Overlapping SETBP1 gain-of-function mutations in Schinzel-Giedion syndrome and hematologic malignancies

Schinzel-Giedion syndrome (SGS) is a rare developmental disorder characterized by multiple malformations, severe neurological alterations and increased risk of malignancy. SGS is caused by de novo germline mutations clustering to a 12bp hotspot in exon 4 of SETBP1. Mutations in this hotspot disrupt a degron, a signal for the regulation of protein degradation, and lead to the accumulation of SETBP1 protein. Overlapping SETBP1 hotspot mutations have been observed recurrently as somatic events in leukemia. We collected clinical information of 47 SGS patients (including 26 novel cases) with germline SETBP1 mutations and of four individuals with a milder phenotype caused by de novo germline mutations adjacent to the SETBP1 hotspot. Different mutations within and around the SETBP1 hotspot have varying effects on SETBP1 stability and protein levels in vitro and in in silico modeling. Substitutions in SETBP1 residue I871 result in a weak increase in protein levels and mutations affecting this residue are significantly more frequent in SGS than in leukemia. On the other hand, substitutions in residue D868 lead to the largest increase in protein levels. Individuals with germline mutations affecting D868 have enhanced cell proliferation in vitro and higher incidence of cancer compared to patients with other germline SETBP1 mutations. Our findings substantiate that, despite their overlap, somatic SETBP1 mutations driving malignancy are more disruptive to the degron than germline SETBP1 mutations causing SGS. Additionally, this suggests that the functional threshold for the development of cancer driven by the disruption of the SETBP1 degron is higher than for the alteration in prenatal development in SGS. Drawing on previous studies of somatic SETBP1 mutations in leukemia, our results reveal a genotype-phenotype correlation in germline SETBP1 mutations spanning a molecular, cellular and clinical phenotype

Mutations in the nebulin gene can cause severe congenital nemaline myopathy.

Item does not contain fulltextPreviously, we reported results indicating that nebulin was the gene causing the typical form of autosomal recessive nemaline (rod) myopathy. Here we describe the identification of mutations in the nebulin gene in seven offspring of five families affected by the severe congenital form of nemaline myopathy. One pregnancy was terminated on the grounds of foetal abnormality, while six affected infants died at ages ranging from the first day of life to 19 months. Only three of the six neonates were able to establish spontaneous respiration. Three had arthrogryposis. In three of the five families, the mutations were located in exon 184. These mutations are predicted to cause absence of the C-terminal part of nebulin

High frequency of mosaic CREBBP deletions in RSTS patients and mapping of somatic and germline breakpoints

Rubinstein-Taybi syndrome (RSTS) is a rare malformation disorder caused by mutations in the CREBBP and EP300 genes accounting for up to 60% and 3% of the tested patients, respectively. About 10% of CREBBP mutations are deletions, often extending to flanking regions, with scattered breakpoints. By FISH and microsatellite analyses as first step of CREBBP mutation screening we identified in 60 Italian RSTS patients, six deletions, three of which present in a mosaic condition, a finding yet unreported. Using BAC clones and small-sized CREBBP- probes we could assess the extent of all deletions. Only two of the twelve breakpoints were found to encompass the same region, confirming the heterogeneity in size and boundaries of CREBBP deletions. However four of our five intragenic breakpoints clustered to the 5\u2019 end of CREBBP, around exon 2, where a peak breakpoints underlying rearrangements in RSTS patients and tumors is apparent too. The search of genomic motifs did not evidence LCRs, as expected by the lack of a recurrent RSTS. By contrast, the percentage of interspersed repetitive elements, mainly Alu and LINEs is in the smaller 5\u2019CREBBP region around exon 2 significantly higher than that in the entire gene or the average in the genome suggesting this feature might be implicated in the vulnerability of the region to breaking. Search of EP300 microdeletions was also afforded by FISH , but no deletion carrier was identified among CREBBP-negative cases, pointing to a minor role of this second gene in the aetiology of RSTS. As to genotype phenotype correlation the clinical presentation was typical in all cases, although more severe in the three patients carrying constitutional deletions, raising.the issue of possible underdiagnosis of a subset of mild RSTS patients. No apparent correlations were observed between increase in the deletion size, from150 Kb to 2.6 Mb, and more severe phenotypic spectrum in the three patients carrying constitutional deletions

CHROMOSOMAL IMBALANCES IN RUBINSTEIN-TAYBI PATIENTS NEGATIVE TO CREBBP MUTATIONAL TEST

Rubinstein-Taybi syndrome (RSTS, OMIM #180849) is a rare autosomal dominant congenital disorder characterized by postnatal growth retardation and psychomotor developmental delay, skeletal anomalies and specific facial dysmorphisms. RSTS is associated with chromosomal microdeletion or point mutations of CREBBP gene in 16p13.3 and mutations of EP300 gene in 22q13, observed in 56% and 3% of the tested patients respectively. Here we report the identification by a-CGH of duplications/deletions in 6 of 25 RSTS patients found negative to point mutations of CREBBP and to chromosomal rearrangements affecting CREBBP and EP300 regions. The imbalances are: i) a de novo 9Mb deletion in 2q24.3q31.1 involving the HOXD genes, ii) a 5,5 Mb duplication in 2q34q35 inherited by the healthy father, probably representing a private CNV, iii) a 500Kb duplication in 17q11.2 upstream the NF1 gene in a region delimited by NF1 REP-P1/P2 iv) a 1,2Mb deletion in 18q21.33q22.1 harbouring one gene, v) a 4,3Mb deletion in 2q22.3q23.1 involving five genes among which ZFHX1B, the gene mutated in Mowat-Wilson, vi) a 466Kb deletion in 7p21.1 containing TWIST1, a proposed candidate for RSTS. The parental origin, gene content and genomic characterization of the last four imbalances is in progress. Although the pathogenetic role is yet unproven in a few cases, this study shows a high fraction of chromosomal rearrangements in regions other than those of CREBBP/EP300 genes. In addition a-CGH is confirmed to be a suitable approach for diagnostic purposes and to highlight novel positional RSTS candidate genes