A recessive PRDM13 mutation results in congenital hypogonadotropic hypogonadism and cerebellar hypoplasia.

The positive regulatory (PR) domain containing 13 (PRDM13) putative chromatin modifier and transcriptional regulator functions downstream of the transcription factor PTF1A, which controls GABAergic fate in the spinal cord and neurogenesis in the hypothalamus. Here, we report a recessive syndrome associated with PRDM13 mutation. Patients exhibited intellectual disability, ataxia with cerebellar hypoplasia, scoliosis, and delayed puberty with congenital hypogonadotropic hypogonadism (CHH). Expression studies revealed Prdm13/PRDM13 transcripts in the developing hypothalamus and cerebellum in mouse and human. An analysis of hypothalamus and cerebellum development in mice homozygous for a Prdm13 mutant allele revealed a significant reduction in the number of Kisspeptin (Kiss1) neurons in the hypothalamus and PAX2+ progenitors emerging from the cerebellar ventricular zone. The latter was accompanied by ectopic expression of the glutamatergic lineage marker TLX3. Prdm13-deficient mice displayed cerebellar hypoplasia and normal gonadal structure, but delayed pubertal onset. Together, these findings identify PRDM13 as a critical regulator of GABAergic cell fate in the cerebellum and of hypothalamic kisspeptin neuron development, providing a mechanistic explanation for the cooccurrence of CHH and cerebellar hypoplasia in this syndrome. To our knowledge, this is the first evidence linking disrupted PRDM13-mediated regulation of Kiss1 neurons to CHH in humans.

WNT1-associated osteogenesis imperfecta with atrophic frontal lobes and arachnoid cysts.

A rare form of osteogenesis imperfecta (OI) caused by Wingless-type MMTV integration site family 1 (WNT1) mutations combines central nervous system (CNS) anomalies with the characteristic increased susceptibility to fractures. We report an additional case where arachnoid cysts extend the phenotype, and that also confirms the association of intellectual disabilities with asymmetric cerebellar hypoplasia here. Interestingly, if the cerebellum is normal in this disorder, intelligence is as well, analogous to an association with similar delays in a subset of patients with sporadic unilateral cerebellar hypoplasia. Those cases typically appear to represent vascular disruptions, and we suggest that most brain anomalies in WNT1-associated OI have vascular origins related to a role for WNT1 in CNS angiogenesis. This unusual combination of benign cerebellar findings with effects on higher functions in these two situations raises the possibility that WNT1 is involved in the pathogenesis of the associated sporadic cases as well. Finally, our patient reacted poorly to pamidronate, which appears ineffective with this form of OI, so that a lack of improvement is an indication for molecular testing that includes WNT1.

Lysine Restriction and Pyridoxal Phosphate Administration in a NADK2 Patient.

We report the case of a 10-year-old Spanish girl with mutations in NADK2 Prenatal central nervous system abnormalities showed ventriculomegaly, colpocephaly, and hypoplasia of the corpus callosum. At birth, axial hypotonia, uncoordinated movements, microcephaly, and generalized cerebellar atrophy were detected. Metabolic investigations revealed high lysine, lactate, and pipecolic acid levels in blood and cerebrospinal fluid. Pyruvate carboxylase and pyruvate dehydrogenase activity in fibroblasts were normal. Beginning at birth she received biotin, thiamine, and carnitine supplementation. A lysine-restricted diet was started when she was 1 month old. Because pipecolic acid was high, pyridoxine was added to treatment. At 3 years old, astatic myoclonic epilepsy appeared, with no response to levetiracetam. We switched pyridoxine to pyridoxal phosphate, with electroclinical improvement. Because the activity of mitochondrial respiratory chain complexes III and IV was slightly low in muscle, other cofactors such as ubidecarenone, idebenone, vitamin E, and creatine were added to the treatment. At 8 years old, plasma acylcarnitine testing was performed, and high levels of 2-trans, 4-cis-decadienoylcarnitine were found. Whole exome sequencing identified a homozygous splice site mutation in NADK2 (c.956+6T>C; p.Trp319Cysfs*21). This substitution generates exon skipping, leading to a truncated protein. In fact, NADK2 messenger RNA and the corresponding protein were almost absent. Now, at 10 years of age she presents with ataxia and incoordination. She has oromotor dysphasia but is able to understand fluid language and is a very friendly girl. We hypothesize that the patient's clinical improvement could be due to her lysine-restricted diet together with cofactors and pyridoxal phosphate administration.

MRI analysis of cerebellar and vestibular developmental phenotypes in Gbx2 conditional knockout mice.

PURPOSE: Our aim in this study was to apply three-dimensional MRI methods to analyze early postnatal morphological phenotypes in a Gbx2 conditional knockout (Gbx2-CKO) mouse that has variable midline deletions in the central cerebellum, reminiscent of many human cerebellar hypoplasia syndromes. METHODS: In vivo three-dimensional manganese-enhanced MRI at 100-µm isotropic resolution was used to visualize mouse brains between postnatal days 3 and 11, when cerebellum morphology undergoes dramatic changes. Deformation-based morphometry and volumetric analysis of manganese-enhanced MRI images were used to, respectively, detect and quantify morphological phenotypes in Gbx2-CKO mice. Ex vivo micro-MRI was performed after perfusion-fixation with supplemented gadolinium for higher resolution (50-µm) analysis. RESULTS: In vivo manganese-enhanced MRI and deformation-based morphometry correctly identified known cerebellar defects in Gbx2-CKO mice, and novel phenotypes were discovered in the deep cerebellar nuclei and the vestibulo-cerebellum, both validated using histology. Ex vivo micro-MRI revealed subtle phenotypes in both the vestibulo-cerebellum and the vestibulo-cochlear organ, providing an interesting example of complementary phenotypes in a sensory organ and its associated brain region. CONCLUSION: These results show the potential of three-dimensional MRI for detecting and analyzing developmental defects in mouse models of neurodevelopmental diseases.

Bilateral subcortical heterotopia with partial callosal agenesis in a mouse mutant.

Cognition and behavior depend on the precise placement and interconnection of complex ensembles of neurons in cerebral cortex. Mutations that disrupt migration of immature neurons from the ventricular zone to the cortical plate have provided major insight into mechanisms of brain development and disease. We have discovered a new and highly penetrant spontaneous mutation that leads to large nodular bilateral subcortical heterotopias with partial callosal agenesis. The mutant phenotype was first detected in a colony of fully inbred BXD29 mice already known to harbor a mutation in Tlr4. Neurons confined to the heterotopias are mainly born in midgestation to late gestation and would normally have migrated into layers 2-4 of overlying neocortex. Callosal cross-sectional area and fiber number are reduced up to 50% compared with coisogenic wildtype BXD29 substrain controls. Mutants have a pronounced and highly selective defect in rapid auditory processing. The segregation pattern of the mutant phenotype is most consistent with a two-locus autosomal recessive model, and selective genotyping definitively rules out the Tlr4 mutation as a cause. The discovery of a novel mutation with strong pleiotropic anatomical and behavioral effects provides an important new resource for dissecting molecular mechanisms and functional consequences of errors of neuronal migration.

Polymorphisms in folate-metabolizing genes and risk of having an offspring with congenital anomalies in the West Siberian region of Russia: a case-control study.

OBJECTIVE: Periconceptional folate supplementation prevents a number of congenital anomalies (CA). The aim of our study was to investigate the association of 11 polymorphisms in the folate-metabolizing genes with the risk of having an offspring with CA in the Russian ethnic group. METHOD: We genotyped 280 mothers having a CA-affected pregnancy and 390 control mothers. The most common malformations among the cases were CA of the nervous, urinary, and cardiovascular systems, and these groups were analyzed separately. RESULTS: In the whole group of CA, we revealed the associations of MTHFR C677T and MTR A2756G loci with increased risk of CA-affected pregnancy. In the group of CA of the cardiovascular system, we observed an association of MTHFR A1298C with decreased risk and an association of MTR A2756G with increased risk of CA. After the Bonferroni correction, only the association between the genotype MTR 2756GG and the risk of having a fetus with CA of the cardiovascular system remained statistically significant (OR = 4.99, P = 0.03). CONCLUSION: These findings indicate that locus A2756G in the MTR gene may play a role in susceptibility to CA of the cardiovascular system in West Siberia, but further research is necessary to confirm the association.

SPG11 compound mutations in spastic paraparesis with thin corpus callosum.

BACKGROUND: Autosomal recessive hereditary spastic paraparesis with thin corpus callosum (ARHSP-TCC) is being increasingly recognized as a variety of spastic paraplegia with mental retardation. SPG11 gene mutations have been reported to be associated with ARHSP-TCC. METHODS: As an independent group, we investigated SPG11 gene involvement in four individuals not previously described with either recessive or sporadic HSP-TCC presentation. RESULTS: Chromosome 15q13-15 segregating autosomal disease haplotypes were different across the kindreds and sequencing of SPG11 identified four novel frameshift/nonsense segregating mutations and the R2034X mutation, which were in heterozygous compound status. The affected examined had decreased thalamic and bilateral paracentral frontal lobe metabolism on (18)F-flurodeoxyglucose PET. CONCLUSIONS: Loss-of-function SPG11 mutations are the major cause of autosomal recessive hereditary spastic paraparesis with thin corpus callosum in Southern Europe, even in apparently sporadic cases. Decreased thalamic metabolism was consistently a phenotypical SPG11 mutation hallmark.

[Risk of recurrence in major craniospinal malformations between 1976 and 2005]. / A jelentosebb craniospinalis rendellenességek ismétlodési kockázatának alakulása 1976-2005 között.

INTRODUCTION: Craniospinal malformations are among the commonest developmental disorders. Due to its incidence the knowledge of the risk of recurrence is very important not only for the geneticist but also for the married couples. METHOD: In the period between January 1st, 1976 and December 31st, 2005, among the 75320 documented cases at the Genetic Counselling Units of the Departments of Obstetrics and Gynecology of the University of Debrecen and Semmelweis University Budapest, consultations were requested due to previous craniospinal malformations in the patients' history in 3030 cases (4.2%). This paper contains the most important informations about these cases of craniospinal malformations. The greatest risk of non-central nervous system developmental anomalies was associated with holoprosencephaly. RESULTS: In approximately two thirds of the cases (65.1%), the couples sought counselling because of malformation in a previous pregnancy. In these cases, the risk of recurrence was thought to be 5.2%, while in the case of two affected children this figure stood at 21.9%. When the risk of recurrence was analysed according to the various types, much lower figures (3.8%) were found for neural tube defects compared to other anomalies in this study. CONCLUSION: Analysing the values for the risk of recurrence in five-year periods, neural tube defects (particularly anencephaly and spina bifida) showed detectable decrease, which could be attributed to a widening use of folic acid supplementation around about the time of conception and during pregnancy.

Epilepsy.

PURPOSE OF REVIEW: The purpose of this review is to consider the current and potential role of neuroimaging from an epilepsy perspective, and to illustrate that by combining appropriate imaging techniques, neuroimaging can contribute greatly to elucidating the basic mechanisms of the various forms of epileptic disorders. RECENT FINDINGS: New magnetic resonance imaging sequences (magnetization transfer imaging) and positron emission tomography ligands (serotonergic system) were biologically validated in large groups of patients with localization-related epilepsies. Investigations in genetically determined homogenous patient populations (PAX6, juvenile myoclonic epilepsy) have strengthened the link between genetic defects and neuropathological targets (anterior commissure, thalamus). Magnetic resonance spectroscopy and electroencephalogram-triggered functional magnetic resonance imaging provided converging evidence for a key role of the thalamus in the generation of generalized seizures. The role of functional magnetic resonance imaging in identifying eloquent areas of cortex and its relationship to structural lesions, in particular malformations of cortical development, has been further elucidated. Longitudinal magnetic resonance imaging studies reported progressive volume loss after febrile convulsions and in active epilepsy. SUMMARY: Neuroimaging is essential for improving the efficacy and safety of therapeutic, in particular, surgical procedures. Investigations of larger, more homogenous genetic disorders and longitudinal rather than cross-sectional neuroimaging studies have advanced our knowledge about the cause and effect of epileptic disorders, and will ultimately link defects in molecular genetics with specific neuropathological targets.

Loss of glutamatergic pyramidal neurons in frontal and temporal cortex resulting from attenuation of FGFR1 signaling is associated with spontaneous hyperactivity in mice.

Fibroblast growth factor receptor (FGFR) gene products (Fgfr1, Fgfr2, Fgfr3) are widely expressed by embryonic neural progenitor cells throughout the CNS, yet their functional role in cerebral cortical development is still unclear. To understand whether the FGF pathways play a role in cortical development, we attenuated FGFR signaling by expressing a tyrosine kinase domain-deficient Fgfr1 (tFgfr1) gene construct during embryonic brain development. Mice carrying the tFgfr1 transgene under the control of the Otx1 gene promoter have decreased thickness of the cerebral cortex in frontal and temporal areas because of decreased number of pyramidal neurons and disorganization of pyramidal cell dendritic architecture. These alterations may be, in part, attributable to decreased genesis of T-Brain-1-positive early glutamatergic neurons and, in part, to a failure to maintain radial glia fibers in medial prefrontal and temporal areas of the cortical plate. No changes were detected in cortical GABAergic interneurons, including Cajal-Retzius cells or in the basal ganglia. Behaviorally, tFgfr1 transgenic mice displayed spontaneous and persistent locomotor hyperactivity that apparently was not attributable to alterations in subcortical monoaminergic systems, because transgenic animals responded to both amphetamine and guanfacine, an alpha2A adrenergic receptor agonist. We conclude that FGF tyrosine kinase signaling may be required for the genesis and growth of pyramidal neurons in frontal and temporal cortical areas, and that alterations in cortical development attributable to disrupted FGF signaling are critical for the inhibitory regulation of motor behavior.

Concurrent generation of subplate and cortical plate neurons in developing trisomy 16 mouse cortex.

During embryonic development of the mammalian cerebral cortex, the generation of the marginal zone (MZ) and subplate (SP) precedes that of the cortical plate (CP). MZ and SP neurons are believed to play a 'pioneering' role in directing the organization of the CP and the specificity of connections between the CP and other brain regions. Here we report that this sequential order of neurogenesis is disrupted in the trisomy 16 (Ts16) mouse, a potential animal model of Down syndrome. Bromodeoxyuridine labeling was used to establish the date of generation of postmitotic SP and CP neurons in the somatosensory cortex. As has been previously reported, most SP neurons in euploid (control) cortex were generated on embryonic day 12.5 (E12.5), and production of CP neurons began a day later. In contrast, in the Ts16 cortex, few SP neurons were born on E12.5 and most were generated on E13.5 and E14.5 when CP neurons were also being produced. Thus, in the Ts16 cortex, many CP neurons are born and arrive at their destinations before the normal complement of SP neurons is present. This disruption of the temporal sequence of SP and CP generation may, therefore, interfere with the pioneering functions of the SP during cortical neurogenesis and may alter the connectivity of the cortex. Indeed, using lipophilic membrane tracers to label axonal projections, we found very little thalamocortical innervation of the Ts16 SP at an age when there is extensive innervation of the euploid SP.

Miswiring of limbic thalamocortical projections in the absence of ephrin-A5.

Axon guidance cues of the ephrin ligand family have been hypothesized to regulate the formation of thalamocortical connections, but in vivo evidence for such a role has not been examined directly. To test whether ephrin-mediated repulsive cues participate in sorting the projections originating from distinct thalamic nuclei, we analyzed the organization of somatosensory and anterior cingulate afferents postnatally in mice lacking ephrin-A5 gene expression. Projections from ventrobasal and laterodorsal nuclei to their respective sensory and limbic cortical areas developed normally. However, a portion of limbic thalamic neurons from the laterodorsal nucleus also formed additional projections to somatosensory cortical territories, thus maintaining inappropriate dual projections to multiple cortical regions. These results suggest that ephrin-A5 is not required for the formation of normal cortical projections from the appropriate thalamic nuclei, but rather acts as a guidance cue that restricts limbic thalamic axons from inappropriate neocortical regions.

Abnormal distributions of callosal commissural and corticothalamic neurons in the cerebral neocortex of Shaking Rat Kawasaki.

Shaking Rat Kawasaki (SRK) is an autosomal recessive mutant rat recognized by unstable gait and tremor and by early death around the time of weaning. We previously reported that corticospinal tract neurons are malpositioned in the motor cortex of the SRK rat [Ikeda and Terashima (1997) J. Comp. Neurol. 383, 370-380]. In the present study, we examined the distribution pattern of callosal commissural (CC) and corticothalamic (CT) neurons of SRK and normal rats with the injection of horseradish peroxidase (HRP) into the contralateral hemisphere or wheat germ agglutinin-conjugated HRP into the ventral lateral thalamic nucleus. The intracortical distribution pattern of retrogradely labeled CC and CT neurons in the motor cortex of SRK rat was abnormal: CC neurons were more deeply situated and CT neurons were more superficially situated in the SRK cortex than the corresponding components in the normal cortex. Most of labeled CC and CT neurons had abnormal dendritic configurations. Statistical analysis revealed that the difference of the mean intracortical position of CC and CT neurons of the SRK was significantly different from the normal counterparts (Student's t-test, P<0.01). Taken together with previous findings, our data demonstrate that the abnormal cytoarchitecture of SRK cortex resembles the reeler cortex.

Cortical and thalamic axon pathfinding defects in Tbr1, Gbx2, and Pax6 mutant mice: evidence that cortical and thalamic axons interact and guide each other.

During development, cortical areas establish precise reciprocal projections with corresponding thalamic nuclei. Pioneer axons from the cortex and thalamus first meet in the intermediate zone of the subcortical telencephalon (subpallium). Their close interactions in the subpallium suggest that they may use each other for guidance. To test this hypothesis, the development of corticothalamic and thalamocortical connections was studied in mice with mutations of transcription factor genes expressed specifically in the cortex (Tbr1), the dorsal thalamus (Gbx2), or both (Pax6). In Tbr1 mutants, cortical pioneer axons entered the subpallium at the appropriate time, but most stopped growing without entering the diencephalon. Surprisingly, thalamic axons (which do not express Tbr1) deviated into the external capsule and amygdala regions, without entering the cortex. Conversely, in most Gbx2 mutants, thalamic axons were reduced in number and grew no farther than the subpallium. Cortical axons (which do not express Gbx2) grew into the subpallium but did not enter the diencephalon. In one Gbx2- /- case, sparse thalamocortical and corticothalamic projections both developed, but in no case did one projection reach its target and not the other. In Pax6 mutants, neither corticothalamic nor thalamocortical axons reached their targets. These results suggest that thalamocortical and corticothalamic projections may not form independently. After reaching the subpallium, each projection may require a molecularly intact reciprocal projection for further guidance. This type of mechanism ensures that thalamocortical and corticothalamic axons project reciprocally. However, the exact nature of the interaction between cortical and thalamic pioneer axons remains to be elucidated.