HDAC8 mutations in Cornelia de Lange syndrome affect the cohesin acetylation cycle.

Cornelia de Lange syndrome (CdLS) is a dominantly inherited congenital malformation disorder, caused by mutations in the cohesin-loading protein NIPBL for nearly 60% of individuals with classical CdLS, and by mutations in the core cohesin components SMC1A (~5%) and SMC3 (<1%) for a smaller fraction of probands. In humans, the multisubunit complex cohesin is made up of SMC1, SMC3, RAD21 and a STAG protein. These form a ring structure that is proposed to encircle sister chromatids to mediate sister chromatid cohesion and also has key roles in gene regulation. SMC3 is acetylated during S-phase to establish cohesiveness of chromatin-loaded cohesin, and in yeast, the class I histone deacetylase Hos1 deacetylates SMC3 during anaphase. Here we identify 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 and inefficient dissolution of the 'used' cohesin complex released from chromatin in both prophase and anaphase. SMC3 with retained acetylation is loaded onto chromatin, and chromatin immunoprecipitation sequencing 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.

Mutations in the facilitative glucose transporter GLUT10 alter angiogenesis and cause arterial tortuosity syndrome.

Arterial tortuosity syndrome (ATS) is an autosomal recessive disorder characterized by tortuosity, elongation, stenosis and aneurysm formation in the major arteries owing to disruption of elastic fibers in the medial layer of the arterial wall. Previously, we used homozygosity mapping to map a candidate locus in a 4.1-Mb region on chromosome 20q13.1 (ref. 2). Here, we narrowed the candidate region to 1.2 Mb containing seven genes. Mutations in one of these genes, SLC2A10, encoding the facilitative glucose transporter GLUT10, were identified in six ATS families. GLUT10 deficiency is associated with upregulation of the TGFbeta pathway in the arterial wall, a finding also observed in Loeys-Dietz syndrome, in which aortic aneurysms associate with arterial tortuosity. The identification of a glucose transporter gene responsible for altered arterial morphogenesis is notable in light of the previously suggested link between GLUT10 and type 2 diabetes. Our data could provide new insight on the mechanisms causing microangiopathic changes associated with diabetes and suggest that therapeutic compounds intervening with TGFbeta signaling represent a new treatment strategy.

Analysis of two Arab families reveals additional support for a DFNB2 nonsyndromic phenotype of MYO7A.

Variants in the head and tail domains of the MYO7A gene, encoding myosin VIIA, cause Usher syndrome type 1B (USH1B) and nonsyndromic deafness (DFNB2, DFNA11). In order to identify the genetic defect(s) underling profound deafness in two consanguineous Arab families living in UAE, we have sequenced a panel of 19 genes involved in Usher syndrome and nonsyndromic deafness in the index cases of the two families. This analysis revealed a novel homozygous insertion of AG (c.1952_1953insAG/p.C652fsX11) in exon 17 of the MYO7A gene in an Iraqi family, and a homozygous point mutation (c.5660C>T/p.P1887L) in exon 41 affecting the same gene in a large Palestinian family. Moreover, some individuals from the Palestinian family also harbored a novel heterozygous truncating variant (c.1267C>T/p.R423X) in the DFNB31 gene, which is involved in autosomal recessive nonsyndromic deafness type DFNB31 and Usher syndrome type II. Assuming an autosomal recessive mode of inheritance in the two inbred families, we conclude that the homozygous variants in the MYO7A gene are the disease-causing mutations in these families. Furthermore, given the absence of retinal disease in all affected patients examined, particularly a 28 year old patient, suggests that at least one family may segregate a DFNB2 presentation rather than USH1B. This finding further supports the premise that the MYO7A gene is responsible for two distinct diseases and gives evidence that the p.P1887L mutation in a homozygous state may be responsible for nonsyndromic hearing loss.

A de novo GLI3 mutation in a patient with acrocallosal syndrome.

Acrocallosal syndrome is characterized by postaxial polydactyly, macrocephaly, agenesis of the corpus callosum, and severe developmental delay. In a few patients with this disorder, a mutation in the KIF7 gene has been reported, which was associated with impaired GLI3 processing and dysregulaton of GLI3 transcription factors. A single patient with acrocallosal syndrome and a de novo p.Ala934Pro mutation in GLI3 has been reported, whereas diverse and numerous GLI3 mutations have also been described in syndromes with overlapping clinical manifestations, including Greig cephalopolysyndactyly syndrome, Pallister-Hall syndrome, trigonocephaly with craniosynostosis and polydactyly, oral-facial-digital syndrome, and non-syndromic polydactyly. Here, we describe a second patient with acrocallosal syndrome, who has a de novo, novel c.2786T>C mutation in GLI3, which predicts p.Leu929Pro. This mutation is in the same domain as the mutation in the previously reported patient. These data confirm that mutations in GLI3 are a cause of the acrocallosal phenotype.

Phenotypic spectrum of the SMAD3-related aneurysms-osteoarthritis syndrome.

BACKGROUND: Aneurysms-osteoarthritis syndrome (AOS) is a new autosomal dominant syndromic form of thoracic aortic aneurysms and dissections characterised by the presence of arterial aneurysms and tortuosity, mild craniofacial, skeletal and cutaneous anomalies, and early-onset osteoarthritis. AOS is caused by mutations in the SMAD3 gene. METHODS: A cohort of 393 patients with aneurysms without mutation in FBN1, TGFBR1 and TGFBR2 was screened for mutations in SMAD3. The patients originated from The Netherlands, Belgium, Switzerland and USA. The clinical phenotype in a total of 45 patients from eight different AOS families with eight different SMAD3 mutations is described. In all patients with a SMAD3 mutation, clinical records were reviewed and extensive genetic, cardiovascular and orthopaedic examinations were performed. RESULTS: Five novel SMAD3 mutations (one nonsense, two missense and two frame-shift mutations) were identified in five new AOS families. A follow-up description of the three families with a SMAD3 mutation previously described by the authors was included. In the majority of patients, early-onset joint abnormalities, including osteoarthritis and osteochondritis dissecans, were the initial symptom for which medical advice was sought. Cardiovascular abnormalities were present in almost 90% of patients, and involved mainly aortic aneurysms and dissections. Aneurysms and tortuosity were found in the aorta and other arteries throughout the body, including intracranial arteries. Of the patients who first presented with joint abnormalities, 20% died suddenly from aortic dissection. The presence of mild craniofacial abnormalities including hypertelorism and abnormal uvula may aid the recognition of this syndrome. CONCLUSION: The authors provide further insight into the phenotype of AOS with SMAD3 mutations, and present recommendations for a clinical work-up.

Mutation in the AP4M1 gene provides a model for neuroaxonal injury in cerebral palsy.

Cerebral palsy due to perinatal injury to cerebral white matter is usually not caused by genetic mutations, but by ischemia and/or inflammation. Here, we describe an autosomal-recessive type of tetraplegic cerebral palsy with mental retardation, reduction of cerebral white matter, and atrophy of the cerebellum in an inbred sibship. The phenotype was recorded and evolution followed for over 20 years. Brain lesions were studied by diffusion tensor MR tractography. Homozygosity mapping with SNPs was performed for identification of the chromosomal locus for the disease. In the 14 Mb candidate region on chromosome 7q22, RNA expression profiling was used for selecting among the 203 genes in the area. In postmortem brain tissue available from one patient, histology and immunohistochemistry were performed. Disease course and imaging were mostly reminiscent of hypoxic-ischemic tetraplegic cerebral palsy, with neuroaxonal degeneration and white matter loss. In all five patients, a donor splice site pathogenic mutation in intron 14 of the AP4M1 gene (c.1137+1G-->T), was identified. AP4M1, encoding for the mu subunit of the adaptor protein complex-4, is involved in intracellular trafficking of glutamate receptors. Aberrant GluRdelta2 glutamate receptor localization and dendritic spine morphology were observed in the postmortem brain specimen. This disease entity, which we refer to as congenital spastic tetraplegia (CST), is therefore a genetic model for congenital cerebral palsy with evidence for neuroaxonal damage and glutamate receptor abnormality, mimicking perinatally acquired hypoxic-ischemic white matter injury.

Phenotypic variability of atypical 22q11.2 deletions not including TBX1.

Interstitial deletions of the chromosome 22q11.2 region are the most common microdeletions in humans. The TBX1 gene is considered to be the major candidate gene for the main features in 22q11.2 deletion syndrome, including congenital heart malformations, (para)thyroid hypoplasia, and craniofacial abnormalities. We report on eight patients with atypical deletions of chromosome 22q11.2. These deletions comprise the distal part of the common 22q11.2 deleted region but do not encompass the TBX1 gene. Ten similar patients with overlapping distal 22q11.2 deletions have been reported previously. The clinical features of these patients are described and compared to those found in the classic 22q11.2 deletion syndrome. We discuss the possible roles of a position effect or haploinsufficiency of distally located genes (e.g., CRKL) in the molecular pathogenesis of the 22q11.2 deletion syndrome.

Novel DNA mutation in the GATA3 gene in an Emirati boy with HDR syndrome and hypomagnesemia.

We report the case of a young Emirati boy with HDR (Hypoparathyroidism, sensorineural Deafness, and Renal hypoplasia) syndrome due to the novel heterozygous deletion of two nucleotides (c.35_36delGC ) in exon 2 of the GATA3 gene. The patient developed hypocalcemia and hypomagnesemia at 3 weeks of age with high fractional excretion of magnesium, indicating renal magnesium loss. This is the first published report of hypomagnesemia in association with HDR syndrome.

Polyalanine expansion in the ZIC3 gene leading to X-linked heterotaxy with VACTERL association: a new polyalanine disorder?

BACKGROUND: The VACTERL association is a non-random association of congenital defects with an unknown aetiology in the majority of patients. METHODS: A male newborn is reported with features of the VACTERL association, including anal atresia, laryngeal and oesophageal atresia with tracheo-oesophageal fistula, dextroposition of the heart with persistent left superior vena cava, and unilateral multicystic kidney. As the clinical picture of this patient overlaps with that of X-linked heterotaxy caused by ZIC3 mutations, the ZIC3 coding region was sequenced. RESULTS: In a patient with the VACTERL association a 6-nucleotide insertion was found in the GCC repeat of the ZIC3 gene, which is predicted to expand the amino-terminal polyalanine repeat from 10 to 12 polyalanines. The polyalanine expansion is a novel ZIC3 mutation which was not found in 336 chromosomes from 192 ethnically matched controls. The mutation was also not present in the mother, suggesting it occurred de novo in the patient and is therefore a pathogenetic mutation. CONCLUSION: It is hypothesized that this novel and de novo polyalanine expansion in ZIC3 contributes to the VACTERL association in this patient. A newborn male is described with features of the VACTERL association, including anal atresia, laryngeal and oesophageal atresia with tracheo-oesophageal fistula, dextroposition of the heart with persistent left superior vena cava, and unilateral multicystic kidney. As the clinical picture of the VACTERL association overlaps with X-linked heterotaxy caused by ZIC3 mutations, the ZIC3 coding region was sequenced, and a 6-nucleotide insertion was found that is predicted to expand the amino-terminal polyalanine repeat from 10 to 12 polyalanines. This novel mutation was not present in the mother, nor in 336 chromosomes from 192 ethnically matched controls. It is hypothesised that this novel and de novo polyalanine expansion in the ZIC3 gene contributes to the VACTERL association in this patient.

Mucopolysaccharidosis type IIID: 12 new patients and 15 novel mutations.

Mucopolysaccharidosis III D (Sanfilippo disease type D, MPS IIID) is a rare autosomal recessive lysosomal storage disorder previously described in only 20 patients. MPS IIID is caused by a deficiency of N-acetylglucosamine-6-sulphate sulphatase (GNS), one of the enzymes required for the degradation of heparan sulphate. So far only seven mutations in the GNS gene have been reported. The clinical phenotype of 12 new MPS IIID patients from 10 families was studied. Mutation analysis of GNS was performed in 16 patients (14 index cases). Clinical signs and symptoms of the MPS IIID patients appeared to be similar to previously described patients with MPS III. Early development was normal with onset of behavioral problems around the age of 4 years, followed by developmental stagnation, deterioration of verbal communication and subsequent deterioration of motor functions. Sequence analysis of the coding regions of the gene encoding GNS (GNS) resulted in the identification of 15 novel mutations: 3 missense mutations, 1 nonsense mutation, 4 splice site mutations, 3 frame shift mutations, 3 large deletions and 1 in-frame small deletion. They include the first missense mutations and a relatively high proportion of large rearrangements, which warrants the inclusion of quantitative techniques in routine mutation screening of the GNS gene.

Dandy-Walker malformation in patients with KID syndrome associated with a heterozygote mutation (p.Asp50Asn) in the GJB2 gene encoding connexin 26.

The Keratitis-Ichthyosis-Deafness syndrome (KIDS) is an autosomal dominant ectodermal dysplasia characterized by ocular, skin, and ear anomalies, including keratitis, palmoplantar keratoderma, and congenital hearing loss. Most cases are due to mutations in the GJB2 gene encoding connexin 26. The Dandy-Walker malformation (DWM) is a developmental anomaly of the midline of the cerebellum with complete or partial agenesis of the vermis and cystic dilatation of the fourth ventricle. The association of KID syndrome with DWM has been reported a few times, but thought to be coincidental. We report 4 additional patients with KIDS and DWM, supporting the possibility that this is an association and not a coincidental finding. This also suggests that the GJB2 gene may have a role in other cases with DWM of, as yet, unknown etiology.

Autosomal dominant syndrome of mental retardation, hypotelorism, and cleft palate resembling Schilbach-Rott syndrome.

We present a family segregating for an autosomal dominant syndrome of hypotelorism, cleft palate/uvula, high-arched palate and mild mental retardation. Although these findings may suggest a form of holoprosencephaly, no holoprosencephaly was found on MRI of the proposita. Results of genetic studies were normal including FISH for deletion of 22q11, karyotype analysis, fragile X testing, high-resolution comparative genomic hybridization and SEPT9, SHH mutation analysis. The syndrome is reminiscent of the infrequently recognized autosomal dominant Schilbach-Rott syndrome.

Autosomal dominant inheritance of cardiac valves anomalies in two families: extended spectrum of left-ventricular outflow tract obstruction.

Only a limited number of families with clear monogenic inheritance of nonsyndromic forms of congenital valve defects have been described. We describe two multiplex pedigrees with a similar nonsyndromic form of heart valve anomalies that segregate as an autosomal dominant condition. The first family is a three-generation pedigree with 10 family members affected with congenital defects of the cardiac valves, including six patients with aortic stenosis and/or aortic regurgitation. Pulmonary and/or tricuspid valve abnormalities were present in three patients, and ventricular septal defect (VSD) was present in two patients. The second family consists of 11 patients in three generations with aortic valve stenosis in seven patients, defects of the pulmonary valves in two patients, and atrial septal defect (ASD) in two patients. Incomplete penetrance was observed in both families. Although left-ventricular outflow tract obstruction was present in most family members, the co-occurrence with pulmonary valve abnormalities and septal defects in both families is uncommon. These families provide evidence that left-sided obstructive defects and thoracic aortic aneurysm may be accompanied by right-sided defects, and even septal defects. These families might be instrumental in identifying genes involved in cardiac valve morphogenesis and malformation.

Bottlenecks in molecular testing for rare genetic diseases.

Despite the impressive progress in our understanding of the genetic causes of genetic diseases over the past decade, molecular diagnosis for rare genetic disorders is still in its infancy, being slow, expensive, unreliable, insufficient, and ill-organized in many countries. This leaves the gap between the hype of the current genomic research and the hope for a simple genetic diagnosis too large for patients and families affected with genetic disease. The bottlenecks in the molecular testing for rare genetic disorders are discussed below.

A new syndrome with noncompaction cardiomyopathy, bradycardia, pulmonary stenosis, atrial septal defect and heterotaxy with suggestive linkage to chromosome 6p.

We report a three-generation family with nine patients affected by a combination of cardiac abnormalities and left isomerism which, to our knowledge, has not been described before. The cardiac anomalies include non-compaction of the ventricular myocardium, bradycardia, pulmonary valve stenosis, and secundum atrial septal defect. The laterality sequence anomalies include left bronchial isomerism, azygous continuation of the inferior vena cava, polysplenia and intestinal malrotation, all compatible with left isomerism. This new syndrome is inherited in an autosomal dominant pattern. A genome-wide linkage analysis suggested linkage to chromosome 6p24.3-21.2 with a maximum LOD score of 2.7 at marker D6S276. The linkage interval is located between markers D6S470 (telomeric side) and D6S1610 (centromeric side), and overlaps with the linkage interval in another family with heterotaxy reported previously. Taken together, the genomic region could be reduced to 9.4 cM (12 Mb) containing several functional candidate genes for this complex heterotaxy phenotype.

Phenotypic variants of the deafness-associated mitochondrial DNA A7445G mutation.

A number of nuclear and mitochondrial mutations have been implicated in non-syndromic hearing loss. Among them, various mutations of mitochondrial Ser(UCN)-tRNA and 12S rRNA genes have been found to be associated with deafness; the A7445G mitochondrial DNA (mtDNA) in this group is unique, simultaneously affecting two different mitochondrial genes, encoding the Ser(UCN)-tRNA and the first subunit of cytochrome oxidase. Besides the hearing loss, it is mainly associated with palmoplantar keratoderma, though; different phenotypic associations have been reported. The current paper reviews the available PubMed reports on the A7445G mtDNA mutation, with special attention to the phenotypic variations. Further, a Hungarian family with the A7445G mutation is reported, in which analysis of both the affected and the non-affected members revealed the mutation in both homo- and heteroplasmic forms, independently of the hearing status of the subjects, a phenomenon previously not reported in other pedigrees. The female lineage represented a rare variant of the U4b haplogroup.

Mutations in sarcomeric protein genes not only lead to cardiomyopathy but also to congenital cardiovascular malformations.

Noncompaction of the ventricular myocardium is associated with de novo mutation in the beta-myosin heavy chain gene Budde et al. (2007) PLoS ONE 2: e1362 Homozygosity for a novel splice site mutation in the cardiac myosin-binding protein C gene causes severe neonatal hypertrophic cardiomyopathy Xin et al. (2007) Am J Med Genet 143: 2662-2667 Alpha-cardiac actin mutations produce atrial septal defects Matsson et al. (2008) Hum Mol Genet 17: 256-265.

The SMAD-binding domain of SKI: a hotspot for de novo mutations causing Shprintzen-Goldberg syndrome.

Shprintzen-Goldberg syndrome (SGS) is a rare, systemic connective tissue disorder characterized by craniofacial, skeletal, and cardiovascular manifestations that show a significant overlap with the features observed in the Marfan (MFS) and Loeys-Dietz syndrome (LDS). A distinguishing observation in SGS patients is the presence of intellectual disability, although not all patients in this series present this finding. Recently, SGS was shown to be due to mutations in the SKI gene, encoding the oncoprotein SKI, a repressor of TGFß activity. Here, we report eight recurrent and three novel SKI mutations in eleven SGS patients. All were heterozygous missense mutations located in the R-SMAD binding domain, except for one novel in-frame deletion affecting the DHD domain. Adding our new findings to the existing data clearly reveals a mutational hotspot, with 73% (24 out of 33) of the hitherto described unrelated patients having mutations in a stretch of five SKI residues (from p.(Ser31) to p.(Pro35)). This implicates that the initial molecular testing could be focused on mutation analysis of the first half of exon 1 of SKI. As the majority of the known mutations are located in the R-SMAD binding domain of SKI, our study further emphasizes the importance of TGFß signaling in the pathogenesis of SGS.

Transcriptional regulator PRDM12 is essential for human pain perception.

Pain perception has evolved as a warning mechanism to alert organisms to tissue damage and dangerous environments. In humans, however, undesirable, excessive or chronic pain is a common and major societal burden for which available medical treatments are currently suboptimal. New therapeutic options have recently been derived from studies of individuals with congenital insensitivity to pain (CIP). Here we identified 10 different homozygous mutations in PRDM12 (encoding PRDI-BF1 and RIZ homology domain-containing protein 12) in subjects with CIP from 11 families. Prdm proteins are a family of epigenetic regulators that control neural specification and neurogenesis. We determined that Prdm12 is expressed in nociceptors and their progenitors and participates in the development of sensory neurons in Xenopus embryos. Moreover, CIP-associated mutants abrogate the histone-modifying potential associated with wild-type Prdm12. Prdm12 emerges as a key factor in the orchestration of sensory neurogenesis and may hold promise as a target for new pain therapeutics.

Congenital diaphragmatic hernia in a female patient with craniofrontonasal syndrome.

A 21-month-old Caucasian female with the combination of craniofrontonasal syndrome and a posterolateral defect of the diaphragm (type Bochdalek) is described. This is thought to be a previously undescribed combination. Pedigree analysis is consistent with an X-linked mode of inheritance of the craniofrontonasal syndrome.