A cryptic familial rearrangement of 11p15.5, involving both imprinting centers, in a family with a history of short stature

Executive functioning in adolescents and adults with Silver-Russell syndrome

Silver-Russell syndrome (SRS) is a rare imprinting disorder characterized by prenatal and postnatal growth retardation. The two principal causes of SRS are loss of methylation on chromosome 11p15 (11p15 LOM) and maternal uniparental disomy of chromosome 7 (UPD(7)mat). Knowledge of the neuropsychological profile of SRS remains sparse and incomplete even if several difficulties related to attention and learning have been reported both in the literature and by patients with SRS. These difficulties could be the result of troubles in different cognitive domains, but also of executive dysfunction. Nevertheless, executive functioning has never been investigated, even though executive functions play an essential role in psychological development, and are extensively involved in daily life. The present study explored the executive functioning of individuals with SRS due to UPD(7)mat or 11p15 LOM. A battery of executive tasks assessing cognitive flexibility, inhibitory control, and working memory, together with a task assessing sustained attention, was administered to 19 individuals with SRS (13-39 years) and 19 healthy controls. The Behavior Rating Inventory of Executive Function was also completed by the participants' families. The results showed that participants with SRS had similar performance (z-scores) to our controls, in a context of normal intellectual efficiency. Group comparisons with Bayesian statistics showed a single difference between the 11p15 LOM and control groups: the completion time for part A of the Trail Making Test appeared to be longer in the 11p15 LOM group than in the control group. However, at the clinical level, several participants with SRS had clinically significant scores on various measures of EFs. Thus, the cognitive phenotype of SRS did not appear to be characterized by executive dysfunction, but individuals with SRS could be at high risk of developing executive dysfunction or attention-deficit/hyperactivity disorder. These results provide new insights into the neuropsychological profile of individuals with SRS.

A paternally inherited 1.4 kb deletion of the 11p15.5 imprinting center 2 is associated with a mild familial Silver-Russell syndrome phenotype

The Silver-Russell syndrome (SRS) is a rare disorder characterized by heterogeneous clinical features, including growth retardation, typical facial dysmorphisms, and body asymmetry. Genetic alterations causative of SRS mostly affect imprinted genes located on chromosomes 7 or 11. Hypomethylation of the Imprinting Center 1 (IC1) of the chromosome 11p15.5 is the most common cause of SRS, while the Imprinting Center 2 (IC2) has been more rarely involved. Specifically, maternally inherited 11p15.5 deletions including the IC2 have been associated with the Beckwith-Wiedemann Syndrome (BWS), while paternal deletions with a variable spectrum of phenotypes. Here, we describe the case of a girl with a mild SRS phenotype associated with a paternally inherited 1.4 kb deletion of IC2. The father of the proband inherited the deletion from his mother and showed normal growth, while the paternal grandmother had the deletion on her paternal chromosome and exhibited short stature. Together with previous findings obtained in mouse and humans, our data support the notion that deletion of the paternal copy of IC2 can cause SRS.

Structural and sequence variants in patients with Silver-Russell syndrome or similar features-Curation of a disease database

Silver-Russell syndrome (SRS) is a clinically and molecularly heterogeneous disorder involving prenatal and postnatal growth retardation, and the term SRS-like is broadly used to describe individuals with clinical features resembling SRS. The main molecular subgroups are loss of methylation of the distal imprinting control region (H19/IGF2:IG-DMR) on 11p15.5 (50%) and maternal uniparental disomy of chromosome 7 (5%-10%). Through a comprehensive literature search, we identified 91 patients/families with various structural and small sequence variants, which were suggested as additional molecular defects leading to SRS/SRS-like phenotypes. However, the molecular and phenotypic data of these patients were not standardized and therefore not comparable, rendering difficulties in phenotype-genotype comparisons. To overcome this challenge, we curated a disease database including (epi)genetic phenotypic data of these patients. The clinical features are scored according to the Netchine-Harbison clinical scoring system (NH-CSS), which has recently been accepted as standard by consensus. The structural and sequence variations are reviewed and where necessary redescribed according to recent recommendations. Our study provides a framework for both research and diagnostic purposes through facilitating a standardized comparison of (epi)genotypes with phenotypes of patients with structural/sequence variants.

Chromosomal rearrangements in the 11p15 imprinted region: 17 new 11p15.5 duplications with associated phenotypes and putative functional consequences

BACKGROUND

The 11p15 region contains two clusters of imprinted genes. Opposite genetic and epigenetic anomalies of this region result in two distinct growth disturbance syndromes: Beckwith-Wiedemann (BWS) and Silver-Russell syndromes (SRS). Cytogenetic rearrangements within this region represent less than 3% of SRS and BWS cases. Among these, 11p15 duplications were infrequently reported and interpretation of their pathogenic effects is complex.

OBJECTIVES

To report cytogenetic and methylation analyses in a cohort of patients with SRS/BWS carrying 11p15 duplications and establish genotype/phenotype correlations.

METHODS

From a cohort of patients with SRS/BWS with an abnormal methylation profile (using ASMM-RTQ-PCR), we used SNP-arrays to identify and map the 11p15 duplications. We report 19 new patients with SRS (n=9) and BWS (n=10) carrying de novo or familial 11p15 duplications, which completely or partially span either both telomeric and centromeric domains or only one domain.

RESULTS

Large duplications involving one complete domain or both domains are associated with either SRS or BWS, depending on the parental origin of the duplication. Genotype-phenotype correlation studies of partial duplications within the telomeric domain demonstrate the prominent role of IGF2, rather than H19, in the control of growth. Furthermore, it highlights the role of CDKN1C within the centromeric domain and suggests that the expected overexpression of KCNQ1OT1 from the paternal allele (in partial paternal duplications, excluding CDKN1C) does not affect the expression of CDKN1C.

CONCLUSIONS

The phenotype associated with 11p15 duplications depends on the size, genetic content, parental inheritance and imprinting status. Identification of these rare duplications is crucial for genetic counselling.

Two familial intrachromosomal insertions with maternal dup(6)(p22.3p25.3) or dup(2)(q24.2q32.1) in recombinant offspring

In this study, we describe two patients with a recombinant chromosome secondary to a maternal intrachromosomal insertion. Patient 1 was a girl with dup(6)(p22.3p25.3). Patient 2 was a boy with dup(2)(q24.2q32.1). Both familial rearrangements were characterized by means of GTG-bands, fluorescence in-situ hybridization, and comparative genomic hybridization microarray analyses. Patient 1 had an ∼23 Mb gain that involved the bands 6p22.3-6p25.3. Patient 2 had an ∼23 Mb gain (cytobands 2q24.2-2q32.1) and a further ∼1.9 Mb gain of 2p16.2-p16.3. The phenotype of each patient was in agreement with the typical 6p duplication or 2q24.2q32.1 duplication syndrome. The compound macular lesion in patient 1 suggests that retinal anomalies may be a part of the 6p trisomy phenotype. Among the 70 intrachromosomal insertions compiled here (including 68 from the literature), four were submicroscopic unbalanced insertions inherited from a balanced carrier and 66 were detectable on banded chromosomes (with or without array comparative genomic hybridization or other high-resolution assessment) and therefore spanned at least 5 Mb. Pericentric insertions are found in most chromosomes, whereas the paracentric ones are mainly observed in large and medium chromosome arms. That the former outnumber the latter in almost a 2 : 1 ratio appears to be related to the technique of diagnosis, size of the insertion, and size of the involved chromosome. Regardless of the apparent excess of carrier mothers, carriers of an intrachromosomal insertion beget almost twice as many children with a duplication than with a deletion.

Silver-Russell Syndrome and Beckwith-Wiedemann Syndrome: Opposite Phenotypes with Heterogeneous Molecular Etiology

Silver-Russell syndrome (SRS) and Beckwith-Wiedemann syndrome (BWS) are 2 clinically opposite growth-affecting disorders belonging to the group of congenital imprinting disorders. The expression of both syndromes usually depends on the parental origin of the chromosome in which the imprinted genes reside. SRS is characterized by severe intrauterine and postnatal growth retardation with various additional clinical features such as hemihypertrophy, relative macrocephaly, fifth finger clinodactyly, and triangular facies. BWS is an overgrowth syndrome with many additional clinical features such as macroglossia, organomegaly, and an increased risk of childhood tumors. Both SRS and BWS are clinically and genetically heterogeneous, and for clinical diagnosis, different diagnostic scoring systems have been developed. Six diagnostic scoring systems for SRS and 4 for BWS have been previously published. However, neither syndrome has common consensus diagnostic criteria yet. Most cases of SRS and BWS are associated with opposite epigenetic or genetic abnormalities in the 11p15 chromosomal region leading to opposite imbalances in the expression of imprinted genes. SRS is also caused by maternal uniparental disomy 7, which is usually identified in 5-10% of the cases, and is therefore the first imprinting disorder that affects 2 different chromosomes. In this review, we describe in detail the clinical diagnostic criteria and scoring systems as well as molecular causes in both SRS and BWS.

Two maternal duplications involving the CDKN1C gene are associated with contrasting growth phenotypes

Background

The overgrowth-associated Beckwith-Wiedemann syndrome (BWS) and the undergrowth-associated Silver-Russell syndrome (SRS) are characterized by heterogeneous molecular defects affecting a large imprinted gene cluster at chromosome 11p15.5-p15.4. While maternal and paternal duplications of the entire cluster consistently result in SRS and BWS, respectively, the phenotypes associated with smaller duplications are difficult to predict due to the complexity of imprinting regulation. Here, we describe two cases with novel inherited partial duplications of the centromeric domain on chromosome 11p15 associated with contrasting growth phenotypes.

Findings

In a male patient affected by intrauterine growth restriction and postnatal short stature, we identified an in cis maternally inherited duplication of 0.88 Mb including the CDKN1C gene that was significantly up-regulated. The duplication did not include the long non-coding RNA KCNQ1OT1 nor the imprinting control region of the centromeric domain (KCNQ1OT1:TSS-DMR or ICR2) in which methylation was normal. In the mother, also referring a growth restriction phenotype in her infancy, the duplication was de novo and present on her paternal chromosome. A different in cis maternal duplication, 1.13 Mb long and including the abovementioned duplication, was observed in a child affected by Tetralogy of Fallot but with normal growth. In this case, the rearrangement also included most of the KCNQ1OT1 gene and resulted in ICR2 loss of methylation (LOM). In this second family, the mother carried the duplication on her paternal chromosome and showed a normal growth phenotype as well.

Conclusions

We report two novel in cis microduplications encompassing part of the centromeric domain of the 11p15.5-p15.4 imprinted gene cluster and both including the growth inhibitor CDKN1C gene. Likely, as a consequence of the differential involvement of the regulatory KCNQ1OT1 RNA and ICR2, the smaller duplication is associated with growth restriction on both maternal and paternal transmissions, while the larger duplication, although it includes the smaller one, does not result in any growth anomaly.

Our study provides further insights into the phenotypes associated with imprinted gene alterations and highlights the importance of carefully evaluating the affected genes and regulatory elements for accurate genetic counselling of the 11p15 chromosomal rearrangements.

Electronic supplementary material

The online version of this article (doi:10.1186/s13148-016-0236-z) contains supplementary material, which is available to authorized users.

Familial 1.3-Mb 11p15.5p15.4 Duplication in Three Generations Causing Silver-Russell and Beckwith-Wiedemann Syndromes

Silver-Russell syndrome (SRS) and Beckwith-Wiedemann syndrome (BWS) are 2 opposite growth-affecting disorders. The common molecular cause for both syndromes is an abnormal regulation of genes in chromosomal region 11p15, where 2 imprinting control regions (ICR) control fetal and postnatal growth. Also, many submicroscopic chromosomal disturbances like duplications in 11p15 have been described among SRS and BWS patients. Duplications involving both ICRs cause SRS or BWS, depending on which parent the aberration is inherited from. We describe to our knowledge the smallest familial pure 1.3-Mb duplication in chromosomal region 11p15.5p15.4 that involves both ICRs and is present in 3 generations causing an SRS or BWS phenotype.