Detection of maternal uniparental disomy at the two imprinted genes on chromosome 7, GRB10 and PEG1/MEST, in a Silver-Russell syndrome patient using methylation-specific PCR assays

Prenatal diagnosis of 7 cases with uniparental disomy by utilization of single nucleotide polymorphism array

Background

The phenotypes of uniparental disomy (UPD) are variable, which may either have no clinical impact, lead to clinical signs and symptoms. Molecular analysis is essential for making a correct diagnosis. This study involved a retrospective analysis of 4512 prenatal diagnosis samples and explored the molecular characteristics and prenatal phenotypes of UPD using a single nucleotide polymorphism (SNP) array.

Results

Out of the 4512 samples, a total of seven cases of UPD were detected with an overall frequency of 0.16%. Among the seven cases of UPD, two cases are associated with chromosomal aberrations (2/7), four cases (4/7) had abnormal ultrasonographic findings. One case presented with iso-UPD (14), and two case presented with mixed hetero/iso-UPD (15), which were confirmed by Methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA) as maternal UPD (15) associated with Prader-Willi syndrome (PWS). Four cases had iso-UPD for chromosome 1, 3, 14, and 16, respectively; this is consistent with the monosomy rescue mechanism. Another three cases presented with mixed hetero/isodisomy were consistent with a trisomy rescue mechanism.

Conclusion

The prenatal phenotypes of UPD are variable and molecular analysis is essential for making a correct diagnosis and genetic counselling of UPD. The SNP array is a useful genetic test in prenatal diagnosis cases with UPD.

[Russell Silver syndrome: report of three cases and review of the literature]

Le syndrome de Silver Russell (SSR) est une maladie génétique rare. Sa prévalence est estimée à 1/100.000. Il s’agit d’une pathologie de l’empreinte parentale, caractérisée par une grande diversité phénotypique. Ses signes cliniques majeurs sont: un retard de croissance intra-utérin sévère, un retard staturo-pondéral post natal, une dysmorphie cranio-faciale particulière et une asymétrie des membres. Nous rapportons dans ce travail les observations de trois patients, qui présentent un retard staturo-pondéral, une dysmorphie faciale caractéristique du SSR et une hemihypertrophie corporelle. Nous discutons à travers ces cas les aspects cliniques et génétiques de ce rare syndrome.

Genomic organization and control of the grb7 gene family

Grb7 and their related family members Grb10 and Grb14 are adaptor proteins, which participate in the functionality of multiple signal transduction pathways under the control of a variety of activated tyrosine kinase receptors and other tyrosine-phosphorylated proteins. They are involved in the modulation of important cellular and organismal functions such as cell migration, cell proliferation, apoptosis, gene expression, protein degradation, protein phosphorylation, angiogenesis, embryonic development and metabolic control. In this short review we shall describe the organization of the genes encoding the Grb7 protein family, their transcriptional products and the regulatory mechanisms implicated in the control of their expression. Finally, the alterations found in these genes and the mechanisms affecting their expression under pathological conditions such as cancer, diabetes and some congenital disorders will be highlighted.

No evidence for isolated imprinting mutations in the PEG1/MEST locus in Silver-Russell patients

Imprinting defects have meanwhile been described in nearly all human imprinting disorders among them Silver-Russell syndrome (SRS). In this disorder, 11p15 epimutations and maternal Uniparental Disomy of chromosome 7 (UPD7) are detectable in approximately 50% of patients. To find out whether isolated imprinting defects on chromosome 7 play a role in the aetiology of SRS we screened a cohort of 54 SRS patients without 11p15 epimutations. Methylation-specific PCR was carried out for the PEG1/MEST locus in 7q31. This test detects all known segmental and complete UPD7 cases. The exclusion of isolated imprinting defects in our study population shows that this type of epimutation at the PEG1/MEST locus in 7q31 does not play a relevant role in SRS. However, the role of imprinting disturbances in other genes cannot be excluded.