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Rett syndrome is caused by mutations in MECP2 and characterized by arrested postnatal neurodevelopment. MECP2 is ubiquitously expressed, but its protein product, methyl-CpG-binding protein 2 (MeCP2), is highly expressed in a subpopulation of cells in the adult brain. Automated quantitation of MeCP2 expression on a human developmental tissue microarray was performed by laser scanning cytometry. A significant correlation between age and MeCP2 level, population heterogeneity, and percentage of MeCP2 high-expressing cells was specifically observed in cerebral but not renal samples. In contrast, an inverse correlation between use of the long 3' UTR of MECP2 and age was observed, suggesting that an acquired switch in polyadenylation is responsible for the elevated MeCP2. Acquired elevated MeCP2 expression in neurons beginning in infancy and progressing through childhood may explain the delayed onset and developmental arrest of Rett syndrome

Nonsyndromic hearing loss is one of the most genetically heterogeneous traits known. A total of 30 autosomal dominant nonsyndromic hearing–loss loci have been mapped, and 11 genes have been isolated. In the majority of cases, autosomal dominant nonsyndromic hearing loss is postlingual and progressive, with the exception of hearing impairment in families in which the impairment is linked to DFNA3, DFNA8/12, and DFNA24, the novel locus described in this report. DFNA24 was identified in a large Swiss German kindred with a history of autosomal dominant hearing loss that dates back to the middle of the 19th century. The hearing-impaired individuals in this kindred have prelingual, nonprogressive, bilateral sensorineural hearing loss affecting mainly mid and high frequencies. The DFNA24 locus maps to 4q35-qter. A maximum multipoint LOD score of 11.6 was obtained at 208.1 cM at marker D4S1652. The 3.0-unit support interval for the map position of this locus ranges from 205.8 cM to 211.7 cM (5.9 cM).

Uniparental disomy (UPD) is defined as the inheritance of both homologous chromosomes from only one parent. So far, maternal UPD 7 has been described in 28 cases. Here, we report 4 new cases, present clinical information of 5 cases previously reported by us, and review the clinical and molecular findings of all 32 cases. We found a phenotype characterized by pre- and postnatal growth retardation, occipitofrontal head circumference in the lower normal range, a triangular face, and retarded bone maturation. Findings of the facial gestalt included a high and broad forehead and a pointed chin. A broad mouth with down-turned corners, prominent ears, cafe-au-lait spots, hemihypotrophy, or clinodactyly were rarely present. Psychomotor development was delayed in 6 cases. The clinical findings strikingly resemble the phenotype of the heterogeneous Silver-Russell syndrome (SRS). Other anomalies were less frequently found than in SRS. Molecular investigations revealed 11 cases with isodisomy and 17 cases with heterodisomy. In 4 cases this information was not available. From the allelic distribution of the microsatellites investigated, 9 cases might be the consequence of an error at maternal meiosis I, and 6 cases might be due to non-disjunction at maternal meiosis II. Three of the 17 heterodisomic cases had trisomy 7 in chorionic villi, in the remaining cases no prenatal diagnosis through chorionic villus sampling was reported. Conclusion Maternal UPD 7 should be investigated in children with pre- and postnatal growth retardation and a facial gestalt characterized by a high and broad forehead and a pointed chin, as well as in confined placental mosaicism for trisomy 7.

By random amplification of a microdissected chromosome using the degenerate oligonucleotide primed polymerase chain reaction (DOP-PCR) and forward painting (microFISH), we characterised an extra structurally abnormal chromosome (ESAC) or supernumerary marker chromosome in a mentally retarded girl with a pattern of dysmorphic features. It could be clearly shown that the small marker chromosome originates from two different regions of chromosome 18, 18p11.1→18q11.1 and 18q12.3→18q21.1 respectively. Maternal origin of the de novo ESAC and biparental origin of the normal homologues of chromosome 18 were shown by PCR of several highly polymorphic microsatellites. In this case, application of microFISH was a prerequisite for rapid and precise characterisation of an ESAC. A definite identification of this discontinuous supernumerary marker chromosome would not have been possible using FISH with centromere specific probes or multicolour FISH approaches. Keywords: supernumerary marker chromosome; microdissection; FISH; chromosome 18

Williams-Beuren syndrome (WBS) results from a deletion of 7q11.23 in 90-95% of all clinically typical cases. Clinical manifestation can be variable and therefore, deletion size, inherited elastin (ELN) and LIM kinase 1 (LIMK1) alleles, gender, and parental origin of deletion have been investigated for associations with clinical outcome. In an analysis of 85 confirmed deletion cases, no statistically significant associations were found after Bonferroni's correction for multiple pairwise comparisons. Furthermore, the present data do not support presence of imprinted genes in the WBS common deletion despite a nonsignificant excess of maternal over paternal deletions. Maternal deletion cases were more likely to have a large head circumference in the present data. Also, pairwise comparisons between individual WBS clinical features have been conducted and revealed significant associations between (1) low birth weight and poor postnatal weight gain (

In a recent study Bugge et al and Kotzot et al reported that isochromosomes 18p originate mainly from maternal meiosis II nondisjunction, followed by misdivision. In order to determine if there is a common mechanism for isochromosome formation, three cases with mosaicism for an additional isochromosome 12p and three cases with tetrasomy 9p were studied. Two probands with isochromosomes 12p and the three cases with isochromosome 9p showed 3 alleles (two different maternal alleles and one paternal allele) at several loci mapping to distal 12p and 9p, respectively. Maternal heterozygosity for distal markers was reduced to homozygosity for markers closer to the centromere in both i(12p) cases and in one i(9p) case. For one patient with isochromosome 12p, the maternal band was clearly stronger than the paternal one at some loci, but two distinct maternal alleles were never seen. For one foetus and the patient with tetrasomy 9p, distal markers showed maternal heterozygosity. All proximal markers were not informative in these two i(9p) cases. Our findings indicate common features in different autosomal isochromosomes: the origin of the isochromosomes analysed in predominantly maternal; and a common mechanism appears to underlie their formation, namely due to meiosis II nondisjunction followed by a rearrangements leading to duplication of the short and loss of the long arm.

Editor—At least 168 cases with a supernumerary marker chromosome (SMC) from all chromosomes not including chromosome 15 have been documented.1 Birth prevalence is estimated at 0.14 to 0.72 per 1000.2 Subjects with a SMC have a partial trisomy (duplication) and in some cases a partial tetrasomy (triplication) of the genetic material contained in the SMC. The risk of an abnormal phenotype associated with a randomly ascertained de novo SMC derived from acrocentric autosomes (excluding chromosome 15) is estimated to be approximately 7% compared with approximately 28% for SMCs derived from non-acrocentric autosomes.1 The great variability of clinical findings in patients with SMCs originating from the same chromosome is probably the result of variation in size and genetic content, the degree of mosaicism, and uniparental disomy of the normal homologues of the chromosome from which the SMC derived. Evidence that subjects with SMCs might have an increased risk for UPD of the structurally normal homologues of the SMCs has been reported by several authors. To the best of our knowledge the coexistence of SMCs with UPD has been described for chromosomes 6, 7, 15, 20, and X.3-7 Here, we describe a further patient with multiple congenital anomalies, developmental delay, and the unique finding of coexistence of SMC 1 mosaicism and maternal uniparental disomy 1. The female patient was born at term after an uneventful pregnancy. At her birth, her mother was 33 years old and her father was 47 years old. Birth weight was 2500 g and length 49 cm. At the age of 6 years, she was investigated because of mental retardation. Height (1.14 m) and weight (17 kg) were within the normal range, but head circumference (44 cm) was far below the 3rd centile. Additional findings were temporal narrowing, downward slanting palpebral fissures, …

Rett syndrome (RTT) is an X-linked, dominant neurodevelopmental disorder caused by mutations in MECP2, encoding the methyl-CpG-binding protein 2 (MeCP2). A major paradox in the pathogenesis of RTT is how mutations in ubiquitously transcribed MECP2 result in a phenotype specific to the central nervous system (CNS) during postnatal development. To address this question, we have used a novel approach for quantitating the level and distribution of wild-type and mutant MeCP2 in situ by immunofluorescence and laser scanning cytometry. Surprisingly, cellular heterogeneity in MeCP2 expression level was observed in normal brain with a subpopulation of cells exhibiting high expression (MeCP2(hi)) and the remainder exhibiting low expression (MeCP2(lo)). MeCP2 expression was significantly higher in CNS compared with non-CNS tissues of human and mouse by automated quantitation of MeCP2 on multiple tissue arrays. Quantitative localization of MeCP2 expression phenotypes in normal human brain showed a mosaic, but distinct, distribution pattern, with MeCP2(hi) neurons highest in layer IV of the cerebrum and MeCP2(lo )neurons highest in the granular layer of the cerebellum. In female RTT brains, MECP2 mutant-expressing cells were identified as cells negative for the MeCP2 C-terminal epitope. MECP2 mutant-expressing cells were randomly localized in Rett cerebrum and cerebellum and showed normal MeCP2 expression with N-terminal-specific anti-MeCP2. These results demonstrate a CNS-specific cellular phenotype of MeCP2 high expression and suggest that MECP2 mutations in RTT are only manifested in MeCP2(hi) cells. In addition, our results demonstrate the power of laser scanning cytometry in examining complex cellular phenotypes in disease pathogenesis.

Triploidy is one of the most frequently observed chromosome abnormalities in spontaneous abortions in humans. The parental origin of the additional chromosome set is known to have a major impact on the phenotype of the foetuses and to result in differences in size and structure of the placenta. Early studies based on cytogenetic polymorphisms indicated a preponderant diandric origin of the triploidies; such detection method, however, is known to be prone to error. Other studies revealed a predominant digynic origin in cases with longer intrauterine survival. It is now thought that, to some extent, a detection bias in favour of cases with associated partial hydatidiform moles may account for the high incidences of diandric cases reported in some studies. Furthermore, depending on the gestational age of the cases analysed there may indeed be differences in the proportion of diandric and digynic triploidies. We investigated the parental origin and mechanisms of formation of triploidy in a group of 25 probands with gestational ages ranging from 8 to 37 weeks. DNA samples were extracted from foetal material and from blood samples of the parents, and were analysed using microsatellite markers. The parental origin of the triploidies was found to be maternal in 20 cases and paternal in 5. Regarding the digynic cases, an error at meiosis I was inferred in 10 cases, whereas in the other half an error occurred at meiosis II. All five diandric cases included in this study were found to be due to dispermy. No significant differences in the average maternal ages were found amongst the different subgroups of patients.

We report on a family with a balanced complex chromosomal rearrangement (CCR) involving eight breakpoints between chromosomes 6, 7, 18, and 21 in the father. All three sons inherited one derivative chromosome from the father and in addition each inherited a different recombinant chromosome resulting in a partial trisomy 6q in the first, an apparently balanced karyotype in the second, and a partial trisomy 7q in the third son. Fluorescence in situ hybridisation (FISH) and microsatellite analysis were essential for the identification of the breakpoints. In addition, the results were confirmed by a 24-colour FISH experiment using the spectral karyotyping (SKYtrade mark) system. Paternal origin of the de novo CCR in the father was demonstrated for the first time by haplotype analysis. This is the second report of a CCR leading to simpler but unbalanced translocations in offspring as a consequence of recombination during gametogenesis, and the first report of a family case of CCR exhibiting as many as eight breakpoints in the transmitting carrier. The initial prediction that viable offspring would be quite unlikely had to be revised after the birth of three children. Genetic counselling of carriers of balanced complex rearrangements has to consider a higher probability for unbalanced recombinations than has been so far commonly assumed.

We report on a maternal uniparental disomy of chromosome 22 in a patient with severe intra-uterine growth retardation. Karyotyping of a placental tissue revealed non-mosaic trisomy 22, whereas lymphocyte chromosomes from the newborn were normal 46,XY. Microsatellite analysis using DNA extracted from white blood cells showed maternal uniparental heterodisomy for chromosome 22. Thus, the conceptus started as maternal trisomy due to meiotic non-disjunction, and trisomy rescue occurred subsequently through loss of the paternal homologue resulting in maternal uniparental disomy. Normal phenotypes in previous reports have suggested that maternal UPD 22 has no impact on the phenotype. Thus, growth retardation in this patient was probably caused by dysfunction of the trisomic placenta.

We report on a 4 year-old girl with a 1p36.3-pter deletion. Clinical findings included minor anomalies of face and distal limbs, patent ductus arteriosus, the Ebstein heart anomaly, and brain atrophy with seizures. Conventional GTG-banded chromosome analysis revealed a normal (46, XX) result, Subsequent analysis by fluorescent in situ hybridization (FISH) using distal probes demonstrated a deletion of 1p36.6-pter. Molecular investigations with microsatellite markers showed hemizygosity at three loci at 1p36.3 with loss of the paternal allele, The deletion of 1p36.3 is difficult to identify by banding alone ; indeed, our patient represents the third reported case with a del(1)(p36.3) that was detected only after more detailed analysis. In all three cases the deletion was detected through screening of patients with multiple congenital anomalies/mental retardation syndromes suggestive of autosomal chromosome aberrations for subtelomeric submicroscopic deletions by means of FISH or microsatellite marker analysis. On the basis of these observations we highly recommend that FISH with a subtelomeric Ip probe be routinely performed in patients with similar facial phenotype, severe mental retardation and seizures, and a heart malformation, particularly the Ebstein anomaly.

The Angelman syndrome (AS) is caused by genetic abnormalities affecting the maternal copy of chromosome region 15q12. Until recently, the molecular diagnosis of AS relied on the detection of either a deletion at 15q11-13, a paternal uniparental disomy (UPD) for chromosome 15 or imprinting mutations. A fourth class of genetic defects underlying AS was recently described and consists of mutations of the UBE3A gene. The vast majority of mutations reported so far are predicted to cause major disruptions at the protein level. It is unclear whether mutations with less drastic consequences for the gene product could lead to milder forms of AS. We report on our results obtained by screening 101 clinically diagnosed AS patients for mutations in the UBE3A gene. Non-stringent clinical criteria were purposely applied for inclusion of AS patients in this study. The mutation search was carried out by single-strand conformation polymorphism (SSCP), and SSCP/restriction fragment length polymorphism (RFLP) analyses and revealed five novel UBE3A gene mutations as well as three different polymorphisms. All five mutations were detected in patients with typical features of AS and are predicted to cause frameshifts in four cases and the substitution of a highly conserved residue in the fifth. The results we obtained add to the as yet limited number of reports concerning UBE3A gene mutations. Important aspects that emerge from the data available to date is that the four classes of genetic defects known to underlie AS do not appear to cover all cases. The genetic defect underlying approximately 10% of AS cases, including some familial cases, remains unknown

Interstitial chromosomal deletions at 22q11.2 and 7q11.23 are detected in the vast majority of patients affected by CATCH 22 syndromes and the Williams-Beuren syndrome, respectively. In a group of 15 Williams-Beuren patients, we have shown previously that a large number of 7q11.23 deletions occur in association with an interchromosomal rearrangement, indicative of an unequal crossing-over event between the two homologous chromosomes 7. In this study, we show that a similar mechanism also underlies the formation of the 22q11.2 deletions associated with CATCH 22. In eight out of 10 families with a proband affected by CATCH 22, we were able to show that a meiotic recombination had occurred at the critical deleted region based on segregation analysis of grandparental haplotypes. The incidences of crossovers observed between the closest informative markers, proximal and distal to the deletion, were compared with the expected recombination frequencies between the markers. A significant number of recombination events occur at the breakpoint of deletions in CATCH 22 patients (P = 2.99x10(-7)). The segregation analysis of haplotypes in three-generation families was also performed on an extended number of Williams-Beuren cases (22 cases in all). The statistically significant occurrence of meiotic crossovers (P = 4.45x10(-9)) further supports the previous findings. Thus, unequal meiotic crossover events appear to play a relevant role in the formation of the two interstitial deletions. The recurrence risk for healthy parents in cases where such meiotic recombinations can be demonstrated is probably negligible. Such a finding is in agreement with the predominantly sporadic occurrence of the 22q11.2 and 7q11. 23 deletions. No parent-of-origin bias was observed in the two groups of patients with regard to the origin of the deletion and to the occurrence of inter- versus intrachromosomal rearrangements.