Lenz microphthalmia is inherited in an X-linked recessive pattern and comprises microphthalmia, mental retardation, and skeletal and other anomalies. Two loci associated with this syndrome, MAA (microphthalmia with associated anomalies) and MAA2, are situated respectively at Xq27-q28 (refs. 1,2) and Xp11.4-p21.2 (ref. 3). We identified a substitution, nt 254C→T; P85L, in BCOR (encoding BCL-6-interacting corepressor, BCOR 4 ) in affected males from the family with Lenz syndrome previously used to identify the MAA2 locus 3 . Oculofaciocardiodental syndrome (OFCD; OMIM 300166) is inherited in an X-linked dominant pattern with presumed male lethality and comprises microphthalmia, congenital cataracts, radiculomegaly, and cardiac and digital abnormalities. Given their phenotypic overlap, we proposed that OFCD and MAA2-associated Lenz microphthalmia were allelic, and we found different frameshift, deletion and nonsense mutations in BCOR in seven families affected with OFCD. Like wild-type BCOR, BCOR P85L and an OFCDmutant form of BCOR can interact with BCL-6 and efficiently repress transcription. This indicates that these syndromes are likely to result from defects in alternative functions of BCOR, such as interactions with transcriptional partners other than BCL-6. We cloned the zebrafish (Danio rerio) ortholog of BCOR and found that knock-down of this ortholog caused developmental perturbations of the eye, skeleton and central nervous system consistent with the human syndromes, confirming that BCOR is a key transcriptional regulator during early embryogenesis.We had previously localized MAA2 to a 10-Mb candidate region of Xp 3 . To identify the gene, we narrowed this region by excluding regions deleted in males with Xp deletions but without microphthalmia. Coriell cell line GM07947 is from a male with Duchenne muscular dystrophy, chronic granulomatous disease, McLeod phenotype and retinitis pigmentosa without microphthalmia 5 . Sequence-tagged site (STS) mapping confirmed previous data and oriented it to current genome maps. The deletion extended from DMD (telomeric) to between RPGR and OTC (centromeric; Fig. 1). The Coriell cell line GM10283 excluded two genes telomeric to DMD. This narrowed the critical region to ∼5 Mb, including 12 identified genes not known to be mutated in humans. One of these, DDX3, has an active Y homolog, and we therefore considered it unlikely to underlie a disorder with X-linked recessive inheritance. We sequenced the remaining 11 genes in members of the family in which MAA2 was originally identified. Ten of these genes showed no alterations, but we identified a missense change (nt 254C→T) in BCOR 4 that co-segregated with the disease phenotype (lod score of 2.46, above the threshold of 2.0 for X linkage 3 ). The corresponding residue of human BCOR, Pro85, is conserved in mouse, rat, chicken and pufferfish (Fig. 2), and we did not detect the nt 254C→T mutation among >450 control chromosomes. X-inactivation studies of peripheral blood leukocytes in two carriers of the mutation showed no ske...

Cantú syndrome is characterized by congenital hypertrichosis, distinctive facial features, osteochondrodysplasia and cardiac defects. By using family-based exome sequencing, we identified a de novo mutation in ABCC9. Subsequently, we discovered novel dominant missense mutations in ABCC9 in 14 of the 16 individuals with Cantú syndrome examined. The ABCC9 protein is part of an ATP-dependent potassium (K(ATP)) channel that couples the metabolic state of a cell with its electrical activity. All mutations altered amino acids in or close to the transmembrane domains of ABCC9. Using electrophysiological measurements, we show that mutations in ABCC9 reduce the ATP-mediated potassium channel inhibition, resulting in channel opening. Moreover, similarities between the phenotype of individuals with Cantú syndrome and side effects from the K(ATP) channel agonist minoxidil indicate that the mutations in ABCC9 result in channel opening. Given the availability of ABCC9 antagonists, our findings may have direct implications for the treatment of individuals with Cantú syndrome.

Background We aimed for a comprehensive delineation of genetic, functional and phenotypic aspects of GRIN2B encephalopathy and explored potential prospects of personalised medicine. Methods Data of 48 individuals with de novo GRIN2B variants were collected from several diagnostic and research cohorts, as well as from 43 patients from the literature. Functional consequences and response to memantine treatment were investigated in vitro and eventually translated into patient care. Results Overall, de novo variants in 86 patients were classified as pathogenic/likely pathogenic. Patients presented with neurodevelopmental disorders and a spectrum of hypotonia, movement disorder, cortical visual impairment, cerebral volume loss and epilepsy. Six patients presented with a consistent malformation of cortical development (MCD) intermediate between tubulinopathies and polymicrogyria. Missense variants cluster in transmembrane segments and ligand-binding sites. Functional consequences of variants were diverse, revealing various potential gain-of-function and loss-of-function mechanisms and a retained sensitivity to the use-dependent blocker memantine. However, an objectifiable beneficial treatment response in the respective patients still remains to be demonstrated. Conclusions In addition to previously known features of intellectual disability, epilepsy and autism, we found evidence that GRIN2B encephalopathy is also frequently associated with movement disorder, cortical visual impairment and MCD revealing novel phenotypic consequences of channelopathies.

PurposeTo characterize the molecular genetics of autosomal recessive Noonan syndrome.MethodsFamilies underwent phenotyping for features of Noonan syndrome in children and their parents. Two multiplex families underwent linkage analysis. Exome, genome, or multigene panel sequencing was used to identify mutations. The molecular consequences of observed splice variants were evaluated by reverse-transcription PCR.ResultsTwelve families with a total of 23 affected children with features of Noonan syndrome were evaluated. The phenotypic range included mildly affected patients, but it was lethal in some, with cardiac disease and leukemia. All of the parents were unaffected. Linkage analysis using a recessive model supported a candidate region in chromosome 22q11, which includes LZTR1, previously shown to harbor mutations in patients with Noonan syndrome inherited in a dominant pattern. Sequencing analyses of 21 liveborn patients and a stillbirth identified biallelic pathogenic variants in LZTR1, including putative loss of function, missense, and canonical and non-canonical splicing variants in the affected children, with heterozygous, clinically unaffected parents and heterozygous or normal genotypes in unaffected siblings.ConclusionThese clinical and genetic data confirm the existence of a form of Noonan syndrome that is inherited in an autosomal recessive pattern and identify biallelic mutations in LZTR1.