Filamin A mutations cause periventricular heterotopia with Ehlers-Danlos syndrome

Ehlers-Danlos syndrome and neurological features: a review

Ehlers-Danlos Syndrome is a term that comprises a variety of inherited connective tissue disorders characterized primarily by skin hyperextensibility, joints hypermobility and excessive dislocations, easy bruisability, generalized fragility. If much is known about orthopedic or physiatric features of this syndrome, poor is known about the neurological ones. Thus neurological assessment is very important due to the possible various clinical manifestations in this syndrome.

Clinical and genetic aspects of Ehlers-Danlos syndrome, classic type

Classic Ehlers-Danlos syndrome is a heritable connective tissue disorder characterized by skin hyperextensibility, fragile and soft skin, delayed wound healing with formation of atrophic scars, easy bruising, and generalized joint hypermobility. It comprises Ehlers-Danlos syndrome type I and Ehlers-Danlos syndrome type II, but it is now apparent that these form a continuum of clinical findings and differ only in phenotypic severity. It is currently estimated that approximately 50% of patients with a clinical diagnosis of classic Ehlers-Danlos syndrome harbor mutations in the COL5A1 and the COL5A2 gene, encoding the α1 and the α2-chain of type V collagen, respectively. However, because no prospective molecular studies of COL5A1 and COL5A2 have been performed in a clinically well-defined patient group, this number may underestimate the real proportion of patients with classic Ehlers-Danlos syndrome harboring a mutation in one of these genes. In the majority of patients with molecularly characterized classic Ehlers-Danlos syndrome, the disease is caused by a mutation leading to a nonfunctional COL5A1 allele and resulting in haploinsufficiency of type V collagen. A smaller proportion of patients harbor a structural mutation in COL5A1 or COL5A2, causing the production of a functionally defective type V collagen protein. Most mutations identified so far result in a reduced amount of type V collagen in the connective tissues available for collagen fibrillogenesis. Inter- and intrafamilial phenotypic variability is observed, but no genotype-phenotype correlations have been observed. No treatment for the underlying defect is presently available for Ehlers-Danlos syndrome. However, a series of preventive guidelines are applicable.

Rare copy number variants disrupt genes regulating vascular smooth muscle cell adhesion and contractility in sporadic thoracic aortic aneurysms and dissections

Thoracic aortic aneurysms and dissections (TAAD) cause significant morbidity and mortality, but the genetic origins of TAAD remain largely unknown. In a genome-wide analysis of 418 sporadic TAAD cases, we identified 47 copy number variant (CNV) regions that were enriched in or unique to TAAD patients compared to population controls. Gene ontology, expression profiling, and network analysis showed that genes within TAAD CNVs regulate smooth muscle cell adhesion or contractility and interact with the smooth muscle-specific isoforms of α-actin and β-myosin, which are known to cause familial TAAD when altered. Enrichment of these gene functions in rare CNVs was replicated in independent cohorts with sporadic TAAD (STAAD, n = 387) and inherited TAAD (FTAAD, n = 88). The overall prevalence of rare CNVs (23%) was significantly increased in FTAAD compared with STAAD patients (Fisher's exact test, p = 0.03). Our findings suggest that rare CNVs disrupting smooth muscle adhesion or contraction contribute to both sporadic and familial disease.

Surgically treated movement disorders associated with heterotopia: report of 2 cases

Heterotopic gray matter has been implicated in epilepsy; however, not much is known regarding heterotopia beyond epilepsy. Here, the authors describe 2 pediatric patients with deep heterotopias contiguous with basal ganglia structures. These heterotopias appear to have manifested as movement disorders. One patient presented with a left-sided myoclonus and choreiform movements associated with a right caudate heterotopia; she experienced vast improvement after resection of periventricular heterotopia. The other patient presented with progressive dystonia and a ballistic movement disorder. Initial bilateral globus pallidus internus stimulation resulted in successful treatment of the dystonia; however, her movement disorder worsened. After an extensive workup, including STATISCOM (statistical ictal SPECT coregistered to MR imaging), the patient underwent cortical stimulation with improvement in her movement disorder. To the best of our knowledge, these cases are the first reported instances of heterotopic gray matter associated with movement disorders. Both patients experienced significant improvements following resection of their heterotopias.

Combined cardiological and neurological abnormalities due to filamin A gene mutation

BACKGROUND

Cardiac defects can be the presenting symptom in patients with mutations in the X-linked gene FLNA. Dysfunction of this gene is associated with cardiac abnormalities, especially in the left ventricular outflow tract, but can also cause a congenital malformation of the cerebral cortex. We noticed that some patients diagnosed at the neurogenetics clinic had first presented to a cardiologist, suggesting that earlier recognition may be possible if the diagnosis is suspected.

METHODS AND RESULTS

From the Erasmus MC cerebral malformations database 24 patients were identified with cerebral bilateral periventricular nodular heterotopia (PNH) without other cerebral cortical malformations. In six of these patients, a pathogenic mutation in FLNA was present. In five a cardiac defect was also found in the outflow tract. Four had presented to a cardiologist before the cerebral abnormalities were diagnosed.

CONCLUSIONS

The cardiological phenotype typically consists of aortic or mitral regurgitation, coarctation of the aorta or other left-sided cardiac malformations. Most patients in this category will not have a FLNA mutation, but the presence of neurological complaints, hyperlaxity of the skin or joints and/or a family history with similar cardiac or neurological problems in a possibly X-linked pattern may alert the clinician to the possibility of a FLNA mutation.

A novel interaction between FlnA and Syk regulates platelet ITAM-mediated receptor signaling and function

Filamin A (FlnA) cross-links actin filaments and connects the Von Willebrand factor receptor GPIb-IX-V to the underlying cytoskeleton in platelets. Because FlnA deficiency is embryonic lethal, mice lacking FlnA in platelets were generated by breeding FlnA^loxP/loxP females with GATA1-Cre males. FlnA^loxP/y GATA1-Cre males have a macrothrombocytopenia and increased tail bleeding times. FlnA-null platelets have decreased expression and altered surface distribution of GPIbα because they lack the normal cytoskeletal linkage of GPIbα to underlying actin filaments. This results in ∼70% less platelet coverage on collagen-coated surfaces at shear rates of 1,500/s, compared with wild-type platelets. Unexpectedly, however, immunoreceptor tyrosine-based activation motif (ITAM)- and ITAM-like–mediated signals are severely compromised in FlnA-null platelets. FlnA-null platelets fail to spread and have decreased α-granule secretion, integrin αIIbβ3 activation, and protein tyrosine phosphorylation, particularly that of the protein tyrosine kinase Syk and phospholipase C–γ2, in response to stimulation through the collagen receptor GPVI and the C-type lectin-like receptor 2. This signaling defect was traced to the loss of a novel FlnA–Syk interaction, as Syk binds to FlnA at immunoglobulin-like repeat 5. Our findings reveal that the interaction between FlnA and Syk regulates ITAM- and ITAM-like–containing receptor signaling and platelet function.

Terminal osseous dysplasia is caused by a single recurrent mutation in the FLNA gene

Terminal osseous dysplasia (TOD) is an X-linked dominant male-lethal disease characterized by skeletal dysplasia of the limbs, pigmentary defects of the skin, and recurrent digital fibroma with onset in female infancy. After performing X-exome capture and sequencing, we identified a mutation at the last nucleotide of exon 31 of the FLNA gene as the most likely cause of the disease. The variant c.5217G>A was found in six unrelated cases (three families and three sporadic cases) and was not found in 400 control X chromosomes, pilot data from the 1000 Genomes Project, or the FLNA gene variant database. In the families, the variant segregated with the disease, and it was transmitted four times from a mildly affected mother to a more seriously affected daughter. We show that, because of nonrandom X chromosome inactivation, the mutant allele was not expressed in patient fibroblasts. RNA expression of the mutant allele was detected only in cultured fibroma cells obtained from 15-year-old surgically removed material. The variant activates a cryptic splice site, removing the last 48 nucleotides from exon 31. At the protein level, this results in a loss of 16 amino acids (p.Val1724_Thr1739del), predicted to remove a sequence at the surface of filamin repeat 15. Our data show that TOD is caused by this single recurrent mutation in the FLNA gene.

Genetic factors in non-syndromic congenital heart malformations

The genetic defect in most patients with non-syndromic congenital heart malformations (CHM) is unknown, although more than 40 different genes have already been implicated. Only a minority of CHM seems to be due to monogenetic mutations, and the majority occurs sporadically. The multifactorial inheritance hypothesis of common diseases suggesting that the cumulative effect of multiple genetic and environmental risk factors leads to disease, might also apply for CHM. We review here the monogenic disease genes with high-penetrance mutations, susceptibility genes with reduced-penetrance mutations, and somatic mutations implicated in non-syndromic CHM.

Novel cardiac findings in periventricular nodular heterotopia

Periventricular nodular heterotopia (PNH) is a set of neuronal migration disorders that occur during fetal development. Neurons in the brain fail to migrate from the lining of the lateral ventricles to the cortex of the brain. When the neurons fail to migrate, ectopic neuronal nodules form. Epilepsy is a common symptom of PNH. The majority of PNH cases appear to be due to mutations in filamin A, an X-linked gene. Most of the affected individuals are female because affected males typically die in utero. Filamin A anchors integral membrane proteins to the cytoskeleton by binding actin filaments in the cytoplasm. Both animal and human studies indicate that filamin A also plays a role in blood vessel development. In this report, we describe novel cardiac findings in an 18-month-old girl with PNH associated with a nonsense mutation in FLNA, including a dysplastic pulmonary valve and clefting of the mitral valve. These findings broaden the range of cardiac anomalies associated with filamin A mutations to include abnormality of the pulmonary valve and clefting of the mitral valve, consistent with a role for filamin A in valve leaflet development.

Periventricular heterotopia in common microdeletion syndromes

Periventricular heterotopia (PH) is a brain malformation characterised by heterotopic nodules of neurons lining the walls of the cerebral ventricles. Mutations in FLNA account for 20-24% of instances but a majority have no identifiable genetic aetiology. Often the co-occurrence of PH with a chromosomal anomaly is used to infer a new locus for a Mendelian form of PH. This study reports four PH patients with three different microdeletion syndromes, each characterised by high-resolution genomic microarray. In three patients the deletions at 1p36 and 22q11 are conventional in size, whilst a fourth child had a deletion at 7q11.23 that was larger in extent than is typically seen in Williams syndrome. Although some instances of PH associated with chromosomal deletions could be attributed to the unmasking of a recessive allele or be indicative of more prevalent subclinical migrational anomalies, the rarity of PH in these three microdeletion syndromes and the description of other non-recurrent chromosomal defects do suggest that PH may be a manifestation of multiple different forms of chromosomal imbalance. In many, but possibly not all, instances the co-occurrence of PH with a chromosomal deletion is not necessarily indicative of uncharacterised underlying monogenic loci for this particular neuronal migrational anomaly.

Disruption of neural progenitors along the ventricular and subventricular zones in periventricular heterotopia

Periventricular heterotopia (PH) is a disorder characterized by neuronal nodules, ectopically positioned along the lateral ventricles of the cerebral cortex. Mutations in either of two human genes, Filamin A (FLNA) or ADP-ribosylation factor guanine exchange factor 2 (ARFGEF2), cause PH (Fox et al. in 'Mutations in filamin 1 prevent migration of cerebral cortical neurons in human periventricular heterotopia'. Neuron, 21, 1315-1325, 1998; Sheen et al. in 'Mutations in ARFGEF2 implicate vesicle trafficking in neural progenitor proliferation and migration in the human cerebral cortex'. Nat. Genet., 36, 69-76, 2004). Recent studies have shown that mutations in mitogen-activated protein kinase kinase kinase-4 (Mekk4), an indirect interactor with FlnA, also lead to periventricular nodule formation in mice (Sarkisian et al. in 'MEKK4 signaling regulates filamin expression and neuronal migration'. Neuron, 52, 789-801, 2006). Here we show that neurons in post-mortem human PH brains migrated appropriately into the cortex, that periventricular nodules were primarily composed of later-born neurons, and that the neuroependyma was disrupted in all PH cases. As studied in the mouse, loss of FlnA or Big2 function in neural precursors impaired neuronal migration from the germinal zone, disrupted cell adhesion and compromised neuroepithelial integrity. Finally, the hydrocephalus with hop gait (hyh) mouse, which harbors a mutation in Napa [encoding N-ethylmaleimide-sensitive factor attachment protein alpha (alpha-SNAP)], also develops a progressive denudation of the neuroepithelium, leading to periventricular nodule formation. Previous studies have shown that Arfgef2 and Napa direct vesicle trafficking and fusion, whereas FlnA associates dynamically with the Golgi membranes during budding and trafficking of transport vesicles. Our current findings suggest that PH formation arises from a final common pathway involving disruption of vesicle trafficking, leading to impaired cell adhesion and loss of neuroependymal integrity.

Novel localization of tenascin-X in adult mouse leptomeninges and choroid plexus

Tenascin-X (Tn-X) belongs to the tenascin family of glycoproteins and is clearly associated with the human connective tissue disorder Ehlers-Danlos syndrome. Recently, human single nucleotide polymorphism analyses showed that Tn-X is associated with schizophrenia. Tn-X-related central nervous system (CNS) disorder has been reported in recent years. However, details of Tn-X localization are not clear in the adult cerebral cortex and its meninges. Using immunohistochemical techniques, we found novel localizations of Tn-X in the leptomeningeal trabecula (TB) of adult mice and in the connective tissue of the choroid plexus (CP) in the brains of mice. Subsequent immunohistochemical studies showed complementary localization of Tn-X in the leptomeninges and CP. Localization of tenascin-C was not detected in the leptomeningeal TB or in the connective tissue of the CP. These results might provide insight into the role of Tn-X in the pathogenesis of disorders in the CNS.

Filamins in cardiovascular development

Filamins are classically recognized as large cytoplasmic proteins that cross-link cortical actin into dynamic 3-dimensional structures and transmit extracellular signals through integrin receptors into the cytoplasm. However, recent reports indicate that filamins interact with a large number of other proteins with diverse functions, including transcriptional factors and cellular molecules involved in signaling, adhesion, and cellular motility, and are also present in the cell nucleus. In addition, genetic mutations in filamins have been linked to a wide range of human genetic disorders, including skeletal, central nervous system, and cardiovascular malformations, highlighting distinct filamin interactions. Here, we update the cardiovascular phenotypes of patients with mutations in filamin genes and mice deficient in filamins and filamin-interacting proteins.

Trouble making the first move: interpreting arrested neuronal migration in the cerebral cortex

Postmitotic cortical neurons that fail to initiate migration can remain near their site of origin and form persistent periventricular nodular heterotopia (PH). In human telencephalon, this malformation is most commonly associated with Filamin-A (FLNa) mutations. The lack of genetic animal models that reliably produce PH has delayed our understanding of the underlying molecular mechanisms. This review examines PH pathogenesis using a new mouse model. Although PH have not been observed in Flna-deficient mice generated thus far, the loss of MEKK4, a regulator of Flna, produces striking PH in mice and offers insight into the mechanisms involved in neuronal migration initiation. Elucidating the basic functions of FLNa and associated molecules is crucial for understanding the causes of PH and for developing prevention for at-risk patients.

Ehlers-Danlos syndrome type IV

Ehlers-Danlos syndrome type IV, the vascular type of Ehlers-Danlos syndromes (EDS), is an inherited connective tissue disorder defined by characteristic facial features (acrogeria) in most patients, translucent skin with highly visible subcutaneous vessels on the trunk and lower back, easy bruising, and severe arterial, digestive and uterine complications, which are rarely, if at all, observed in the other forms of EDS. The estimated prevalence for all EDS varies between 1/10,000 and 1/25,000, EDS type IV representing approximately 5 to 10% of cases. The vascular complications may affect all anatomical areas, with a tendency toward arteries of large and medium diameter. Dissections of the vertebral arteries and the carotids in their extra- and intra-cranial segments (carotid-cavernous fistulae) are typical. There is a high risk of recurrent colonic perforations. Pregnancy increases the likelihood of a uterine or vascular rupture. EDS type IV is inherited as an autosomal dominant trait that is caused by mutations in the COL3A1 gene coding for type III procollagen. Diagnosis is based on clinical signs, non-invasive imaging, and the identification of a mutation of the COL3A1 gene. In childhood, coagulation disorders and Silverman's syndrome are the main differential diagnoses; in adulthood, the differential diagnosis includes other Ehlers-Danlos syndromes, Marfan syndrome and Loeys-Dietz syndrome. Prenatal diagnosis can be considered in families where the mutation is known. Choriocentesis or amniocentesis, however, may entail risk for the pregnant woman. In the absence of specific treatment for EDS type IV, medical intervention should be focused on symptomatic treatment and prophylactic measures. Arterial, digestive or uterine complications require immediate hospitalisation, observation in an intensive care unit. Invasive imaging techniques are contraindicated. Conservative approach is usually recommended when caring for a vascular complication in a patient suffering from EDS type IV. Surgery may, however, be required urgently to treat potentially fatal complications.

The pathomechanism of filaminopathy: altered biochemical properties explain the cellular phenotype of a protein aggregation myopathy

Myofibrillar myopathy (MFM) is a pathologically defined group of hereditary human muscle diseases, characterized by focal myofibrillar destruction and cytoplasmic aggregates that contain several Z-disc-related proteins. The previously reported MFM-associated mutation (8130G --> A; W2710X) in the filamin C gene (FLNC) leads to a partial disturbance of the secondary structure of the dimerization domain of filamin C, resulting in massive protein aggregation in skeletal muscle fibers of the patients. Here, we provide a thorough characterization of the biochemical, biophysical and cellular properties of the mutated filamin C polypeptide. Our experiments revealed that the mutant dimerization domain is less stable and more susceptible to proteolysis. As a consequence, it does not dimerize properly and forms aggregates in vitro. Furthermore, the expression of mutant filamin in cultured cells results in the formation of protein aggregates. The mutant filamin does not associate with wild type filamin. These findings are of great importance to explain the pathomechanism of this disease.

Bilateral periventricular nodular heterotopia, severe learning disability, and epilepsy in a male patient with 46,XY,der(19)t(X;19) (q11.1-11.2;p13.3)

Periventricular nodular heterotopia (PNH) is a rare neuronal migration disorder in which immature neurons fail to undergo a directed migration from the ventricular and subventricular zones to the cerebral cortex. Classic PNH occurs predominantly in females and is associated with periods of epilepsy and near-normal intelligence. One gene associated with PNH was mapped to chromosome Xq28. PNH with learning disability is reported in 15 male patients with several syndromes and various congenital abnormalities such as craniosynostosis, frontonasal malformation, and agenesis of the corpus callosum. We present a 26-year-old male patient who was followed up with the diagnosis of epilepsy from the age of 1 year. Additionally the patient had severe learning disability, obesity, and hypogonadism. Imaging of his brain demonstrated PNH. Klinefelter syndrome was clinically suspected, and analysis of his chromosomes revealed a karyotype 46,XY,der(19)t(X;19) (q11.1-11.2;p13.3). Molecular techniques, such as subtelomere-specific fluorescent in-situ hybridization and multicolour banding, were also used. The same translocation was demonstrated in his mother and his maternal grandmother. This family might help to explain the gene localization of X-linked recessive PNH. In our patient, PNH is associated with familial (X;19) translocation. To our knowledge, this unique combination has not been reported in the medical literature.

MEKK4 signaling regulates filamin expression and neuronal migration

Periventricular heterotopia (PVH) is a congenital malformation of human cerebral cortex frequently associated with Filamin-A (FLN-A) mutations but the pathogenetic mechanisms remain unclear. Here, we show that the MEKK4 (MAP3K4) pathway is involved in Fln-A regulation and PVH formation. MEKK4(-/-) mice developed PVH associated with breaches in the neuroependymal lining which were largely comprised of neurons that failed to reach the cortical plate. RNA interference (RNAi) targeting MEKK4 also impaired neuronal migration. Expression of Fln was elevated in MEKK4(-/-) forebrain, most notably near sites of failed neuronal migration. Importantly, recombinant MKK4 protein precipitated a complex containing MEKK4 and Fln-A, and MKK4 mediated signaling between MEKK4 and Fln-A, suggesting that MKK4 may bridge these molecules during development. Finally, we showed that wild-type FLN-A overexpression inhibited neuronal migration. Collectively, our results demonstrate a link between MEKK4 and Fln-A that impacts neuronal migration initiation and provides insight into the pathogenesis of human PVH.

Mutations in the gene encoding filamin A as a cause for familial cardiac valvular dystrophy

BACKGROUND

Myxomatous dystrophy of the cardiac valves affects approximately 3% of the population and remains one of the most common indications for valvular surgery. Familial inheritance has been demonstrated with autosomal and X-linked transmission, but no specific molecular abnormalities have been documented in isolated nonsyndromic forms. We have investigated the genetic causes of X-linked myxomatous valvular dystrophy (XMVD) previously mapped to chromosome Xq28.

METHODS AND RESULTS

A familial and genealogical survey led us to expand the size of a large, previously identified family affected by XMVD and to refine the XMVD locus to a 2.5-Mb region. A standard positional cloning approach identified a P637Q mutation in the filamin A (FLNA) gene in all affected members. Two other missense mutations (G288R and V711D) and a 1944-bp genomic deletion coding for exons 16 to 19 in the FLNA gene were identified in 3 additional, smaller, unrelated families affected by valvular dystrophy, which demonstrates the responsibility of FLNA as a cause of XMVD. Among carriers of FLNA mutation, the penetrance of the disease was complete in men and incomplete in women. Female carriers could be mildly affected, and the severity of the disease was highly variable among mutation carriers.

CONCLUSIONS

Our data demonstrate that FLNA is the first gene known to cause isolated nonsyndromic MVD. This is the first step to understanding the pathophysiological mechanisms of the disease and to defining pathways that may lead to valvular dystrophy. Screening for FLNA mutations could be important for families affected by XMVD to provide adequate follow-up and genetic counseling.

Otopalatodigital syndrome spectrum disorders: otopalatodigital syndrome types 1 and 2, frontometaphyseal dysplasia and Melnick-Needles syndrome

The term otopalatodigital syndrome spectrum disorders is an umbrella category that includes four phenotypically related conditions, otopalatodigital syndrome types 1 and 2, frontometaphyseal dysplasia and Melnick - Needles syndrome. The phenotype of these conditions in the male ranges from a severe perinatally lethal multiple malformation syndrome to a mild skeletal dysplasia. Most, but not all, instances of these conditions are associated by mutations in the X-linked gene encoding the cytoskeletal protein filamin A. Mutations in this gene are clustered, exhibit a strong genotype-phenotype correlation and are presumed to exert their effect by a gain-of-function mechanism.

Cardiac malformations and midline skeletal defects in mice lacking filamin A

The X-linked gene filamin A (Flna) encodes a widely expressed actin-binding protein that crosslinks actin into orthogonal networks and interacts with a variety of other proteins including membrane proteins, integrins, transmembrane receptor complexes and second messengers, thus forming an important intracellular signalling scaffold. Heterozygous loss of function of human FLNA causes periventricular nodular heterotopia in females and is generally lethal (cause unknown) in hemizygous males. Missense FLNA mutations underlie a spectrum of disorders affecting both sexes that feature skeletal dysplasia accompanied by a variety of other abnormalities. Dilp2 is an X-linked male-lethal mouse mutation that was induced by N-ethyl-N-nitrosourea. We report here that Dilp2 is caused by a T-to-A transversion that converts a tyrosine codon to a stop codon in the Flna gene (Y2388X), leading to absence of the Flna protein and male lethality because of incomplete septation of the outflow tract of the heart, which produces common arterial trunk. A proportion of both male and female mutant mice have other cardiac defects including ventricular septal defect. In addition, mutant males have midline fusion defects manifesting as sternum and palate abnormalities. Carrier females exhibit milder sternum and palate defects and misshapen pupils. These results define crucial roles for Flna in development, demonstrate that X-linked male lethal mutations can be recovered from ENU mutagenesis screens and suggest possible explanations for lethality of human males hemizygous for null alleles of FLNA.

Mutation in filamin A causes periventricular heterotopia, developmental regression, and West syndrome in males

PURPOSE

Familial periventricular heterotopia (PH) represents a disorder of neuronal migration resulting in multiple gray-matter nodules along the lateral ventricular walls. Prior studies have shown that mutations in the filamin A (FLNA) gene can cause PH through an X-linked dominant pattern. Heterozygotic female patients usually remain asymptomatic until the second or third decade of life, when they may have predominantly focal seizures, whereas hemizygotic male fetuses typically die in utero. Recent studies have also reported mutations in FLNA in male patients with PH who are cognitively normal. We describe PH in three male siblings with PH due to FLNA, severe developmental regression, and West syndrome.

METHODS

The study includes the three affected brothers and their parents. Video-EEG recordings and magnetic resonance image (MRI) scanning were performed on all individuals. Mutations for FLNA were detected by using polymerase chain reaction (PCR) on genomic DNA followed by single-stranded conformational polymorphism (SSCP) analysis or sequencing.

RESULTS

Two of the siblings are monozygotic twins, and all had West syndrome with hypsarrhythmia on EEG. MRI of the brain revealed periventricular nodules of cerebral gray-matter intensity, typical for PH. Mutational analyses demonstrated a cytosine-to-thymidine missense mutation (c. C1286T), resulting in a threonine-to-methionine amino acid substitution in exon 9 of the FLNA gene.

CONCLUSIONS

The association between PH and West syndrome, to our knowledge, has not been previously reported. Males with PH have been known to harbor FLNA mutations, although uniformly, they either show early lethality or survive and have a normal intellect. The current studies show that FLNA mutations can cause periventricular heterotopia, developmental regression, and West syndrome in male patients, suggesting that this type of FLNA mutation may contribute to severe neurologic deficits.

Postzygotic mutation and germline mosaicism in the otopalatodigital syndrome spectrum disorders

The otopalatodigital syndrome (OPD) spectrum disorders are a heterogeneous group of skeletal dysplasias caused by mutations in the X-linked gene, FLNA. All OPD spectrum disorders (otopalatodigital syndromes types 1 and 2, frontometaphyseal dysplasia and Melnick-Needles syndrome) exhibit significant interfamilial variability in their expressivity, especially in female subjects. Factors contributing to this may include allelic heterogeneity, variation in the degree of skewing of X inactivation or, conceivably, mosaicism for the underlying causative mutation. We report here monozygotic twin sisters who are discordant for the severe phenotype, Melnick-Needles syndrome, associated with the heterozygous mutation, 3596C>T. We also describe two brothers with otopalatodigital syndrome type 1 due to the FLNA mutation 620G>A. The mutation is not detectable in the blood leucocytes of their clinically unaffected mother, indicating that she is a germline mosaic for the condition. The description of somatic mutations and germline mosaicism in FLNA has implications for clinical and molecular diagnosis, phenotypic expression and genetic counseling of families with these disorders.

Steroid sulfatase deficiency with bilateral periventricular nodular heterotopia

This report presents a case of steroid sulfatase deficiency with bilateral periventricular nodular heterotopia. A 13-year-old male was diagnosed as having steroid sulfatase deficiency because steroid sulfatase activity was not detected in his leukocytes. In deoxyribonucleic acid studies, steroid sulfatase locus and adjacent loci were found to be deleted in his deoxyribonucleic acid. Cranial magnetic resonance imaging revealed periventricular nodular heterotopia, disclosing an irregular contour of the lateral walls of the lateral ventricles due to small nodular masses that were isointense as to the gray matter. In steroid sulfatase deficiency patients, bilateral periventricular nodular heterotopia must be considered.

The new bone biology: Pathologic, molecular, and clinical correlates

Bone and cartilage and their disorders are addressed under the following headings: functions of bone; normal and abnormal bone remodeling; osteopetrosis and osteoporosis; epithelial-mesenchymal interaction, condensation and differentiation; osteoblasts, markers of bone formation, osteoclasts, components of bone, and pathology of bone; chondroblasts, markers of cartilage formation, secondary cartilage, components of cartilage, and pathology of cartilage; intramembranous and endochondral bone formation; RUNX genes and cleidocranial dysplasia (CCD); osterix; histone deacetylase 4 and Runx2; Ligand to receptor activator of NFkappaB (RANKL), RANK, osteoprotegerin, and osteoimmunology; WNT signaling, LRP5 mutations, and beta-catenin; the role of leptin in bone remodeling; collagens, collagenopathies, and osteogenesis imperfecta; FGFs/FGFRs, FGFR3 skeletal dysplasias, craniosynostosis, and other disorders; short limb chondrodysplasias; molecular control of the growth plate in endochondral bone formation and genetic disorders of IHH and PTHR1; ANKH, craniometaphyseal dysplasia, and chondrocalcinosis; transforming growth factor beta, Camurati-Engelmann disease (CED), and Marfan syndrome, types I and II; an ACVR1 mutation and fibrodysplasia ossificans progressiva; MSX1 and MSX2: biology, mutations, and associated disorders; G protein, activation of adenylyl cyclase, GNAS1 mutations, McCune-Albright syndrome, fibrous dysplasia, and Albright hereditary osteodystrophy; FLNA and associated disorders; and morphological development of teeth and their genetic mutations.

Periventricular nodular heterotopia and Williams syndrome

We report here on the first case of a child with bilateral periventricular nodular heterotopia (PNH) and Williams syndrome. Fluorescent in situ hybridization (FISH) analyses demonstrated a deletion of the elastin gene in the Williams syndrome critical region (WSCR). Further mapping by loss of heterozygosity analysis both by microsatellite marker and SNP profiling demonstrated a 1.5 Mb deletion beyond the telomeric end of the typical WSCR. No mutations were identified in the X-linked filamin-A gene (the most common cause of PNH). These findings suggest another dominant PNH disorder along chromosome 7q11.23.

Report from a U.S. conference on essential tremor

Seventy researchers met in Washington, DC, on 20-21 October 2005 to identify and discuss the most pressing research issues in essential tremor (ET). The conference attendees concluded that the following six objectives are of immediate and overriding importance: (1) a collaborative network of research centers; (2) an international committee for developing a standard protocol for the diagnosis and quantification of ET; (3) the identification of one or more genes for ET; (4) a centralized repository of DNA and, ideally, immortalized cell lines from well-characterized ET families and healthy controls; (5) a reliable and efficient repository of optimally prepared and categorized brain samples for hypothesis-driven neuropathological examinations in well-characterized ET patients; and (6) animal models of ET for screening promising drugs. The conference attendees hope that this statement from the United States will engender international collaboration in finding a cure for ET.

Periventricular heterotopia: new insights into Ehlers-Danlos syndrome

Nature often employs similar mechanisms to complete similar tasks, thus the evolution of homologous proteins across various organ systems to perform similar but slightly different functions. In this respect, disorders attributed to specific genetic mutations, while initially thought to be restricted in function and purpose, may provide broad insight into general cellular and molecular mechanisms of development and maintenance. One such example can be seen in the brain malformation, periventricular heterotopia (PH), which is characterized by very specific nodules of neurons that line the lateral ventricles beneath the cerebral cortex. PH is seen as a disorder of neuronal migration and can be caused by mutations in filamin A (FLNA), which encodes an actin-binding protein that regulates the cytoskeleton and cell motility. Recent advances in our understanding of the genetic causes of PH suggest that mutations in this gene, however, are also associated with the connective tissue disorder, Ehlers-Danlos syndrome (EDS), in which affected individuals present with joint and skin hyperextensibility and vascular problems including aortic dissection, excessive bleeding and bruisability. While much still remains unknown regarding the mechanistic role of FLNA in giving rise to PH and EDS, a common cellular and molecular basis likely gives rise to these two seemingly unrelated clinical disorders.

Filamin A: phenotypic diversity

Filamins cross-link the actin cytoskeleton into orthogonal networks and modulate the response of cells to their chemical and mechanical environment by regulating changes in shape and motility. Null mutations in FLNA, the gene that encodes filamin A, lead to defects in neuronal migration, vascular function and connective tissue integrity. By contrast, missense mutations in this same gene produce a spectrum of malformations in multiple organ systems, especially the skeleton. The production of such distinctly different phenotypes from loss- and gain-of-function mechanisms provokes questions as to how a ubiquitously expressed structural protein can subserve crucial but discrete roles during development in many organ systems.

Periventricular heterotopia

Periventricular heterotopia (PH) is clinically diagnosed on the basis of the radiographic characteristics of heterotopic nodules composed of disorganized neurons along the lateral ventricles of the brain. Epilepsy is the main presenting symptom of patients with PH. Behaviorally, patients generally are of normal intelligence, although there have been associated findings of learning disabilities, namely, dyslexia. Two genes responsible for PH have been identified: FilaminA, which encodes for the protein filamin A, and ARFGEF2, which encodes for the vesical transport-regulating protein ARFGEF2. The much more common X-linked dominant form of this disorder is due to filamin A, affects females, and is typically lethal in males. A much rarer autosomal recessive form due to ARFGEF2 mutations leads to microcephaly and developmental delay in addition to PH. Cell motility, adhesion defects, and weakening along the neuroepithelial lining may result from defects in these genes during cortical development and contribute to PH, but the mechanisms are not clear yet. Treatment of PH is largely symptomatic, following basic principles for epilepsy management and genetic counseling.

Overlapping expression of ARFGEF2 and Filamin A in the neuroependymal lining of the lateral ventricles: Insights into the cause of periventricular heterotopia

Periventricular heterotopia (PH) is a malformation of cortical development characterized by nodules of neurons, ectopically located along the lateral ventricles of the brain. Mutations in the vesicle transport ADP-ribosylation factor guanine exchange factor 2 gene (ARFGEF2) or the actin-binding Filamin A (FLNA) gene cause PH. Previous studies have shown that FLNA expression is developmentally regulated, with strongest expression observed along the ventricular zone (VZ) and to a lesser degree in postmitotic neurons in the cortex. Here we characterize the expression patterns for ARFGEF2 within the central nervous systems of human and mouse in order to better understand their potential roles in causing PH. ARFGEF2 mRNA was widely expressed in all cortical layers, especially in the neural precursors of the ventricular and subventricular zones (SVZ) during development, with persistent but diminished expression in adulthood. ARFGEF2 encodes for the protein brefeldin-inhibited guanine exchange factor 2 (BIG2). BIG2 protein immunoreactivity was most strongly localized to the neural progenitors along the neuroependymal lining of the VZ during development, with decreased expression in adulthood. Furthermore, overlapping BIG2 and FLNA expression was greatest in these same neuroependymal cells of human embryonic brain and was co-expressed in progenitors by Western blot. Finally, transfection of a dominant-negative construct of ARFGEF2 in SHSY5Y neuroblastoma cells partially blocked FLNA transport from the Golgi apparatus to the cell membrane. These results suggest that mutations in ARFGEF2 may impair targeted transport of FLNA to the cell surface within neural progenitors along the neuroependyma and that disruption of these cells could contribute to PH formation.