Oto-palatal-digital syndrome type II with X-linked cerebellar hypoplasia/hydrocephalus

Case Report: Pansynostosis, Chiari I Malformation and Syringomyelia in a Child With Frontometaphyseal Dysplasia 1

Frontometaphyseal dysplasia 1 (FMD1) is a rare otopalatodigital spectrum disorder (OPDSD) that is inherited as an X-linked trait and it is caused by gain-of-function mutations in the FLNA. It is characterized by generalized skeletal dysplasia, and craniofacial abnormalities including facial dysmorphism (supraorbital hyperostosis, hypertelorism, and down-slanting palpebral fissures). The involvement of the central nervous system in patients with OPDSD is rare. Herein, we present the case of a 12-year-old boy with facial dysmorphism, multiple joint contractures, sensorineural hearing loss, scoliosis, craniosynostosis, and irregular sclerosis with hyperostosis of the skull. Brain and whole-spine magnetic resonance imaging revealed Chiari I malformation with extensive hydrosyringomyelia from the C1 to T12 levels. Targeted next-generation sequencing identified a hemizygous pathologic variant (c.3557C>T/p.Ser1186Leu) in the FLNA, confirming the diagnosis of FMD1. This is the first report of a rare case of OPDSD with pansynostosis and Chiari I malformation accompanied by extensive syringomyelia.

Filamin A: key actor in platelet biology

Filamins (FLNs) are large dimeric actin-binding proteins that regulate actin cytoskeleton remodeling. In addition, FLNs serve as scaffolds for signaling proteins, such as tyrosine kinases, GTPases, or phosphatases, as well as for adhesive receptors, such as integrins. Thus, they connect adhesive receptors to signaling pathways and to cytoskeleton. There are 3 isoforms of FLN (filamin a [FLNa], FLNb, FLNc) that originate from 3 homologous genes. FLNa has been the recent focus of attention because its mutations are responsible for a wide spectrum of defects called filaminopathies A, affecting brain (peri-ventricular nodular heterotopia), heart (valve defect), skeleton, gastrointestinal tract, and, more recently, the megakaryocytic lineage. This review will focus on the physiological and pathological roles of FLNa in platelets. Indeed, FLNa mutations alter platelet production from their bone marrow precursors, the megakaryocytes, yielding giant platelets in reduced numbers (macrothrombocytopenia). In platelets per se, FLNa mutations may lead to impaired αIIbβ3 integrin activation or in contrast, increased αIIbβ3 activation, potentially enhancing the risk of thrombosis. Experimental work delineating the interaction of FLNa with its platelet partners, including αIIbβ3, the von Willebrand factor receptor GPIb-IX-V, the tyrosine kinase Syk, and the signaling pathway of the collagen receptor GPVI, will also be reviewed.

Otopalatodigital spectrum disorders: refinement of the phenotypic and mutational spectrum

Otopalatodigital spectrum disorders (OPDSD) constitute a group of dominant X-linked osteochondrodysplasias including four syndromes: otopalatodigital syndromes type 1 and type 2 (OPD1 and OPD2), frontometaphyseal dysplasia, and Melnick-Needles syndrome. These syndromes variably associate specific facial and extremities features, hearing loss, cleft palate, skeletal dysplasia and several malformations, and show important clinical overlap over the different entities. FLNA gain-of-function mutations were identified in these conditions. FLNA encodes filamin A, a scaffolding actin-binding protein. Here, we report phenotypic descriptions and molecular results of FLNA analysis in a large series of 27 probands hypothesized to be affected by OPDSD. We identified 11 different missense mutations in 15 unrelated probands (n=15/27, 56%), of which seven were novel, including one of unknown significance. Segregation analyses within families made possible investigating 20 additional relatives carrying a mutation. This series allows refining the phenotypic and mutational spectrum of FLNA mutations causing OPDSD, and providing suggestions to avoid the overdiagnosis of OPD1.

Bifid tongue, corneal clouding, and Dandy-Walker malformation in a male infant with otopalatodigital syndrome type 2

We report on a male infant with otopalatodigital syndrome type 2 (OPD2) associated with a novel c.514C>G FLNA mutation and unusual clinical features including bifid tongue and congenital corneal clouding. Bifid tongue and congenital corneal clouding have each only been described once previously in a patient with OPD2, and this is the first description of Dandy-Walker malformation (DWM) in OPD2. The presence of these clinical findings in a mutation-confirmed case of OPD2 supports the notion that corneal clouding, bifid tongue, and DWM are part of the constellation of abnormalities caused by mutations in FLNA.

Expansion of the Spectrum of FLNA Mutations Associated with Melnick-Needles Syndrome

Melnick-Needles syndrome (MNS) is a rare X-linked bone dysplasia characterised by facial dysmorphology and radiographic abnormalities [Melnick and Needles, 1966;97:39-48]. Previously, all published cases of MNS were associated with only 4 mutations [Robertson et al., 2003;33:487-491; Santos et al., 2010;152A:726-731], all localised within exon 22 of FLNA, the gene encoding the cytoskeletal protein filamin A. Here we report 3 new mutations in FLNA that are associated with MNS. One affected member of the first family with the mutation p.Y1229S presented with a stroke while this patient's daughter, previously known to be affected from a young age, developed multiple sclerosis. A second unrelated patient with a typical phenotype is shown to have the mutation c.1054G>T (p.G352W) within exon 7 of FLNA. A third individual with an atypical presentation but radiological findings very similar to those seen in classic MNS has a deletion likely to affect residues within repeat domain 14. These findings indicate that the mutational spectrum for MNS is wider than previously appreciated and has implications for genetic testing strategies employed to confirm a diagnosis of this rare disorder.

Otopalatodigital syndrome type 2 in two siblings with a novel filamin A 629G>T mutation: clinical, pathological, and molecular findings

Otopalatodigital syndrome type 2 (OPD2) is an uncommon X-linked condition characterized by dysmorphic facies, a skeletal dysplasia affecting the axial and appendicular skeleton and extraskeletal anomalies including malformations of the brain, heart, genitourinary system, and intestines. Missense mutations of the FLNA gene, which encodes for the protein filamin A, have recently been shown to cause OPD2 and the allelic syndromes otopalatodigital type 1, Melnick-Needles, and frontometaphyseal dysplasia. Collectively these conditions constitute the otopalatodigital spectrum disorders. We report on two sibs affected by OPD2. The diagnosis was achieved at autopsy of a macerated male stillborn with typical external and skeletal findings of OPD2. A subsequent pregnancy was terminated due to ultrasonographic findings resembling those observed in the previous sibling. Histopathological studies revealed osseus sclerosis and do not support the previously reported membranous ossification defect observed in this condition. Mutation analysis demonstrated a novel mutation, 629G>T, in FLNA that had arisen de novo in the mother. This missense mutation predicts the substitution C210F within the second calponin homology domain of the actin-binding domain of filamin A. The identical substitution has been recently identified in an analogous amino-acid position within the actin binding domain of beta-spectrin leading to hereditary spherocytosis. The observation that phenylalanine is normally present in the same position in other proteins (utrophin, dystrophin) but leads to disease when present in filamin A implies that the function and/or structure of these actin binding domains are not entirely equivalent.

Uveal coloboma: clinical and basic science update

PURPOSE OF REVIEW

To integrate knowledge on the embryologic and molecular basis of optic fissure closure with clinical observations in patients with uveal coloboma.

RECENT FINDINGS

Closure of the optic fissure has been well characterized and many genetic alterations have been associated with coloboma; however, molecular mechanisms leading to coloboma remain largely unknown. In the past decade, we have gained better understanding of genes critical to eye development; however, mutations in these genes have been found in few individuals with coloboma. CHD7 mutations have been identified in patients with CHARGE syndrome (coloboma, heart defects, choanal atresia, retarded growth, genital anomalies, and ear anomalies or deafness). Animal models are bringing us closer to a molecular understanding of optic fissure closure.

SUMMARY

Optic fissure closure requires precise orchestration in timing and apposition of two poles of the optic cup. The relative roles of genetics and environment on this process remain elusive. While most cases of coloboma are sporadic, autosomal dominant, autosomal recessive, and X-linked inheritance patterns have been described. Genetically, colobomata demonstrate pleiotropy, heterogeneity, variable expressivity, and reduced penetrance. Coloboma is a complex disorder with a variable prognosis and requires regular examination to optimize visual acuity and to monitor for potential complications.

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.

A new osteochondrodysplasia with severe osteopenia, preaxial polydactyly, clefting and dysmorphic features resembling filamin-related disorders

BACKGROUND

We report a 19-week gestation female foetus with a new syndrome characterised by increased nuchal translucency and severe micromelia with campomelia evident from the early second trimester.

METHODS AND RESULTS

Cytogenetic studies performed on amniocytes revealed a normal female karyotype. Autopsy after termination of pregnancy showed facial dysmorphism, cleft palate, bowed, shortened limbs, hypoplasia of the preaxial elements in all four limbs with accompanying accessory ossification centres in the feet, and severe calvarial underossification. A diagnosis of otopalatodigital syndrome type 2, associated with mutations in FLNA, a gene encoding the cytoskeletal protein filamin A, was considered but discarded due to the severity of micromelia, early lethality, and the presence of generalised osteopenia instead of hyperostosis. The degree of undermodelling and campomelia was reminiscent of another group of conditions that include atelosteogenesis types 1 and 3, caused by mutations in FLNB. Sequencing analysis did not reveal any pathogenic mutation in the three paralogous filamin genes: FLNA, FLNB and FLNC.

CONCLUSION

Clinical, radiological and cytogenetic findings suggest that this phenotype is a new entity whose aetiopathogenesis may be functionally related to the filaminopathies.

Ocular coloboma: a reassessment in the age of molecular neuroscience

Congenital colobomata of the eye are important causes of childhood visual impairment and blindness. Ocular coloboma can be seen in isolation and in an impressive number of multisystem syndromes, where the eye phenotype is often seen in association with severe neurological or craniofacial anomalies or other systemic developmental defects. Several studies have shown that, in addition to inheritance, environmental influences may be causative factors. Through work to identify genes underlying inherited coloboma, significant inroads are being made into understanding the molecular events controlling closure of the optic fissure. In general, severity of disease can be linked to the temporal expression of the gene, but this is modified by factors such as tissue specificity of gene expression and genetic redundancy.

The many faces of filamin: a versatile molecular scaffold for cell motility and signalling

Filamins were discovered as the first family of non-muscle actin-binding protein. They are lage cytoplasmic proteins that cross-link cortical actin into a dynamic three-dimensional structure. Filamins have also been reported to interact with a large number of cellular proteins of great functional diversity, suggesting that they are unusually versatile signalling scaffolds. More recently, genetic mutations in filamin A and B have been reported to cause a wide range of human diseases, suggesting that different diseases highlight distinct filamin interactions.

Molecular pathology of filamin A: diverse phenotypes, many functions

Defective cell signalling during embryonic development is a well-recognized modus operandi of mutations in genes that lead to congenital malformations. This signalling occurs within and around a dynamic cellular cytoskeleton that is continuously under modulating influences during morphogenesis. Evidence is accumulating to suggest that filamin A, an actin-binding protein and the product of one of three paralogous filamin genes in humans, represents a key molecule that connects such signalling events to modulation of the cellular cytoskeletal architecture. This review summarizes the clinical consequences of mutations in the gene encoding filamin A, FLNA. The molecular pathology of this gene suggests remarkable functional pleiotropy, indicative of diverse roles in embryonic, fetal and postnatal development.

Localized mutations in the gene encoding the cytoskeletal protein filamin A cause diverse malformations in humans

Remodeling of the cytoskeleton is central to the modulation of cell shape and migration. Filamin A, encoded by the gene FLNA, is a widely expressed protein that regulates re-organization of the actin cytoskeleton by interacting with integrins, transmembrane receptor complexes and second messengers. We identified localized mutations in FLNA that conserve the reading frame and lead to a broad range of congenital malformations, affecting craniofacial structures, skeleton, brain, viscera and urogenital tract, in four X-linked human disorders: otopalatodigital syndrome types 1 (OPD1; OMIM 311300) and 2 (OPD2; OMIM 304120), frontometaphyseal dysplasia (FMD; OMIM 305620) and Melnick-Needles syndrome (MNS; OMIM 309350). Several mutations are recurrent, and all are clustered into four regions of the gene: the actin-binding domain and rod domain repeats 3, 10 and 14/15. Our findings contrast with previous observations that loss of function of FLNA is embryonic lethal in males but manifests in females as a localized neuronal migration disorder, called periventricular nodular heterotopia (PVNH; refs. 3-6). The patterns of mutation, X-chromosome inactivation and phenotypic manifestations in the newly described mutations indicate that they have gain-of-function effects, implicating filamin A in signaling pathways that mediate organogenesis in multiple systems during embryonic development.

Ocular colobomata

Ocular colobomata present diagnostic and therapeutic challenges in patients of all ages, but especially in young children. The "typical" coloboma, caused by defective closure of the fetal fissure, is located in the inferonasal quadrant, and it may affect any part of the globe traversed by the fissure from the iris to the optic nerve. Ocular colobomata are often associated with microphthalmia, and they may be idiopathic or associated with various syndromes. Types and severity of complications vary depending on the location and size of the colobomata. This article reviews the pathogeneses, categorization, genetic bases, differential diagnoses and management of ocular coloboma.

Fronto-otopalatodigital osteodysplasia: clinical evidence for a single entity encompassing Melnick-Needles syndrome, otopalatodigital syndrome types 1 and 2, and frontometaphyseal dysplasia

Otopalatodigital syndrome type 2 is an X-linked disorder with minimal expression in carrier females and comprises typical facial anomalies and a generalized bone dysplasia with osteodysplastic changes, brachydactyly, and impaired survival. Recently several other severe malformations were reported in the condition. Melnick-Needles syndrome is an X-linked dominant disorder. Affected males are usually sporadic cases. The exceptional males born to symptomatic women present with a lethal disorder comprising generalized osteodysplasia, deficiency of the first ray, and facial anomalies strikingly similar to those of otopalatodigital syndrome type 2. We report here on three boys with classical, severe, and lethal otopalatodigital type 2 syndrome, and three boys with severe (lethal) Melnick-Needles syndrome, born to affected mothers. We suggest that otopalatodigital type 1 and 2, Melnick-Needles syndrome and frontometaphyseal dysplasia, sharing many clinical manifestations and a similar mode of inheritance, are variants of the same condition: fronto-otopalatodigital osteodysplasia. The relationships to similar syndromes (i.e., Saint-Martin-Gardner-Morrisson syndrome, serpentine fibula syndrome, atelosteogenesis type 3, boomerang dysplasia, and Yunis-Varon syndrome) are discussed.

Non-progressive congenital ataxias

Congenital ataxias (CA) are rare, predominantly non-progressive syndromes characterized by marked hypotonia, developmental delay followed by the appearance of ataxia. Most children show marked speech and cognitive developmental problems. Non- progressive CA (NPCA) can be divided into pure CA without additional symptoms and syndromes with CA. Pure CA can be due to cerebellar malformations as (hereditary or non-hereditary) cerebellar hypoplasia, Dandy Walker syndrome, or occasionally supratentorial abnormalities. Ataxic syndromes are less frequent, but more distinctive. There are syndromes (e.g. Joubert syndrome) where ataxia is a cardinal feature and others where ataxia is only an occasional symptom. Acquired ataxias, due to congenital cytomegalovirus infection or perinatal problems, form a small third group. In about half of all cases with NPCA, aetiology and inheritance are still unknown. Diagnosis of NPCA is made by a typical history and careful clinical examination. Diagnosis of a more distinctive ataxic syndrome may be possible on clinical grounds. Neuroimaging with special attention to the posterior fossa will aid accurate clinical classification. Early progressive ataxias require careful differentiation from other types.

Hydrocephalus, skeletal anomalies, and mental disturbances in a mother and three daughters: a new syndrome

We report on a family in which a mother and her 3 daughters have delayed psychomotor development and/or psychosis, hydrocephalus with white matter alterations, arachnoid cysts, skeletal anomalies consisting of brachydactyly, and Sprengel anomaly. Biochemical and cytogenetic analyses were normal on all 4 patients. The pattern of inheritance, clinical manifestations, and variability of expression suggest that this is a new hydrocephalus syndrome possibly transmitted as an X-linked dominant trait.

Oto-palato-digital syndrome type II in two unrelated boys

We report on two boys with oto-palato-digital syndrome type II, characterized by growth retardation, bowed long bones, missing or hypoplastic fibulae, sclerosis of the skull base and wavy, irregular clavicles and ribs. The facial appearance is distinctive due to prominent forehead, widely spaced eyes, antimongologid slant of palpebral fissures, flattened nasal bridge and retrogenia. The mother of one patient showed a mild manifestation of oto-palato-digital syndrome type II. Only about 20 cases of this rare X-linked disorder have been reported so far. The similarities and dissimilarities to oto-palato-digital syndrome type I are discussed.

Pontocerebellar hypoplasias. An overview of a group of inherited neurodegenerative disorders with fetal onset

Cerebellar hypoplasia is common to a variety of congenital disorders. Both stable conditions and progressive (degenerative) disorders may cause cerebellar hypoplasia. Pontocerebellar hypoplasia (PCH) is distinct from cerebellar hypoplasias in general, because the ventral pons is affected. Reviewing both clinical and neuropathological evidence, two specific neurogenetic entities are delineated. It is proposed to call these, respectively, type 1 (PCH-1) and type 2 (PCH-2). In type 1 the hallmark is the presence of spinal anterior horn degeneration similar to Werdnig-Hoffmann disease. Presentation in the neonatal period is characterized by respiratory insufficiency, frequent congenital contractures, and a combination of central and peripheral motor signs. Patients die early, usually before 1 year of age. In type 2 the hallmark is the presence of chorea/dystonia, which is often severe, while spinal anterior horn pathology is absent. Patients have microcephaly and severely impaired mental and motor development. They frequently die during childhood. Neuronal degeneration in both types of PCH is non-specific. Reactive changes in the degenerated parts appear more extensive in type 1. Examples of both types are given. Differentiation of the two types appears straightforward and possible by clinical means. Carbohydrate-deficient glycoprotein syndrome, one other cause of (ponto)cerebellar hypoplasia, should be excluded in all cases of PCH by appropriate means.

Agenesis of the corpus callosum with mental retardation and osseous lesions

We report on a patient with agenesis of corpus callosum, mental retardation, and unusual hitherto undescribed bone changes. The latter include multiple Wormian bones, thin ribs, short, straight, laterally tapering clavicles, small iliac bodies, high iliac angles, triangular areas of sclerosis in the iliac bones, minimal metaphyseal irregularity, striated trabecular pattern in some metaphyses, granular ossification pattern of the patellae, hypoplastic distal phalanges, minimal flatness of phalangeal epiphyses, and retarded bone age. This patient represents a new mental retardation syndrome with agenesis of corpus callosum and unusual bone changes.

Otopalatodigital syndrome type II associated with omphalocele: report of three cases

We present 3 patients with otopalatodigital (OPD) syndrome type II and omphalocele; 2 of the cases are brothers. There are now 6 known cases of OPD type I or II with omphalocele. We propose that this combination is not coincidental and discuss mechanisms that may result in the combination of OPD, omphalocele, and other midline defects.