Segmental Maternal UPD of Chromosome 7q in a Patient With Pendred and Silver Russell Syndromes-Like Features

Pendred syndrome (PS) is an autosomal recessive disorder due to mutations in the SLC26A4 gene (chr7q22. 3) and characterized by sensorineural hearing loss and variable thyroid phenotype. Silver-Russell syndrome (SRS) is a heterogeneous imprinting disorder including severe intrauterine and postnatal growth retardation, and dysmorphic features. Maternal uniparental disomy of either the whole chromosome 7 (upd(7)mat) or 7q (upd(7q)mat) is one of the multiple mechanisms impacting the expression of imprinted genes in SRS, and is associated with milder clinical features. Here, we report genetic and clinical characterization of a female child with PS, postnatal growth retardation, and minor dysmorphic features. A gross homozygous deletion of SLC26A4 exons 17-20 was suspected by Sanger sequencing and then confirmed by array-CGH. Moreover, an insertion of about 1 kb of the CCDC126 gene (7p15.3), which does not appear to be clinically relevant, was detected. The possible occurrence of a balanced rearrangement between 7p and 7q was excluded. The absence of the deletion in the father led to the investigation of upd, and microsatellite segregation analysis revealed a segmental 7q (upd(7q)mat), leading to SLC26A4 homozygosity and responsible for both PS and SRS-like traits. The proband matched 3 out of 6 major SRS criteria. In conclusion, this is the first report of uniparental isodisomy encompassing almost the whole long arm of chromosome 7 resulting in PS and SRS-like features. Whereas, the inner ear phenotype of PS is typical, the clinical features suggestive of SRS might have been overlooked

Recombinant Chromosome 7 Driven by Maternal Chromosome 7 Pericentric Inversion in a Girl with Features of Silver-Russell Syndrome

Maternal uniparental disomy of chromosome 7 is present in 5–10% of patients with Silver-Russell syndrome (SRS), and duplication of 7p including GRB10 (Growth Factor Receptor-Bound Protein 10), an imprinted gene that affects pre-and postnatal growth retardation, has been associated with the SRS phenotype. Here, we report on a 17 year old girl referred to array-CGH analysis for short stature, psychomotor delay, and relative macrocephaly. Array-CGH analysis showed two copy number variants (CNVs): a ~12.7 Mb gain in 7p13-p11.2, involving GRB10 and an ~9 Mb loss in 7q11.21-q11.23. FISH experiments performed on the proband’s mother showed a chromosome 7 pericentric inversion that might have mediated the complex rearrangement harbored by the daughter. Indeed, we found that segmental duplications, of which chromosome 7 is highly enriched, mapped at the breakpoints of both the mother’s inversion and the daughter’s CNVs. We postulate that pairing of highly homologous sequences might have perturbed the correct meiotic chromosome segregation, leading to unbalanced outcomes and acting as the putative meiotic mechanism that was causative of the proband’s rearrangement. Comparison of the girl’s phenotype to those of patients with similar CNVs supports the presence of 7p in a locus associated with features of SRS syndrome

Germline variants in genes of the subcortical maternal complex and Multilocus Imprinting Disturbance are associated with miscarriage/infertility or Beckwith-Wiedemann progeny

Beckwith-Wiedemann syndrome (BWS, OMIM # 130650) is an imprinting disorder, associated with overgrowth and increased risk of embryonal tumors. Patients carrying hypomethylation in the KCNQ1OT1:TSS DMR (11p15.5) show MLID (Multilocus Imprinting Disturbance) upon epimutations at other imprinted regions. Few cases of BWS MLID's mothers with biallelic pathogenetic variants in maternal effect genes, mainly components of the subcortical maternal complex, are reported. We describe two families, one with a history of conception difficulties with a novel homozygous nonsense NLRP2 variant and another experiencing 8 miscarriages with a compound heterozygous PADI6 variant

Somatic Mosaicism as Modulator of the Global and Intellectual Phenotype in Epimutated Angelman Syndrome Patients

Angelman Syndrome (AS) is due to the loss of function of the single UBE3A gene, mapping to chromosome 15q11-q13 and encoding the E6AP ubiquitin ligase. Expression of UBE3A is subject to genomic imprinting which is restricted to the brain, where only the maternal allele is transcribed. AS pathogenetic mechanisms include deletion of the maternal 15q11-13 chromosomal region, chromosome 15 paternal uniparental disomy (UPD), Imprinting Defects (ImpD) leading to silencing of the maternal allele and intragenic mutations of the maternal UBE3A allele. From our AS cohort we sorted out for detailed clinical-molecular characterization six mosaic cases, five with ImpD epimutations and one with patUPD15. This latter case referred for intellectual disability and fortuitously solved by SNP array, is, to our knowledge, the unique patient reported with mosaic patUPD of this imprinted region. Somatic epimutation mosaicism represents a challenge for both clinical and molecular diagnostics. The described patients, referred to our center either for uncertain AS or simply for intellectual disability, could be molecularly characterized by applying a multi-method approach including Methylation-Sensitive PCR and MS-MLPA without a strict cut off. The percentage of normal cells detected ranged up to 40%. We confirm the mild phenotype reported in mosaic AS ImpD and provide a detailed analysis of IQ. Mild mental retardation, with significant difficulties in language expression, but only mildly impaired performance skills, together with pathognomonic EEG, is a cue not to overlook in mosaic AS patients. Mosaic epimutations should be searched also in patients with minor AS features and presenting only with intellectual disability

Somatic Mosaicism as Modulator of the Global and Intellectual Phenotype in Epimutated Angelman Syndrome Patients

Abstract: Angelman Syndrome (AS) is due to the loss of function of the single UBE3A gene, mapping to chromosome 15q11-q13 and encoding the E6AP ubiquitin ligase. Expression of UBE3A is subject to genomic imprinting which is restricted to the brain, where only the maternal allele is transcribed. AS pathogenetic mechanisms include deletion of the maternal 15q11-13 chromosomal region, chromosome 15 paternal uniparental disomy (UPD), Imprinting Defects (ImpD) leading to silencing of the maternal allele and intragenic mutations of the maternal UBE3A allele. From our AS cohort we sorted out for detailed clinical-molecular characterization six mosaic cases, five with ImpD epimutations and one with patUPD15. This latter case referred for intellectual disability and fortuitously solved by SNP array, is, to our knowledge, the unique patient reported with mosaic patUPD of this imprinted region. Somatic epimutation mosaicism represents a challenge for both clinical and molecular diagnostics. The described patients, referred to our center either for uncertain AS or simply for intellectual disability, could be molecularly characterized by applying a multi-method approach including Methylation-Sensitive PCR and MS-MLPA without a strict cut off. The percentage of normal cells detected ranged up to 40%. We confirm the mild phenotype reported in mosaic AS ImpD and provide a detailed analysis of IQ. Mild mental retardation, with significant difficulties in language expression, but only mildly impaired performance skills, together with pathognomonic EEG, is a cue not to overlook in mosaic AS patients. Mosaic epimutations should be searched also in patients with minor AS features and presenting only with intellectual disabilit

A multi-method approach to the molecular diagnosis of overt and borderline 11p15.5 defects underlying Silver-Russell and Beckwith-Wiedemann syndromes

reserved23noBACKGROUND: Multiple (epi)genetic defects affecting the expression of the imprinted genes within the 11p15.5 chromosomal region underlie Silver-Russell (SRS) and Beckwith-Wiedemann (BWS) syndromes. The molecular diagnosis of these opposite growth disorders requires a multi-approach flowchart to disclose known primary and secondary (epi)genetic alterations; however, up to 20 and 30 % of clinically diagnosed BWS and SRS cases remain without molecular diagnosis. The complex structure of the 11p15 region with variable CpG methylation and low-rate mosaicism may account for missed diagnoses. Here, we demonstrate the relevance of complementary techniques for the assessment of different CpGs and the importance of testing multiple tissues to increase the SRS and BWS detection rate. RESULTS: Molecular testing of 147 and 450 clinically diagnosed SRS and BWS cases provided diagnosis in 34 SRS and 185 BWS patients, with 9 SRS and 21 BWS cases remaining undiagnosed and herein referred to as "borderline." A flowchart including complementary techniques and, when applicable, the analysis of buccal swabs, allowed confirmation of the molecular diagnosis in all borderline cases. Comparison of methylation levels by methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA) in borderline and control cases defined an interval of H19/IGF2:IG-DMR loss of methylation that was distinct between "easy to diagnose" and "borderline" cases, which were characterized by values ≤mean -3 standard deviations (SDs) compared to controls. Values ≥mean +1 SD at H19/IGF2: IG-DMR were assigned to borderline hypermethylated BWS cases and those ≤mean -2 SD at KCNQ1OT1: TSS-DMR to hypomethylated BWS cases; these were supported by quantitative pyrosequencing or Southern blot analysis. Six BWS cases suspected to carry mosaic paternal uniparental disomy of chromosome 11 were confirmed by SNP array, which detected mosaicism till 10 %. Regarding the clinical presentation, borderline SRS were representative of the syndromic phenotype, with exception of one patient, whereas BWS cases showed low frequency of the most common features except hemihyperplasia.CONCLUSIONS: A conclusive molecular diagnosis was reached in borderline methylation cases, increasing the detection rate by 6 % for SRS and 5 % for BWS cases. The introduction of complementary techniques and additional tissue analyses into routine diagnostic work-up should facilitate the identification of cases undiagnosed because of mosaicism, a distinctive feature of epigenetic disorders.mixedRusso S, Calzari L, Mussa A, Mainini E, Cassina M, Di Candia S, Clementi M, Guzzetti S, Tabano S, Miozzo M, Sirchia S, Finelli P, Prontera P, Maitz S, Sorge G, Calcagno A, Maghnie M, Divizia MT, Melis D, Manfredini E, Ferrero GB, Pecile V, Larizza L.Russo, S; Calzari, L; Mussa, A; Mainini, E; Cassina, M; Di Candia, S; Clementi, M; Guzzetti, Sara; Tabano, S; Miozzo, M; Sirchia, S; Finelli, P; Prontera, P; Maitz, S; Sorge, G; Calcagno, A; Maghnie, M; Divizia, Mt; Melis, D; Manfredini, E; Ferrero, Gb; Pecile, V; Larizza, L