Identification of a 21q22 duplication in a Silver-Russell syndrome patient further narrows down the Down syndrome critical region.

Several duplications of chromosome 21q helped to narrow down the Down syndrome (DS) critical region (DSCR) to chromosomal band 21q22 with an approximate length of 5.4 Mb. Recently, it has been suggested that the facial gestalt of DS has been linked to the distal part of the DSCR whereas the proximal region harboring DSCR1/RCAN and DSCAM should be associated with the cardiac abnormalities. Here, we report on a patient with Silver-Russell syndrome (SRS) and a paternally inherited 0.46 Mb duplication in 21q22 affecting the KCNE1 and DSCR1/RCAN genes. The identification of an involvement of KCNE1 was interesting because it encodes the beta-subunit of the KvLQT1 channel as the slow component of the cardiac delayed rectifier K(+) current. Since duplication of the KCNQ1 gene encoding the alpha-subunit of the same channel was reported recently in another SRS patient, we screened both genes for mutations in a cohort of SRS patients without detecting pathologic variants. We presume that the duplication of the two functionally linked genes in different patients with the same disorder is a coincidental finding. However, the lack of DS typical clinical features in our case allows us to further narrow down the DSCR in 21q22. We conclude that DSCR1/RCAN is not sufficient for generating phenotypic features associated with DS but our observation does not contradict a possible role for DSCR1/RCAN in mediating DYRK1A-based effects.

Pure distal trisomy 2q: a rare chromosomal abnormality with recognizable phenotype.

We present clinical and molecular cytogenetic results of two unrelated patients with isolated distal trisomy of 2q33-qter and 2q35-q37.3 and a remarkable similar facial appearance. Common craniofacial features included a high hairline, broad nasal bridge, prominent nasal tip, thin upper lip vermillion, and large ears. Contrary to patients with duplications proximal to 2q33, the children with pure trisomy distal to 2q35 have normal or increased body measurements and show no major malformations. Moderate psychomotor delay was a constant finding.

LOT1 (ZAC1/PLAGL1) as member of an imprinted gene network does not harbor Silver-Russell specific variants.

Silver-Russell syndrome (SRS) is a heterogeneous disease associated with intrauterine and postnatal growth retardation (IUGR/PNGR), asymmetry and craniofacial dysmorphisms. In 7-10% of patients with SRS, maternal uniparental disomy of chromosome 7 can be detected; more than 38% carry hypomethylation of the imprinting region 1 in 11p15. These chromosomes harbor the imprinted genes IGF2, H19, LIT1 and MEST. In mice, interaction of these genes with the prenatally rexpressed Plagl1/Zac1 has been reported. The aim of this study was to identify mutations in the maternally imprinted LOT1(ZAC1/PLAGL1) gene in 6q24 in patients with SRS. We screened 30 patients with SRS and 14 patients with isolated IUGR/PNGR by SSCP and/or direct sequencing. Mutation analysis revealed nine genomic variants. Seven were novel but classified as apathogenic. Interestingly, two of these variants, g.10212T/A and g.10214C/A, showed strict association. However, our results do not indicate a relevant role of mutations in LOT1(ZAC1/PLAGL1) in the etiology of SRS.

Screening for genomic variants in ZFP57 in Silver-Russell syndrome patients with 11p15 epimutations.

Silver-Russell syndrome (SRS) describes a uniform malformation syndrome characterized by intrauterine and postnatal growth restriction and morphological abnormalities including a small triangular face, relative macrocephaly, asymmetry of the head and limbs, and clinodactyly V. In >38% of SRS cases a hypomethylation of the H19/IGF2 DMR in 11p15 can be detected. Recently, ZFP57 mutations have been identified as a cause of hypomethylation of multiple imprinted loci. To determine whether ZFP57 mutations influence the H19/IGF2 DMR we screened 30 SRS patients with 11p15-hypomethylation for mutations within the coding region of this gene. Thereby homozygosity for a novel variant in exon 6 of ZFP57 was detected in one patient. Heterozygosity for this variant was found in the patients' parents as well as in 2.5% of healthy controls. Except this new and probably apathogenic polymorphism and some registered SNPs no further variants were detected. In conclusion, this study does not provide evidence that ZFP57 mutations are the cause of 11p15-hypomethylation in SRS patients and contribute to the aetiology of SRS.

Broad clinical spectrum in Silver-Russell syndrome and consequences for genetic testing in growth retardation.

OBJECTIVE: Silver-Russell syndrome is a heterogenous disorder characterized by severe intrauterine growth restriction, lack of catch-up after birth, and specific dysmorphisms. In approximately 10% of patients, maternal uniparental disomy of chromosome 7 is detectable, but hypomethylation of the imprinting in 11p15 is the major epigenetic disturbance in Silver-Russell syndrome. The use of strict clinical criteria, indeed, results in relatively high detection rates for the 11p15 epimutation, but we feel that the application of a strict clinical scoring system is not useful in clinical workaday life because of the broad clinical spectrum in 11p15 epimutation and maternal uniparental disomy of chromosome 7 carriers. PATIENTS AND METHODS: We report on our experience of molecular testing in 188 patients referred for routine diagnostics of Silver-Russell syndrome and in a group of 20 patients with isolated intrauterine growth restriction/postnatal growth retardation. RESULTS: The molecular genetic results in both groups of data showed that 11p15 epimutation and maternal uniparental disomy of chromosome 7 carriers did not always show the unambiguous Silver-Russell syndrome phenotype. CONCLUSIONS: In addition to patients with the classical Silver-Russell syndrome phenotype fulfilling the Silver-Russell syndrome-specific scores, genetic testing for the 11p15 epimutation and/or maternal uniparental disomy of chromosome 7 should also be considered in case of "Silver-Russell syndrome-like" phenotypes, for example, mild intrauterine growth restriction and postnatal growth retardation associated with a prominent forehead and triangular face or asymmetry as the only clinical signs. In particular, the lack of intrauterine growth restriction in patients with a Silver-Russell syndrome-like phenotype should not automatically result in exclusion from molecular testing.

A 10.7 Mb interstitial deletion of 13q21 without phenotypic effect defines a further non-pathogenic euchromatic variant.

Chromosome 13 deletions are associated with widely varying phenotypes but the clinical picture nearly almost includes mental and growth retardation, craniofacial dysmorphisms, and/or malformations. Several attempts have been made to link monosomy 13q intervals with specific clinical features, but a genotype-phenotype correlation could not be delineated. We report on a woman with a normal phenotype and intelligence referred for chromosomal analysis because of recurrent abortions followed by reproductive loss. Conventional karyotyping revealed an interstitial deletion of chromosome 13q21. By SNP array analysis and FISH the deletion was shown to comprise nearly 10.7 Mb of euchromatic material. This region harbors several genes but an association with recurrent miscarriages has not yet been reported. This is the second report of a 13q21 deletion without psychomotoric retardation, dysmorphisms and malformations. Both cases indicate that this 13q21 deletion can be added to the growing list of euchromatic imbalances without obvious phenotypic abnormalities.

Growth retardation versus overgrowth: Silver-Russell syndrome is genetically opposite to Beckwith-Wiedemann syndrome.

Human growth is a complex process that requires the appropriate interaction of many players. Central members in the growth pathways are regulated epigenetically and thereby reflect the profound significance of imprinting for correct mammalian ontogenesis. In this review, we show that the growth retardation disorder Silver-Russell syndrome (SRS) is a suitable model to decipher the role of imprinting in growth. As we will show, SRS should not only be regarded as the genetically (and clinically) opposite disease to Beckwith-Wiedemann syndrome, but it also represents the first human disorder with imprinting disturbances that affect two different chromosomes (i.e. chromosomes 7 and 11). Thus, a functional interaction between factors encoded by chromosomes 7 and 11 is likely.

Search for subtelomeric imbalances by multiplex ligation-dependent probe amplification in Silver-Russell syndrome.

Chromosomal aberrations are typically associated with primordial growth retardation, psychomotoric constrictions, and dysmorphisms. Since these features may be present in patients with Silver-Russell syndrome (SRS) and chromosomal disturbances are also detected in a subgroup of SRS patients, we screened a cohort of 45 SRS patients for cryptic subtelomeric imbalances. Submicroscopic deletions/duplications in the telomere regions are meanwhile well known to cause a broad spectrum of conspicuous phenotypes, characterized by mental retardation and multiple further congenital anomalies. We hypothesize that SRS might represent at the mild end of the broad phenotypic range of subtelomeric imbalances. Screening of the patients was performed by multiplex ligation-dependent probe amplification (MLPA), a technique that has already been shown to be effective and reliable for measuring copy numbers. We excluded pathogenetically relevant copy number variations in the subtelomeres in our SRS patient cohort, but one patient carried an apathogenic polymorphic Yq deletion. It can therefore be concluded that this type of chromosomal aberration does not belong to the genetic causes of SRS and it is not necessary to include this test in the diagnostic algorithm of the disease.

Are H19 variants associated with Silver-Russell syndrome?

Opposite (epi)mutations affecting the imprinted region 11p15 are associated with Silver-Russell (SRS) and Beckwith-Wiedemann syndrome (BWS). Apart from other disturbances more than 35% of patients with SRS show hypomethylation at the imprinting control region 1 (ICR1) in 11p15. ICR1 is paternally methylated and regulates the expression of the paternally expressed growth factor IGF2 and the maternally expressed gene H19. The exact function of the non-coding RNA H19 is still unknown. However, the finding that this gene is highly conserved in mammals indicates profound functional relevance. Due to the supposed function of H19 in the regulation of the imprinted region 11p15 we searched for mutations in the transcribed sequence and the CTCF binding sites of H19 in 44 patients with SRS. In two cases different 3 base-pair (bp) deletions in exon 1 could be identified. A third patient carried a 39 bp duplication affecting exon 2 and intron 2. These three variants were not detected in 100 controls and 42 patients with isolated growth retardation. One of the patients carrying a mutation also showed hypomethylation at the ICR1 in 11p15. Splicing studies in HEK cells transfected with constructs carrying the three different variants revealed a deviation from the normal H19 splicing pattern in two of these individuals. However, analysis of lymphocytes of one of these two patients did not verify an altered expression pattern of H19. Nevertheless, our results indicate a relevant role of H19 in the aetiology of SRS: functional effects of these variants on chromatin restructuring of the ICR1, or altered function of H19 as a posttranslational modifying factor (microRNA/antisense RNA) are conceivable.

The centromeric 11p15 imprinting centre is also involved in Silver-Russell syndrome.

Silver-Russell syndrome (SRS) is a heterogeneous disorder characterised by severe intrauterine and postnatal growth retardation, limb and body asymmetry, a typical facial appearance and less common dysmorphisms. Recently, epimutations and maternal duplications affecting the short arm of chromosome 11 have been shown to have a crucial role in the aetiology of the disease. Disturbances in the same genomic region cause the overgrowth disorder Beckwith-Wiedemann syndrome (BWS). In BWS, mutations in the telomeric as well as in the centromeric imprinting centres (ICR1 and ICR2) in 11p15 can be observed. In SRS, methylation defects in the imprinted region in 11p15 were considered to be restricted to the telomeric ICR1. They can be detected in about 30% of patients. This article reports on the first patient with SRS with a cryptic duplication restricted to the centromeric ICR2 domain in 11p15. The maternally inherited duplication in this patient included a region of 0.76-1 Mbp and affected the genes regulated by the ICR2, among them CDKN1C and LIT1. This study provides evidence for a role for this imprinting centre in the aetiology of SRS and shows that SRS presents a picture genetically opposite to that of BWS.

No evidence for additional imprinting defects in Silver-Russell syndrome patients with maternal uniparental disomy 7 or 11p15 epimutation.

Silver-Russell syndrome (SRS) is mainly characterised by intrauterine and postnatal growth retardation (IUGR and PNGR), asymmetry, clinodactyly V and craniofacial abnormalities. More than 35% of patients carry a hypomethylation of the telomeric imprinting centre region 1 (ICR1) in 11p15; single patients show a maternal duplication of 11p15. An additional 7-10% of patients with SRS have maternal uniparental disomy of chromosome 7 (mUPD7). Another disorder caused by epigenetic defects is transient neonatal diabetes mellitus (TNDM) which is associated with loss of methylation (LOM) in 6q24. After detecting methylation loss at multiple imprinted loci in patients with TNDM, Mackay et al. recently proposed the existence of a maternal hypomethylation syndrome presenting as TNDM. They therefore concluded that patients with other disorders associated with LOM at one (maternally) methylated locus might also carry LOM at multiple loci. Similar observations have also been reported in Beckwith-Wiedemann syndrome (BWS): nearly 25% of patients displayed abnormal methylation patterns of ICRs additional to those in 11p15. To show whether general hypomethylation is a common phenomenon in imprinting disorders we carried out methylation analyses for the imprinted regions 14q32, 6q24 and the centromeric imprinting region ICR2 on 11p15 for 10 patients with SRS carrying mUPD7 and 22 patients with LOM at the telomeric imprinting region ICR1. We showed that further epigenetic defects did not occur in the groups of SRS with LOM of ICR1 or mUPD7, and that these subentities do not belong to the diseases with a general hypomethylation defect, such as TNDM and BWS.