unit containing a 3.0-kb (GATA)11-positive, middle repetitive element

The sex chromosomes of Microtus agrestis are extremely large due to the accumulation of constitutive heterochromatin. We have cloned and characterized a 2,999-bp (GATA)n-positive sequence, following HaeIII digestion, that is confined to the noncentromeric heterochromatin of the X chromosome. The cloned element exhibits an accumulation of certain oligomers, which are scattered throughout its entire length, and several copies of Chi-related sequence motifs, which are thought to be implicated in recombination. The latter might have been responsible for the extensive amplification of homologous genomic elements. The sequence has been amplified to a copy number of 1-2 x 10(4) within the genome of M. agrestis. In contrast to many satellite DNAs, which are thought to be an inevitable constituent of constitutive heterochromatin, the sequence exhibits a tissue-specific methylation pattern and is organized, not as a simple tandem array, but as a component of an extremely large, multimeric, higher-order repeat unit with a length of over 20 kb. This higher-order repeat accounts for at least 15-30% of the gonosomal heterochromatin in M. agrestis. Sequences homologous to pMAHAE2 are abundant in the genomes of all Microtus species. The copy number varies from approximately 100 per diploid genome in M. arvalis, M. oeconomus, and M. cabrerae to approximately 500 per diploid genome in M. guentheri and up to 1-2 x 10(4) in M. agrestis. Our molecular data indicate that the sequences of the pMAHAE2 family probably arose during the evolution of the common ancestor of Microtus and have subsequently been amplified extensively in the X chromosomes of M. agrestis in the phylogenetically very short period of less than 1 million years.

Arylamine N-acetyltransferase (NAT2) mutations and their allelic linkage in unrelated Caucasian individuals: correlation with phenotypic activity

The polymorphic arylamine N-acetyltransferase (NAT2; EC 2.3.1.5) is supposed to be a susceptibility factor for several drug side effects and certain malignancies. A group of 844 unrelated German subjects was genotyped for their acetylation type, and 563 of them were also phenotyped. Seven mutations of the NAT2 gene were evaluated by allele-specific PCR (mutation 341C to T) and PCR-RFLP for mutations at nt positions 191, 282, 481, 590, 803, and 857. From the mutation pattern eight different alleles, including the wild type coding for rapid acetylation and seven alleles coding for slow phenotype, were determined. Four hundred ninety-seven subjects had a genotype of slow acetylation (58.9%; 95% confidence limits 55.5%-62.2%). Phenotypic acetylation capacity was expressed as the ratio of 5-acetylamino-6-formylamino-3-methyluracil and 1-methylxanthine in urine after caffeine intake. Some 6.7% of the cases deviated in genotype and phenotype, but sequencing DNA of these probands revealed no new mutations. Furthermore, linkage pattern of the mutations was always confirmed, as tested in 533 subjects. In vivo acetylation capacity of homozygous wild-type subjects (NAT2*4/*4) was significantly higher than in heterozygous genotypes (P = .001). All mutant alleles showed low in vivo acetylation capacities, including the previously not-yet-defined alleles *5A, *5C, and *13. Moreover, distinct slow genotypes differed significantly among each other, as reflected in lower acetylation capacity of *6A, *7B, and *13 alleles than the group of *5 alleles. The study demonstrated differential phenotypic activity of various NAT2 genes and gives a solid basis for clinical and molecular-epidemiological investigations.

Irreversible repression of DNA synthesis in Fanconi anemia cells is alleviated by the product of a novel cyclin-related gene

Primary fibroblasts from patients with the genetic disease Fanconi anemia, which are hypersensitive to cross-linking agents, were used to screen a cDNA library for sequences involved in their abnormal cellular response to a cross-linking challenge. By using library partition and microinjection of in vitro-transcribed RNA, a cDNA clone, pSPHAR (S-phase response), which is able to correct the permanent repression of semiconservative DNA synthesis rates characteristic of these cells, was isolated. Wild-type SPHAR mRNA is expressed in all fibroblasts so far analyzed, including those of Fanconi anemia patients. Correction of the abnormal response in these cells appears therefore to be due to overexpression after cDNA transfer rather than to genetic complementation. The cDNA contains an open reading frame coding for a polypeptide of 7.5 kDa. Rabbit antiserum directed against a SPHAR peptide detects a protein of 7.9 kDa in Western blots (immunoblots) of whole-cell extracts from proliferating, but not resting, fibroblasts. The deduced amino acid sequence of SPHAR contains a motif found in the cyclins, and it is proposed that SPHAR acts within the injected cell by interfering with the cyclin-controlled maintenance of S phase. In agreement with this proposal, normal cells transfected with an antisense SPHAR expression vector have a significantly reduced rate of DNA synthesis during S phase and a prolonged G2 phase, reflecting the need for postreplicative DNA processing before entry into mitosis.