Consistent chromosome abnormalities identify novel polymicrogyria loci in 1p36.3, 2p16.1-p23.1, 4q21.21-q22.1, 6q26-q27, and 21q2

Microdeletion at 4q21.3 is associated with intellectual disability, dysmorphic facies, hypotonia, and short stature

Chromosomal imbalances are a major cause of intellectual disability (ID) and multiple congenital anomalies. We have clinically and molecularly characterized two patients with chromosome translocations and ID. Using whole genome array CGH analysis, we identified a microdeletion involving 4q21.3, unrelated to the translocations in both patients. We confirmed the 4q21.3 microdeletions using fluorescence in situ hybridization and quantitative genomic PCR. The corresponding deletion boundaries in the patients were further mapped and compared to previously reported 4q21 deletions and the associated clinical features. We determined a common region of deletion overlap that appears unique to ID, short stature, hypotonia, and dysmorphic facial features.

Whole-exome sequencing identifies compound heterozygous mutations in WDR62 in siblings with recurrent polymicrogyria

Polymicrogyria is a disorder of neuronal development resulting in structurally abnormal cerebral hemispheres characterized by over-folding and abnormal lamination of the cerebral cortex. Polymicrogyria is frequently associated with severe neurologic deficits including intellectual disability, motor problems, and epilepsy. There are acquired and genetic causes of polymicrogyria, but most patients with a presumed genetic etiology lack a specific diagnosis. Here we report using whole-exome sequencing to identify compound heterozygous mutations in the WD repeat domain 62 (WDR62) gene as the cause of recurrent polymicrogyria in a sibling pair. Sanger sequencing confirmed that the siblings both inherited 1-bp (maternal allele) and 2-bp (paternal allele) frameshift deletions, which predict premature truncation of WDR62, a protein that has a role in early cortical development. The probands are from a non-consanguineous family of Northern European descent, suggesting that autosomal recessive PMG due to compound heterozygous mutation of WDR62 might be a relatively common cause of PMG in the population. Further studies to identify mutation frequency in the population are needed.

Copy number variants and infantile spasms: evidence for abnormalities in ventral forebrain development and pathways of synaptic function

Infantile spasms (ISS) are an epilepsy disorder frequently associated with severe developmental outcome and have diverse genetic etiologies. We ascertained 11 subjects with ISS and novel copy number variants (CNVs) and combined these with a new cohort with deletion 1p36 and ISS, and additional published patients with ISS and other chromosomal abnormalities. Using bioinformatics tools, we analyzed the gene content of these CNVs for enrichment in pathways of pathogenesis. Several important findings emerged. First, the gene content was enriched for the gene regulatory network involved in ventral forebrain development. Second, genes in pathways of synaptic function were overrepresented, significantly those involved in synaptic vesicle transport. Evidence also suggested roles for GABAergic synapses and the postsynaptic density. Third, we confirm the association of ISS with duplication of 14q12 and maternally inherited duplication of 15q11q13, and report the association with duplication of 21q21. We also present a patient with ISS and deletion 7q11.3 not involving MAGI2. Finally, we provide evidence that ISS in deletion 1p36 may be associated with deletion of KLHL17 and expand the epilepsy phenotype in that syndrome to include early infantile epileptic encephalopathy. Several of the identified pathways share functional links, and abnormalities of forebrain synaptic growth and function may form a common biologic mechanism underlying both ISS and autism. This study demonstrates a novel approach to the study of gene content in subjects with ISS and copy number variation, and contributes further evidence to support specific pathways of pathogenesis.

Congenital intra-abdominal bilateral juvenile granulosa cell tumors of the testis associated with constitutional loss of material from chromosome 4

Juvenile granulosa cell tumor (JGCT) is an uncommon gonadal stromal tumor that occurs rarely in the testis. We report a newborn boy with bilateral intra-abdominal JGCT presenting with abdominal distention and respiratory distress at birth. He was taken to the operating room emergently, and 2 large masses connected by gubernacula to the inguinal canals were resected. Associated abnormalities included a constitutional chromosome 4 abnormality, polymicrogyria, and renal cysts. This report describes a rare presentation of JGCT with abdominal compression and expands the literature to include bilateral testicular involvement. Additionally, it is the 1st report of JGCT associated with a chromosome 4 abnormality, highlighting a genetic region that may be important in JGCT development.

Polymicrogyria and infantile spasms in a patient with 1p36 deletion syndrome

A 3-months-old boy presented with partial seizures that soon evolved into infantile spasms. Magnetic resonance imaging revealed bilateral perisylvian polymicrogyria with right-sided predominance. ACTH therapy successfully controlled epilepsy and electroencephalograms were normalized. Conventional G-banded chromosomal analysis was performed due to his distinctive features and a derivative chromosome 1 derived from parental balanced translocation with a karyoptype of 46,XY,der(1)t(1;4)(p36.23;q35) was detected. Fluorescent in situ hybridization analysis confirmed the deleted region of 1p36 as large as 8.6Mb. This is the first delineation of concurrent complications of infantile spasms and polymicrogyria in patient with 1p36 deletion. 1p36 deletion syndrome should be broadly recognized as a differential diagnosis of regional polymicrogyria and/or infantile spasms.

Distinctive Phenotypic Abnormalities Associated with Submicroscopic 21q22 Deletion Including DYRK1A

Partial monosomy 21 has been reported, but the phenotypes described are variable with location and size of the deletion. We present 2 patients with a partially overlapping microdeletion of 21q22 and a striking phenotypic resemblance. They both presented with severe psychomotor delay, behavioral problems, no speech, microcephaly, feeding problems with frequent regurgitation, idiopathic thrombocytopenia, obesity, deep set eyes, down turned corners of the mouth, dysplastic ears, and small chin. Brain MRI showed cerebral atrophy mostly evident in frontal and temporal lobes, widened ventricles and thin corpus callosum in both cases, and in one patient evidence of a migration disorder. The first patient also presented with epilepsy and a ventricular septum defect. The second patient had a unilateral Peters anomaly. Microarray analysis showed a partially overlapping microdeletion spanning about 2.5 Mb in the 21q22.1-q22.2 region including the DYRK1A gene and excluding RUNX1. These patients present with a recognizable phenotype specific for this 21q22.1-q22.2 locus. We searched the literature for patients with overlapping deletions including the DYRK1A gene, in order to define other genes responsible for this presentation.

Recessive mutations in the gene encoding the tight junction protein occludin cause band-like calcification with simplified gyration and polymicrogyria

Band-like calcification with simplified gyration and polymicrogyria (BLC-PMG) is a rare autosomal-recessive neurological disorder showing highly characteristic clinical and neuroradiological features. Affected individuals demonstrate early-onset seizures, severe microcephaly, and developmental arrest with bilateral, symmetrical polymicrogyria (PMG) and a band of gray matter calcification on brain imaging; as such, the disorder can be considered as a "pseudo-TORCH" syndrome. By using autozygosity mapping and copy number analysis we identified intragenic deletions and mutations in OCLN in nine patients from six families with BLC-PMG. The OCLN gene encodes occludin, an integral component of tight junctions. Neuropathological analysis of an affected individual showed similarity to the mouse model of occludin deficiency with calcification predominantly associated with blood vessels. Both intracranial calcification and PMG are heterogeneous in etiology. Neuropathological and clinical studies of PMG have suggested that in utero ischemic or vascular insults may contribute to this common cortical abnormality. Tight junctions are functional in cerebral blood vessels early in fetal development and continue to play a vital role in maintenance of the blood-brain barrier during postnatal life. We provide evidence that the tight junction protein occludin (encoded by the OCLN gene) is involved in the pathogenesis of malformations of cortical development.

Chediak-Higashi syndrome with early developmental delay resulting from paternal heterodisomy of chromosome 1

Chediak-Higashi syndrome (CHS) is a rare autosomal recessive disease characterized by variable oculocutaneous albinism, immunodeficiency, mild bleeding diathesis, and an accelerated lymphoproliferative state. Abnormal lysosome-related organelle membrane function leads to the accumulation of large intracellular vesicles in several cell types, including granulocytes, melanocytes, and platelets. This report describes a severe case of CHS resulting from paternal heterodisomy of chromosome 1, causing homozygosity for the most distal nonsense mutation (p.E3668X, exon 50) reported to date in the LYST/CHS1 gene. The mutation is located in the WD40 region of the CHS1 protein. The patient's fibroblasts expressed no detectable CHS1. Besides manifesting the classical CHS findings, the patient exhibited hypotonia and global developmental delays, raising concerns about other effects of heterodisomy. An interstitial 747 kb duplication on 6q14.2-6q14.3 was identified in the propositus and paternal samples by comparative genomic hybridization. SNP genotyping revealed no additional whole chromosome or segmental isodisomic regions or other dosage variations near the crossover breakpoints on chromosome 1. Unmasking of a separate autosomal recessive cause of developmental delay, or an additive effect of the paternal heterodisomy, could underlie the severity of the phenotype in this patient.

Cerebral malformations without antenatal diagnosis

Cerebral malformations are usually described following the different steps in development. Disorders of neurulation (dysraphisms), or diverticulation (holoprosencephalies and posterior fossa cysts), and total commissural agenesis are usually diagnosed in utero. In contrast, disorders of histogenesis (proliferation-differentiation, migration, organization) are usually discovered in infants and children. The principal clinical symptoms that may be a clue to cerebral malformation include congenital hemiparesis, epilepsy and mental or psychomotor retardation. MRI is the imaging method of choice to assess cerebral malformations.

Unbalanced der(5)t(5;20) translocation associated with megalencephaly, perisylvian polymicrogyria, polydactyly and hydrocephalus

The combination of megalencephaly, perisylvian polymicrogyria, polydactyly and hydrocephalus (MPPH) is a rare syndrome of unknown cause. We observed two first cousins affected by an MPPH-like phenotype with a submicroscopic chromosome 5q35 deletion as a result of an unbalanced der(5)t(5;20)(q35.2;q13.3) translocation, including the NSD1 Sotos syndrome locus. We describe the phenotype and the deletion breakpoints of the two MPPH-like patients and compare these with five unrelated MPPH and Sotos patients harboring a 5q35 microdeletion. Mapping of the breakpoints in the two cousins was performed by MLPA, FISH, high density SNP-arrays and Q-PCR for the 5q35 deletion and 20q13 duplication. The 5q35 deletion area of the two cousins almost completely overlaps with earlier described patients with an atypical Sotos microdeletion, except for the DRD1 gene. The five unrelated MPPH patients neither showed submicroscopic chromosomal aberrations nor DRD1 mutations. We reviewed the brain MRI of 10 Sotos patients and did not detect polymicrogyria in any of them. In our two cousins, the MPPH-like phenotype is probably caused by the contribution of genes on both chromosome 5q35 and 20q13. Some patients with MPPH may harbor a submicroscopic chromosomal aberration and therefore high-resolution array analysis should be part of the diagnostic workup.

Clinical and imaging heterogeneity of polymicrogyria: a study of 328 patients

Polymicrogyria is one of the most common malformations of cortical development and is associated with a variety of clinical sequelae including epilepsy, intellectual disability, motor dysfunction and speech disturbance. It has heterogeneous clinical manifestations and imaging patterns, yet large cohort data defining the clinical and imaging spectrum and the relative frequencies of each subtype are lacking. The aims of this study were to determine the types and relative frequencies of different polymicrogyria patterns, define the spectrum of their clinical and imaging features and assess for clinical/imaging correlations. We studied the imaging features of 328 patients referred from six centres, with detailed clinical data available for 183 patients. The ascertainment base was wide, including referral from paediatricians, geneticists and neurologists. The main patterns of polymicrogyria were perisylvian (61%), generalized (13%), frontal (5%) and parasagittal parieto-occipital (3%), and in 11% there was associated periventricular grey matter heterotopia. Each of the above patterns was further divided into subtypes based on distinguishing imaging characteristics. The remaining 7% were comprised of a number of rare patterns, many not described previously. The most common clinical sequelae were epileptic seizures (78%), global developmental delay (70%), spasticity (51%) and microcephaly (50%). Many patients presented with neurological or developmental abnormalities prior to the onset of epilepsy. Patients with more extensive patterns of polymicrogyria presented at an earlier age and with more severe sequelae than those with restricted or unilateral forms. The median age at presentation for the entire cohort was 4 months with 38% presenting in either the antenatal or neonatal periods. There were no significant differences between the prevalence of epilepsy for each polymicrogyria pattern, however patients with generalized and bilateral forms had a lower age at seizure onset. There was significant skewing towards males with a ratio of 3:2. This study expands our understanding of the spectrum of clinical and imaging features of polymicrogyria. Progression from describing imaging patterns to defining anatomoclinical syndromes will improve the accuracy of prognostic counselling and will aid identification of the aetiologies of polymicrogyria, including genetic causes.

Ophthalmologic abnormalities in a de novo terminal 6q deletion

PURPOSE

To correlate the clinical phenotype with the genotype of a boy with a terminal deletion of chromosome 6q and to compare these observations to previous reports of 6q deletions and review of the literature.

METHODS

Careful clinical evaluation, conventional cytogenetic analysis on GTG-banded chromosomes and 244K array CGH analysis.

RESULTS

This 14 year old Saudi boy had modest mental retardation, seizures, microcephaly, cortical dysplasia, a non-comitant esotropia, impersistent eccentric gaze, congenital nystagmus, thick corneas, and substantial myopia. He had a de novo 10.79 Mb deletion on chromosome 6 from 6q25.3 to 6qter. The deleted region extended from nucleotide 159929512 to 170723629 and encompassed 87 genes. Eleven genes remained within the proband's deleted region after excluding genes located in deleted areas reported in phenotypically normal individuals. Among those 11 genes, only the TBP (TATA box binding protein) gene has been associated with any symptom or sign observed in our patient.

CONCLUSIONS

This boy had clinical features similar to patients reported with the 6q terminal deletion syndrome. In addition, he had an unusual ocular motility pattern and thick corneas, features that may be more common than previously recognized. Deleted genes in this area of chromosome 6 may contribute to ophthalmic abnormalities in addition to mental retardation.

Current concepts of polymicrogyria

Polymicrogyria is one of the most common malformations of cortical development. It has been known for many years and its clinical and MRI manifestations are well described. Recent advances in imaging, however, have revealed that polymicrogyria has many different appearances on MR imaging, suggesting that is may be a more heterogeneous malformation than previously suspected. The clinical and imaging heterogeneity of polymicrogyria is explored in this review.

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.

Angeborene Hirnfehlbildungen und geistige Behinderung

Hirnfehlbildungen sind klinisch und genetisch bedeutsame Ursachen für psychomotorische Entwicklungsstörungen und Epilepsien. Die diagnostische Einordnung erfolgt durch bildgebende Verfahren und ist die Grundlage für eine individuelle genetische Abklärung und für zuverlässige prognostische Aussagen. Für einen beträchtlichen Teil der Hirnfehlbildungen sind die molekularen Ursachen bereits bekannt. Mutationen in diesen Genen können mit milden Verlaufsformen assoziiert sein, bis hin zur geistigen Behinderung ohne strukturelle Hirnfehlbildungen. Die Aufklärung der molekulargenetischen Ursachen von Hirnfehlbildungen trägt zum besseren Verständnis der Gehirnentwicklung bei und eröffnet gleichzeitig neue Einsichten in die Pathophysiologie von geistiger Behinderung und Epilepsie. Darüber hinaus ermöglicht sie die Erkennung und individuelle genetische Beratung von Anlageträgern und ist eine Voraussetzung für die pränatale molekulargenetische Diagnostik in Risikofamilien.

Bilateral operculum syndrome in childhood

We describe 3 patients with bilateral operculum syndrome. They presented with various degrees of suprabulbar (pseudobulbar) signs in addition to delay in cognitive, motor, and speech development in 2 children and developmental language disorder in the third one. A patient with schizencephaly in the left perisylvian area and contralateral polymicrogyria had spastic hemiparesis on the right side, whereas another patient showed bilateral underdevelopment of the opercula in association with axial hypotonia and spastic diplegia. Both of them had epileptiform discharges on the electroencephalogram without clinical manifestations of seizures. The magnetic resonance imaging of the third child with developmental language disorder was normal; however, his electroencephalogram showed frequent bilateral subclinical centrotemporal epileptiform discharges, probably responsible for the speech delay. Structural or functional involvement of the opercula bilaterally was a common finding in all the 3 patients and they had symptoms similar to those described in the developmental type of Foix-Chavany-Marie and Worster-Drought syndromes.

Polymicrogyria in a child with inv dup del(9p) and 22q11.2 microduplication

Polymicrogyria (PMG) is a relatively common malformation of the cortex for which the pathogenesis remains poorly understood. Both acquired and genetic causes are known, and to date more than 70 cases of PMG have been associated with chromosomal abnormalities. Here we report on a 12-year-old girl presenting with asymmetrical PMG predominantly affecting the right occipital lobe. She was the only child of consanguineous parents. At 7 years of age she was referred for mental retardation with speech delay and seizures. Cytogenetic studies of the patient revealed an inverted 9p duplication/deletion and bacterial artificial chromosomes (BACs)-array also showed a 22q11.2 microduplication confirmed by quantitative PCR. This case is of interest in the search for candidate genes and emphasizes the importance of the 22q11 region in PMG. It also highlights the efficiency of BACs-array in detecting complex rearrangements.

Neuronal migration disorders

Lissencephaly-pachygyria-severe band heterotopia are diffuse neuronal migration disorders (NMDs) causing severe, global neurological impairment. Abnormalities of the LIS1, DCX, ARX, TUBA1A and RELN genes have been associated with these malformations. NMDs only affecting subsets of neurons, such as mild subcortical band heterotopia and periventricular heterotopia, cause neurological and cognitive impairment that vary from severe to mild deficits. They have been associated with abnormalities of the DCX, FLN1A, and ARFGEF2 genes. Polymicrogyria results from abnormal late cortical organization and is inconstantly associated with abnormal neuronal migration. Localized polymicrogyria has been associated with anatomo-specific deficits, including disorders of language and higher cognition. Polymicrogyria is genetically heterogeneous and only in a small minority of patients a definite genetic cause has been identified. Mutations of the GPR56 and SRPX2 genes have been related to isolated polymicrogyria. Focal migration abnormalities associated with abnormal cell types, such as focal cortical dysplasia, are highly epileptogenic and variably influence the functioning of the affected cortex. The functional consequences of abnormal neuronal migration are still poorly understood. Conservation of function in the malformed cortex, its atypical representation, and relocation outside the malformed area are all possible. Localization of function based on anatomic landmarks may not be reliable.