K. Wagner

Heterozygous missense mutations in BSCL2 are associated with distal hereditary motor neuropathy and Silver syndrome

Distal hereditary motor neuropathy (dHMN) or distal spinal muscular atrophy (OMIM #182960) is a heterogeneous group of disorders characterized by an almost exclusive degeneration of motor nerve fibers, predominantly in the distal part of the limbs. Silver syndrome (OMIM #270685) is a rare form of hereditary spastic paraparesis mapped to chromosome 11q12–q14 (SPG17) in which spasticity of the legs is accompanied by amyotrophy of the hands and occasionally also the lower limbs. Silver syndrome and most forms of dHMN are autosomal dominantly inherited with incomplete penetrance and a broad variability in clinical expression. A genome-wide scan in an Austrian family with dHMN-V (ref. 4) showed linkage to the locus SPG17, which was confirmed in 16 additional families with a phenotype characteristic of dHMN or Silver syndrome. After refining the critical region to 1 Mb, we sequenced the gene Berardinelli-Seip congenital lipodystrophy (BSCL2) and identified two heterozygous missense mutations resulting in the amino acid substitutions N88S and S90L. Null mutations in BSCL2, which encodes the protein seipin, were previously shown to be associated with autosomal recessive Berardinelli-Seip congenital lipodystrophy (OMIM #269700). We show that seipin is an integral membrane protein of the endoplasmic reticulum (ER). The amino acid substitutions N88S and S90L affect glycosylation of seipin and result in aggregate formation leading to neurodegeneration.

Phenotype–genotype correlations in a CMT2B family with refined 3q13-q22 locus

Objective: To perform genotype–phenotype correlation and genetic linkage analysis in a family with axonal Charcot-Marie-Tooth (CMT) syndrome and ulcero-mutilating features. Background: CMT2B is a rare disorder belonging to the group of axonal CMT syndromes that is clinically characterized by marked distal muscle weakness and wasting as well as a high frequency of foot ulcers, infections, and amputations. So far only two families with this disorder have been described in which molecular genetic studies have shown evidence of autosomal dominant inheritance with linkage to chromosome 3q13-q22. Methods: The authors report a large Austrian family presenting with the typical clinical features of CMT2B. Detailed clinical and electrophysiologic data were obtained in 15 at-risk individuals and DNA samples from 19 family members were collected for genetic linkage studies. Results: Eight family members were definitely affected upon clinical and electrophysiologic examination and the majority revealed pronounced distal muscle wasting and weakness as well as prominent sensory abnormalities, which were frequently complicated by infections and amputations. Electrophysiologic studies showed normal or slightly to moderately slowed motor nerve conduction velocities, markedly reduced compound motor action potential amplitudes with chronodispersion, and absent or reduced amplitudes of sensory nerve action potentials. The molecular genetic study demonstrates linkage to chromosome 3q13-q22. Haplotype analysis in affected individuals indicates that the CMT2B locus is located between the flanking markers D3S1589 and D3S1549, representing a region of 10 cM. Conclusions: This family is the third CMT2B family reported so far and confirms the existence of the CMT2B locus on chromosome 3q13-q22, which is responsible for a clinically and electrophysiologically homogeneous disorder with prominent distal muscle weakness and wasting, and ulcero-mutilating features. Marked sensory disturbances and the high frequency of foot ulcers, infections, and amputations in our patients seem to be typical for CMT2B. Recombination events in affected individuals reduce the CMT2B candidate gene interval considerably from 25 to 10 cM.–1557

Mutations in B4GALNT1 (GM2 synthase) underlie a new disorder of ganglioside biosynthesis

Glycosphingolipids are ubiquitous constituents of eukaryotic plasma membranes, and their sialylated derivatives, gangliosides, are the major class of glycoconjugates expressed by neurons. Deficiencies in their catabolic pathways give rise to a large and well-studied group of inherited disorders, the lysosomal storage diseases. Although many glycosphingolipid catabolic defects have been defined, only one proven inherited disease arising from a defect in ganglioside biosynthesis is known. This disease, because of defects in the first step of ganglioside biosynthesis (GM3 synthase), results in a severe epileptic disorder found at high frequency amongst the Old Order Amish. Here we investigated an unusual neurodegenerative phenotype, most commonly classified as a complex form of hereditary spastic paraplegia, present in families from Kuwait, Italy and the Old Order Amish. Our genetic studies identified mutations in B4GALNT1 (GM2 synthase), encoding the enzyme that catalyzes the second step in complex ganglioside biosynthesis, as the cause of this neurodegenerative phenotype. Biochemical profiling of glycosphingolipid biosynthesis confirmed a lack of GM2 in affected subjects in association with a predictable increase in levels of its precursor, GM3, a finding that will greatly facilitate diagnosis of this condition. With the description of two neurological human diseases involving defects in two sequentially acting enzymes in ganglioside biosynthesis, there is the real possibility that a previously unidentified family of ganglioside deficiency diseases exist. The study of patients and animal models of these disorders will pave the way for a greater understanding of the role gangliosides play in neuronal structure and function and provide insights into the development of effective treatment therapies.

Hypomorphic PCNA mutation underlies a human DNA repair disorder

Numerous human disorders, including Cockayne syndrome, UV-sensitive syndrome, xeroderma pigmentosum, and trichothiodystrophy, result from the mutation of genes encoding molecules important for nucleotide excision repair. Here, we describe a syndrome in which the cardinal clinical features include short stature, hearing loss, premature aging, telangiectasia, neurodegeneration, and photosensitivity, resulting from a homozygous missense (p.Ser228Ile) sequence alteration of the proliferating cell nuclear antigen (PCNA). PCNA is a highly conserved sliding clamp protein essential for DNA replication and repair. Due to this fundamental role, mutations in PCNA that profoundly impair protein function would be incompatible with life. Interestingly, while the p.Ser228Ile alteration appeared to have no effect on protein levels or DNA replication, patient cells exhibited marked abnormalities in response to UV irradiation, displaying substantial reductions in both UV survival and RNA synthesis recovery. The p.Ser228Ile change also profoundly altered PCNAs interaction with Flap endonuclease 1 and DNA Ligase 1, DNA metabolism enzymes. Together, our findings detail a mutation of PCNA in humans associated with a neurodegenerative phenotype, displaying clinical and molecular features common to other DNA repair disorders, which we showed to be attributable to a hypomorphic amino acid alteration.

Ulcero-mutilating neuropathy in an Austrian kinship without linkage to hereditary motor and sensory neuropathy IIB and hereditary sensory neuropathy I loci

Objective: To elucidate genetic heterogeneity in ulcero-mutilating neuropathy. Background: Ulcero-mutilating features and sensory loss have been observed in hereditary sensory neuropathy (HSN) and hereditary motor and sensory neuropathy (HMSN). HSN is characterized by marked distal sensory loss, frequent toe and foot ulcerations, osteomyelitis, and necrosis, which may be complicated by toe or limb amputations. Motor and autonomic nerve involvement can also occur to a variable degree. Recently, autosomal-dominant HSN type I was mapped to chromosome 9q22 in four families. In two other families with ulcero-mutilating neuropathy, a gene locus was assigned to chromosome 3q13-q22. Because motor symptoms were prominent in these latter two kinships, the disease was designated HMSN type IIB or Charcot–Marie–Tooth type 2B (CMT2B) neuropathy. Methods: We report detailed clinical, electrophysiologic, and genetic data on a large Austrian family with ulcero-mutilating neuropathy, sensory loss, and amputations. Results: Linkage analysis with chromosomal markers representing the HSN I and HMSN IIB loci excluded these gene loci in our family. Conclusions: These findings therefore indicate the existence of a third gene locus in autosomal-dominant inherited ulcero-mutilating neuropathies, showing that these neuropathies are genetically highly heterogeneous.

Mutation of HERC2 causes developmental delay with Angelman-like features

Background Deregulation of the activity of the ubiquitin ligase E6AP (UBE3A) is well recognised to contribute to the development of Angelman syndrome (AS). The ubiquitin ligase HERC2, encoded by the HERC2 gene is thought to be a key regulator of E6AP. Methods and results Using a combination of autozygosity mapping and linkage analysis, we studied an autosomal-recessive neurodevelopmental disorder with some phenotypic similarities to AS, found among the Old Order Amish. Our molecular investigation identified a mutation in HERC2 associated with the disease phenotype. We establish that the encoded mutant HERC2 protein has a reduced half-life compared with its wild-type counterpart, which is associated with a significant reduction in HERC2 levels in affected individuals. Conclusions Our data implicate a model in which disruption of HERC2 function relates to a reduction in E6AP activity resulting in neurodevelopmental delay, suggesting a previously unrecognised role of HERC2 in the pathogenesis of AS.

Late onset Charcot-Marie-Tooth 2 syndrome caused by two novel mutations in the MPZ gene

MPZ gene mutations cause demyelinating and axonal Charcot–Marie–Tooth (CMT) disease. Two novel MPZ mutations are reported in very late onset and progressive CMT syndrome. The N60H caused axonal CMT in a large family, whereas the I62M occurred in a single patient presenting with a primary axonal neuropathy. Previously, chronic polyradiculoneuritis was assumed in two patients. Molecular genetic testing and particularly screening for MPZ mutations in late onset neuropathies are important to differentiate acquired and inherited neuropathies.

Molecular characterisation of a 3.5 Mb interstitial 14q deletion in a child with several phenotypic anomalies

Interstitial deletions of the long arm of chromosome 14 are infrequent. Molecular and clinical studies on patients with deletions involving 14q11.2-q21 have recently been reported.1 Most of these deletion patients share common clinical signs, such as midline defects of the central nervous system, feeding problems, growth abnormalities, hypotonia, developmental delay, mental retardation, and craniofacial anomalies.1 Here we present the phenotypic, cytogenetic, and molecular genetic findings of a 2½12 year old boy with a 14q12-q13.1 deletion. To our knowledge this is the second case described of a patient with a deletion of less than 3.5 Mb within chromosome bands 14q12-q13.1. Using the genomic sequence between markers D14S1060 and D14S286, we have constructed a transcription map of the genomic interval deleted in our patient. Our proband (fig 1) is the 40 week product of a second, uncomplicated pregnancy and delivery. Maternal age was 27 years. Birth weight was 4435 g (>90th centile), length 55 cm (>90th centile), and head circumference 34 cm (10th-25th centile). Apgar score was 7/9/10. The neonatal period was complicated by pneumonia, treated with parenteral antibiotic therapy over 10 days. Besides relative microcephaly, hypertelorism, epicanthic folds, a long and flat philtrum, hypodontia, laterally placed, hypoplastic mamillae, second degree hypospadias, bifid scrotum, and bilateral cryptorchidism were noticed. Cranial ultrasound was normal; ultrasound of the kidneys and pelvic region showed bilateral second degree hydronephrosis, and both testes were visible in the inguinal region. Screening for connatal infections (toxoplasmosis, rubella, cytomegalovirus, and parvovirus B19) was negative. Psychomotor development was severely impaired from early infancy. Lack of vision was evident at 3 months and, apart from head control, no gain of motor milestones or social contact was achieved until the age of 29 months. Muscle tone of the trunk was decreased while it was increased and dystonic in the upper and …

Assignment1 of the human GABAA receptor delta-subunit gene (GABRD) to chromosome band 1p36.3 distal to marker NIB1364 by radiation hybrid mapping

The gamma-aminobutyric acid type A (GABAA; Kuriyama et al., 1993) receptor represents a mechanism integral in functioning of the central nervous system and a locus for the action of many moodand emotion-altering agents such as benzodiazepines, barbiturates, steroids, and alcohol. Anxiety syndromes, sleep disorders, and convulsive disorders have been treated with therapeutic agents that enhance the action of gamma-aminobutyric acid (GABA) at the GABAA receptor or increase the concentration of GABA in nervous tissue (Rabow et al., 1995). GABAA receptors are heterooligomeric ligandgated ion channels that mediate the effect of the inhibitory neurotransmitter GABA which represents the main means of synaptic inhibition in neuronal tissue. The GABAA receptors consist of at least 15 different receptor subunits that can be classified into five subfamilies (alpha, beta, gamma, delta, rho). Sommer et al. isolated and characterized the murine gene for the GABAA receptor delta subunit (GABRD) by high-resolution mapping and DNA sequencing and they localized the human delta subunit gene to the short arm of chromosome 1. Materials and methods

Localization1 of the human anterior gradient-2 gene (AGR2) to chromosome band 7p21.3 by radiation hybrid mapping and fluorescencein situ hybridisation

Kuang et al. (1998) isolated 29 gene fragments that were coexpressed with ER (estrogen receptor) in breast carcinoma cell lines using the technique of suppression subtractive hybridization. One of these gene fragments, DEME-2 (GenBank EST accession AA506763), could be identified as a part of the human Anterior Gradient-2 (AGR2) gene, the human homologue of the Xenopus laevis cement gland gene Xenopus Anterior Gradient-2 (XAG-2, GenBank accession AF025474; Aberger et al., 1998; Thompson et al., 1998). The 1,702 nucleotide cDNA sequence of AGR2 was obtained by combination of sequence data derived from three individual mRNA transcripts differing in their 3)-untranslated regions (GenBank accession No. AF007791 for AGR2/C, AF038452 for AGR2/I and AF038451 for AGR2/R; Thompson et al., 1998). Detailed chromosome mapping of this gene will be important to explore its genomic organization, its regulation and therefore its function in hormone-responsive breast carcinomas. Materials and methods