The Rubinstein-Taybi syndrome (RTS) is a well-defined syndrome with facial abnormalities, broad thumbs, broad big toes and mental retardation as the main clinical features. Many patients with RTS have been shown to have breakpoints in, and microdeletions of, chromosome 16p13.3 (refs 4-8). Here we report that all these breakpoints are restricted to a region that contains the gene for the human CREB binding protein (CBP), a nuclear protein participating as a co-activator in cyclic-AMP-regulated gene expression. We show that RTS results not only from gross chromosomal rearrangements of chromosome 16p, but also from point mutations in the CBP gene itself. Because the patients are heterozygous for the mutations, we propose that the loss of one functional copy of the CBP gene underlies the developmental abnormalities in RTS and possibly the propensity for malignancy.

Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant neuromuscular disorder which maps to chromosome 4qter, distal to the D4S139 locus. The cosmid clone 13E, isolated in a search for homeobox genes, was subsequently mapped to 4q35, also distal to D4S139. A subclone, p13E-11, detects in normal individuals a polymorphic EcoRI fragment usually larger than 28 kilobases (kb). Surprisingly, using the same probe we detected de novo DNA rearrangements, characterized by shorter EcoRI fragments (14-28 kb), in 5 out of 6 new FSHD cases. In 10 Dutch families analysed, a specific shorter fragment between 14-28 kb cosegregates with FSHD. Both observations indicate that FSHD is caused by independent de novo DNA rearrangements in the EcoRI fragment detected by p13E-11.

Pseudoxanthoma elasticum (PXE) is a heritable disorder of the connective tissue. PXE patients frequently experience visual field loss and skin lesions, and occasionally cardiovascular complications. Histopathological findings reveal calcification of the elastic fibres and abnormalities of the collagen fibrils. Most PXE patients are sporadic, but autosomal recessive and dominant inheritance are also observed. We previously localized the PXE gene to chromosome 16p13.1 (refs 8,9) and constructed a physical map. Here we describe homozygosity mapping in five PXE families and the detection of deletions or mutations in ABCC6 (formerly MRP6) associated with all genetic forms of PXE in seven patients or families.

Only a small proportion of cancers result from familial cancer syndromes with Mendelian inheritance. Nonfamilial, 'sporadic' cancers, which represent most cancer cases, also have a significant hereditary component, but the genes involved have low penetrance and are extremely difficult to detect. Therefore, mapping and cloning of quantitative trait loci (QTLs) for cancer susceptibility in animals could help identify homologous genes in humans. Several cancer-susceptibility QTLs have been mapped in mice and rats, but none have been cloned so far. Here we report the positional cloning of the mouse gene Scc1 (Susceptibility to colon cancer 1) and the identification of Ptprj, encoding a receptor-type protein tyrosine phosphatase, as the underlying gene. In human colon, lung and breast cancers, we show frequent deletion of PTPRJ, allelic imbalance in loss of heterozygosity (LOH) and missense mutations. Our data suggest that PTPRJ is relevant to the development of several different human cancers.

ObjectiveTo determine the frequency of distinctive EGFr cysteine altering NOTCH3 mutations in the 60,706 exomes of the exome aggregation consortium (ExAC) database.MethodsExAC was queried for mutations distinctive for cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), namely mutations leading to a cysteine amino acid change in one of the 34 EGFr domains of NOTCH3. The genotype‐phenotype correlation predicted by the ExAC data was tested in an independent cohort of Dutch CADASIL patients using quantified MRI lesions. The Dutch CADASIL registry was probed for paucisymptomatic individuals older than 70 years.ResultsWe identified 206 EGFr cysteine altering NOTCH3 mutations in ExAC, with a total prevalence of 3.4/1000. More than half of the distinct mutations have been previously reported in CADASIL patients. Despite the clear overlap, the mutation distribution in ExAC differs from that in reported CADASIL patients, as mutations in ExAC are predominantly located outside of EGFr domains 1–6. In an independent Dutch CADASIL cohort, we found that patients with a mutation in EGFr domains 7–34 have a significantly lower MRI lesion load than patients with a mutation in EGFr domains 1–6.InterpretationThe frequency of EGFr cysteine altering NOTCH3 mutations is 100‐fold higher than expected based on estimates of CADASIL prevalence. This challenges the current CADASIL disease paradigm, and suggests that certain mutations may more frequently cause a much milder phenotype, which may even go clinically unrecognized. Our data suggest that individuals with a mutation located in EGFr domains 1–6 are predisposed to the more severe “classical” CADASIL phenotype, whereas individuals with a mutation outside of EGFr domains 1–6 can remain paucisymptomatic well into their eighth decade.

Charcot-Marie-Tooth disease type 1A (CMT1A) is associated with a DNA duplication at chromosome 17p11.2. In view of the point mutation in the gene for peripheral myelin protein pmp-22/gas-3 in Trembler mice, a murine model for CMT1A, we have analysed whether this gene is altered in CMT1A. Here we show that the human homologue of the murine pmp-22 gene is located within the CMT1A DNA duplication, which is a direct repeat and does not interrupt the coding region of PMP-22. Expression of PMP-22 in CMT1A fibroblasts is similar to expression in control fibroblasts. Increased gene dosage or altered PMP-22 expression in the peripheral nervous system are therefore possible mechanisms by which PMP-22 is involved in CMT1A.

Rubinstein-Taybi syndrome (RTS) is a malformation syndrome characterised by facial abnormalities, broad thumbs, broad big toes, and mental retardation. In a subset of RTS patients, microdeletions, translocations, and inversions involving chromosome band 16p13.3 can be detected. We have previously shown that disruption of the human CREB binding protein (CREBBP or CBP) gene, either by these gross chromosomal rearrangements or by point mutations, leads to RTS. CBP is a large nuclear protein involved in transcription regulation, chromatin remodelling, and the integration of several diVerent signal transduction pathways. Here we report diagnostic analysis of CBP in 194 RTS patients, divided into several subsets. In one case the mother is also suspect of having RTS. Analyses of the entire CBP gene by the protein truncation test showed 4/37 truncating mutations. Two point mutations, one 11 bp deletion, and one mutation aVecting the splicing of the second exon were detected by subsequent sequencing. Screening the CBP gene for larger deletions, by using diVerent cosmid probes in FISH, showed 14/171 microdeletions. Using five cosmid probes that contain the entire gene, we found 8/89 microdeletions of which 4/8 were 5' or interstitial. This last subset of microdeletions would not have been detected using the commonly used 3' probe RT1, showing the necessity of using all five probes.

Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant, neuromuscular disorder characterized by progressive weakness of muscles in the face, shoulder and upper arm. Deletion of integral copies of a 3.3 kb repeated unit from the subtelomeric region on chromosome 4q35 has been shown to be associated with FSHD. These repeated units which are apparently not transcribed, map very close to the 4q telomere and belong to a 3.3 kb repeat family dispersed over heterochromatic regions of the genome. Hence, position effect variegation (PEV), inducing allele-specific transcriptional repression of a gene located more centromeric, has been postulated as the underlying genetic mechanism of FSHD. This hypothesis has directed the search for the FSHD gene to the region centromeric to the repeated units. A CpG island was identified and found to be associated with the 5' untranslated region of a novel human gene, FRG1 (FSHD Region Gene 1). This evolutionary conserved gene is located about 100 kb proximal to the repeated units and belongs to a multigene family with FRG1 related sequences on multiple chromosomes. The mature chromosome 4 FRG1 transcript is 1042 bp in length and contains nine exons which encode a putative protein of 258 amino acid residues. Transcription of FRG1 was detected in several human tissues including placenta, lymphocytes, brain and muscle. To investigate a possible PEV mechanism, allele-specific FRG1 steady-state transcript levels were determined using RNA-based single-strand conformation polymorphism (SSCP) analysis. A polymorphic fragment contained within the first exon of FRG1 was amplified from reverse transcribed RNA from lymphocytes and muscle biopsies of patients and controls. No evidence for PEV mediated repression of allelic transcription was obtained in these tissues. However, detection of PEV in FSHD patients may require analysis of more specific cell types at particular developmental stages.