Claudia Gross

An autosomal recessive limb girdle muscular dystrophy (LGMD2) with mild mental retardation is allelic to Walker-Warburg syndrome (WWS) caused by a mutation in the POMT1 gene

Mutations of the protein O-mannosyltransferase (POMT1) gene affect glycosylation of alpha-dystroglycan, leading to Walker-Warburg syndrome, a lethal disorder in early life with severe congenital muscular dystrophy, and brain and eye malformations. Recently, we described a novel form of recessive limb girdle muscular dystrophy with mild mental retardation, associated with an abnormal alpha-dystroglycan pattern in the muscle, suggesting a glycosylation defect. Here, we present evidence that this distinct phenotype results from a common mutation (A200P) in the POMT1 gene. Our findings further expand the phenotype of glycosylation disorders linked to POMT1 mutations. Furthermore, the A200P mutation is part of a conserved core haplotype, indicating an ancestral founder mutation.

Physical activity fails to rescue hippocampal neurogenesis deficits in the R6/2 mouse model of Huntington's disease

Huntingtons disease (HD) is an autosomal dominant neurodegenerative disorder linked to a mutation in the huntingtin gene leading to protein aggregation in neurons. The generation of new neurons in neurogenic regions, such as the subventricular zone of the lateral ventricle and the dentate gyrus of the hippocampus, is affected by these aggregation processes. In particular, hippocampal neurogenesis is reduced in the R6/2 transgenic mouse model of HD. Since physical activity stimulates adult hippocampal neurogenesis, we examined whether running is capable to rescue the impaired hippocampal neurogenesis in R6/2 mice. Proliferation of hippocampal cells measured by proliferating cell nuclear antigen (PCNA) marker was reduced in R6/2 animals by 64% compared to wild type mice. Accordingly, newly generated neurons labeled with doublecortin (DCX) were diminished by 60% in the hippocampus of R6/2 mice. Furthermore, the number of newly generated mature neurons was decreased by 76%. Within the hippocampus of wild type animals, a four-week running period resulted in a doubling of PCNA-, DCX-, and bromo-deoxyuridine (BrdU)-labeled cells. However, physical exercise failed to stimulate proliferation and survival of newly generated neurons in R6/2 transgenic mouse model of HD. These findings suggest that mutant huntingtin alters the hippocampal microenvironment thus resulting in an impaired neurogenesis. Importantly, this adverse microenvironment impeded neurogenesis upregulation such as induced by physical exercise. Future studies need to decipher the molecular pathways involved in repressing the generation of new neurons after physical activity in huntingtin transgenic rodents.

ARX mutations in X-linked lissencephaly with abnormal genitalia

X-linked lissencephaly with abnormal genitalia (XLAG) is a distinct form of lissencephaly associated with absent corpus callosum. Recently, forms of syndromic and nonspecific X-linked mental retardation have been found to be associated with mutations in the Aristaless-related homeobox gene ARX. The authors assessed ARX as a candidate gene for XLAG in a genetic analysis of neuronal migration disorders and found two different point mutations in two XLAG pedigrees affecting the homeodomain of the protein, confirming that ARX is a causative gene for XLAG.

Novel POMGnT1 mutations define broader phenotypic spectrum of muscle–eye–brain disease

Muscle–eye–brain disease (MEB, OMIM 253280) is an autosomal recessive disorder characterized by a distinct triad of congenital muscular dystrophy, structural eye abnormalities, and cobblestone lissencephaly. Clinically, MEB patients present with early onset muscular hypotonia, severely compromised motor development, and mental retardation. Magnetic resonance imaging reveals a lissencephaly type II with hypoplasia of the brainstem and cerebellum. MEB is associated with mutations in the gene for protein O-mannose beta-1,2-N-acetylglucosaminyltransferase (POMGnT1, OMIM 606822). In this paper, we report the clinical findings of nine MEB patients from eight families. Eight of the nine patients presented typical features of MEB. However, a broad phenotypic variability was observed, ranging from two patients with severe autistic features to another patient with an unusually mild phenotype, initially diagnosed as congenital muscular dystrophy. Furthermore, severe hydrocephalus was reported in two families during a previous pregnancy, emphasizing the phenotypic overlap with Walker–Warburg syndrome. In addition to three previously reported mutations, we identified six novel POMGnT1 mutations (one missense, five truncating) in the present patient cohort. Our data suggest mutational hotspots within the minimal catalytic domain at arginine residue 442 (exon 16) and in intron 17. It is interesting to note that all mutations analyzed so far result in a complete loss of enzyme activity. Therefore, we conclude that the type and position of the POMGnT1 mutations are not of predictive value for the clinical severity. This supports the notion that additional environmental and/or genetic factors may contribute to the observed broad spectrum of POMGnT1-associated phenotypes.

Wide phenotypic variability in families with holoprosencephaly and a sonic hedgehog mutation

Mutations in the human sonic hedgehog gene ( SHH) are the most frequent cause of autosomal dominant inherited holoprosencephaly (HPE), a complex brain malformation resulting from incomplete cleavage of the developing forebrain into two separate hemispheres and ventricles. Here we report the clinical and molecular findings in five unrelated patients with HPE and their relatives with an identified SHH mutation. Three new and one previously reported SHH mutations were identified, a fifth proband was found to carry a reciprocal subtelomeric rearrangement involving the SHH locus in 7q36. An extremely wide intrafamilial phenotypic variability was observed, ranging from the classical phenotype with alobar HPE accompanied by typical severe craniofacial abnormalities to very mild clinical signs of choanal stenosis or solitary median maxillary central incisor (SMMCI) only. Two families were initially ascertained because of microcephaly in combination with developmental delay and/or mental retardation and SMMCI, the latter being a frequent finding in patients with an identified SHH mutation. In other affected family members a delay in speech acquisition and learning disabilities were the leading clinical signs. Conclusion: mutational analysis of the sonic hedgehog gene should not only be considered in patients presenting with the classical holoprosencephaly phenotype but also in those with two or more clinical signs of the wide phenotypic spectrum of associated abnormalities, especially in combination with a positive family history.

Location and type of mutation in the LIS1 gene do not predict phenotypic severity

Background: Lissencephaly is a neuronal migration disorder leading to absent or reduced gyration and a broadened but poorly organized cortex. The most common form of lissencephaly is isolated, referred as classic or type 1 lissencephaly. Type 1 lissencephaly is mostly associated with a heterozygous deletion of the entire LIS1 gene, whereas intragenic heterozygous LIS1 mutations or hemizygous DCX mutations in males are less common. Methods: Eighteen unrelated patients with type 1 lissencephaly were clinically and genetically assessed. In addition, patients with subcortical band heterotopia (n = 1) or lissencephaly with cerebellar hypoplasia (n = 2) were included. Results: Fourteen new and seven previously described LIS1 mutations were identified. We observed nine truncating mutations (nonsense, n = 2; frameshift, n = 7), six splice site mutations, five missense mutations, and one in-frame deletion. Somatic mosaicism was assumed in three patients with partial subcortical band heterotopia in the occipital-parietal lobes or mild pachygyria. We report three mutations in exon 11, including a frameshift which extends the LIS1 protein, leading to type 1 lissencephaly and illustrating the functional importance of the WD domains at the C terminus. Furthermore, we present two patients with novel LIS1 mutations in exon 10 associated with lissencephaly with cerebellar hypoplasia type a. Conclusion: In contrast to previous reports, our data suggest that neither type nor position of intragenic mutations in the LIS1 gene allows an unambiguous prediction of the phenotypic severity. Furthermore, patients presenting with mild cerebral malformations such as subcortical band heterotopia or cerebellar hypoplasia should be considered for genetic analysis of the LIS1 gene.

Novel truncating and missense mutations of the KCC3 gene associated with Andermann syndrome

Background: Andermann syndrome (OMIM 218000) is an autosomal recessive motor-sensory neuropathy associated with developmental and neurodegenerative defects. The cerebral MRI reveals a variable degree of agenesis of the corpus callosum. Recently, truncating mutations of the KCC3 gene (also known as SLC12A6) have been associated with Andermann syndrome. Methods: The authors assessed clinically and genetically three isolated cases from Germany and Turkey with symptoms consistent with Andermann syndrome. Results: The authors detected four novel mutations within the KCC3 gene in their patients: two different truncating mutations in the first patient, a homozygous truncating mutation in the second, and a homozygous missense mutation in the third patient. In contrast to the classic phenotype of the Andermann syndrome linked to truncating KCC3 mutations the phenotype and the course of the disease linked to the missense mutation appeared to be different (i.e., showing additional features like diffuse and widespread white matter abnormalities). Conclusions: Not only truncating but also missense mutations of the KCC3 gene are associated with Andermann syndrome. Different types of KCC3 mutations may determine different clinical phenotypes.

Familial West syndrome and dystonia caused by an Aristaless related homeobox gene mutation

Boys with unexplained West syndrome should be examined for a mutation in the Aristaless related homeobox gene, especially, when the family history is positive for mental retardation and epilepsy. X-linked West syndrome is very rare. We report on two brothers with West syndrome and dystonia with polyalanine expansion of the Aristaless related homeobox gene (ARX). The index patient (Fig. 1a; III-2) was the second child of non-consanguineous parents, born in 2001 at term, after an uneventful pregnancy and delivery (birth weight 3659 g, 75th percentile; length 51 cm, 75th percentile; head circumference 35 cm, 50th percentile). At the age of 3 months he developed infantile spasms and a hypsarrhythmic EEG pattern. He promptly responded to vigabatrin therapy. At 5 months a generalised dystonia, i.e. increased muscle tone with dystonic posturing of limbs, was evident. At the age of 3 years, he is able to walk a few steps with help and grasping objects is very difficult. He has no expressive speech. The elder brother of the index patient (Fig. 1a; III-1) was born in 1996 by caesarean section because of neonatal macrosomia (birth weight 4200 g, 90th percentile; length 53 cm, 90th percentile; head circumference 38 cm, >90th percentile). At the age of 3 months he showed dystonic movements and marked truncal hypotonia. One month later he developed infantile spasms and a hypsarrhythmic EEG pattern. He did not respond to vigabatrin, but to ACTH. At the age of 8 years he is wheel-chair bound, not talking, grasping objects is not possible. In both children metabolic tests and neuroimaging (MRI) were normal. Actually, both brothers suffer from a severe dystonia, mental impairment and rare generalised tonic-clonic seizures (the older brother), treated with valproic acid. The family history was remarkable. In the maternal uncle (Fig. 1a; II-3, now 37 years old), spastic tetraplegia, mental retardation and epilepsy have been present since early infancy. In retrospect, the epilepsy syndrome could not be classified. MRI was not performed in this uncle, the mother or the grandmother. From the pedigree and the clinical findings we suspected a mutation in the ARX gene. Following informed consent, a sequence analysis of the coding region and flanking intronic sequences of the ARX gene was performed. The male proband (index patient; Fig. 1a; III-2) as well as his brother and uncle were found to be hemizygous for a 21 bp GCG repeat expansion in exon 2 of the ARX gene c.333_334ins(GCG)7, which expands the first of four alanine tracts from normally 16 to 23 alanine residues (Fig. 1b,c). Both the mother (Fig. 11; II-2) and the maternal grandmother (Fig. 1a; I-2) were identified as heterozygous mutation carriers using an optimised fluorescence-based PCR assay. Mutations in the ARX gene have been found in a broad spectrum of disorders including X-linked infantile spasms (ISSX)/West syndrome, mental retardation [2], ataxia and dystonia (Partington syndrome), syndromic and non-syndromic forms of mental retardation, myoclonic epilepsy and X-linked lissencephaly with abnormal genitalia (XLAG) [5, 6,8]. The mutation found in our Swiss family, which is not related to previously reported families, has been described before in boys with infantile spasms and normal MRI, severe mental and motor retardation [7]. In addition to Partington syndrome, dystonia was described in a few unpublished Australian and Norwegian cases [6], but G. Wohlrab (&) AE B. Schmitt AE E. Boltshauser Department of Neuropaediatrics and Neurophysiology, University Children’s Hospital, Steinwiesstrasse 75, 8032 Zurich, Switzerland E-mail: gabriele.wohlrab@kispi.unizh.ch Tel.: +41-1-2667701 Fax: +41-1-2667165

Thin corpus callosum and amyotrophy in spastic paraplegia--case report and review of literature.

We report the clinical, structural, functional and genetic characterization of a 37-year-old Caucasian female, presenting as a sporadic case of complicated spastic paraplegia with thin corpus callosum (CC), cognitive impairment, amyotrophy of the hand muscles and a sensorimotor neuropathy and review the literature for spastic paraplegia with thin CC. Magnetic resonance imaging (MRI) examination revealed a thin CC with fronto-parietal cortical atrophy. 18Fluordesoxyglucose positron emission tomography (FDG-PET) showed reduced cortical and thalamic metabolism. By transcranial magnetic stimulation, we delineated a severe impairment of transcallosal inhibition. Sequence analysis did not reveal disease causing mutations in the genes SLC12A6 (Andermann), Spastin (SPG 4), BSCL2 (SPG 17) and Spartin (SPG 20). We reviewed the literature for HSP with thin CC and found 113 HSP patients with thin CC previously described (35 with linkage to chromosome 15q13-15). Thin CC and peripheral neuropathy often appear together in spastic paraplegia and might be indicative for combined degeneration mechanism of central and peripheral axons.

POMT1-Associated Walker-Warburg Syndrome: A Disorder of Dendritic Development of Neocortical Neurons

We have analyzed the morphology and dendritic development of neocortical neurons in a 2.5-month-old infant with Walker-Warburg syndrome homozygotic for a novel POMT1 gene mutation, by Golgi methods. We found that pyramidal neurons frequently displayed abnormal (oblique, horizontal, or inverted) orientation. A novel finding of this study is that members of the same population of pyramidal neurons display different stages of development of their dendritic arborizations: some neurons had poorly developed dendrites and thus resembled pyramidal neurons of the late fetal cortex; for some neurons, the level of differentiation corresponded to that in the newborn cortex; finally, some neurons had quite elaborate dendritic trees as expected for the cortex of 2.5-month-old infant. In addition, apical dendrites of many pyramidal neurons were conspiciously bent to one side, irrespective to the general orientation of the pyramidal neuron. These findings suggest that Walker-Warburg lissencephaly is characterized by two hitherto unnoticed pathogenetic changes in the cerebral cortex: (a) heterochronic decoupling of dendritic maturation within the same neuronal population (with some members significantly lagging behind the normal maturational schedule) and (b) anisotropically distorted shaping of dendritic trees, probably caused by patchy displacement of molecular guidance cues for dendrites in the malformed cortex.