Further delineation of novel 1p36 rearrangements by array-CGH analysis: narrowing the breakpoints and clarifying the "extended" phenotype

PRDM16 co-operates with LHX2 to shape the human brain

PRDM16 is a dynamic transcriptional regulator of various stem cell niches, including adipocytic, hematopoietic, cardiac progenitors, and neural stem cells. PRDM16 has been suggested to contribute to 1p36 deletion syndrome, one of the most prevalent subtelomeric microdeletion syndromes. We report a patient with a de novo nonsense mutation in the PRDM16 coding sequence, accompanied by lissencephaly and microcephaly features. Human stem cells were genetically modified to mimic this mutation, generating cortical organoids that exhibited altered cell cycle dynamics. RNA sequencing of cortical organoids at day 32 unveiled changes in cell adhesion and WNT-signaling pathways. ChIP-seq of PRDM16 identified binding sites in postmortem human fetal cortex, indicating the conservation of PRDM16 binding to developmental genes in mice and humans, potentially at enhancer sites. A shared motif between PRDM16 and LHX2 was identified and further examined through comparison with LHX2 ChIP-seq data from mice. These results suggested a collaborative partnership between PRDM16 and LHX2 in regulating a common set of genes and pathways in cortical radial glia cells, possibly via their synergistic involvement in cortical development.

PRDM16 co-operates with LHX2 to shape the human brain

PRDM16 is a dynamic transcriptional regulator of various stem cell niches, including adipocytic, hematopoietic, cardiac progenitors, and neural stem cells. PRDM16 has been suggested to contribute to 1p36 deletion syndrome, one of the most prevalent subtelomeric microdeletion syndromes. We report a patient with a de novo nonsense mutation in the PRDM16 coding sequence, accompanied by lissencephaly and microcephaly features. Human stem cells were genetically modified to mimic this mutation, generating cortical organoids that exhibited altered cell cycle dynamics. RNA sequencing of cortical organoids at day 32 unveiled changes in cell adhesion and WNT-signaling pathways. ChIP-seq of PRDM16 identified binding sites in postmortem human fetal cortex, indicating the conservation of PRDM16 binding to developmental genes in mice and humans, potentially at enhancer sites. A shared motif between PRDM16 and LHX2 was identified and further examined through comparison with LHX2 ChIP-seq data from mice. These results suggested a collaborative partnership between PRDM16 and LHX2 in regulating a common set of genes and pathways in cortical radial glia cells, possibly via their synergistic involvement in cortical development.

Clinical characterization of familial 1p36.3 microduplication

Unlike the 1p36 microdeletion syndrome, which has been extensively described, 1p36.3 microduplications have rarely been reported. We report the two siblings of familial 1p36.3 microduplication, presenting with a severe global developmental delay, epilepsy, and a few dysmorphic features. They were referred to moderate-to-severe developmental delay (DD) and intellectual disability (ID). Both were considered eyelid myoclonus with absence of epilepsy (Jeavons syndrome). The EEG is characterized by widespread 2.5-3.5 Hz spikes and spike slow complex wave, eye closure sensitivity, and photosensitivity. The children has same dysmorphic features, including mild bitemporal narrowing and sloping forehead, sparse eyebrows, hypertelorism, ptosis, strabismus, infraorbital creases, wide nasal bridge with bulbous nasal tip, dystaxia, hallux valgus, and flat feet. Family exome sequencing revealed a maternally inherited 3.2-Mb microduplication of chromosomal band 1p36.3p36.2. However, DNA purified from blood samples of either parent did not find evidence for a microduplication of 1p36 in somatic tissue, indicating that such a mutation might be carried in the germline of the parents as gonadal mosaicism. No other family members of the affected siblings' parents were reported to be affected by the symptoms found.

Triplications of chromosome 1p36.3, including the genes GABRD and SKI, are associated with a developmental disorder and a facial gestalt

Triplication of chromosomal region 1p36.3 is a rare genomic rearrangement. In this report, we delineate the phenotypic spectrum associated with 1p36.3 triplications. We describe four patients with microtriplications of variable size, but with a strong phenotypic overlap, and compare them to previously described patients with an isolated triplication or duplication of this region. The 1p36.3 triplication syndrome is associated with a distinct phenotype, characterized by global developmental delay, moderate intellectual disability, seizures, behavioral problems, and specific facial dysmorphic features, including ptosis, hypertelorism, and arched eyebrows. The de novo occurrence of these microtriplications demonstrates the reduced reproductive fitness associated with this genotype, in contrast to 1p36.3 duplications which are mostly inherited and can be associated with similar facial features but with a less severe developmental phenotype. The shared triplicated region encompasses four disease-related genes of which GABRD and SKI are most likely to contribute to the phenotype.

Clinical evaluation of rare copy number variations identified by chromosomal microarray in a Hungarian neurodevelopmental disorder patient cohort

BACKGROUND

Neurodevelopmental disorders are genetically heterogeneous pediatric conditions. The first tier diagnostic method for uncovering copy number variations (CNVs), one of the most common genetic etiologies in affected individuals, is chromosomal microarray (CMA). However, this methodology is not yet a routine molecular cytogenetic test in many parts of the world, including Hungary. Here we report clinical and genetic data of the first, relatively large Hungarian cohort of patients whose genetic testing included CMA.

METHODS

Clinical data were retrospectively collected for 78 children who were analyzed using various CMA platforms. Phenotypes of patients with disease-causing variants were compared to patients with negative results using the chi squared/Fisher exact tests.

RESULTS

A total of 30 pathogenic CNVs were identified in 29 patients (37.2%). Postnatal growth delay (p = 0.05564), pectus excavatum (p = 0.07484), brain imaging abnormalities (p = 0.07848), global developmental delay (p = 0.08070) and macrocephaly (p = 0.08919) were more likely to be associated with disease-causing CNVs.

CONCLUSION

Our results allow phenotypic expansion of 14q11.2 microdeletions encompassing SUPT16H and CHD8 genes. Variants of unknown significance (n = 24) were found in 17 patients. We provide detailed phenotypic and genetic data of these individuals to facilitate future classification efforts, and spotlight two patients with potentially pathogenic alterations. Our results contribute to unraveling the diagnostic value of rare CNVs.

Non-classical 1p36 deletion in a patient with Duane retraction syndrome: case report and literature review

Background

Monosomy of 1p36 is considered the most common terminal microdeletion syndrome. It is characterized by intellectual disability, growth retardation, seizures, congenital anomalies, and distinctive facial features that are absent when the deletion is proximal, beyond the 1p36.32 region. In patients with proximal deletions, little is known about the associated phenotype, since only a few cases have been reported in the literature. Ocular manifestations in patients with classical 1p36 monosomy are frequent and include strabismus, myopia, hypermetropia, and nystagmus. However, as of today only one patient with 1p36 deletion and Duane retraction syndrome (DRS) has been reported.

Case presentation

We describe a patient with intellectual disability, facial dysmorphism, and bilateral Duane retraction syndrome (DRS) type 1. Array CGH showed a 7.2 Mb de novo deletion from 1p36.31 to 1p36.21.

Discussion

Our patient displayed DRS, which is not part of the classical phenotype and is not a common clinical feature in 1p36 deletion syndrome; we hypothesized that this could be associated with the overlapping deletion between the distal and proximal 1p36 regions. DRS is one of the Congenital Cranial Dysinnervation Disorders, and a genetic basis for the syndrome has been extensively reported. The HES3 gene is located at 1p36.31 and could be associated with oculomotor alterations, including DRS, since this gene is involved in the development of the 3rd cranial nerve and the 6th cranial nerve’s nucleus. We propose that oculomotor anomalies, including DRS, could be related to proximal 1p36 deletion, warranting a detailed ophthalmologic evaluation of these patients.

Molecular characterization of a 1p36 chromosomal duplication and in utero interference define ENO1 as a candidate gene for polymicrogyria

While chromosome 1p36 deletion syndrome is one of the most common terminal subtelomeric microdeletion syndrome, 1p36 microduplications are rare events. Polymicrogyria (PMG) is a brain malformation phenotype frequently present in patients with 1p36 monosomy. The gene whose haploinsufficiency could cause this phenotype remains to be identified. We used high-resolution arrayCGH in patients with various forms of PMG in order to identify chromosomal variants associated to the malformation and characterized the genes included in these regions in vitro and in vivo. We identified the smallest case of 1p36 duplication reported to date in a patient presenting intellectual disability, microcephaly, epilepsy, and perisylvian polymicrogyria. The duplicated segment is intrachromosomal, duplicated in mirror and contains two genes: enolase 1 (ENO1) and RERE, both disrupted by the rearrangement. Gene expression analysis performed using the patient cells revealed a reduced expression, mimicking haploinsufficiency. We performed in situ hybridization to describe the developmental expression profile of the two genes in mouse development. In addition, we used in utero electroporation of shRNAs to show that Eno1 inactivation in the rat causes a brain development defect. These experiments allowed us to define the ENO1 gene as the most likely candidate to contribute to the brain malformation phenotype of the studied patient and consequently a candidate to contribute to the malformations of the cerebral cortex observed in patients with 1p36 monosomy.

Recurrent Copy Number Variants Associated with Syndromic Short Stature of Unknown Cause

BACKGROUND/AIMS

Genetic imbalances are responsible for many cases of short stature of unknown etiology. This study aims to identify recurrent pathogenic copy number variants (CNVs) in patients with syndromic short stature of unknown cause.

METHODS

We selected 229 children with short stature and dysmorphic features, developmental delay, and/or intellectual disability, but without a recognized syndrome. All patients were evaluated by chromosomal microarray (array-based comparative genomic hybridization/single nucleotide polymorphism array). Additionally, we searched databases and previous studies to recover recurrent pathogenic CNVs associated with short stature.

RESULTS

We identified 32 pathogenic/probably pathogenic CNVs in 229 patients. By reviewing the literature, we selected 4 previous studies which evaluated CNVs in cohorts of patients with short stature. Taken together, there were 671 patients with short stature of unknown cause evaluated by chromosomal microarray. Pathogenic/probably pathogenic CNVs were identified in 87 patients (13%). Seven recurrent CNVs, 22q11.21, 15q26, 1p36.33, Xp22.33, 17p13.3, 1q21.1, 2q24.2, were observed. They are responsible for about 40% of all pathogenic/probably pathogenic genomic imbalances found in short stature patients of unknown cause.

CONCLUSION

CNVs seem to play a significant role in patients with short stature. Chromosomal microarray should be used as a diagnostic tool for evaluation of growth disorders, especially for syndromic short stature of unknown cause.

Electroclinical features of epilepsy associated with 1p36 deletion syndrome: A review

1p36 terminal deletion is a recently recognized syndrome with multiple congenital anomalies and intellectual disability. It occurs approximately in 1 out of 5000 to 10,000 live births and is the most common subtelomeric microdeletion observed in human. Medical problems commonly caused by terminal deletions of 1p36 include developmental delay, intellectual disability, seizures, vision problems, hearing loss, short stature, brain anomalies, congenital heart defects, cardiomyopathy, renal anomalies and distinctive facial features. Although the syndrome is considered clinically recognizable, there is significant phenotypic variation among affected individuals. Genotype-phenotype correlation in this syndrome is complicated, because of the similar clinical evidence seen in patients with different deletion sizes. We review 34 scientific articles from 1996 to 2016 that described 315 patients with 1p36 delection syndrome. The aim of this review is to find a correlation between size of the 1p36-deleted segments and the neurological clinical phenotypes with the analysis of electro-clinical patterns associated with chromosomal aberrations, that is a major tool in the identification of epilepsy susceptibility genes. Our finding suggest that developmental delay and early epilepsy are frequent findings in 1p36 deletion syndrome that can contribute to a poor clinical outcome for this reason this syndrome should be searched for in patients presenting with infantile spasms associated with a hypsarrhythmic EEG, particulary if they are combined with dismorphic features, severe hypotonia and developmental delay.

Genetic Diagnosis of Chromosomal Congenital Anomalies in Albanian Pediatric Patients by Array CGH

AIM

The aim of our study was to identify chromosomal imbalances by whole-genome microarray-based comparative genomic hybridization (array CGH) in DNA samples of children in which karyotype results cannot be obtained. The present paper describes the first Albanian experience of an array CGH application.

MATERIAL AND METHODS

The cohort included seven children with developmental delay or intellectual disability, facial dysmorphism and congenital anomalies according to clinical criteria, suggestive of chromosomal anomalies. The age range was from newborn to five years old. The cytogenetic analysis determined by a standard method of G-banding according to the International System for Human Cytogenetic Nomenclature (ISCN 2005) was performed for all our patients, while array CGH was performed on genomic DNA isolated from the blood of 7 cases.

RESULTS

Among the seven patients analysed with array CGH, three patients resulted in duplication and one deletion, one patient with a microdeletion and three patients with duplication. Array CGH facilitated the recognition of submicroscopic deletions and duplications as risk factors for genetic diagnosis in all our patients.

CONCLUSIONS

Our case series with congenital chromosomal anomalies confirms the high diagnostic value of the method, as suggested by previous studies. The technique must be available also in less developed countries, to significantly improve the genetic diagnosis of paediatric patients with developmental delay or intellectual disability, congenital anomalies and dysmorphic features. The identification of chromosomal abnormalities in these patients and the genetic counselling will provide family members with an explanation for their child's developmental disability or birth defect, allowing better information about recurrence risks, and permit the anticipation of certain medical problems that require intervention.

Familial 1p36.3 microduplication resulting from a 1p-9q non-reciprocal translocation

Unlike the 1p36 microdeletion syndrome, which has been extensively described, 1p36 microduplications have rarely been reported. We describe a three years old boy presenting with a severe global developmental delay and a few dysmorphic features. Cytogenetic analyses revealed a maternally inherited 3.35 Mb microduplication of chromosomal band 1p36.3. The maternal grandfather is also carrier of the same chromosomal rearrangement. Interestingly, the duplicated 1p36.3 segment was found to be localized at the telomeric end of the long arms of a chromosome 9, probably deriving from a 1p36.3-9qter non-reciprocal translocation. This particular type of chromosomal translocation has rarely been reported, and its mechanism is unclear. The phenotypical features associated with 1p36.3 microduplication vary due to the non-recurrent breakpoints of the rearrangements in this particular region. However when compiling the few described cases the phenotypical spectrum seems to include mainly developmental delay, mild facial dysmorphism, and neurological, cardiac and skeletal anomalies. The description of new patients carrying a 1p36.3 duplication like ours will lead to further delineation of the phenotypical spectrum and may help to find critical regions and causative genes implicated in the phenotype.

Application of high-resolution array comparative genomic hybridization in children with unknown syndromic microcephaly

BackroundMicrocephaly can either be isolated or it may coexist with other neurological entities and/or multiple congenital anomalies, known as syndromic microcephaly. Although many syndromic cases can be classified based on the characteristic phenotype, some others remain uncertain and require further investigation. The present study describes the application of array-comparative genomic hybridization (array-CGH) as a diagnostic tool for the study of patients with clinically unknown syndromic microcephaly.MethodsFrom a cohort of 210 unrelated patients referred with syndromic microcephaly, we applied array-CGH analysis in 53 undiagnosed cases. In all the 53 cases except one, previous standard karyotype was negative. High-resolution 4 × 180K and 1 × 244K Agilent arrays were used in this study.ResultsIn 25 out of the 53 patients with microcephaly among other phenotypic anomalies, array-CGH revealed copy number variations (CNVs) ranging in size between 15 kb and 31.6 Mb. The identified CNVs were definitely causal for microcephaly in 11/53, probably causal in 7/53, and not causal for microcephaly in 7/53 patients. Genes potentially contributing to brain deficit were revealed in 16/53 patients.ConclusionsArray-CGH contributes to the elucidation of undefined syndromic microcephalic cases by permitting the discovery of novel microdeletions and/or microduplications. It also allows a more precise genotype-phenotype correlation by the accurate definition of the breakpoints in the deleted/duplicated regions.

CNV analysis in 169 patients with bladder exstrophy-epispadias complex

Background

The bladder exstrophy-epispadias complex (BEEC) represents the severe end of the congenital uro-rectal malformation spectrum. Initial studies have implicated rare copy number variations (CNVs), including recurrent duplications of chromosomal region 22q11.21, in BEEC etiology.

Methods

To detect further CNVs, array analysis was performed in 169 BEEC patients. Prior to inclusion, 22q11.21 duplications were excluded using multiplex ligation-dependent probe amplification.

Results

Following the application of stringent filter criteria, seven rare CNVs were identified: n = 4, not present in 1307 in-house controls; n = 3, frequency of <0.002 in controls. These CNVs ranged from 1 to 6.08 Mb in size. To identify smaller CNVs, relaxed filter criteria used in the detection of previously reported BEEC associated chromosomal regions were applied. This resulted in the identification of six additional rare CNVs: n = 4, not present in 1307 in-house controls; n = 2, frequency <0.0008 in controls. These CNVs ranged from 0.03–0.08 Mb in size. For 10 of these 13 CNVs, confirmation and segregation analyses were performed (5 of maternal origin; 5 of paternal origin). Interestingly, one female with classic bladder extrophy carried a 1.18 Mb duplication of 22q11.1, a chromosomal region that is associated with cat eye syndrome.

Conclusions

A number of rare CNVs were identified in BEEC patients, and these represent candidates for further evaluation. Rare inherited CNVs may constitute modifiers of, or contributors to, multifactorial BEEC phenotypes.

Analysis of rare copy number variation in absence epilepsies

OBJECTIVE

To identify shared genes and pathways between common absence epilepsy (AE) subtypes (childhood absence epilepsy [CAE], juvenile absence epilepsy [JAE], and unclassified absence epilepsy [UAE]) that may indicate common mechanisms for absence seizure generation and potentially a diagnostic continuum.

METHODS

We used high-density single-nucleotide polymorphism arrays to analyze genome-wide rare copy number variation (CNV) in a cohort of 144 children with AEs (95 CAE, 26 UAE, and 23 JAE).

RESULTS

We identified CNVs that are known risk factors for AE in 4 patients, including 3x 15q11.2 deletion. We also expanded the phenotype at 4 regions more commonly identified in other neurodevelopmental disorders: 1p36.33 duplication, 1q21.1 deletion, 22q11.2 duplication, and Xp22.31 deletion and duplication. Fifteen patients (10.5%) were found to carry rare CNVs that disrupt genes associated with neuronal development and function (8 CAE, 2 JAE, and 5 UAE). Four categories of protein are each disrupted by several CNVs: (1) synaptic vesicle membrane or vesicle endocytosis, (2) synaptic cell adhesion, (3) synapse organization and motility via actin, and (4) gap junctions. CNVs within these categories are shared across the AE subtypes.

CONCLUSIONS

Our results have reinforced the complex and heterogeneous nature of the AEs and their potential for shared genetic mechanisms and have highlighted several pathways that may be important in epileptogenesis of absence seizures.

1p36 deletion syndrome: an update

Deletions of chromosome 1p36 affect approximately 1 in 5,000 newborns and are the most common terminal deletions in humans. Medical problems commonly caused by terminal deletions of 1p36 include developmental delay, intellectual disability, seizures, vision problems, hearing loss, short stature, distinctive facial features, brain anomalies, orofacial clefting, congenital heart defects, cardiomyopathy, and renal anomalies. Although 1p36 deletion syndrome is considered clinically recognizable, there is significant phenotypic variation among affected individuals. This variation is due, at least in part, to the genetic heterogeneity seen in 1p36 deletions which include terminal and interstitial deletions of varying lengths located throughout the 30 Mb of DNA that comprise chromosome 1p36. Array-based copy number variant analysis can easily identify genomic regions of 1p36 that are deleted in an affected individual. However, predicting the phenotype of an individual based solely on the location and extent of their 1p36 deletion remains a challenge since most of the genes that contribute to 1p36-related phenotypes have yet to be identified. In addition, haploinsufficiency of more than one gene may contribute to some phenotypes. In this article, we review recent successes in the effort to map and identify the genes and genomic regions that contribute to specific 1p36-related phenotypes. In particular, we highlight evidence implicating MMP23B, GABRD, SKI, PRDM16, KCNAB2, RERE, UBE4B, CASZ1, PDPN, SPEN, ECE1, HSPG2, and LUZP1 in various 1p36 deletion phenotypes.

The first patient with a pure 1p36 microtriplication associated with severe clinical phenotypes

BACKGROUND

Copy Number Variants (CNVs) is a new molecular frontier in clinical genetics. CNVs in 1p36 are usually pathogenic and have attracted the attention of cytogeneticists worldwide. None of 1p36 triplication has been reported thus far.

RESULTS

We present three patients with CNVs in 1p36. Among them one is the first 1p36 tetrasomy due to a pure microtriplication and the other two are 1p36 microdeletion. Traditional chromosome G-banding technique showed a normal karyotype. Single nucleotide polymorphism (SNP) microarray analysis combined with multiplex ligation-dependent probe amplification (MLPA) and fluorescence in situ hybridization (FISH) were used to identify and confirm the chromosome microdeletion/microtriplication. The facial dysmorphisms of the patient with 1p36 tetrasomy differed from those two patients with 1p36 monosomy. The expression levels of B3GALT6, MIB2, PEX10 and PANK4 in the blood were determined, and differential expressions were observed between the patients and controls.

CONCLUSIONS

Our study shows the first case of 1p36 tetrasomy due to a pure microtriplication in a patient with severe intellectual disability and seizures. The study provides a new resource for studying the mechanisms of microtriplication formation, and provides an evidence that overexpression of the specific genes might be related the specific phenotype of 1p36 microtriplication.

Complex structural rearrangement features suggesting chromoanagenesis mechanism in a case of 1p36 deletion syndrome

Genome rearrangements are caused by the erroneous repair of DNA double-strand breaks, leading to several alterations that result in loss or gain of the structural genomic of a dosage-sensitive genes. However, the mechanisms that promote the complexity of rearrangements of congenital or developmental defects in human disease are unclear. The investigation of complex genomic abnormalities could help to elucidate the mechanisms and causes for the formation and facilitate the understanding of congenital or developmental defects in human disease. We here report one case of a patient with atypical clinical features of the 1p36 syndrome and the use of cytogenomic techniques to characterize the genomic alterations. Analysis by multiplex ligation-dependent probe amplification and array revealed a complex rearrangement in the 1p36.3 region with deletions and duplication interspaced by normal sequences. We also suggest that chromoanagenesis could be a possible mechanism involved in the repair and stabilization of this rearrangement.

Monosomy 1p36 - a multifaceted and still enigmatic syndrome: four clinically diverse cases with shared white matter abnormalities

Monosomy 1p36 is the most common subtelomeric deletion syndrome seen in humans. Uniform features of the syndrome include early developmental delay and consequent intellectual disability, muscular hypotonia, and characteristic dysmorphic facial features. The gene-rich nature of the chromosomal band, inconsistent deletion sizes and overlapping clinical features have complicated relevant genotype-phenotype correlations. We describe four patients with isolated chromosome 1p36 deletions. All patients shared white matter abnormalities, allowing us to narrow the critical region for white matter involvement to the deletion size of up to 2.5 Mb from the telomere. We hypothesise that there might be a gene(s) responsible for myelin development in the 1p36 subtelomeric region. Other significant clinical findings were progressive spastic paraparesis, epileptic encephalopathy, various skeletal anomalies, Prader-Willi-like phenotype, neoplastic changes - a haemangioma and a benign skin tumour, and in one case, sleep myoclonus, a clinical entity not previously described in association with 1p36 monosomy. Combined with prior studies, our results suggest that the clinical features seen in monosomy 1p36 have more complex causes than a classical contiguous gene deletion syndrome.

Accurate, fast and cost-effective diagnostic test for monosomy 1p36 using real-time quantitative PCR

Monosomy 1p36 is considered the most common subtelomeric deletion syndrome in humans and it accounts for 0.5–0.7% of all the cases of idiopathic intellectual disability. The molecular diagnosis is often made by microarray-based comparative genomic hybridization (aCGH), which has the drawback of being a high-cost technique. However, patients with classic monosomy 1p36 share some typical clinical characteristics that, together with its common prevalence, justify the development of a less expensive, targeted diagnostic method. In this study, we developed a simple, rapid, and inexpensive real-time quantitative PCR (qPCR) assay for targeted diagnosis of monosomy 1p36, easily accessible for low-budget laboratories in developing countries. For this, we have chosen two target genes which are deleted in the majority of patients with monosomy 1p36: PRKCZ and SKI. In total, 39 patients previously diagnosed with monosomy 1p36 by aCGH, fluorescent in situ hybridization (FISH), and/or multiplex ligation-dependent probe amplification (MLPA) all tested positive on our qPCR assay. By simultaneously using these two genes we have been able to detect 1p36 deletions with 100% sensitivity and 100% specificity. We conclude that qPCR of PRKCZ and SKI is a fast and accurate diagnostic test for monosomy 1p36, costing less than 10 US dollars in reagent costs.

Clinical, genetic and imaging findings identify new causes for corpus callosum development syndromes

The corpus callosum is the largest fibre tract in the brain, connecting the two cerebral hemispheres, and thereby facilitating the integration of motor and sensory information from the two sides of the body as well as influencing higher cognition associated with executive function, social interaction and language. Agenesis of the corpus callosum is a common brain malformation that can occur either in isolation or in association with congenital syndromes. Understanding the causes of this condition will help improve our knowledge of the critical brain developmental mechanisms required for wiring the brain and provide potential avenues for therapies for callosal agenesis or related neurodevelopmental disorders. Improved genetic studies combined with mouse models and neuroimaging have rapidly expanded the diverse collection of copy number variations and single gene mutations associated with callosal agenesis. At the same time, advances in our understanding of the developmental mechanisms involved in corpus callosum formation have provided insights into the possible causes of these disorders. This review provides the first comprehensive classification of the clinical and genetic features of syndromes associated with callosal agenesis, and provides a genetic and developmental framework for the interpretation of future research that will guide the next advances in the field.

Fine mapping of the 1p36 deletion syndrome identifies mutation of PRDM16 as a cause of cardiomyopathy

Deletion 1p36 syndrome is recognized as the most common terminal deletion syndrome. Here, we describe the loss of a gene within the deletion that is responsible for the cardiomyopathy associated with monosomy 1p36, and we confirm its role in nonsyndromic left ventricular noncompaction cardiomyopathy (LVNC) and dilated cardiomyopathy (DCM). With our own data and publically available data from array comparative genomic hybridization (aCGH), we identified a minimal deletion for the cardiomyopathy associated with 1p36del syndrome that included only the terminal 14 exons of the transcription factor PRDM16 (PR domain containing 16), a gene that had previously been shown to direct brown fat determination and differentiation. Resequencing of PRDM16 in a cohort of 75 nonsyndromic individuals with LVNC detected three mutations, including one truncation mutant, one frameshift null mutation, and a single missense mutant. In addition, in a series of cardiac biopsies from 131 individuals with DCM, we found 5 individuals with 4 previously unreported nonsynonymous variants in the coding region of PRDM16. None of the PRDM16 mutations identified were observed in more than 6,400 controls. PRDM16 has not previously been associated with cardiac disease but is localized in the nuclei of cardiomyocytes throughout murine and human development and in the adult heart. Modeling of PRDM16 haploinsufficiency and a human truncation mutant in zebrafish resulted in both contractile dysfunction and partial uncoupling of cardiomyocytes and also revealed evidence of impaired cardiomyocyte proliferative capacity. In conclusion, mutation of PRDM16 causes the cardiomyopathy in 1p36 deletion syndrome as well as a proportion of nonsyndromic LVNC and DCM.