Neuroimaging Findings in Axenfeld-Rieger Syndrome: A Case Series

Axenfeld-Rieger syndrome is an autosomal dominant condition associated with multisystemic features including developmental anomalies of the anterior segment of the eye. Single nucleotide and copy number variants in the paired-like homeodomain transcription factor 2 (PITX2) and forkhead box C1 (FOXC1) genes are associated with Axenfeld-Rieger syndrome as well as other CNS malformations. We determined the association between Axenfeld-Rieger syndrome and specific brain MR imaging neuroradiologic anomalies in cases with or without a genetic diagnosis. This case series included 8 individuals with pathogenic variants in FOXC1; 2, in PITX2; and 2 without a genetic diagnosis. The most common observation was vertebrobasilar artery dolichoectasia, with 46% prevalence. Other prevalent abnormalities included WM hyperintensities, cerebellar hypoplasia, and ventriculomegaly. Vertebrobasilar artery dolichoectasia and absent/hypoplastic olfactory bulbs were reported in >50% of individuals with FOXC1 variants compared with 0% of PITX2 variants. Notwithstanding the small sample size, neuroimaging abnormalities were more prevalent in individuals with FOXC1 variants compared those with PITX2 variants.

Axenfeld-Rieger syndrome: A systematic review examining genetic, neurological, and neurovascular associations to inform screening

Axenfeld-Rieger Syndrome (ARS) is comprised of a group of autosomal dominant disorders that are each characterized by anterior segment abnormalities of the eye. Mutations in the transcription factors FOXC1 or PITX2 are the most well-studied genetic manifestations of this syndrome. Due to the rarity this syndrome, ARS-associated neurological manifestations have not been well characterized. The purpose of this systematic review is to characterize and describe ARS neurologic manifestations that affect the cerebral vasculature and their early and late sequelae. PRISMA guidelines were followed; studies meeting inclusion criteria were analyzed for study design, evidence level, number of patients, patient age, whether the patients were related, genotype, ocular findings, and nervous system findings, specifically neurostructural and neurovascular manifestations. 63 studies met inclusion criteria, 60 (95%) were case studies or case series. The FOXC1 gene was most commonly found, followed by COL4A1, then PITX2. The most commonly described structural neurological findings were white matter abnormalities in 26 (41.3%) of studies, followed by Dandy-Walker Complex 12 (19%), and agenesis of the corpus callosum 11 (17%). Neurovascular findings were examined in 6 (9%) of studies, identifying stroke, cerebral small vessel disease (CSVD), tortuosity/dolichoectasia of arteries, among others, with no mention of moyamoya. This is the first systematic review investigating the genetic, neurological, and neurovascular associations with ARS. Structural neurological manifestations were common, yet often benign, perhaps limiting the utility of MRI screening. Neurovascular abnormalities, specifically stroke and CSVD, were identified in this population. Stroke risk was present in the presence and absence of cardiac comorbidities. These findings suggest a relationship between ARS and neurovascular findings; however, larger scale studies are necessary inform therapeutic decisions.

Case report: Extending the spectrum of clinical and molecular findings in FOXC1 haploinsufficiency syndrome

FOXC1 is a ubiquitously expressed forkhead transcription factor that plays a critical role during early development. Germline pathogenic variants in FOXC1 are associated with anterior segment dysgenesis and Axenfeld-Rieger syndrome (ARS, #602482), an autosomal dominant condition with ophthalmologic anterior segment abnormalities, high risk for glaucoma and extraocular findings including distinctive facial features, as well as dental, skeletal, audiologic, and cardiac anomalies. De Hauwere syndrome is an ultrarare condition previously associated with 6p microdeletions and characterized by anterior segment dysgenesis, joint instability, short stature, hydrocephalus, and skeletal abnormalities. Here, we report clinical findings of two unrelated adult females with FOXC1 haploinsufficiency who have ARS and skeletal abnormalities. Final molecular diagnoses of both patients were achieved using genome sequencing. Patient 1 had a complex rearrangement involving a 4.9 kB deletion including FOXC1 coding region (Hg19; chr6:1,609,721-1,614,709), as well as a 7 MB inversion (Hg19; chr6:1,614,710-8,676,899) and a second deletion of 7.1 kb (Hg19; chr6:8,676,900-8,684,071). Patient 2 had a heterozygous single nucleotide deletion, resulting in a frameshift and a premature stop codon in FOXC1 (NM_001453.3): c.467del, p.(Pro156Argfs*25). Both individuals had moderate short stature, skeletal abnormalities, anterior segment dysgenesis, glaucoma, joint laxity, pes planovalgus, dental anomalies, hydrocephalus, distinctive facial features, and normal intelligence. Skeletal surveys revealed dolichospondyly, epiphyseal hypoplasia of femoral and humeral heads, dolichocephaly with frontal bossin gand gracile long bones. We conclude that haploinsufficiency of FOXC1 causes ARS and a broad spectrum of symptoms with variable expressivity that at its most severe end also includes a phenotype overlapping with De Hauwere syndrome.

The phenotypic spectrum of terminal and subterminal 6p deletions based on a social media-derived cohort and literature review

BACKGROUND

Terminal 6p deletions are rare, and information on their clinical consequences is scarce, which impedes optimal management and follow-up by clinicians. The parent-driven Chromosome 6 Project collaborates with families of affected children worldwide to better understand the clinical effects of chromosome 6 aberrations and to support clinical guidance. A microarray report is required for participation, and detailed phenotype information is collected directly from parents through a multilingual web-based questionnaire. Information collected from parents is then combined with case data from literature reports. Here, we present our findings on 13 newly identified patients and 46 literature cases with genotypically well-characterised terminal and subterminal 6p deletions. We provide phenotype descriptions for both the whole group and for subgroups based on deletion size and HI gene content.

RESULTS

The total group shared a common phenotype characterised by ocular anterior segment dysgenesis, vision problems, brain malformations, congenital defects of the cardiac septa and valves, mild to moderate hearing impairment, eye movement abnormalities, hypotonia, mild developmental delay and dysmorphic features. These characteristics were observed in all subgroups where FOXC1 was included in the deletion, confirming a dominant role for this gene. Additional characteristics were seen in individuals with terminal deletions exceeding 4.02 Mb, namely complex heart defects, corpus callosum abnormalities, kidney abnormalities and orofacial clefting. Some of these additional features may be related to the loss of other genes in the terminal 6p region, such as RREB1 for the cardiac phenotypes and TUBB2A and TUBB2B for the cerebral phenotypes. In the newly identified patients, we observed previously unreported features including gastrointestinal problems, neurological abnormalities, balance problems and sleep disturbances.

CONCLUSIONS

We present an overview of the phenotypic characteristics observed in terminal and subterminal 6p deletions. This reveals a common phenotype that can be highly attributable to haploinsufficiency of FOXC1, with a possible additional effect of other genes in the 6p25 region. We also delineate the developmental abilities of affected individuals and report on previously unrecognised features, showing the added benefit of collecting information directly from parents. Based on our overview, we provide recommendations for clinical surveillance to support clinicians, patients and families.

Chromosome 6p25 deletion syndrome: A case report and review of ophthalmic features

The 6p25 deletion syndrome is a rare genetic disorder characterized by a wide spectrum of congenital anomalies. Ophthalmic abnormalities appear to be highly associated with the syndrome, although this relationship has not been well characterized to date. We conducted a systematic literature review to highlight the ocular features in patients with this deletion syndrome and describe a 7-month-old female who has a 6.07 MB 6p25.1p25.3 deletion and a 4.25 MB 17q25.3 duplication. Our patient presented with multiple congenital anomalies, including macrocephaly, frontal bossing, low set ears, tent-shaped mouth, saddle nose, flat midface, and hearing impairment. Her ophthalmic features included proptosis, down-slanting palpebral fissures, hypertelorism, nystagmus, bilateral posterior embryotoxon, and decentered and abnormally shaped pupils. A systematic review of the published cases with sufficient clinical eye descriptions included 63 cases with a confirmed 6p25 deletion. The most common eye findings observed were posterior embryotoxon, iris hypoplasia, corectopia, cornea opacity, and glaucoma.

Ischemic Stroke Genetics: What Is New and How to Apply It in Clinical Practice?

The etiology of ischemic stroke is multifactorial. Although receiving less emphasis, genetic causes make a significant contribution to ischemic stroke genesis, especially in early-onset stroke. Several stroke classification systems based on genetic information corresponding to various stroke phenotypes were proposed. Twin and family history studies, as well as candidate gene approach, are common methods to discover genetic causes of stroke, however, both have their own limitations. Genome-wide association studies and next generation sequencing are more efficient, promising and increasingly used for daily diagnostics. Some monogenic disorders, despite covering only about 7% of stroke etiology, may cause well-known clinical manifestations that include stroke. Polygenic disorders are more frequent, causing about 38% of all ischemic strokes, and their identification is a rapidly developing field of modern stroke genetics. Current advances in human genetics provide opportunity for personalized prevention of stroke and novel treatment possibilities. Genetic risk scores (GRS) and extended polygenic risk scores (PRS) estimate cumulative contribution of known genetic factors to a specific outcome of stroke. Combining those scores with clinical information and risk factor profiles might result in better primary stroke prevention. Some authors encourage the use of stroke gene panels for stroke risk evaluation and further stroke research. Moreover, new biomarkers for stroke genetic causes and novel targets for gene therapy are on the horizon. In this article, we summarize the latest evidence and perspectives of ischemic stroke genetics that could be of interest to the practitioner and useful for day-to-day clinical work.

Genetic disorders with central nervous system white matter abnormalities: An update

Several genetic disorders have variable degree of central nervous system white matter abnormalities. We retrieved and reviewed 422 genetic conditions with prominent and consistent involvement of white matter from the literature. We herein describe the current definitions, classification systems, clinical spectrum, neuroimaging findings, genomics, and molecular mechanisms of these conditions. Though diagnosis for most of these disorders relies mainly on genomic tests, specifically exome sequencing, we collate several clinical and neuroimaging findings still relevant in diagnosis of clinically recognizable disorders. We also review the current understanding of pathophysiology and therapeutics of these disorders.

A case of childhood glaucoma with a combined partial monosomy 6p25 and partial trisomy 18p11 due to an unbalanced translocation

Background: Chromosomal deletion involving the 6p25 region results in a clinically recognizable syndrome characterized by anterior eye chamber anomalies with risk of glaucoma and non-ocular malformations (6p25 deletion syndrome). We report a newborn infant case of childhood glaucoma with a combination of partial monosomy 6p25 and partial trisomy 18p11 due to an unbalanced translocation.Materials and methods: The patient was a 0-year-old girl. Both eyes showed aniridia and left eye Peters anomaly with multiple malformations. To identify the chromosomal aberrations in the patient with clinically suspected 6p25 deletion syndrome, we performed cytogenetic analysis (G-banding and multicolor fluorescent in-situ hybridization) and array-based comparative genomic hybridization (array-CGH) analysis.Results: Cytogenetic analyses revealed a derivative chromosome 6 with its distal short arm replaced by an extra copy of the short arm of chromosome 18. Array-CGH analysis detected a 4.6-Mb deletion at 6pter to 6p25.1 and 8.9-Mb duplication at 18pter to 18p11.22. To determine the breakpoint of the unbalanced rearrangement at the single-base level, we performed a long-range PCR for amplifying the junctional fragment of the translocation breakpoint. By sequencing the junctional fragment, we defined the unbalanced translocation as g.chr6:pter_4594783delinschr18:pter_8911541.Conclusions: A phenotype corresponding to combined monosomy 6p25 and trisomy 18p11 presented as childhood glaucoma associated with non-acquired (congenital) ocular anomalies consist of aniridia and Peters anomaly and other systemic malformations. To the best of our knowledge, this is the first report which demonstrated the breakpoint sequence of an unbalanced translocation in a Japanese infant with childhood glaucoma.

Childhood glaucoma genes and phenotypes: Focus on FOXC1 mutations causing anterior segment dysgenesis and hearing loss

Childhood glaucoma is an important cause of blindness world-wide. Eleven genes are currently known to cause inherited forms of glaucoma with onset before age 20. While all the early-onset glaucoma genes cause severe disease, considerable phenotypic variability is observed among mutations carriers. In particular, FOXC1 genetic variants are associated with a broad range of phenotypes including multiple forms of glaucoma and also systemic abnormalities, especially hearing loss. FOXC1 is a member of the forkhead family of transcription factors and is involved in neural crest development necessary for formation of anterior eye structures and also pharyngeal arches that form the middle ear bones. In this study we review the clinical phenotypes reported for known FOXC1 mutations and show that mutations in patients with reported ocular anterior segment abnormalities and hearing loss primarily disrupt the critically important forkhead domain. These results suggest that optimal care for patients affected with anterior segment dysgenesis should include screening for FOXC1 mutations and also testing for hearing loss.

Multiple genomic copy number variants associated with periventricular nodular heterotopia indicate extreme genetic heterogeneity

Periventricular nodular heterotopia (PNH) is a brain malformation in which nodules of neurons are ectopically retained along the lateral ventricles. Genetic causes include FLNA abnormalities (classical X-linked PNH), rare variants in ARFGEF2, DCHS1, ERMARD, FAT4, INTS8, MAP1B, MCPH1, and NEDD4L, as well as several chromosomal abnormalities. We performed array-CGH in 106 patients with different malformations of cortical development (MCD) and looked for common pathways possibly involved in PNH. Forty-two patients, including two parent/proband couples, exhibited PNH associated or not with other brain abnormalities, 44 had polymicrogyria and 20 had rarer MCDs. We found an enrichment of either large rearrangements or cryptic copy number variants (CNVs) in PNH (15/42, 35.7%) vs polymicrogyria (4/44, 9.1%) (i.e., 5.6 times increased risk for PNH of carrying a pathogenic CNV). CNVs in seven genomic regions (2p11.2q12.1, 4p15, 14q11.2q12, 16p13.3, 19q13.33, 20q13.33, 22q11) represented novel, potentially causative, associations with PNH. Through in silico analysis of genes included in imbalances whose breakpoints were clearly detailed, we detected in 9/12 unrelated patients in our series and in 15/24 previously published patients, a significant (P < 0.05) overrepresentation of genes involved in vesicle-mediated transport. Rare genomic imbalances, either small CNVs or large rearrangements, are cumulatively a frequent cause of PNH. Dysregulation of specific cellular mechanisms might play a key pathogenic role in PNH but it remains to be determined whether this is exerted through single genes or the cumulative dosage effect of more genes. Array-CGH should be considered as a first-line diagnostic test in PNH, especially if sporadic and non-classical.

Prenatally diagnosed periventricular nodular heterotopia: Further delineation of the imaging phenotype and outcome

OBJECTIVES

Periventricular nodular heterotopia (PNH) is a malformation of cortical development which presents with heterogeneous imaging, neurological phenotype and outcome. There is a paucity of comprehensive description detailing the prenatal diagnosis of PNH. The aim of this study is to report neuroimaging features and correlated outcomes in order to delineate the spectrum of prenatally diagnosed PNH.

METHODS

It was a retrospective study over 15 years in five tertiary centers. All fetuses with prenatally diagnosed PNH were collected. Fetal ultrasound and MRI were reviewed and genetic screening collected. Prenatal findings were analyzed in correlation to fetopathological analyses and post-natal follow up.

RESULTS

Thirty fetuses (22 females and 8 males) with PNH were identified. The two major ultrasound signs were ventriculomegaly associated with dysmorphic frontal horns (60%) and posterior fossa anomalies (73.3%). On MRI, two groups of PNH were identified: the contiguous and diffuse PNH (n = 15, 50%), often associated with megacisterna magna, and the non-diffuse, either anterior, posterior or unilateral PNH. FLNA mutations were found in 6/11 cases with diffuse PNH. Additional cortical malformations were exclusively observed in non diffuse PNH (9/15; 60%). Twenty-four pregnancies (80%) were terminated. Six children aged 6 months to 5 years are alive. Five have normal neurodevelopment (all had diffuse PNH) whereas one case with non diffuse PNH has developmental delay and epilepsy.

CONCLUSION

PNH is heterogeneous but patients with diffuse PNH are a common subgroup with specific findings on prenatal imaging and implications for prenatal counseling.

A Novel Strategy Combining Array-CGH, Whole-exome Sequencing and In Utero Electroporation in Rodents to Identify Causative Genes for Brain Malformations

Birth defects that involve the cerebral cortex - also known as malformations of cortical development (MCD) - are important causes of intellectual disability and account for 20-40% of drug-resistant epilepsy in childhood. High-resolution brain imaging has facilitated in vivo identification of a large group of MCD phenotypes. Despite the advances in brain imaging, genomic analysis and generation of animal models, a straightforward workflow to systematically prioritize candidate genes and to test functional effects of putative mutations is missing. To overcome this problem, an experimental strategy enabling the identification of novel causative genes for MCD was developed and validated. This strategy is based on identifying candidate genomic regions or genes via array-CGH or whole-exome sequencing and characterizing the effects of their inactivation or of overexpression of specific mutations in developing rodent brains via in utero electroporation. This approach led to the identification of the C6orf70 gene, encoding for a putative vesicular protein, to the pathogenesis of periventricular nodular heterotopia, a MCD caused by defective neuronal migration.

New insights into mechanisms of small vessel disease stroke from genetics

Cerebral small vessel disease (SVD) is a common cause of lacunar strokes, vascular cognitive impairment (VCI) and vascular dementia. SVD is thought to result in reduced cerebral blood flow, impaired cerebral autoregulation and increased blood–brain barrier (BBB) permeability. However, the molecular mechanisms underlying SVD are incompletely understood. Recent studies in monogenic forms of SVD, such as cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), and ‘sporadic’ SVD have shed light on possible disease mechanisms in SVD. Proteomic and biochemical studies in post-mortem monogenic SVD patients, as well as in animal models of monogenic disease have suggested that disease pathways are shared between different types of monogenic disease, often involving the impairment of extracellular matrix (ECM) function. In addition, genetic studies in ‘sporadic’ SVD have also shown that the disease is highly heritable, particularly among young-onset stroke patients, and that common variants in monogenic disease genes may contribute to disease processes in some SVD subtypes. Genetic studies in sporadic lacunar stroke patients have also suggested distinct genetic mechanisms between subtypes of SVD. Genome-wide association studies (GWAS) have also shed light on other potential disease mechanisms that may be shared with other diseases involving the white matter, or with pathways implicated in monogenic disease. This review brings together recent data from studies in monogenic SVD and genetic studies in ‘sporadic’ SVD. It aims to show how these provide new insights into the pathogenesis of SVD, and highlights the possible convergence of disease mechanisms in monogenic and sporadic SVD.

Phenotype of a Belgian Family With 6p25 Deletion Syndrome

BACKGROUND

The 6p25 deletion syndrome is one of the many syndromes with both hearing impairment as well as vision impairment. However, the audiometric characteristics and radiological findings of patients with 6p25 deletions are only scarcely described in literature. This study focused on characterizing the audiometric and radiological features of a Belgian family with a chromosome 6p25 deletion.

OBJECTIVE

To evaluate the hearing impairment, audiometric testing and radiological examination of the temporal bones in 3 family members with a 3.4 Mb deletion in chromosome band 6p25.

RESULTS

All 3 family members demonstrated slowly progressive sensorineural or mixed hearing impairment. Radiologic examination revealed thickened and sclerotic stapes in all patients and a minor internal partition type II of the cochlea in 2 patients.

CONCLUSION

There is a significant phenotypic variability within and among families with the 6p25 deletion syndrome. A thorough genotype-phenotype correlation is difficult because of the small number of affected patients and the limited clinical data available. More clinical data of families with 6p25 deletions need to be published in order to create a reliable and precise phenotypic characterization. However, our findings can facilitate counseling of hearing impairment caused by 6p25 deletions.

22q11.2 Deletion Syndrome due to a Translocation t(6;22) in a Patient Conceived via in vitro Fertilization

We report on a patient conceived via in vitro fertilization (IVF) with a 22q11.2 deletion due to an unusual unbalanced translocation involving chromosomes 6 and 22 in a karyotype with 45 chromosomes. Cytogenomic studies showed that the patient has a 3.3-Mb deletion of chromosome 22q and a 0.4-Mb deletion of chromosome 6p, which resulted in haploinsufficiency of the genes responsible for the 22q11.2 deletion syndrome and also of the IRF4 gene, a member of the interferon regulatory factor family of transcription factors, which is expressed in the immune system cells. The rearrangement could be due to the manipulation of the embryo or as a sporadic event unrelated to IVF. Translocation involving chromosome 22 in a karyotype with 45 chromosomes is a rare event, with no previous reports involving chromosomes 6p and 22q.

Brain imaging and genetic risk in the pediatric population, part 1: inherited metabolic diseases

In this article, the genotype-MR phenotype correlation of the most common or clinically important inherited metabolic diseases (IMD) in the pediatric population is reviewed. A nonsystematic search of the PubMed/Medline database of relevant studies about "genotype-phenotype correlation" in IMD was performed. Some MR phenotypes related to specific gene mutations were found, such as bilateral hypertrophy of inferior olives in patients harboring POLG and SURF1 mutations, and central lesions in the cervical spinal cord in patients with nonketotic hyperglycinemia harboring GLRX5 gene mutation.

Foxf2 Is Required for Brain Pericyte Differentiation and Development and Maintenance of the Blood-Brain Barrier

Pericytes are critical for cerebrovascular maturation and development of the blood-brain barrier (BBB), but their role in maintenance of the adult BBB, and how CNS pericytes differ from those of other tissues, is less well understood. We show that the forkhead transcription factor Foxf2 is specifically expressed in pericytes of the brain and that Foxf2(-/-) embryos develop intracranial hemorrhage, perivascular edema, thinning of the vascular basal lamina, an increase of luminal endothelial caveolae, and a leaky BBB. Foxf2(-/-) brain pericytes were more numerous, proliferated faster, and expressed significantly less Pdgfrβ. Tgfβ-Smad2/3 signaling was attenuated, whereas phosphorylation of Smad1/5 and p38 were enhanced. Tgfβ pathway components, including Tgfβ2, Tgfβr2, Alk5, and integrins αVβ8, were reduced. Foxf2 inactivation in adults resulted in BBB breakdown, endothelial thickening, and increased trans-endothelial vesicular transport. On the basis of these results, FOXF2 emerges as an interesting candidate locus for stroke susceptibility in humans.

Monogenic causes of stroke: now and the future

Most stroke is multifactorial with multiple polygenic risk factors each conferring small increases in risk interacting with environmental risk factors, but it can also arise from mutations in a single gene. This review covers single-gene disorders which lead to stroke as a major phenotype, with a focus on those which cause cerebral small vessel disease (SVD), an area where there has been significant recent progress with findings that may inform us about the pathogenesis of SVD more broadly. We also discuss the impact that next generation sequencing technology (NGST) is likely to have on clinical practice in this area. The most common form of monogenic SVD is cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy, due to the mutations in the NOTCH3 gene. Several other inherited forms of SVD include cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy, retinal vasculopathy with cerebral leukodystrophy, collagen type IV α1 and α2 gene-related arteriopathy and FOXC1 deletion related arteriopathy. These monogenic forms of SVD, with overlapping clinical phenotypes, are beginning to provide insights into how the small arteries in the brain can be damaged and some of the mechanisms identified may also be relevant to more common sporadic SVD. Despite the discovery of these disorders, it is often challenging to clinically and radiologically distinguish between syndromes, while screening multiple genes for causative mutations that can be costly and time-consuming. The rapidly falling cost of NGST may allow quicker diagnosis of these rare causes of SVD, and can also identify previously unknown disease-causing variants.

Malformations of cortical development and epilepsy

Malformations of cortical development (MCDs) are an important cause of epilepsy and an extremely interesting group of disorders from the perspective of brain development and its perturbations. Many new MCDs have been described in recent years as a result of improvements in imaging, genetic testing, and understanding of the effects of mutations on the ability of their protein products to correctly function within the molecular pathways by which the brain functions. In this review, most of the major MCDs are reviewed from a clinical, embryological, and genetic perspective. The most recent literature regarding clinical diagnosis, mechanisms of development, and future paths of research are discussed.

Periventricular nodular heterotopia in Smith-Magenis syndrome

Smith-Magenis syndrome (SMS) is caused by an interstitial microdeletion of chromosome 17p11.2. A few patients with the typical SMS phenotype have RAI1 gene mutations. The syndrome is characterized by minor craniofacial anomalies, short stature, sleep disturbances, behavioural and neurocognitive abnormalities, as well as variable multisystemic manifestations. Periventricular nodular heterotopia (PNH) is a genetically heterogeneous neuronal migration disorder characterized by subependymal heterotopic nodules, and is variably associated with other brain malformations, epileptic seizures and intellectual disability. Here we report on two patients harboring deletions of the 17p11.2 region in whom the SMS typical phenotype was associated with bilateral PNH. Our observations expand the spectrum of chromosomal rearrangements associated with PNH and indicate that abnormal neuronal migration may contribute to the neurocognitive phenotype of SMS.

Malformations of cortical development: clinical features and genetic causes

Malformations of cortical development are common causes of developmental delay and epilepsy. Some patients have early, severe neurological impairment, but others have epilepsy or unexpected deficits that are detectable only by screening. The rapid evolution of molecular biology, genetics, and imaging has resulted in a substantial increase in knowledge about the development of the cerebral cortex and the number and types of malformations reported. Genetic studies have identified several genes that might disrupt each of the main stages of cell proliferation and specification, neuronal migration, and late cortical organisation. Many of these malformations are caused by de-novo dominant or X-linked mutations occurring in sporadic cases. Genetic testing needs accurate assessment of imaging features, and familial distribution, if any, and can be straightforward in some disorders but requires a complex diagnostic algorithm in others. Because of substantial genotypic and phenotypic heterogeneity for most of these genes, a comprehensive analysis of clinical, imaging, and genetic data is needed to properly define these disorders. Exome sequencing and high-field MRI are rapidly modifying the classification of these disorders.

Periventricular heterotopia in 6q terminal deletion syndrome: role of the C6orf70 gene

Periventricular nodular heterotopia is caused by defective neuronal migration that results in heterotopic neuronal nodules lining the lateral ventricles. Mutations in filamin A (FLNA) or ADP-ribosylation factor guanine nucleotide-exchange factor 2 (ARFGEF2) cause periventricular nodular heterotopia, but most patients with this malformation do not have a known aetiology. Using comparative genomic hybridization, we identified 12 patients with developmental brain abnormalities, variably combining periventricular nodular heterotopia, corpus callosum dysgenesis, colpocephaly, cerebellar hypoplasia and polymicrogyria, harbouring a common 1.2 Mb minimal critical deletion in 6q27. These anatomic features were mainly associated with epilepsy, ataxia and cognitive impairment. Using whole exome sequencing in 14 patients with isolated periventricular nodular heterotopia but no copy number variants, we identified one patient with periventricular nodular heterotopia, developmental delay and epilepsy and a de novo missense mutation in the chromosome 6 open reading frame 70 (C6orf70) gene, mapping in the minimal critical deleted region. Using immunohistochemistry and western blots, we demonstrated that in human cell lines, C6orf70 shows primarily a cytoplasmic vesicular puncta-like distribution and that the mutation affects its stability and subcellular distribution. We also performed in utero silencing of C6orf70 and of Phf10 and Dll1, the two additional genes mapping in the 6q27 minimal critical deleted region that are expressed in human and rodent brain. Silencing of C6orf70 in the developing rat neocortex produced periventricular nodular heterotopia that was rescued by concomitant expression of wild-type human C6orf70 protein. Silencing of the contiguous Phf10 or Dll1 genes only produced slightly delayed migration but not periventricular nodular heterotopia. The complex brain phenotype observed in the 6q terminal deletion syndrome likely results from the combined haploinsufficiency of contiguous genes mapping to a small 1.2 Mb region. Our data suggest that, of the genes within this minimal critical region, C6orf70 plays a major role in the control of neuronal migration and its haploinsufficiency or mutation causes periventricular nodular heterotopia.

6p25 microdeletion: white matter abnormalities in an adult patient

We report on a 41-year-old woman of normal intelligence with a complicated past medical history including unilateral profound hearing loss, unilateral Axenfeld-Rieger anomaly, and leukoencephalopathy. She was referred to an adult neurology clinic because of a previous diagnosis of multiple sclerosis, which was non-responsive to multiple medications. Due to her complicated past medical history, the medical genetics service was consulted. She was found to have a chromosome 6p25.3-6p25.2 deletion on SNP array. This report highlights chromosome 6p subtelomeric deletions as a possible underlying cause for periventricular white matter abnormalities in an adult. It emphasizes the importance of genetic testing in an adult with leukoencephalopathy and congenital anomalies.