Identification of interstitial maternal uniparental disomy (UPD) (14) and complete maternal UPD(20) in a cohort of growth retarded patients.

The association of uniparental disomy (UPD) and short stature has been reported for different chromosomes and in several conditions. Therefore, we investigated a cohort of 21 patients referred because of intrauterine and postnatal growth retardation for UPD of chromosomes 2, 7, 9, 14, 16, and 20. Typing of short tandem repeats showed maternal UPD(14) and maternal UPD(20) in two cases. In the first case, an interstitial UPD(14) was detected and the growth retarded newborn showed some additional clinical signs in common with the putative "maternal UPD(14) syndrome". The maternal UPD(20) patient showed minor features. However, since it is only the second maternal UPD(20) case it is too early to delineate a specific syndrome and the role of this constitution in growth remains to be investigated. Our data suggest that searching for UPD in growth retarded patients is a helpful approach to getting more information on the role of UPD in growth retardation. Based on our results, general considerations and indications for UPD testing are discussed.

Gene dosage analysis in Silver-Russell syndrome: use of quantitative competitive PCR and dual-color FISH to estimate the frequency of duplications in 7p11.2-p13.

Silver-Russell syndrome (SRS) describes a heterogeneous malformation syndrome mainly characterized by intrauterine and postnatal growth retardation (IUGR/PNGR). Approximately 10% of SRS cases have been associated with maternal uniparental disomy (matUPD) 7. This suggests the involvement of at least one imprinted gene on chromosome 7 in the pathogenesis of SRS. Additionally, two familial and one single SRS patients have been published with an interstitial duplication in 7p11.2-p13, including the genes GRB10 and IGFBP1; IGFBP3 was investigated in only one case revealing duplication; conversely, double gene dosage of EGFR was excluded in all 3 patients. Two further cytogenetically abnormal cases, one with a paracentric inversion (7)(p14p12) and one with matUPD7/partial trisomy for 7p13-q11, confirmed that the proximal short arm of chromosome represents an interesting region possibly harboring (a) candidate gene(s) for SRS. Although previously published investigations on the genes GRB10, IGFBP1, IGFBP3, and EGFR report neither disease-relevant mutations nor abnormal imprinting patterns, the SRS cases with chromosomal duplications suggest that variation of gene copy number might be a further type of mutation. To obtain meaningful results on the frequency of duplications in proximal 7p, we screened 32 SRS patients using quantitative PCR assays for GRB10, IGFBP1, IGFBP3, and EGFR. The data were confirmed by dual-color fluorescence in situ hybridization (FISH) of spot check samples. Results obtained by both methods exclude duplications in all analyzed patients and indicate an overall percentage of duplication among SRS patients between 2.4% (GRB10) and 5% (IGFBP1). By testing and evaluating quantitative competitive PCR for various loci, we developed a practical approach for gene dosage analysis which can be easily established for routine purposes.

[Uniparental disomy 7 in the pathogenesis of Silver-Russell syndrome]. / A 7-es kromoszóma uniparentalis disomiája a Silver-Russel-syndroma kóreredetében.

The authors report the frequency and the clinical signs of uniparental disomy of chromosome 7 in Silver-Russell syndrome patients. A cohort of 73 families were typed with Short Tandem Repeat markers from chromosomes 7. In 6 patients maternal uniparental disomy 7 (UPD7) was detected. Summarising their data and those from the literature, an overall frequency of maternal uniparental disomy 7 of approximately 10% can be estimated. Allelic distribution in two of their maternal uniparental disomy 7 families indicates complete isodisomy whereas allelic patterns in the other four families are consistent with partial and complete heterodisomy, respectively. The clinical features of maternal uniparental disomy 7 patients do not show any deviation from the non-uniparental disomy 7 patients. Additionally, there was not hint for possible influences of iso- or heterodisomy, possibly associated with different stages of mosaicism. Their results demonstrate the necessity to screen SRS patients for UPD7 although the effect of UPD7 cannot be correlated to the SRS phenotype yet. Furthermore, an association between UPD for chromosomes other than 7 and SRS seems to be negligible. Vice versa, maternal UPD7 is not detectable in non-SRS patients. Therefore, testing for maternal UPD7 can be restricted to SRS families, searching for other UPDs in this population does not seem to be reasonable. Additionally, cytogenetic analysis should also be performed in SRS patients: identification of commonly involved chromosomal regions should allow narrowing down a SRS-relevant region.

Formation of uniparental disomy 7 delineated from new cases and a UPD7 case after trisomy 7 rescue. Presentation of own results and review of the literature.

Maternal uniparental disomy for the entire chromosome 7 (matUPD7) has been reported several times in Silver-Russell syndrome (SRS) and growth-restricted patients. Here we present our results from the analysis of an abortion with confined placental mosaicism (CPM) for trisomy 7 which showed a maternal meiotic origin of the trisomy in the placenta and rescue to maternal UPD7 in foetal membrane. Furthermore, two newly detected SRS cases with maternal UPD7 revealed isodisomy and partial heterodisomy, respectively. Summarising these results with those published previously on the origin of UPD7, similar numbers of isodisomy (n=11) and cases with complete or partial heterodisomy (n=12) have been reported. In respect to the different formation mechanisms of UPD, complete isodisomy should be the result of a post-zygotic mitotic segregation error, whereas heterodisomic UPDs should be caused by trisomic rescue after meiotic non-disjunction events. In maternal UPD7, 50% of cases seem to be caused by post-zygotic mitotic segregation errors, which is similar to the situation in trisomy 7. This result corresponds to the situation in trisomy 8 but is in contrast to observations in the frequent aneuploidies. Thus, the different findings in these aberrations reflect the presence of multiple factors that act to ensure normal segregation, varying in importance for each chromosome.

Origin of uniparental disomy 6: presentation of a new case and review on the literature.

Paternal uniparental disomy (UPD) of chromosome 6 has been reported several times in patients with (transient) neonatal diabetes mellitus ((T)NDM). Here we present our short tandem repeat typing results in a new patient with NDM, revealing a paternal isodisomy (UPiD). Summarising these data with those published previously on complete paternal (n=13) and maternal (n=2) UPD6, all cases show isodisomy. In general, several modes of UPD formation have been suggested: While a meiotic origin of UPD mainly results in a uniparental heterodisomy (UPhD), UPiD is probably the result of a post-zygotic mitotic error. This mode of formation consists of a mitotic nondisjunction in a disomic zygote, followed by either a trisomic rescue or a reduplication. Endoduplication in a monosomic zygote is another possible but less probable mechanism, taking into consideration that monosomic zygotes are not viable. The exclusive finding of isodisomy in case of chromosome 6 therefore gives strong evidence that segregational errors of this chromosome are mainly influenced by postzygotic factors. This hypothesis is supported by the observation of two cases with partial paternal UPiD6 originating from mitotic recombination events. The influence of mitotic segregational errors in UPD6 formation is in agreement with the results in trisomy/UPD of other chromosomes of the C group (7 and 8), and is in remarkable contrast to the findings in studies on the origin of the frequent aneuploidies. Multiple factors ensure normal segregation and we speculate that they vary in importance for each chromosome.

Paternally inherited deletion of CSH1 in a patient with Silver-Russell syndrome.

In a continuing study on the aetiology of Silver-Russell syndrome (SRS), we detected a patient with a heterozygous deletion in the growth hormone gene cluster (17q22-q24). The deletion of the chorionic somatomammotrophin hormone 1 (CSH1) gene was inherited from the patient's father. The patient shows typical symptoms of SRS. Though deletions of CSH1 have been reported without any phenotypic consequences, the heterozygous deletion might be involved in the aetiology of SRS in the case presented here. Apart from other observations in SRS, like maternal uniparental disomy 7, changes in the genomic region 17q22-qter might be responsible for the expression of this syndrome for at least some of the patients, leading to the heterogeneity of SRS.

Human GRB10 is imprinted and expressed from the paternal and maternal allele in a highly tissue- and isoform-specific fashion.

As part of a systematic screen for novel imprinted genes of human chromosome 7 we have investigated GRB10, which belongs to a small family of adapter proteins, known to interact with a number of receptor tyrosine kinases and signalling molecules. Upon allele-specific transcription analysis involving multiple distinct splice variants in various fetal tissues, we found that human GRB10 is imprinted in a highly isoform- and tissue-specific manner. In fetal brains, most variants are transcribed exclusively from the paternal allele. Imprinted expression in this tissue is not accompanied by allele-specific methylation of the most 5' CpG island. In skeletal muscle, one GRB10 isoform, gamma1, is expressed from the maternal allele alone, whereas in numerous other fetal tissues, all GRB10 splice variants are transcribed from both parental alleles. A remarkable finding is paternal-specific expression of GRB10 in the human fetal brain, since, in the mouse, this gene is transcribed exclusively from the maternal allele. To our knowledge, this is the first example of a gene that is oppositely imprinted in mouse and human.