Cornelia de Lange syndrome (CdLS; OMIM 122470) is a dominantly inherited multisystem developmental disordercharacterized by growth and cognitive retardation; abnormalities of the upper limbs; gastroesophageal dysfunction; cardiac, ophthalmologic and genitourinary anomalies; hirsutism; and characteristic facial features 1-3 . Genital anomalies, pyloric stenosis, congenital diaphragmatic hernias, cardiac septal defects, hearing loss and autistic and selfinjurious tendencies also frequently occur 2 . Prevalence is estimated to be as high as 1 in 10,000 (ref. 4). We carried out genome-wide linkage exclusion analysis in 12 families with CdLS and identified four candidate regions, of which chromosome 5p13.1 gave the highest multipoint lod score of 2.7. This information, together with the previous identification of a child with CdLS with a de novo t(5;13)(p13.1;q12.1) translocation, allowed delineation of a 1.1-Mb critical region on chromosome 5 for the gene mutated in CdLS. We identified mutations in one gene in this region, which we named NIPBL, in four sporadic and two familial cases of CdLS. We characterized the genomic structure of NIPBL and found that it is widely expressed in fetal and adult tissues. The fly homolog of NIPBL, Nipped-B, facilitates enhancer-promoter communication and regulates Notch signaling and other developmental pathways in Drosophila melanogaster 5 .CdLS is a dominantly inherited disorder with characteristic facial appearance, limb defects ( Fig. 1) and growth and cognitive retardation. We carried out a genome-wide linkage analysis in nine families with CdLS with more than one affected family member. Under a model of genetic homogeneity, we used a linkage exclusion mapping approach,

Brain malformations are individually rare but collectively common causes of developmental disabilities1–3. Many forms occur sporadically and have reduced reproductive fitness, pointing towards a causative role for de novo mutations4,5. Here we report our studies of Baraitser-Winter syndrome, a well-defined syndrome characterized by distinct craniofacial features, ocular colobomata and a neuronal migration defect6,7. By using whole-exome sequencing in three proband-parent trios, we identified de novo missense changes in the cytoplasmic actin genes ACTB and ACTG1 in one and two probands, respectively. Sequencing of both genes in fifteen additional patients revealed disease-causing mutations in all probands, including two recurrent de novo mutations (ACTB p.Arg196His and ACTG1 p.Ser155Phe). Our results confirm that trio-based exome sequencing is a powerful approach to discover the genes causing sporadic developmental disorders, emphasize the overlapping roles of cytoplasmic actins in development, and suggest that Baraitser-Winter syndrome is the predominant phenotype associated with mutations of these two genes.

Baraitser-Winter, Fryns-Aftimos and cerebrofrontofacial syndrome types 1 and 3 have recently been associated with heterozygous gain-of-function mutations in one of the two ubiquitous cytoplasmic actin-encoding genes ACTB and ACTG1 that encode b-and c-actins. We present detailed phenotypic descriptions and neuroimaging on 36 patients analyzed by our group and six cases from the literature with a molecularly proven actinopathy (9 ACTG1 and 33 ACTB). The major clinical anomalies are striking dysmorphic facial features with hypertelorism, broad nose with large tip and prominent root, congenital non-myopathic ptosis, ridged metopic suture and arched eyebrows. Iris or retinal coloboma is present in many cases, as is sensorineural deafness. Cleft lip and palate, hallux duplex, congenital heart defects and renal tract anomalies are seen in some cases. Microcephaly may develop with time. Nearly all patients with ACTG1 mutations, and around 60% of those with ACTB mutations have some degree of pachygyria with anteroposterior severity gradient, rarely lissencephaly or neuronal heterotopia. Reduction of shoulder girdle muscle bulk and progressive joint stiffness is common. Early muscular involvement, occasionally with congenital arthrogryposis, may be present. Progressive, severe dystonia was seen in one family. Intellectual disability and epilepsy are variable in severity and largely correlate with CNS anomalies. One patient developed acute lymphocytic leukemia, and another a cutaneous lymphoma, indicating that actinopathies may be cancerpredisposing disorders. Considering the multifaceted role of actins in cell physiology, we hypothesize that some clinical manifestations may be partially mutation specific. Baraitser-Winter cerebrofrontofacial syndrome is our suggested designation for this clinical entity.

Mutations in FOXP2 cause developmental verbal dyspraxia (DVD), but only a few cases have been described. We characterize 13 patients with DVD--5 with hemizygous paternal deletions spanning the FOXP2 gene, 1 with a translocation interrupting FOXP2, and the remaining 7 with maternal uniparental disomy of chromosome 7 (UPD7), who were also given a diagnosis of Silver-Russell Syndrome (SRS). Of these individuals with DVD, all 12 for whom parental DNA was available showed absence of a paternal copy of FOXP2. Five other individuals with deletions of paternally inherited FOXP2 but with incomplete clinical information or phenotypes too complex to properly assess are also described. Four of the patients with DVD also meet criteria for autism spectrum disorder. Individuals with paternal UPD7 or with partial maternal UPD7 or deletion starting downstream of FOXP2 do not have DVD. Using quantitative real-time polymerase chain reaction, we show the maternally inherited FOXP2 to be comparatively underexpressed. Our results indicate that absence of paternal FOXP2 is the cause of DVD in patients with SRS with maternal UPD7. The data also point to a role for differential parent-of-origin expression of FOXP2 in human speech development.

Freeman-Sheldon syndrome, or distal arthrogryposis type 2A (DA2A), is an autosomal-dominant condition caused by mutations in MYH3 and characterized by multiple congenital contractures of the face and limbs and normal cognitive development. We identified a subset of five individuals who had been putatively diagnosed with "DA2A with severe neurological abnormalities" and for whom congenital contractures of the limbs and face, hypotonia, and global developmental delay had resulted in early death in three cases; this is a unique condition that we now refer to as CLIFAHDD syndrome. Exome sequencing identified missense mutations in the sodium leak channel, non-selective (NALCN) in four families affected by CLIFAHDD syndrome. We used molecular-inversion probes to screen for NALCN in a cohort of 202 distal arthrogryposis (DA)-affected individuals as well as concurrent exome sequencing of six other DA-affected individuals, thus revealing NALCN mutations in ten additional families with "atypical" forms of DA. All 14 mutations were missense variants predicted to alter amino acid residues in or near the S5 and S6 pore-forming segments of NALCN, highlighting the functional importance of these segments. In vitro functional studies demonstrated that NALCN alterations nearly abolished the expression of wild-type NALCN, suggesting that alterations that cause CLIFAHDD syndrome have a dominant-negative effect. In contrast, homozygosity for mutations in other regions of NALCN has been reported in three families affected by an autosomal-recessive condition characterized mainly by hypotonia and severe intellectual disability. Accordingly, mutations in NALCN can cause either a recessive or dominant condition characterized by varied though overlapping phenotypic features, perhaps based on the type of mutation and affected protein domain(s).