Novel Variant in PLAG1 in a Familial Case with Silver-Russell Syndrome Suspicion

Prenatal diagnosis of Silver-Russell syndrome with 8q12 deletion including the PLAG1 gene: a case report and review

Silver-Russell syndrome (SRS) is a clinically and genetically heterogeneous disorder. A retrospective analysis predicted that the live birth prevalence of SRS in Estonia is 1:15,886 [Yakoreva et al., Eur J Hum Genet, 2019, 27(11), 1649-1658]. The most common causative genetic mechanism in the proband is loss of paternal methylation in the imprinted control region 1 (ICR1) at 11p15.5 chromosome. A few studies suggested that inherited or de novo loss-of-function alterations of the PLAG1 gene, including the whole-gene deletion and intragenic pathogenic variants, could cause a rare type of SRS. To date, less than 20 unrelated PLAG1-related SRS cases have been reported, and the clinical information about these cases is limited. We report the first prenatal case of SRS with 8q12 deletion (including the PLAG1 gene). The fetus presented with intrauterine growth retardation, small for gestational age, relative macrocephaly at birth, and a protruding forehead. Unlike classical SRS cases, the fetus had micrognathia and did not show body asymmetry. We hope that the literature review in this study provides new insights into genotype-phenotype relationships of PLAG1-related SRS.

Clinical characterization of PLAG1- related Silver-Russell syndrome：A clinical report

BACKGROUND

Silver-Russell syndrome (SRS) is a rare genetic disorder that is mainly associated with prenatal and postnatal growth retardation. Loss of methylation on chromosome 11p15 and maternal uniparental disomy on chromosome 7 (upd(7)mat) are two common causes, accounting for approximately 50% and 10% of all patients, respectively. Pathogenic variants of genes, such as HMGA2, IGF2, CDKN1C, and PLAG1, have also been detected in patients with SRS. So far, SRS caused by PLAG1 alterations have only been described in two sporadic cases and three families.

PATIENT PRESENTATION

The genetic and clinical manifestations of SRS in a patient carrying a novel variant of PLAG1 were reported and these results were compared with those of five previously reported cases. Trio-based whole-exome sequencing revealed a heterozygous variation in PLAG1 (NM_002655.3: c.131del; p.(Asn44Thrfs*6)) in an infant girl with clinical suspicion of SRS. Familial studies confirmed that the mutation was inherited from her father. As seen in previously reported cases, the patient presented with prenatal and postnatal growth retardation, relative macrocephaly at birth, prominent forehead during infancy, and triangular face. However, no clinical characteristics such as feeding difficulties, hypothyroidism, or psychomotor and speech delay.

CONCLUSIONS

This study identified the sixth documented case of PLAG1 variants leading to SRS and expanded our knowledge of the molecular spectrum of SRS phenotypes.

Maternally inherited autosomal dominant PLAG-1 related Silver Russell syndrome in a fetus with intra-uterine growth restriction

We report a case of maternally inherited autosomal dominant PLAG-1 related Silver Russell syndrome (SRS) in a fetus with IUGR and a mother who had growth and feeding problems in early life, dextrocardia and an atrio-ventricular septal defect. Amniocentesis was performed due to marked intra-uterine growth restriction (IUGR). The array was normal. Whole exome sequencing (WES) revealed a maternally inherited heterozygous likely pathogenic variant in PLAG1 (NM_002655.3): c.402delT p.(Gly135Aspfs*94). This variant has not been reported previously. PLAG1 pathogenic variants are associated with autosomal dominant Silver Russell syndrome, which fits with the clinical phenotypes of both fetus and mother. PLAG1 variants have previously been reported post-natally in Silver Russell syndrome, but the phenotype tends to be milder than in 11p15.5 methylation-related cases with fewer physical features. Although cardiac anomalies are uncommon in SRS, they have been previously reported. To our knowledge, dextrocardia has not been previously associated with SRS and there were no other potential causative genetic variants found. This report aims to highlight this rare type of SRS as a cause of IUGR.

Routine Diagnostics Confirm Novel Neurodevelopmental Disorders

Routine diagnostics is biased towards genes and variants with satisfactory evidence, but rare disorders with only little confirmation of their pathogenicity might be missed. Many of these genes can, however, be considered relevant, although they may have less evidence because they lack OMIM entries or comprise only a small number of publicly available variants from one or a few studies. Here, we present 89 individuals harbouring variants in 77 genes for which only a small amount of public evidence on their clinical significance is available but which we still found to be relevant enough to be reported in routine diagnostics. For 21 genes, we present case reports that confirm the lack or provisionality of OMIM associations (ATP6V0A1, CNTN2, GABRD, NCKAP1, RHEB, TCF7L2), broaden the phenotypic spectrum (CC2D1A, KCTD17, YAP1) or substantially strengthen the confirmation of genes with limited evidence in the medical literature (ADARB1, AP2M1, BCKDK, BCORL1, CARS2, FBXO38, GABRB1, KAT8, PRKD1, RAB11B, RUSC2, ZNF142). Routine diagnostics can provide valuable information on disease associations and support for genes without requiring tremendous research efforts. Thus, our results validate and delineate gene-disorder associations with the aim of motivating clinicians and scientists in diagnostic departments to provide additional evidence via publicly available databases or by publishing short case reports.

Chromosome Translocations, Gene Fusions, and Their Molecular Consequences in Pleomorphic Salivary Gland Adenomas

Salivary gland tumors are a heterogeneous group of tumors originating from the major and minor salivary glands. The pleomorphic adenoma (PA), which is the most common subtype, is a benign lesion showing a remarkable morphologic diversity and that, upon recurrence or malignant transformation, can cause significant clinical problems. Cytogenetic studies of >500 PAs have revealed a complex and recurrent pattern of chromosome rearrangements. In this review, we discuss the specificity and frequency of these rearrangements and their molecular/clinical consequences. The genomic hallmark of PA is translocations with breakpoints in 8q12 and 12q13-15 resulting in gene fusions involving the transcription factor genes PLAG1 and HMGA2. Until recently, the association between these two oncogenic drivers was obscure. Studies of the Silver−Russel syndrome, a growth retardation condition infrequently caused by mutations in IGF2/HMGA2/PLAG1, have provided new clues to the understanding of the molecular pathogenesis of PA. These studies have demonstrated that HMGA2 is an upstream regulator of PLAG1 and that HMGA2 regulates the expression of IGF2 via PLAG1. This provides a novel explanation for the 8q12/12q13-15 aberrations in PA and identifies IGF2 as a major oncogenic driver and therapeutic target in PA. These studies have important diagnostic and therapeutic implications for patients with PA.

Microdeletions in 1q21 and 8q12.1 depict two additional molecular subgroups of Silver-Russell syndrome like phenotypes

Background

Silver-Russell syndrome (SRS) is a genetic disorder characterized by intrauterine and postnatal growth restriction, relative macrocephaly at birth, body asymmetry and typical facial features. Clinical and molecular heterogeneity is described in SRS. Common causes are loss of methylation of the imprinting center 1 in 11p15 and maternal uniparental disomy of chromosome 7. Other genetic alterations include disturbances of imprinted regions in 14q32, 7q32 and 11p15 as well as submicroscopic deletions and duplications. Single nucleotide variants in genes like IGF2, HMGA2, PLAG1, CDKN1C have also been identified in patients with SRS phenotypes. However, routine molecular diagnostics usually focus on 11p15 and chromosome 7, while less frequent causes are not systematically addressed.

Results

Here we report two patients with SRS features in which molecular karyotyping revealed microdeletions in 1q21 and 8q12.1 respectively. In a 3.5-year-old girl with postnatal growth restriction, feeding difficulties, relative macrocephaly and distinct SRS features a 2 Mb deletion in 1q21.1q21.2 was identified. Our second case is a 1.5-year-old boy with intrauterine and postnatal growth restriction, feeding difficulties and distinct facial features with a 77 kb deletion in 8q12.1 affecting PLAG1 as the only protein-encoding gene with known function.

Conclusions

The 1q21 region has not yet been assigned as an SRS region, although six patients with the same deletion and SRS features including relative macrocephaly have been described before. This new case adds to the evidence that distal 1q21 should be annotated as an SRS candidate region. The PLAGL1 alteration is the smallest deletion in 8q12.1 ever reported in a patient with SRS phenotype and it finally confirms that PLAG1 is the SRS causing gene in 8q12.1. To increase the diagnostic yield in patients with suspected SRS, we recommend both molecular karyotyping and next generation sequencing-based approaches.

Further heterogeneity in Silver-Russell syndrome: PLAG1 deletion in association with a complex chromosomal rearrangement

Silver-Russell syndrome (SRS) is a rare genetic condition primarily characterized by growth restriction and facial dysmorphisms. While hypomethylation of H19/IGF2:IG-DMR (imprinting control region 1 [IC1]) located at 11p15.5 and maternal uniparental disomy of chromosome 7 (upd[7]mat) are the most common genetic mechanisms responsible for SRS, the expanding body of literature describing alternative causative variants suggests SRS is a highly heterogeneous condition, also involving variation in the HMGA2-PLAG1-IGF2 pathway. We report a familial PLAG1 deletion in association with a complex chromosomal rearrangement. We describe two siblings with differing unbalanced chromosomal rearrangements inherited from a mother with a 5-breakpoint balanced complex rearrangement involving chromosomes 2, 8, and 21. The overlapping but diverse phenotypes in the siblings were characterized by shared SRS-like features, underlined by a PLAG1 whole gene deletion. Genetic analysis and interpretation was further complicated by a meiotic recombination event occurring in one of the siblings. This family adds to the limited literature available on PLAG1-related SRS. We have reviewed all currently known cases aiming to define the associated phenotype and guide future genetic testing strategies. The heterogeneity of SRS is further expanded by the involvement of complex cytogenomic abnormalities, imposing requirements for a comprehensive approach to testing and genetic counseling.

New Horizons in Short Children Born Small for Gestational Age

Children born small for gestational age (SGA) comprise a heterogeneous group due to the varied nature of the cause. Approximately 85-90% have catch-up growth within the first 4 postnatal years, while the remainder remain short. In later life, children born SGA have an increased risk to develop metabolic abnormalities, including visceral adiposity, insulin resistance, and cardiovascular problems, and may have impaired pubertal onset and growth. The third "360° European Meeting on Growth and Endocrine Disorders" in Rome, Italy, in February 2018, funded by Merck KGaA, Germany, included a session that examined aspects of short children born SGA, with three presentations followed by a discussion period, on which this report is based. Children born SGA who remain short are eligible for GH treatment, which is an approved indication. GH treatment increases linear growth and can also improve some metabolic abnormalities. After stopping GH at near-adult height, metabolic parameters normalize, but pharmacological effects on lean body mass and fat mass are lost; continued monitoring of body composition and metabolic changes may be necessary. Guidelines have been published on diagnosis and management of children with Silver-Russell syndrome, who comprise a specific group of those born SGA; these children rarely have catch-up growth and GH treatment initiation as early as possible is recommended. Early and moderate pubertal growth spurt can occur in children born SGA, including those with Silver-Russell syndrome, and reduce adult height. Treatments that delay puberty, specifically metformin and gonadotropin releasing hormone analogs in combination with GH, have been proposed, but are used off-label, currently lack replication of data, and require further studies of efficacy and safety.

ε-Sarcoglycan: Unraveling the Myoclonus-Dystonia Gene

Myoclonus-dystonia (MD) is a rare childhood-onset movement disorder, with an estimated prevalence of about 2 per 1,000,.000 in Europe, characterized by myoclonic jerks in combination with focal or segmental dystonia. Pathogenic variants in the gene encoding ε-sarcoglycan (SGCE), a maternally imprinted gene, are the most frequent genetic cause of MD. To date, the exact role of ε-sarcoglycan and the pathogenic mechanisms that lead to MD are still unknown. However, there are more than 40 reported isoforms of human ε-sarcoglycan, pointing to a complex biology of this protein. Additionally, some of these are brain-specific isoforms, which may suggest an important role within the central nervous system. In the present review, we aim to provide an overview of the current state of knowledge of ε-sarcoglycan. We will focus on the genetic landscape of SGCE and the presence and plausible role of ε-sarcoglycan in the brain. Finally, we discuss the importance of the brain-specific isoforms and hypothesize that SGCE may play essential roles in normal synaptic functioning and their alteration will be strongly related to MD.