High frequency of mosaic CREBBP deletions in Rubinstein–Taybi syndrome patients and mapping of somatic and germ-line breakpoints

Abstract

Rubinstein-Taybi syndrome (RSTS) is a rare malformation disorder caused by mutations in the closely related CREBBP and EP300 genes, accounting respectively for up to 60 and 3% of cases. About 10% of CREBBP mutations are whole gene deletions often extending into flanking regions. Using FISH and microsatellite analyses as a first step in the CREBBP mutation screening of 42 Italian RSTS patients, we identified six deletions, three of which were in a mosaic condition that has not been previously reported in RSTS. The use of region-specific BAC clones and small CREBBP probes allowed us to assess the extent of all of the deletions by mapping their endpoints to genomic intervals of 5-10 kb. Four of our five intragenic breakpoints cluster at the 5' end of CREBBP, where there is a peak of breakpoints underlying rearrangements in RSTS patients and tumors. The search for genomic motifs did not reveal any low-copy repeats (LCRs) or any greater density of repetitive sequences. In contrast, the percentage of interspersed repetitive elements (mainly Alu and LINEs in the CREBBP exon 2 region) is significantly higher than that in the entire gene or the average in the genome, thus suggesting that this characteristic may be involved in the region's vulnerability to breaking and nonhomologous pairing. The FISH analysis extended to the EP300 genomic region did not reveal any deletions. The clinical presentation was typical in all cases, but more severe in the three patients carrying constitutional deletions, raising a question about the possible underdiagnosis of a few cases of mild RSTS.

Mosaic CREBBP mutation causes overlapping clinical features of Rubinstein–Taybi and Filippi syndromes

“…[17][18][19] However, previous mosaic variants involving CREBBP have been identified in peripheral blood samples. [17][18][19] The current case is the first case in which the variant was detected solely in buccal mucosa and not in blood samples. Mosaic de novo variants absent from blood samples have also been described in other conditions.…”

Rubinstein–Taybi syndrome (CREBBP, EP300)

“…At present, more than 100 pathogenic mutations are known for the two genes together, but mutations in EP300 are much less common (only 11 so far). [2][3][4][5][6][7][8][9] Mutations may remove the 5¢ or the 3¢end of CREBBP and adjacent genomic segments, which causes the 16p13.3 contiguous gene deletion syndrome. [10][11][12] For both genes a mutation database is available that also includes unpublished mutations:…”

High frequency of copy number imbalances in Rubinstein–Taybi patients negative to CREBBP mutational analysis

“…The CREBBP and EP300 encompassing BAC probes were selected on the basis of their physical location (http://www.genome.ucsc.edu/): details are reported in Gervasini et al, 2007. DNA was isolated from liquid cultures using a plasmid purification kit (Nucleobond PC20, Macherey-Nagel, GmbH & Co.KG, Duren, Germany).…”

“…6 Both genes encode histone acetyltransferases (HATs), transcriptional co-activators that are involved in cell processes such as growth, differentiation, DNA repair, apoptosis and many others, 7 and which also have an important role in the development of the skeletal and nervous central systems, thus accounting for the growth and psychomotor development delay typical of RSTS patients. Various techniques have been used to identify the genetic lesion underlying RSTS, including fluorescence in situ hybridisation (FISH), [8][9][10][11] real-time quantitative PCR, 12 multiplex ligation-dependent probe amplification (MLPA), 13 denaturing high performance liquid chromatography (DHPLC) 14 and sequencing. 15,16 Deletions of part or all of the CREBBP gene and flanking regions (also in mosaic condition), 11 may account for 5-10% of the cases, whereas frameshift, nonsense, splice-site and missense point mutations (in decreasing order of prevalence) are found in approximately 46-51%; 17 there have also been reports of a few gene-disrupting translocations and inversions.…”

“…Various techniques have been used to identify the genetic lesion underlying RSTS, including fluorescence in situ hybridisation (FISH), [8][9][10][11] real-time quantitative PCR, 12 multiplex ligation-dependent probe amplification (MLPA), 13 denaturing high performance liquid chromatography (DHPLC) 14 and sequencing. 15,16 Deletions of part or all of the CREBBP gene and flanking regions (also in mosaic condition), 11 may account for 5-10% of the cases, whereas frameshift, nonsense, splice-site and missense point mutations (in decreasing order of prevalence) are found in approximately 46-51%; 17 there have also been reports of a few gene-disrupting translocations and inversions. 10 EP300 mutations are comparatively rare as only six have been described so far, in six patients with a mild clinical presentation.…”