Cornelia de Lange syndrome (CdLS) is a dominantly inherited congenital malformation disorder caused by mutations in the cohesin-loading protein NIPBL1,2 for nearly 60% of individuals with classical CdLS3-5 and in the core cohesin components SMC1A (~5%) and SMC3 (<1%) for a smaller fraction of probands6,7. In humans, the multi-subunit complex cohesin is comprised of SMC1, SMC3, RAD21 and a STAG protein to form a ring structure proposed to encircle sister chromatids to mediate sister chromatid cohesion (SCC)8 as well as play key roles in gene regulation9. SMC3 is acetylated during S-phase to establish cohesiveness of chromatin-loaded cohesin10-13 and in yeast, HOS1, a class I histone deacetylase, deacetylates SMC3 during anaphase14-16. Here we report the identification of HDAC8 as the vertebrate SMC3 deacetylase as well as loss-of-function HDAC8 mutations in six CdLS probands. Loss of HDAC8 activity results in increased SMC3 acetylation (SMC3-ac) and inefficient dissolution of the “used” cohesin complex released from chromatin in both prophase and anaphase. While SMC3 with retained acetylation is loaded onto chromatin, ChIP-Seq analysis demonstrates decreased occupancy of cohesin localization sites that results in a consistent pattern of altered transcription seen in CdLS cell lines with either NIPBL or HDAC8 mutations.

Cornelia de Lange syndrome (CdLS) is a multisystem genetic disorder with distinct facies, growth failure, intellectual disability, distal limb anomalies, gastrointestinal and neurological disease. Mutations in NIPBL, encoding a cohesin regulatory protein, account for >80% of cases with typical facies. Mutations in the core cohesin complex proteins, encoded by the SMC1A, SMC3 and RAD21 genes, together account for ∼5% of subjects, often with atypical CdLS features. Recently, we identified mutations in the X-linked gene HDAC8 as the cause of a small number of CdLS cases. Here, we report a cohort of 38 individuals with an emerging spectrum of features caused by HDAC8 mutations. For several individuals, the diagnosis of CdLS was not considered prior to genomic testing. Most mutations identified are missense and de novo. Many cases are heterozygous females, each with marked skewing of X-inactivation in peripheral blood DNA. We also identified eight hemizygous males who are more severely affected. The craniofacial appearance caused by HDAC8 mutations overlaps that of typical CdLS but often displays delayed anterior fontanelle closure, ocular hypertelorism, hooding of the eyelids, a broader nose and dental anomalies, which may be useful discriminating features. HDAC8 encodes the lysine deacetylase for the cohesin subunit SMC3 and analysis of the functional consequences of the missense mutations indicates that all cause a loss of enzymatic function. These data demonstrate that loss-of-function mutations in HDAC8 cause a range of overlapping human developmental phenotypes, including a phenotypically distinct subgroup of CdLS.

BackgroundWhereas mutations affecting the helical domain of type I procollagen classically cause Osteogenesis Imperfecta (OI), helical mutations near the amino (N)-proteinase cleavage site have been suggested to result in a mixed OI/Ehlers-Danlos syndrome (EDS)-phenotype.MethodsWe performed biochemical and molecular analysis of type I (pro-) collagen in a cohort of seven patients referred with a clinical diagnosis of EDS and showing only subtle signs of OI. Transmission electron microscopy of the dermis was available for one patient.ResultsAll of these patients harboured a COL1A1 / COL1A2 mutation residing within the most N-terminal part of the type I collagen helix. These mutations affect the rate of type I collagen N-propeptide cleavage and disturb normal collagen fibrillogenesis. Importantly, patients with this type of mutation do not show a typical OI phenotype but mainly present as EDS patients displaying severe joint hyperlaxity, soft and hyperextensible skin, abnormal wound healing, easy bruising, and sometimes signs of arterial fragility. In addition, they show subtle signs of OI including blue sclerae, relatively short stature and osteopenia or fractures.ConclusionRecognition of this distinct phenotype is important for accurate genetic counselling, clinical management and surveillance, particularly in relation to the potential risk for vascular rupture associated with these mutations. Because these patients present clinical overlap with other EDS subtypes, biochemical collagen analysis is necessary to establish the correct diagnosis.

Cohen syndrome, caused by mutations in the COH1 gene, is an autosomal recessive disorder consisting of mental retardation, microcephaly, growth delay, severe myopia, progressive chorioretinal dystrophy, facial anomalies, slender limbs with narrow hands and feet, tapered fingers, short stature, kyphosis and/or scoliosis, pectus carinatum, joint hypermobility, pes calcaneovalgus, and, variably, truncal obesity. Here, we describe the clinical and molecular findings in 14 patients from an isolated Greek island population. The clinical phenotype was fairly homogeneous, although microcephaly was not constant, and some patients had severe visual disability. All patients were homozygous for a novel intragenic COH1 deletion spanning exon 6 to exon 16, suggesting a founder effect. The discovery of this mutation has made carrier detection and prenatal diagnosis possible in this population.

The basic genomic defect in Wolf-Hirschhorn syndrome (WHS), including isolated 4p deletions and various unbalanced de novo 4p;autosomal translocations and above all t(4p;8p), is heterogeneous. Olfactory receptor gene clusters (ORs) on 4p were demonstrated to mediate a group of WHS-associated t(4p;8p)dn translocations. The breakpoint of a 4-Mb isolated deletion was also recently reported to fall within the most distal OR. However, it is still unknown whether ORs mediate all 4p-autosomal translocations, or whether they are involved in the origin of isolated 4p deletions. Another unanswered question is whether a parental inversion polymorphism on 4p16 can act as predisposing factor in the origin of WHS-associated rearrangements. We investigated the involvement of the ORs in the origin of 73 WHS-associated rearrangements. No hotspots for rearrangements were detected. Breakpoints on 4p occurred within the proximal or the distal olfactory receptor gene cluster in 8 of 73 rearrangements (11%). These were five t(4p;8p) translocations, one t(4p;7p) translocation and two isolated terminal deletions. ORs were not involved in one additional t(4p;8p) translocation, in a total of nine different 4p;autosomal translocations and in the majority of isolated deletions. The presence of a parental inversion polymorphism on 4p was investigated in 30 families in which the 4p rearrangements, all de novo, were tested for parental origin (7 were maternal and 23 paternal). It was detected only in the mothers of 3 t(4p;8p) cases. We conclude that WHS-associated chromosome changes are not usually mediated by low copy repeats. The 4p16.3 inversion polymorphism is not a risk factor for their origin.