Agenesis of the corpus callosum associated with DiGeorge-velocardiofacial syndrome: a case report and review of the literature

Manifestation of recessive combined D-2-, L-2-hydroxyglutaric aciduria in combination with 22q11.2 deletion syndrome

22q11.2 deletion syndrome is one of the most common human microdeletion syndromes. The clinical phenotype of 22q11.2 deletion syndrome is variable, ranging from mild to life-threatening symptoms, depending mainly on the extent of the deleted region. Brain malformations described in association with 22q11.2 deletion syndrome include polymicrogyria, cerebellar hypoplasia, megacisterna magna, and agenesis of the corpus callosum (ACC), although these are rare. We report here for the first time a patient who manifested combined D-2- and L-2-hydroxyglutaric aciduria as a result of a hemizygous mutation in SLC25A1 in combination with 22q11.2 deletion. The girl was diagnosed to have ACC shortly after birth and a deletion of 22q11.2 was identified by genetic analysis. Although the patient showed cardiac anomalies, which is one of the typical symptoms of 22q11.2 deletion syndrome, her rather severe phenotype and atypical face prompted us to search for additional pathogenic mutations. Three genes present in the deleted 22q11.2 region, SLC25A1, TUBA8, and SNAP29, which have been reported to be associated with brain malformation, were analyzed for the presence of pathogenic mutations. A frameshift mutation, c.18_24dup (p.Ala9Profs*82), was identified in the first exon of the remaining SLC25A1 allele, resulting in the complete loss of normal SLC25A1 function in the patient's cells. Our results support the notion that the existence of another genetic abnormality involving the retained allele on 22q11.2 should be considered when atypical or rare phenotypes are observed.

Neuroradiographic findings in 22q11.2 deletion syndrome

22q11.2 deletion syndrome (22q11.2DS) is a common genetic disorder with enormous phenotypic heterogeneity. Despite the established prevalence of developmental and neuropsychiatric issues in this syndrome, its neuroanatomical correlates are not as well understood. A retrospective chart review was performed on 111 patients diagnosed with 22q11.2DS. Of the 111 patients, 24 with genetically confirmed 22q11.2 deletion and brain MRI or MRA were included in this study. The most common indications for imaging were unexplained developmental delay (6/24), seizures of unknown etiology (5/24), and unilateral weakness (3/24). More than half (13/24) of the patients had significant radiographic findings, including persistent cavum septi pellucidi and/or cavum vergae (8/24), aberrant cortical veins (6/24), polymicrogyria or cortical dysplasia (4/24), inner ear deformities (3/24), hypoplastic internal carotid artery (2/24), and hypoplastic cerebellum (1/24). These findings reveal the types and frequencies of brain malformations in this case series, and suggest that the prevalence of neuroanatomical abnormalities in 22q11.2DS may be underestimated. Understanding indications for imaging and frequently encountered brain malformations will result in early diagnosis and intervention in an effort to optimize patient outcomes.

The Corpus Callosum and Forensic Issues-An Overview

The corpus callosum is a large central white matter tract that connects the right and left cerebral hemispheres. It permits placental mammals to have a more sophisticated interhemispheric integration of sensory cortices and allows communication between cortical and subcortical neurons. Search of the literature and the pathology archives at The University of Adelaide was undertaken to identify lesions and injuries within the corpus callosum that may have forensic significance. These include developmental/congenital lesions with agenesis/dysgenesis, vascular malformations, and lipomas; inherited syndromes such as neurofibromatosis; and acquired lesions involving trauma, neoplasia, demyelination, vascular conditions, infections, fat embolism, aging/dementia, and the effects of toxins. The finding of lesions within the corpus callosum should initiate careful examination of the adjacent brain and other organ systems for related phenomena as this may shed some light on the nature of the underlying condition, and also help to determine whether there are any forensic implications.

Modeling a model: Mouse genetics, 22q11.2 Deletion Syndrome, and disorders of cortical circuit development

Understanding the developmental etiology of autistic spectrum disorders, attention deficit/hyperactivity disorder and schizophrenia remains a major challenge for establishing new diagnostic and therapeutic approaches to these common, difficult-to-treat diseases that compromise neural circuits in the cerebral cortex. One aspect of this challenge is the breadth and overlap of ASD, ADHD, and SCZ deficits; another is the complexity of mutations associated with each, and a third is the difficulty of analyzing disrupted development in at-risk or affected human fetuses. The identification of distinct genetic syndromes that include behavioral deficits similar to those in ASD, ADHC and SCZ provides a critical starting point for meeting this challenge. We summarize clinical and behavioral impairments in children and adults with one such genetic syndrome, the 22q11.2 Deletion Syndrome, routinely called 22q11DS, caused by micro-deletions of between 1.5 and 3.0 MB on human chromosome 22. Among many syndromic features, including cardiovascular and craniofacial anomalies, 22q11DS patients have a high incidence of brain structural, functional, and behavioral deficits that reflect cerebral cortical dysfunction and fall within the spectrum that defines ASD, ADHD, and SCZ. We show that developmental pathogenesis underlying this apparent genetic "model" syndrome in patients can be defined and analyzed mechanistically using genomically accurate mouse models of the deletion that causes 22q11DS. We conclude that "modeling a model", in this case 22q11DS as a model for idiopathic ASD, ADHD and SCZ, as well as other behavioral disorders like anxiety frequently seen in 22q11DS patients, in genetically engineered mice provides a foundation for understanding the causes and improving diagnosis and therapy for these disorders of cortical circuit development.

Bridging the gene-behavior divide through neuroimaging deletion syndromes: Velocardiofacial (22q11.2 Deletion) and Williams (7q11.23 Deletion) syndromes

Investigating the relationship between genes and the neural substrates of complex human behavior promises to provide essential insight into the pathophysiology of mental disorders. One approach to this inquiry is through neuroimaging of individuals with microdeletion syndromes that manifest in specific neuropsychiatric phenotypes. Both Velocardiofacial syndrome (VCFS) and Williams syndrome (WS) involve haploinsufficiency of a relatively small set of identified genes on the one hand and association with distinct, clinically relevant behavioral and cognitive profiles on the other hand. In VCFS, there is a deletion in chromosomal region 22q11.2 and a resultant predilection toward psychosis, poor arithmetic proficiency, and low performance intelligence quotients. In WS, there is a deletion in chromosomal region 7q11.23 and a resultant predilection toward hypersociability, non-social anxiety, impaired visuospatial construction, and often intellectual impairment. Structural and functional neuroimaging studies have begun not only to map these well-defined genetic alterations to systems-level brain abnormalities, but also to identify relationships between neural phenotypes and particular genes within the critical deletion regions. Though neuroimaging of both VCFS and WS presents specific, formidable methodological challenges, including comparison subject selection and accounting for neuroanatomical and vascular anomalies in patients, and many questions remain, the literature to date on these syndromes, reviewed herein, constitutes a fruitful "bottom-up" approach to defining gene-brain relationships.

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.

Alterations in midline cortical thickness and gyrification patterns mapped in children with 22q11.2 deletions

The 22q11.2 deletion syndrome (velocardiofacial/DiGeorge syndrome) is a neurogenetic condition associated with visuospatial deficits, as well as elevated rates of attentional disturbance, mood disorder, and psychosis. Previously, we detected pronounced cortical thinning in superior parietal and right parieto-occipital cortices in patients with this syndrome, regions critical for visuospatial processing. Here we applied cortical pattern-matching algorithms to structural magnetic resonance images obtained from 21 children with confirmed 22q11.2 deletions (ages 8-17) and 13 demographically matched comparison subjects, in order to map cortical thickness across the medial hemispheric surfaces. In addition, cortical models were remeshed in frequency space to compute their surface complexity. Cortical maps revealed a pattern of localized thinning in the ventromedial occipital-temporal cortex, critical for visuospatial representation, and the anterior cingulate, a key area for attentional control. However, children with 22q11.2DS showed significantly increased gyral complexity bilaterally in occipital cortex. Regional gray matter volumes, particularly in medial frontal cortex, were strongly correlated with both verbal and nonverbal cognitive functions. These findings suggest that aberrant parieto-occipital brain development, as evidenced by both increased complexity and cortical thinning in these regions, may be a neural substrate for the deficits in visuospatial and numerical understanding characteristic of this syndrome.

Genes, brain development and psychiatric phenotypes in velo-cardio-facial syndrome

Velo-cardio-facial syndrome (VCFS) has been in the focus of intensive research over the last 15 years. The syndrome represents a homogeneous model for studying the effect of a decreased dosage of genes on the development of brain structure and function and, consequently, on the emergence of schizophrenia-like psychotic disorder. In this review, we describe the psychiatric phenotype of children, adolescents, and young adults with VCFS. We redefine the concept of "behavioral phenotype" and suggest that psychosis fulfills the criteria of a behavioral phenotype of the syndrome. Identifying the risk factors for the emergence of psychosis in VCFS is a major goal of several large-scale longitudinal studies that are currently underway. We review the knowledge gained so far about risk factors for psychosis in VCFS, including early neuropsychiatric symptoms, development of brain structure and function, and the effect of a reduced dosage of genes from the 22q11 deletion region. Although the brain structure in subjects with VCFS is not drastically different from typically developing controls, newer imaging modalities that measure white matter tracts, cortical thickness, and cortical gyrification are likely to identify more subtle and specific neuroanatomical substrates of the syndrome. Among the 24 genes within the deletion region, the role of catechol-O-methyltransferase (COMT) on the VCFS phenotype has been investigated in depth. The findings suggest that because of haploinsufficiency of the COMT gene individuals with VCFS are exposed to a high level of prefrontal dopamine, and this interferes with their prefrontal cognitive functioning and may contribute to their high rate of psychosis and other psychiatric disorders. The other genes and environmental factors that shape the unique neuropsychiatric phenotype of VCFS are yet to be discovered.

Polymicrogyria and deletion 22q11.2 syndrome: window to the etiology of a common cortical malformation

Several brain malformations have been described in rare patients with the deletion 22q11.2 syndrome (DEL22q11) including agenesis of the corpus callosum, pachygyria or polymicrogyria (PMG), cerebellar anomalies and meningomyelocele, with PMG reported most frequently. In view of our interest in the causes of PMG, we reviewed clinical data including brain-imaging studies on 21 patients with PMG associated with deletion 22q11.2 and another 11 from the literature. We found that the cortical malformation consists of perisylvian PMG of variable severity and frequent asymmetry with a striking predisposition for the right hemisphere (P = 0.008). This and other observations suggest that the PMG may be a sequela of abnormal embryonic vascular development rather than a primary brain malformation. We also noted mild cerebellar hypoplasia or mega-cisterna magna in 8 of 24 patients. Although this was not the focus of the present study, mild cerebellar anomalies are probably the most common brain malformation associated with DEL22q11.

A case of schizophrenia with complete agenesis of the corpus callosum

OBJECTIVE

To describe the case of a person with schizophrenia and agenesis of the corpus callosum.

CONCLUSION

A 24-year-old Caucasian woman with schizophrenia was incidentally found to have complete agenesis of the corpus callosum. A comprehensive neuropsychiatric assessment allowed management to be specifically tailored to the patient's unique clinical profile.

Diseases of white matter and schizophrenia-like psychosis

OBJECTIVE

To analyse the available data regarding the presentation of psychosis in diseases of central nervous system (CNS) white matter.

METHOD

The available neurological and psychiatric literature on developmental, neoplastic, infective, immunological and other white matter diseases was reviewed.

RESULTS

A number of diseases of the white matter can present as schizophrenia-like psychoses, including leukodystrophies, neoplasms, velocardiofacial syndrome, callosal anomalies and inflammatory diseases.

CONCLUSIONS

Production of psychotic symptoms may result from functional asynchrony of interdependent regions, due to alterations in critical circuits as a result of pathology. The nature, location and timing of white matter pathology seem to be the key factors in the development of psychosis, especially during the critical adolescent period of association area myelination. Diseases that disrupt the normal formation of myelin appear to cause psychosis at higher rates than those that disrupt mature myelinated structures. Diffuse rather than discrete lesions, in particular those affecting frontotemporal zones, are also more strongly associated with schizophrenia-like psychosis. These illnesses point to the central role that white matter plays in maintaining CNS connectivity and to how pathology of the white matter may contribute to the neurobiology of psychosis.

Behavior and corpus callosum morphology relationships in velocardiofacial syndrome (22q11.2 deletion syndrome)

Velocardiofacial syndrome (VCFS) is a neurodevelopmental disorder caused by a microdeletion on chromosome 22q11.2 that predisposes affected individuals to learning disabilities and psychiatric conditions. Previous research has indicated that compared with comparison children, children with VCFS have larger corpus callosal areas. Children with VCFS are often diagnosed with comorbid attention deficit hyperactivity disorder (ADHD), and previous research has indicated that children with ADHD often have smaller corpus callosal areas than controls. The present study investigated two hypotheses: children with VCFS would have larger callosal areas than controls, and children with VCFS+ADHD would have smaller callosal areas than children with VCFS. Corpus callosum area was obtained from the mid-sagittal slice and was assessed in children with VCFS (n=60) and age- and gender-matched control participants (n=52). Results indicated that all of the corpus callosum measures were significantly different between the two groups except for the genu. Across all measures, children with VCFS demonstrated a larger corpus callosum area. Within the VCFS sample, children with VCFS+ADHD (n=30) had smaller total callosal, splenium, and genu areas than children with VCFS alone. Although children with VCFS+ADHD had smaller total callosal areas than children with VCFS, relative to control participants, these children had larger total callosal and subregion areas except for the genu. In addition to other anatomic anomalies, corpus callosal abnormalities appear to be another variable to consider when analyzing brain/behavior relations in this population.

Clinical, MRI, and pathological features of polymicrogyria in chromosome 22q11 deletion syndrome

Polymicrogyria is a brain malformation due to abnormal cortical organization. Two histological types, unlayered or four-layered can be distinguished. Polymicrogyria is a rare manifestation of chromosome 22q11 deletion syndrome. We report two boys with chromosome 22q11 deletion syndrome and polymicrogyria, and describe the neuropathological features of the malformation in one of them. Clinical examinations, EEG, brain MRI, chromosomal analysis with FISH, and neuropathological studies of surgically resected cortical tissue were performed. Both patients showed severe developmental delay with cardiovascular malformations and one of them had drug resistant epilepsy. Polymicrogyria was found in the frontal, parietal, and temporal areas, unilaterally in one patient and bilaterally in the other. Histology revealed four-layered polymicrogyria. The pathogenesis of polymicrogyria in 22q11 deletion syndrome is discussed.

Agenesis and dysgenesis of the corpus callosum

Agenesis and dysgenesis of the corpus callosum is a frequent anomaly that presents with a spectrum of clinical features and exhibits variable findings in neurological studies. Clinical signs and symptoms are the result of cerebral and extracerebral malformations associated with callosal dysgenesis. Callosal agenesis may be an isolated anomaly or may be syndromic as part of more extensive malformations, metabolic and genetic disorders. The advent of modern techniques and equipment for neuroimaging have allowed us to define with more precision the type and severity of the callosal dysgenesis and accompanying other cerebral malformations. Molecular genetic studies allow the recognition and confirmation of new syndromes that until now were incompletely defined. In the context of these new pathologic entities, a new classification is proposed that may prove to be more useful than the traditional single category, "agenesis of the corpus callosum" and can serve as a basis for a later, more detailed, etiologic classification that integrates morphology and molecular genetics.

DiGeorge syndrome associated with left lung aplasia

We report a patient with clinical and cytogenetic findings consistent with DiGeorge-velocardiofacial syndrome and aplasia of the left lung. To the best of our knowledge, this is the first reported case of DiGeorge-velocardiofacial syndrome associated with unilateral lung aplasia. Gadolinium enhanced three-dimensional magnetic resonance angiography demonstrated associated right-sided aortic arch and left pulmonary artery agenesis.

Three new patients with congenital unilateral facial nerve palsy due to chromosome 22q11 deletion

We report three unrelated patients with congenital facial nerve palsy and chromosome 22q11 deletion, a condition hitherto poorly recognized. In the first case, facial palsy was associated with aortic coarctation, ductus arteriosus, and ostium secundum atrial septal defect. In the second case, facial palsy was associated with ostium secundum atrial septal defect, obstruction of the ureteropelvic junction, double ureteropelvic-calicial system, and distal metaphyseal widening of the forearm and leg bones. In both cases, facial palsy was the presenting feature. In the third case, an ostium secundum atrial septal defect was also present, but involvement of cranial nerves III, VI, and VIII, in addition to hypoplastic structures of cerebellar and cerebral peduncles, were the predominant features. There were no inherited deletions within chromosome band 22q11 and the de novo deletions detected in each case belonged to the paternally derived chromosome 22. Association of facial nerve palsy and congenital heart disease versus cardiofacial syndrome are different only on clinical grounds, so both conditions can be genetically identical and form part of the spectrum of defects associated with chromosome 22q11 deletions. We recommend investigation for chromosome 22q11 deletions in patients with complete nerve facial palsy.