Increased risk for developmental delay in Saethre-Chotzen syndrome is associated with TWIST deletions: an improved strategy for TWIST mutation screening

Abstract

The majority of patients with Saethre-Chotzen syndrome have mutations in the TWIST gene, which codes for a basic helix-loop-helix transcription factor. Of the genetic alterations identified in TWIST, nonsense mutations, frameshifts secondary to small deletions or insertions, and large deletions implicate haploinsufficiency as the pathogenic mechanism. We identified three novel intragenic mutations and six deletions in our patients by using a new strategy to screen for TWIST mutations. We used polymerase chain reaction (PCR) amplification with subsequent sequencing to identify point mutations and small insertions or deletions in the coding region, and real-time PCR-based gene dosage analysis to identify large deletions encompassing the gene, with confirmation by microsatellite and fluorescence in situ hybridization (FISH) analyses. The size of the deletions can also be analyzed by using the gene dosage assay with "PCR walking" across the critical region. In 55 patients with features of Saethre-Chotzen syndrome, 11% were detected to have deletions by real-time gene dosage analysis. Two patients had a translocation or inversion at least 260 kb 3' of the gene, suggesting they had position-effect mutations. Of the 37 patients with classic features of Saethre-Chotzen syndrome, the overall detection rate for TWIST mutations was 68%. The risk for developmental delay in patients with deletions involving the TWIST gene is approximately 90% or eight times more common than in patients with intragenic mutations.

Saethre–Chotzen syndrome caused by TWIST 1 gene mutations: functional differentiation from Muenke coronal synostosis syndrome

“…32 With respect to mental performance, carriers of TWIST mutations in the present series did not differ from the average population. 20 Contrary to other authors, 33,34 we found that even deletions of the entire TWIST gene did not adversely affect cognitive function in our SCS patients. Compared to three deletion cases reported by Johnson et al, 33 the size of the deletions in our patients appears to be smaller, particularly in the 3 0 -direction (Table 3), but further analysis is necessary.…”

Quebec platelet disorder is linked to the urokinase plasminogen activator gene (PLAU) and increases expression of the linked allele in megakaryocytes

“…As these possibilities were fully excluded, the search for the cis regulatory mutation that causes QPD must now extend beyond PLAU to identify the unique sequence changes that markedly increase transcription of the linked PLAU allele during megakaryocyte differentiation. In some disorders, the causative mutation that alters transcription is quite far (5Ј and 3Ј) from the dysregulated gene, 13,14 and it can be in an unrelated, neighboring gene. 15,16 Regulatory elements with cis or trans effects have been identified as far as 1 Mb away from the genes transcribed.…”

Two New de novo Interstitial Duplications Covering 2p14–p22.1: Clinical and Molecular Analysis

“…The duplication is located right downstream of the NSD1 gene, a region which appears critical for the expression of the gene, and regulatory elements might be disrupted or the expression of a not amplified critical gene might be otherwise affected by the duplicated region [Kasnauskiene et al, 2011]. Other position-effect genes have been reported in which functions were disturbed by breakpoints of 125 kb, 260 kb, or 120 kb downstream of the critical genes in cases of aniridia [Kleinjan et al, 2001], Saethre-Chotzen syndrome [Cai et al, 2007], and lymphedema distichiasis [Fang et al, 2000], respectively. Gene function disturbance by the second mechanism could be associated with the inappropriate spreading of repressive (or active) chromatin across a gene locus by juxtaposition next to specific sequences (e.g.…”