[Show abstract][Hide abstract] ABSTRACT: Walker-Warburg syndrome (WWS) is clinically defined as congenital muscular dystrophy that is accompanied by a variety of brain and eye malformations. It represents the most severe clinical phenotype in a spectrum of diseases associated with abnormal post-translational processing of a-dystroglycan that share a defect in laminin-binding glycan synthesis1. Although mutations in six genes have been identified as causes of WWS, only half of all individuals with the disease can currently be diagnosed on this basis2. A cell fusion complementation assay in fibroblasts from undiagnosed individuals with WWS was used to identify five new complementation groups. Further evaluation of one group by linkage analysis and targeted sequencing identified recessive mutations in the ISPD gene (encoding isoprenoid synthase domain containing). The pathogenicity of the identified ISPD mutations was shown by complementation of fibroblasts with wild-type ISPD. Finally, we show that recessive mutations in ISPD abolish the initial step in laminin-binding glycan synthesis by disrupting dystroglycan O-mannosylation. This establishes a new mechanism for WWS pathophysiology.
[Show abstract][Hide abstract] ABSTRACT: We sought to create a classification system for pediatric corpus callosal abnormalities (CCA) based upon midline sagittal brain MRI. We used the term CCA for patients with structural variants of the corpus callosum, excluding patients with interhemispheric cyst variant or pure dysplasia without hypoplasia. Currently, no system exists for nonsyndromic forms of CCA, and attempts to create such a system have been hampered by highly variable morphology in patients with sporadic CCA. We reasoned that any useful strategy should classify affected family members within the same type, and that phenotypic variability should be minimized in patients with recessive disease.
We focused recruitment toward multiplex consanguineous families, ascertained 30 patients from 19 consanguineous families, and analyzed clinical features together with brain imaging.
We identified 3 major CCA classes, including hypoplasia, hypoplasia with dysplasia, and complete agenesis. Affected individuals within a given multiplex family usually displayed the same variant of the class of abnormality and they always displayed the same class of abnormality within each family, or they displayed complete agenesis. The system was validated among a second cohort of 10 sporadic patients with CCA.
The data suggest that complete agenesis may be a common end-phenotype, and implicate multiple overlapping pathways in the etiology of CCA.
[Show abstract][Hide abstract] ABSTRACT: Ciliopathies are an expanding group of rare conditions characterized by multiorgan involvement, that are caused by mutations in genes encoding for proteins of the primary cilium or its apparatus. Among these genes, CEP290 bears an intriguing allelic spectrum, being commonly mutated in Joubert syndrome and related disorders (JSRD), Meckel syndrome (MKS), Senior-Loken syndrome and isolated Leber congenital amaurosis (LCA). Although these conditions are recessively inherited, in a subset of patients only one CEP290 mutation could be detected. To assess whether genomic rearrangements involving the CEP290 gene could represent a possible mutational mechanism in these cases, exon dosage analysis on genomic DNA was performed in two groups of CEP290 heterozygous patients, including five JSRD/MKS cases and four LCA, respectively. In one JSRD patient, we identified a large heterozygous deletion encompassing CEP290 C-terminus that resulted in marked reduction of mRNA expression. No copy number alterations were identified in the remaining probands. The present work expands the CEP290 genotypic spectrum to include multiexon deletions. Although this mechanism does not appear to be frequent, screening for genomic rearrangements should be considered in patients in whom a single CEP290 mutated allele was identified.
American Journal of Medical Genetics Part A 09/2009; 149A(10):2173-80. · 2.30 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The acronym COACH defines an autosomal recessive condition of Cerebellar vermis hypo/aplasia, Oligophrenia, congenital Ataxia, Coloboma and Hepatic fibrosis. Patients present the "molar tooth sign", a midbrain-hindbrain malformation pathognomonic for Joubert Syndrome (JS) and Related Disorders (JSRDs). The main feature of COACH is congenital hepatic fibrosis (CHF), resulting from malformation of the embryonic ductal plate. CHF is invariably found also in Meckel syndrome (MS), a lethal ciliopathy already found to be allelic with JSRDs at the CEP290 and RPGRIP1L genes. Recently, mutations in the MKS3 gene (approved symbol TMEM67), causative of about 7% MS cases, have been detected in few Meckel-like and pure JS patients. Analysis of MKS3 in 14 COACH families identified mutations in 8 (57%). Features such as colobomas and nephronophthisis were found only in a subset of mutated cases. These data confirm COACH as a distinct JSRD subgroup with core features of JS plus CHF, which major gene is MKS3, and further strengthen gene-phenotype correlates in JSRDs.
Human Mutation 01/2009; 30(2):E432-42. · 5.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To delineate a new syndrome of brain dysgenesis and cutis laxa based on the description of 11 patients belonging to nine unrelated families recruited through an international collaboration effort.
Careful clinical assessment of patients from birth to the age of 23 years with follow-up studies ranging from 3 to 20 years. Biochemical studies of serum proteins glycosylation by isoelectric focusing and capillary zone electrophoresis were performed in 10 patients. Brain MRI studies using conventional methods were analyzed in eight patients.
An expanded clinical spectrum of a syndrome comprising facial dysmorphia (enlarged anterior fontanelles, downward slant of palpebral fissures, prominent root of the nose), a connective tissue disorder (inguinal hernia, hip dislocation, high myopia), and neurologic impairment was defined. Early developmental delay was followed by onset of generalized seizures by the end of the first decade and a subsequent neurodegenerative course. A defect of N- or N- plus O-glycosylation of serum transferrins and ApoCIII was observed in 10 patients. An unusual cobblestone-like cortical malformation over the frontal and parietal regions was seen in eight patients and cerebellar abnormalities, including two patients with Dandy-Walker malformation, were observed in three patients.
Our results suggest that autosomal recessive cutis laxa, Debré type, initially considered a dermatologic syndrome, is a multisystemic disorder with cobblestone-like brain dysgenesis manifesting as developmental delay and an epileptic neurodegenerative syndrome. It might represent a metabolic cause of Dandy-Walker malformation. It is associated with a deficient N- and-O glycosylation of proteins and shares many similarities with muscle-eye-brain syndromes.
[Show abstract][Hide abstract] ABSTRACT: Joubert syndrome and related cerebellar disorders (JSRD) are a group of recessive congenital ataxia conditions usually showing neonatal hypotonia, dysregulated breathing rhythms, oculomotor apraxia, and mental retardation. The pathognomonic finding in JSRD is the unique molar tooth sign (MTS) on brain imaging. There is a tremendously broad spectrum of signs and symptoms mainly including kidney, retina, and liver disease, along with polydactyly and facial dysmorphisms. Here we propose a new diagnostic classification within JSRD that includes four major subtypes. To test this classification, we performed a systematic recruitment and genetic evaluation from a single referral center in Egypt. Thirteen families were identified, four showed evidence of linkage to one of the four known genetic loci, three showed novel AHI1 mutations, and nine were excluded from known loci. Each family could be classified into one of the four subtypes. This classification may thus be useful in the evaluation of patients with JSRD.
[Show abstract][Hide abstract] ABSTRACT: ARX is a paired-type homeobox gene located on the X chromosome that contains five exons with four polyalanine (PolyA) tracts, a homeodomain, and a conserved C-terminal aristaless domain. Studies in humans have demonstrated remarkable pleiotropy: malformation phenotypes are associated with protein truncation mutations and missense mutations in the homeobox; nonmalformation phenotypes, including X-linked infantile spasms (ISS), are associated with missense mutations outside of the homeobox and expansion of the PolyA tracts.
To investigate the role of ARX, we performed mutation analysis in 115 boys with cryptogenic ISS. This included two pairs of brothers.
We found an expansion of the trinucleotide repeat that codes for the first PolyA tract from 10 to 17 GCG repeats (c.333_334ins[GCG]7) in six boys (5.2%) ages 2 to 14, from four families, including the two pairs of brothers. In addition to ISS, all six boys had severe mental retardation and generalized dystonia that appeared around the age of 6 months and worsened, eventually leading to stable severe quadriplegic dyskinesia within age 2 years. Three children experienced recurrent, life-threatening status dystonicus. In four children brain MRI showed multiple small foci of abnormal cavitation on T1 and increased signal intensity on T2 in the putamina, possibly reflecting progressive multifocal loss of tissue.
The phenotype of infantile spasms with severe dyskinetic quadriparesis increases the number of human disorders that result from the pathologic expansion of single alanine repeats. ARX gene testing should be considered in boys with infantile spasms and dyskinetic cerebral palsy in the absence of a consistent perinatal history.
[Show abstract][Hide abstract] ABSTRACT: Periventricular heterotopia (PH) occurs when collections of neurons lay along the lateral ventricles or just beneath. Human Filamin A gene (FLNA) mutations are associated with classical X-linked bilateral periventricular nodular heterotopia (PNH), featuring contiguous heterotopic nodules, mega cisterna magna, cardiovascular malformations and epilepsy. FLNA encodes an F-actin-binding cytoplasmic phosphoprotein and is involved in early brain neurogenesis and neuronal migration. A rare, recessive form of bilateral PNH with microcephaly and severe delay is associated with mutations of the ADP-ribosylation factor guanine nucleotide-exchange factor-2 (ARFGEF2) gene, required for vesicle and membrane trafficking from the trans-Golgi. However, PH is a heterogeneous disorder. We studied clinical and brain MRI of 182 patients with PH and, based on its anatomic distribution and associated birth defects, identified 15 subtypes. Classical bilateral PNH represented the largest group (98 patients: 54%). The 14 additional phenotypes (84 patients: 46%) included PNH with Ehlers-Danlos syndrome (EDS), temporo-occipital PNH with hippocampal malformation and cerebellar hypoplasia, PNH with fronto-perisylvian or temporo-occipital polymicrogyria, posterior PNH with hydrocephalus, PNH with microcephaly, PNH with frontonasal dysplasia, PNH with limb abnormalities, PNH with fragile-X syndrome, PNH with ambiguous genitalia, micronodular PH, unilateral PNH, laminar ribbon-like and linear PH. We performed mutation analysis of FLNA in 120 patients, of whom 72 (60%) had classical bilateral PNH and 48 (40%) other PH phenotypes, and identified 25 mutations in 40 individuals. Sixteen mutations had not been reported previously. Mutations were found in 35 patients with classical bilateral PNH, in three with PNH with EDS and in two with unilateral PNH. Twenty one mutations were nonsense and frame-shift and four missense. The high prevalence of mutations causing protein truncations confirms that loss of function is the major cause of the disorder. FLNA mutations were found in 100% of familial cases with X-linked PNH (10 families: 8 with classical bilateral PNH, 1 with EDS and 1 with unilateral PH) and in 26% of sporadic patients with classical bilateral PNH. Overall, mutations occurred in 49% of individuals with classical bilateral PNH irrespective of their being familial or sporadic. However, the chances of finding a mutation were exceedingly gender biased with 93% of mutations occurring in females and 7% in males. The probability of finding FLNA mutations in other phenotypes was 4% but was limited to the minor variants of PNH with EDS and unilateral PNH. Statistical analysis considering all 42 mutations described so far identifies a hotspot region for PNH in the actin-binding domain (P < 0.05).
[Show abstract][Hide abstract] ABSTRACT: Joubert syndrome (JS) is an autosomal recessive disorder characterised by hypotonia, ataxia, mental retardation, altered respiratory pattern, abnormal eye movements, and a brain malformation known as the molar tooth sign (MTS) on cranial MRI. Four genetic loci have been mapped, with two genes identified (AHI1 and NPHP1).
We screened a cohort of 117 JS subjects for AHI1 mutations by a combination of haplotype analysis and sequencing of the gene, and for the homozygous NPHP1 deletion by sequencing and marker analysis.
We identified a total of 15 novel AHI1 mutations in 13 families, including nonsense, missense, splice site, and insertion mutations, with some clustering in the WD40 domains. Eight families were consanguineous, but no single founder mutation was apparent. In addition to the MTS, retinal dystrophy was present in 11 of 12 informative families; however, no subjects exhibited variable features of JS such as polydactyly, encephalocele, colobomas, or liver fibrosis. In contrast to previous reports, we identified two families with affected siblings who developed renal disease consistent with nephronophthisis (NPH) in their 20s. In addition, two individuals with classic NPH were found to have homozygous NPHP1 deletions.
Overall, 11% of subjects had AHI1 mutations, while approximately 2% had the NPHP1 deletion, representing a total of less than 15% in a large JS cohort. Some preliminary genotype-phenotype correlations are possible, notably the association of renal impairment, specifically NPH, in those with NPHP1 deletions. Subjects with AHI1 mutations may be at risk of developing both retinal dystrophy and progressive kidney disease.
Journal of Medical Genetics 05/2006; 43(4):334-9. · 5.70 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Increasing recognition of malformations of cortical development and continuing improvements in imaging techniques, molecular biologic techniques, and knowledge of mechanisms of brain development have resulted in continual improvement of the understanding of these disorders. The authors propose a revised classification based on the stage of development (cell proliferation, neuronal migration, cortical organization) at which cortical development was first affected. The categories are based on known developmental steps, known pathologic features, known genetics (when possible), and, when necessary, neuroimaging features. In those cases in which the precise developmental and genetic features are uncertain, classification is based on known relationships among the genetics, pathologic features, and neuroimaging features. The major change since the prior classification has been a shift to using genotype, rather than phenotype, as the basis for classifying disorders wherever the genotype-phenotype relationship is adequately understood. Other substantial changes include more detailed classification of congenital microcephalies, particularly those in which the genes have been mapped or identified, and revised classification of congenital muscular dystrophies and polymicrogyrias. Information on genetic testing is also included. This classification allows a better conceptual understanding of the disorders, and the use of neuroimaging characteristics allows it to be applied to all patients without necessitating brain biopsy, as in pathology-based classifications.
[Show abstract][Hide abstract] ABSTRACT: Oculocerebrocutaneous syndrome (OCCS) is characterised by orbital cysts and anophthalmia or microphthalmia, focal aplastic or hypoplastic skin defects, skin appendages, and brain malformations. The eye and skin abnormalities are well described but the neuropathological features less so. To date, 28 patients with an unequivocal diagnosis of OCCS have been reported, with a preponderance of males.
To evaluate the brain imaging studies, clinical records, photographs, and pathological material of two new and nine previously reported cases of OCCS.
There was a consistent pattern of malformations in eight of the 11 cases, consisting of frontal predominant polymicrogyria and periventricular nodular heterotopia, enlarged lateral ventricles or hydrocephalus, agenesis of the corpus callosum sometimes associated with interhemispheric cysts, and a novel mid-hindbrain malformation. The latter consisted of a giant and dysplastic tectum, absent cerebellar vermis, small cerebellar hemispheres in most cases, and a large posterior fossa fluid collection.
The mid-hindbrain malformation appears pathognomonic for OCCS. The eye and skin features of OCCS show considerable overlap with several other syndromes, such as encephalocraniocutaneous lipomatosis, oculo-auriculo-vertebral spectrum, and focal dermal hypoplasia, none of which has a comparable pattern of brain malformations. In particular the unique mid-hindbrain malformation also distinguishes OCCS from related syndromes with comparable forebrain anomalies. The pattern of malformation described thus helps in differentiating OCCS from other entities. The mid-hindbrain malformation points to a defect of the mid-hindbrain organiser as the underlying pathogenic mechanism.
Journal of Medical Genetics 01/2006; 42(12):913-21. · 5.70 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Megalencephaly (MEG) or enlarged brain occurs as a mild familial variant with normal brain structure, but otherwise is an uncommon human brain malformation that may be associated with significant developmental and neurological problems. It has been classified into anatomic and metabolic subtypes. The clinical findings associated with anatomic megalencephaly have been variable and few distinct subtypes have been described. We report five unrelated children with severe congenital MEG associated with polymicrogyria (PMG), postaxial polydactyly (POLY) and hydrocephalus (HYD).
The clinical records and brain MRI of five patients have been reviewed.
All patients had striking MEG that was symmetric in three of the five patients, and mildly asymmetric in two. The birth OFC was between +2 and +4 SD. The gyral pattern was irregular with microgyri typical of PMG, which was most severe in the perisylvian region in all five patients. Four of the five had hydrocephalus treated with a shunt. Subsequently, one of the shunted patients had small ventricles while the others had mildly to moderately enlarged lateral ventricles. Three of the five patients had postaxial polydactyly of all four limbs. The corpus callosum was dysmorphic in one patient with a fused rostrum and genu, and intact although mildly thin in the others. None were abnormally thick. All patients had severe mental retardation; three had seizures and another had an epileptiform EEG.
We believe this constellation of findings (MEG-PMG-POLY-HYD) comprises a new and distinct malformation syndrome that we designate the MPPH syndrome.
[Show abstract][Hide abstract] ABSTRACT: To describe the phenotypic spectrum and genetics of periventricular nodular heterotopia (PNH) caused by FLN1 mutations in four men.
X-linked PNH caused by FLN1 mutations (MIM #300049) implies prenatal or early postnatal lethality in boys and 50% recurrence risk in daughters of affected women.
Clinical examination, cognitive testing, MRI, and mutation analysis (denaturing high-performance liquid chromatography and direct sequencing) on blood lymphocytes and single hair roots were performed for nine affected individuals, including three men. Neuropathologic study of the brain was performed for an affected boy.
In two families, missense mutations were transmitted from mother to son (Met102Val) and from father to daughter (Ser149Phe), causing mild phenotypes in both genders, including unilateral PNH. In a third family, a man was mosaic for an A>G substitution (intron 11 acceptor splice site) on leukocyte DNA and hair roots (mutant = 42% and 69%). Single hair root analysis confirmed that the mutation was not present in all ectodermal derivative cells. A healthy daughter had inherited the X chromosome from her father's wild-type germinal cell population. In the fourth family, an eight-base deletion (AGGAGGTG, intron 25 donor splice site) led to early deaths of boys. Postmortem study in a newborn boy revealed PNH and cardiovascular, genitourinary, and gut malformations.
Periventricular nodular heterotopia caused by FLN1 mutations in men has a wide clinical spectrum and is caused by different genetic mechanisms, including somatic mosaicism. Mutation analysis of FLN1 should support genetic counseling in men with periventricular nodular heterotopia.
[Show abstract][Hide abstract] ABSTRACT: Baraitser-Winter syndrome is a rare autosomal recessive disorder characterized by developmental delay, dysmorphic features, and multiple malformations also involving the brain. We report a further case and provide updated information about an unrelated girl reported in the original paper by Baraitser and Winter. Both of them presented with pachygyria and the latter case was recently found to have subcortical band heterotopia on high resolution brain MRI imaging. These two patients and a review of the previously reported cases indicate that a specific pattern of brain anomalies falling in the agyria-pachygyria-band spectrum is associated with this dysmorphic syndrome, which may be considered another example of syndromic neuronal migration defect.
[Show abstract][Hide abstract] ABSTRACT: Subcortical band heterotopia (SBH) is a neuronal migration disorder. DCX mutations are responsible for almost all familial cases, 80% of sporadic female cases, and 25% of sporadic male cases of SBH, and are associated with more severe gyral and migration abnormality over the anterior brain regions. Somatic mosaicism has previously been hypothesized in a patient with posteriorly predominant SBH and a mutation of the LIS1 gene, which is usually mutated in patients with severe lissencephaly. The authors identified mosaic mutations of LIS1 in two patients (Patients 1 and 2) with predominantly posterior SBH.
After ruling out DCX mutations, the authors performed sequencing of the LIS1 gene in lymphocyte DNA. Because sequence peaks in both patients were suggestive of mosaic mutations, they followed up with denaturing high-pressure liquid chromatography analysis on blood and hair root DNA and compared the areas of heteroduplex and homoduplex peaks. A third patient showing the same mutation as Patient 2 but with no evidence of mosaicism was used for comparing the phenotype of mosaic vs full mutation.
The two patients with posterior SBH harbored a missense (Arg241Pro) and a nonsense (R8X) mosaic mutation of LIS1. The rate of mosaicism in Patient 1 was 18% in the blood and 21% in the hair roots, whereas in Patient 2 it was 24% and 31% in the same tissues. The patient with a full R8X mutation of LIS1 had severe lissencephaly.
Subcortical band heterotopia can occur with mosaic mutations of the LIS1 gene. Mutation analysis of LIS1, using highly sensitive techniques such as denaturing high-pressure liquid chromatography, should be considered for patients with posteriorly predominant subcortical band heterotopia and pachygyria.