TANGO: a placebo-controlled randomized phase 2 study of efficacy and safety of the anti-tau monoclonal antibody gosuranemab in early Alzheimer's disease.

In Alzheimer's disease, the spread of aberrantly phosphorylated tau is an important criterion in the Braak staging of disease severity and correlates with disease symptomatology. Here, we report the results of TANGO ( NCT03352557 ), a randomized, double-blind, placebo-controlled, parallel-group and multiple-dose long-term trial of gosuranemab-a monoclonal antibody to N-terminal tau-in patients with early Alzheimer's disease. The primary objective was to assess the safety and tolerability of gosuranemab compared to placebo. The secondary objectives were to assess the efficacy of multiple doses of gosuranemab in slowing cognitive and functional impairment (using the Clinical Dementia Rating Scale Sum of Boxes (CDR-SB) scores at week 78) and evaluate the immunogenicity of gosuranemab (using the incidence of anti-gosuranemab antibody responses). Participants were randomized (n = 654); received (n = 650) low-dose (125 mg once every 4 weeks (q4w), n = 58; 375 mg q12w, n = 58), intermediate-dose (600 mg q4w, n = 106) or high-dose (2,000 mg q4w, n = 214) gosuranemab or placebo (q4w, n = 214) intravenously for 78 weeks; and assigned to cerebrospinal fluid (n = 327) and/or tau positron emission tomography (n = 357) biomarker substudies. Gosuranemab had an acceptable safety profile and was generally well tolerated (incidence of serious adverse events: placebo, 12.1%; low dose, 10.3%; intermediate dose, 12.3%; high dose, 11.7%). The incidence of treatment-emergent gosuranemab antibody responses was low at all time points. No significant effects were identified in cognitive and functional tests as no dose resulted in a favorable change from the baseline CDR-SB score at week 78 compared to placebo control (adjusted mean change: placebo, 1.85; low dose, 2.20; intermediate dose, 2.24; high dose, 1.85). At week 76, all doses caused significant (P < 0.0001) reductions in the cerebrospinal fluid levels of unbound N-terminal tau compared to placebo.

A novel pathogenic variant in DYNC1H1 causes various upper and lower motor neuron anomalies.

OBJECTIVE: To perform genotype-phenotype, clinical and molecular analysis in a large 3-generation family with autosomal dominant congenital spinal muscular atrophy. METHODS: Using a combined genetic approach including whole genome scanning, next generation sequencing-based multigene panel, whole genome sequencing, and targeted variant Sanger sequencing, we studied the proband and multiple affected individuals of this family who presented bilateral proximal lower limb muscle weakness and atrophy. RESULTS: We identified a novel heterozygous variant, c.1826T > C; p.Ile609Thr, in the DYNC1H1 gene localized within the common haplotype in the 14q32.3 chromosomal region which cosegregated with disease in this large family. Within the family, affected individuals were found to have a wide array of clinical variability. Although some individuals presented the typical lower motor neuron phenotype with areflexia and denervation, others presented with muscle weakness and atrophy, hyperreflexia, and absence of denervation suggesting a predominant upper motor neuron disease. In addition, some affected individuals presented with an intermediate phenotype characterized by hyperreflexia and denervation, expressing a combination of lower and upper motor neuron defects. CONCLUSION: Our study demonstrates the wide clinical variability associated with a single disease causing variant in DYNC1H1 gene and this variant demonstrated a high penetrance within this large family.

Research conference summary from the 2014 International Task Force on ATP1A3-Related Disorders.

OBJECTIVE: ATP1A3-related neurologic disorders encompass a broad range of phenotypes that extend well beyond initial phenotypic criteria associated with alternating hemiplegia of childhood (AHC) and rapid-onset dystonia parkinsonism. METHODS: In 2014, the Alternating Hemiplegia of Childhood Foundation hosted a multidisciplinary workshop intended to address fundamental challenges surrounding the diagnosis and management of individuals with ATP1A3-related disorders. RESULTS: Workshop attendees were charged with the following: (1) to achieve consensus on expanded diagnostic criteria to facilitate the identification of additional patients, intended to supplement existing syndrome-specific diagnostic paradigms; (2) to standardize definitions for the broad range of paroxysmal manifestations associated with AHC to disseminate to families; (3) to create clinical recommendations for common recurrent issues facing families and medical care providers; (4) to review data related to the death of individuals in the Alternating Hemiplegia of Childhood Foundation database to guide future efforts in identifying at-risk subjects and potential preventative measures; and (5) to identify critical gaps where we most need to focus national and international research efforts. CONCLUSIONS: This report summarizes recommendations of the workshop committee, highlighting the key phenotypic features to facilitate the diagnosis of possible ATP1A3 mutations, providing recommendations for genetic testing, and outlining initial acute management for common recurrent clinical conditions, including epilepsy.

Alternating Hemiplegia of Childhood: Retrospective Genetic Study and Genotype-Phenotype Correlations in 187 Subjects from the US AHCF Registry.

Mutations in ATP1A3 cause Alternating Hemiplegia of Childhood (AHC) by disrupting function of the neuronal Na+/K+ ATPase. Published studies to date indicate 2 recurrent mutations, D801N and E815K, and a more severe phenotype in the E815K cohort. We performed mutation analysis and retrospective genotype-phenotype correlations in all eligible patients with AHC enrolled in the US AHC Foundation registry from 1997-2012. Clinical data were abstracted from standardized caregivers' questionnaires and medical records and confirmed by expert clinicians. We identified ATP1A3 mutations by Sanger and whole genome sequencing, and compared phenotypes within and between 4 groups of subjects, those with D801N, E815K, other ATP1A3 or no ATP1A3 mutations. We identified heterozygous ATP1A3 mutations in 154 of 187 (82%) AHC patients. Of 34 unique mutations, 31 (91%) are missense, and 16 (47%) had not been previously reported. Concordant with prior studies, more than 2/3 of all mutations are clusteredin exons 17 and 18. Of 143 simplex occurrences, 58 had D801N (40%), 38 had E815K(26%) and 11 had G947R (8%) mutations [corrected].Patients with an E815K mutation demonstrate an earlier age of onset, more severe motor impairment and a higher prevalence of status epilepticus. This study further expands the number and spectrum of ATP1A3 mutations associated with AHC and confirms a more deleterious effect of the E815K mutation on selected neurologic outcomes. However, the complexity of the disorder and the extensive phenotypic variability among subgroups merits caution and emphasizes the need for further studies.

Resistance strength training exercise in children with spinal muscular atrophy.

INTRODUCTION: Preliminary evidence in adults with spinal muscular atrophy (SMA) and in SMA animal models suggests exercise has potential benefits in improving or stabilizing muscle strength and motor function. METHODS: We evaluated feasibility, safety, and effects on strength and motor function of a home-based, supervised progressive resistance strength training exercise program in children with SMA types II and III. Up to 14 bilateral proximal muscles were exercised 3 times weekly for 12 weeks. RESULTS: Nine children with SMA, aged 10.4 ± 3.8 years, completed the resistance training exercise program. Ninety percent of visits occurred per protocol. Training sessions were pain-free (99.8%), and no study-related adverse events occurred. Trends in improved strength and motor function were observed. CONCLUSIONS: A 12-week supervised, home-based, 3-day/week progressive resistance training exercise program is feasible, safe, and well tolerated in children with SMA. These findings can inform future studies of exercise in SMA.

Orthopedic Management of Scoliosis by Garches Brace and Spinal Fusion in SMA Type 2 Children.

BACKGROUND: Scoliosis is the most debilitating issue in SMA type 2 patients. No evidence confirms the efficacy of Garches braces (GB) to delay definitive spinal fusion. OBJECTIVE: Compare orthopedic and pulmonary outcomes in children with SMA type 2 function to management. METHOD: We carried out a monocentric retrospective study on 29 SMA type 2 children who had spinal fusion between 1999 and 2009. Patients were divided in 3 groups: group 1-French patients (12 children) with a preventive use of GB; group 2-French patients (10 children) with use of GB after the beginning of the scoliosis curve; and group 3-Italian patients (7 children) with use of GB after the beginning of the scoliosis curve referred to our centre to perform orthopedic preoperative management. RESULTS: Mean preoperative and postoperative Cobb angle were significantly lower in the group 1 of proactively braced than in group 2 or 3 (Anova p = 0.03; Kruskal Wallis test p = 0.05). Better surgical results were observed in patients with a minor preoperative Cobb angle (r = 0.92 p <  0.0001). Fewer patients in the group 1 proactively braced required trunk casts and/or halo traction and an additional anterior fusion in comparison with patients in the group 2 and 3. Moreover, major complications tend to be less in the group 1 proactively braced. No significant differences were found between groups in pulmonary outcome measures. CONCLUSIONS: A proactive orthotic management may improve orthopedic outcome in SMA type 2. Further prospective studies comparing SMA management are needed to confirm these results. LEVEL OF EVIDENCE: Therapeutic Level III. See Instructions to Authors on jbjs.org for a complete description of levels of evidence (Retrospective comparative study).

Spinal muscular atrophies.

Spinal muscular atrophies (SMA) are genetic disorders characterized by degeneration of lower motor neurons. The most frequent form is caused by mutations of the survival motor neuron 1 gene (SMN1). The identification of this gene greatly improved diagnostic testing and family-planning options of SMA families. SMN plays a key role in metabolism of RNA. However, the link between RNA metabolism and motor neuron degeneration remains unknown. A defect in mRNA processing likely generates either a loss of function of some critical RNA or abnormal transcripts with toxic property for motor neurons. Mutations of SMN in various organisms highlighted an essential role of SMN in motor axon and neuromuscular junction development or maintenance. The quality of life of patients has greatly improved over recent decades through the improvement of care and management of patients. In addition, major advances in translational research have been made in the field of SMA. Various therapeutic strategies have been successfully developed aiming at acting on SMN2, a partially functional copy of the SMN1 gene which remains present in patients. Drugs have been identified and some are already at preclinical stages. Identifying molecules involved in the SMA degenerative process should represent additional attractive targets for therapeutics in SMA.

De novo mutations in ATP1A3 cause alternating hemiplegia of childhood.

Alternating hemiplegia of childhood (AHC) is a rare, severe neurodevelopmental syndrome characterized by recurrent hemiplegic episodes and distinct neurological manifestations. AHC is usually a sporadic disorder and has unknown etiology. We used exome sequencing of seven patients with AHC and their unaffected parents to identify de novo nonsynonymous mutations in ATP1A3 in all seven individuals. In a subsequent sequence analysis of ATP1A3 in 98 other patients with AHC, we found that ATP1A3 mutations were likely to be responsible for at least 74% of the cases; we also identified one inherited mutation in a case of familial AHC. Notably, most AHC cases are caused by one of seven recurrent ATP1A3 mutations, one of which was observed in 36 patients. Unlike ATP1A3 mutations that cause rapid-onset dystonia-parkinsonism, AHC-causing mutations in this gene caused consistent reductions in ATPase activity without affecting the level of protein expression. This work identifies de novo ATP1A3 mutations as the primary cause of AHC and offers insight into disease pathophysiology by expanding the spectrum of phenotypes associated with mutations in ATP1A3.

Study of LPIN1, LPIN2 and LPIN3 in rhabdomyolysis and exercise-induced myalgia.

BACKGROUND: Recessive LPIN1 mutations were identified as a cause of severe rhabdomyolysis in pediatric patients. The human lipin family includes two other closely related members, lipin-2 and 3, which share strong homology and similar activity. The study aimed to determine the involvement of the LPIN family genes in a cohort of pediatric and adult patients (n = 171) presenting with muscular symptoms, ranging from severe (CK >10 000 UI/L) or moderate (CK <10 000 UI/L) rhabdomyolysis (n = 141) to exercise-induced myalgia (n = 30), and to report the clinical findings in patients harboring mutations. METHODS: Coding regions of LPIN1, LPIN2 and LPIN3 genes were sequenced using genomic or complementary DNAs. RESULTS: Eighteen patients harbored two LPIN1 mutations, including a frequent intragenic deletion. All presented with severe episodes of rhabdomyolysis, starting before age 6 years except two (8 and 42 years). Few patients also suffered from permanent muscle symptoms, including the eldest ones (≥ 40 years). Around 3/4 of muscle biopsies showed accumulation of lipid droplets. At least 40% of heterozygous relatives presented muscular myalgia. Nine heterozygous SNPs in LPIN family genes were identified in milder phenotypes (mild rhabdomyolysis or myalgia). These variants were non-functional in yeast complementation assay based on respiratory activity, except the LPIN3-P24L variant. CONCLUSION: LPIN1-related myolysis constitutes a major cause of early-onset rhabdomyolysis and occasionally in adults. Heterozygous LPIN1 mutations may cause mild muscular symptoms. No major defects of LPIN2 or LPIN3 genes were associated with muscular manifestations.

A rare recessive distal hereditary motor neuropathy with HSJ1 chaperone mutation.

OBJECTIVE: Distal hereditary motor neuropathies (dHMN) form a clinically and genetically heterogeneous group of disorders, characterized by muscle weakness and atrophy predominating at the distal part of the limbs, due to the progressive degeneration of motor neurons in the spinal cord. We report here a novel rare variant of dHMN with autosomal recessive inheritance in a large Jewish family originating from Morocco. The disease is characterized by a predominance of paralysis at the lower limbs and an early adulthood onset. We performed a genetic study in this family to identify and characterized the causing mutation. METHODS: Homozygosity mapping strategy and sequencing of the candidate genes were performed. Expression studies were made on patient fibroblasts. Functional experiments were performed on a cellular model of motor neuron disease. RESULTS: We mapped the disease to the 2q34-q36.1 chromosomal region and identified a homozygous splice mutation in the gene HSJ1 (DNAJB2) decreasing the expression of the 2 main isoforms HSJ1a and HSJ1b. Overexpression of both HSJ1a and HSJ1b reduced inclusion formation induced by the mutated SOD1-A4V in a neuronal cellular model. INTERPRETATION: HSJ1 is a neuronal enriched member of the HSP40/DNAJ co-chaperone family. Previous studies have shown that HSP40 proteins play a crucial role in protein aggregation and neurodegeneration in several neuronal types, in animal models and human diseases. Interestingly, this mutation causing a loss-of-function of HSJ1 is linked to a pure lower motor neuron disease, strongly suggesting that HSJ1 also plays an important and specific role in motor neurons.

Riluzole pharmacokinetics in young patients with spinal muscular atrophy.

AIMS: The objective of the present study was to assess the pharmacokinetics of riluzole in patients with spinal muscular atrophy (SMA). METHODS: Fourteen patients were enrolled in an open-label, nonrandomized and repeat-dose pharmacokinetic study. All participants were assigned to receive 50mg riluzole orally for 5 days. Riluzole plasma concentrations were determined from samples obtained at day 5. RESULTS: The pharmacokinetic analysis demonstrated that a dose of 50mg once a day was sufficient to obtain a daily total exposure [AUC(0,24h)=2257ng ml(-1) h] which was comparable with results obtained in adult healthy volunteers or ALS patients in whom a dose of 50mg twice a day is recommended. The pharmacokinetic simulation demonstrated that the administration of 50mg twice a day could result in higher concentrations, hence reduced safety margin. CONCLUSION: The dose of 50mg once a day was chosen for the clinical trial evaluating the efficacy of riluzole in SMA patients.

Early onset collagen VI myopathies: Genetic and clinical correlations.

OBJECTIVE: Mutations in the genes encoding the extracellular matrix protein collagen VI (ColVI) cause a spectrum of disorders with variable inheritance including Ullrich congenital muscular dystrophy, Bethlem myopathy, and intermediate phenotypes. We extensively characterized, at the clinical, cellular, and molecular levels, 49 patients with onset in the first 2 years of life to investigate genotype-phenotype correlations. METHODS: Patients were classified into 3 groups: early-severe (18%), moderate-progressive (53%), and mild (29%). ColVI secretion was analyzed in patient-derived skin fibroblasts. Chain-specific transcript levels were quantified by quantitative reverse transcriptase polymerase chain reaction (qRT-PCR), and mutation identification was performed by sequencing of complementary DNA. RESULTS: ColVI secretion was altered in all fibroblast cultures studied. We identified 56 mutations, mostly novel and private. Dominant de novo mutations were detected in 61% of the cases. Importantly, mutations causing premature termination codons (PTCs) or in-frame insertions strikingly destabilized the corresponding transcripts. Homozygous PTC-causing mutations in the triple helix domains led to the most severe phenotypes (ambulation never achieved), whereas dominant de novo in-frame exon skipping and glycine missense mutations were identified in patients of the moderate-progressive group (loss of ambulation). INTERPRETATION: This work emphasizes that the diagnosis of early onset ColVI myopathies is arduous and time-consuming, and demonstrates that quantitative RT-PCR is a helpful tool for the identification of some mutation-bearing genes. Moreover, the clinical classification proposed allowed genotype-phenotype relationships to be explored, and may be useful in the design of future clinical trials.

Paternal uniparental isodisomy of chromosome 6 causing a complex syndrome including complete IFN-gamma receptor 1 deficiency.

Mendelian susceptibility to mycobacterial disease (MSMD) is a rare primary immunodeficiency associated with clinical disease caused by weakly virulent mycobacterial species. Interferon gamma receptor 1 (IFN-gammaR1) deficiency is a genetic etiology of MSMD. We describe the clinical and genetic features of a 7-year-old Italian boy suffering from MSMD associated with a complex phenotype, including neonatal hyperglycemia, neuromuscular disease, and dysmorphic features. The child also developed necrotizing pneumonia caused by Rhodococcus equi. The child is homozygous for a nonsense mutation in exon 3 of IFNGR1 as a result of paternal uniparental disomy (UPD) of the entire chromosome 6. This is the first reported case of uniparental disomy resulting in a complex phenotype including MSMD.

The loss of the snoRNP chaperone Nopp140 from Cajal bodies of patient fibroblasts correlates with the severity of spinal muscular atrophy.

Spinal muscular atrophy (SMA) is a common autosomal recessive neurodegenerative disease caused by reduced survival motor neuron (SMN) levels. The assembly machinery containing SMN is implicated in the biogenesis of the spliceosomal small nuclear ribonucleoproteins (snRNPs). SMN is present in both the cytoplasm and nucleus, where it transiently accumulates in subnuclear domains named Cajal bodies (CBs) and functions in the maturation of snRNPs and small nucleolar (sno)RNPs. The impact of lowering SMN levels on the composition of CBs in SMA cells is still not completely understood. Here, we analyse the CB composition in immortalized and primary fibroblasts from SMA patients. We show that the U snRNA export factors PHAX and chromosome region maintenance 1 and the box C/D snoRNP core protein fibrillarin concentrate in CBs from SMA cells, whereas the box H/ACA core proteins GAR1 and NAP57/dyskerin show reduced CB localization. Remarkably, the functional deficiency in SMA cells is associated with decreased localization of the snoRNP chaperone Nopp140 in CBs that correlates with disease severity. Indeed, RNA interference knockdown experiments in control fibroblasts demonstrate that SMN is required for accumulation of Nopp140 in CBs. Conversely, overexpression of SMN in SMA cells restores the CB localization of Nopp140, whereas SMN mutants found in SMA patients are defective in promoting the association of Nopp140 with CBs. Taken together, we demonstrate that only a subset of CB functions (as indicated by the association of representative factors) are impaired in SMA cells and, importantly, we identify the decrease of Nopp140 localization in CBs as a phenotypic marker for SMA.

A sensitive assay for measuring SMN mRNA levels in peripheral blood and in muscle samples of patients affected with spinal muscular atrophy.

Different therapeutic strategies are currently evaluated in spinal muscular atrophy (SMA) that are aimed at increasing full-length (FL) mRNA levels produced from the SMN2 gene. Assays measuring SMN mRNA levels are needed. We have developed a sensitive, comparative assay based on multiplex fluorescent reverse-transcription polymerase chain reaction (RT-PCR) that can measure, in the same reaction, the levels of SMN mRNA with and without exon 7 sequences as well as those of total SMN mRNA. This assay allows to calculate directly the ratios of FL SMN mRNA to SMN mRNA without exon 7 (Delta7). We have used this assay to compare the levels of SMN transcripts in the blood of 75 unrelated normal subjects and of 48 SMA patients, and in muscle samples of 8 SMA patients. The SMN1 and the SMN2 genes produced very similar levels of total mRNA. Levels of transcripts lacking exon 7 were linearly dependent on the number of SMN2 copies, both in SMA patients and in controls. In patients, FL mRNA levels correlated with SMN2 copy number. A significant but weaker inverse correlation was also observed between FL or Delta7 mRNA levels and disease severity, but patients with three SMN2 copies and different SMA types displayed similar mRNA levels. A significantly higher FL to Delta7 ratio was measured in blood cells than in skeletal muscle (0.80+/-0.18 versus 0.47+/-0.11). This assay can be used as a sensitive biomarker for monitoring the effects of various drugs in forthcoming clinical trials of SMA.

The nuclear factor kappaB-activator gene PLEKHG5 is mutated in a form of autosomal recessive lower motor neuron disease with childhood onset.

Lower motor neuron diseases (LMNDs) include a large spectrum of clinically and genetically heterogeneous disorders. Studying a large inbred African family, we recently described a novel autosomal recessive LMND variant characterized by childhood onset, generalized muscle involvement, and severe outcome, and we mapped the disease gene to a 3.9-cM interval on chromosome 1p36. We identified a homozygous missense mutation (c.1940 T-->C [p.647 Phe-->Ser]) of the Pleckstrin homology domain-containing, family G member 5 gene, PLEKHG5. In transiently transfected HEK293 and MCF10A cell lines, we found that wild-type PLEKHG5 activated the nuclear factor kappa B (NF kappa B) signaling pathway and that both the stability and the intracellular location of mutant PLEKHG5 protein were altered, severely impairing the NF kappa B transduction pathway. Moreover, aggregates were observed in transiently transfected NSC34 murine motor neurons overexpressing the mutant PLEKHG5 protein. Both loss of PLEKHG5 function and aggregate formation may contribute to neurotoxicity in this novel form of LMND.

Distinct domains of the spinal muscular atrophy protein SMN are required for targeting to Cajal bodies in mammalian cells.

Mutations of the survival motor neuron gene SMN1 cause the inherited disease spinal muscular atrophy (SMA). The ubiquitous SMN protein facilitates the biogenesis of spliceosomal small nuclear ribonucleoproteins (snRNPs). The protein is detected in the cytoplasm, nucleoplasm and enriched with snRNPs in nuclear Cajal bodies. It is structurally divided into at least an amino-terminal region rich in basic amino acid residues, a central Tudor domain, a self-association tyrosine-glycine-box and an exon7-encoded C-terminus. To examine the domains required for the intranuclear localization of SMN, we have used fluorescently tagged protein mutants transiently overexpressed in mammalian cells. The basic amino acid residues direct nucleolar localization of SMN mutants. The Tudor domain promotes localization of proteins in the nucleus and it cooperates with the basic amino acid residues and the tyrosine-glycine-box for protein localization in Cajal bodies. Moreover, the most frequent disease-linked mutant SMNDeltaex7 reduces accumulation of snRNPs in Cajal bodies, suggesting that the C-terminus of SMN participates in targeting to Cajal bodies. A reduced number of Cajal bodies in patient fibroblasts associates with the absence of snRNPs in Cajal bodies, revealing that intranuclear snRNA organization is modified in disease. These results indicate that direct and indirect mechanisms regulate localization of SMN in Cajal bodies.

Brain MRI abnormalities in muscular dystrophy due to FKRP mutations.

INTRODUCTION: FKRP mutations cause a muscular dystrophy which may present in the neonatal period (MDC1C) or later in life (LGMD2I). Intelligence and brain imaging have been previously reported as being normal in FKRP-associated muscular dystrophy, except in rare cases presenting with mental retardation associated with structural brain abnormalities. PATIENTS AND METHODS: We studied cerebral MRIs in twelve patients with FKRP-associated muscular dystrophy presenting in infancy or early childhood, at ages between 14 months and 43 years. Two patients had severe cognitive deficits, four had mild-moderate mental retardation and the rest were considered to have normal intelligence. All, but one were wheelchair-bound and 7 were mechanically ventilated. RESULTS: Brain MRI was abnormal in 9 of 12 patients. Brain atrophy was seen in 8 patients. One child had isolated ventricular enlargement at 4 years. Cortical atrophy involved predominantly temporal and frontal lobes and was most important at later ages. In two cases with serial images this atrophy seemed progressive. Three patients, two with severe and one with moderate mental retardation, showed structural abnormalities of the posterior fossa with hypoplasia of the vermis and pons, and cerebellar hemispheric cysts. These abnormalities were stable with time. Two of these three patients also showed diffuse white matter abnormalities in early childhood, which regressed with time. CONCLUSIONS: MRI abnormalities are common in patients with FKRP-associated muscular dystrophy presenting at birth or in early childhood. Progressive brain atrophy is the most frequent finding. Posterior fossa malformations and transient white matter changes may be seen in patients with associated mental retardation.

Refined genetic mapping of autosomal recessive chronic distal spinal muscular atrophy to chromosome 11q13.3 and evidence of linkage disequilibrium in European families.

Chronic distal spinal muscular atrophy (Chronic DSMA, MIM (*)607088) is a rare autosomal recessive disorder characterized by a progressive motor weakness and muscular atrophy, predominating in the distal parts of the limbs. A form of Chronic DSMA gene has been previously mapped to chromosome 11q13 in the 10.3 cM interval defined by loci D11S1889 and D11S1321. By linkage analysis in 12 European Chronic DSMA families, we showed that a disease gene maps to chromosome 11q13.3 (Z(max)=6.66 at theta=0.00 at the DSM4 locus) and suggested that this condition is genetically homogeneous. Recombination events allowed us to reduce the genetic interval to a 2.6 cM region, telomeric to the IGHMBP2 gene, excluding this gene as the disease causing gene in Chronic DSMA. Moreover, partial linkage disequilibrium was found between three rare alleles at loci D11S1369, DSM4 and D11S4184 and the mutant chromosome in European patients. Analysis of the markers at these loci strongly suggests that most Chronic DSMA chromosomes are derived from a single ancestor. Refinement of the Chronic DSMA locus will hopefully allow to test candidate genes and lead to identification of the disease-causing mutations.