A novel SACS mutation results in non-ataxic spastic paraplegia and peripheral neuropathy.

BACKGROUND AND PURPOSE: Mutations in the SACS gene are commonly associated with autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS), a complex neurodegenerative disorder characterized by progressive degeneration of the cerebellum and spinal cord tracts. The aim of this study was to identify the genetic cause of the disease in an Italian family with spastic paraplegia and peripheral neuropathy. METHODS: Affected subjects were subjected to a comprehensive neurological examination including electromyography and brain magnetic resonance imaging. Genetic studies included exclusion of known disease genes, genome-wide linkage analysis using high density single nucleotide polymorphism genotyping and candidate gene sequencing. RESULTS: Molecular analyses revealed a novel missense mutation in the SACS gene (c.11,104A>G) occurring in a homozygous state in patients and absent in 700 Italian control chromosomes. The mutation led to the amino acid substitution p.Thr3702Ala in the sacsin protein, in a possible protein-protein interaction site of UBE3A binding domain. CONCLUSION: This study broadens the genetic spectrum of SACS mutations and expands the clinical ARSACS phenotype suggesting that the SACS gene can be considered in patients with non-canonical ARSACS clinical presentations.

Point mutations and a large intragenic deletion in SPG11 in complicated spastic paraplegia without thin corpus callosum.

BACKGROUND: Hereditary spastic paraplegia (HSP) with thin corpus callosum (HSP-TCC) is a frequent subtype of complicated HSP clinically characterised by slowly progressive spastic paraparesis with cognitive impairment and thin corpus callosum (TCC). SPG11, the gene associated with the major locus involved, encodes spatacsin, a protein of unknown function. METHODS: Different types of mutations were identified in patients with the complex form of HSP (cHSP) including TCC. We screened a series of 45 index patients with different types of cHSP with (n = 10) and without (n = 35) TCC. RESULTS: Ten mutations, of which five are novel, were detected in seven patients. Of importance, three out of seven mutated patients present with cHSP without TCC. Among the novel mutations identified, we characterised a large intragenic rearrangement deleting 2.6 kb of the SPG11 gene. The rearrangement is due to non-allelic homologous recombination between Alu sequences flanking the breakpoints. CONCLUSIONS: These findings expand the mutation spectrum of SPG11 and suggest that SPG11 mutations may occur more frequently in familial than sporadic forms of cHSP without TCC. This helps to define further clinical and molecular criteria for a correct diagnosis of the SPG11 related form of cHSP. In addition, the intragenic deletion detected here, and the mechanism involved, both provide clues to address the issue of SPG11 missing mutant alleles previously reported.

Facioscapulohumeral muscular dystrophy: epidemiological and molecular study in a north-east Italian population sample.

Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant disease associated with a partial deletion on chromosome 4q35. Few relevant investigations have been reported on its epidemiology and were essentially based on clinical diagnosis, having been performed before recognition of the molecular mutation. We report an epidemiological survey on FSHD patients, in which the diagnosis was obtained by combined clinical and molecular evaluation. The survey concerned the north-east Italian province of Padova, an area of 871,190 inhabitants (1 January 2004). We identified 40 patients affected by FSHD based on clinical diagnosis. In 33 of them, the EcoRI fragment size in the 4q35 region ranged from 14 to 35 kb. Four other patients belonging to the same family harbored a 38-kb fragment. In these four cases, the relationship between the borderline deletion with the mild FSHD phenotype was corroborated by additional haplotype reconstruction and segregation analysis. Interestingly, the same mild facial-sparing clinical pattern was apparent only in one other patient with an EcoRI fragment of 32 kb, suggesting that this unusual FSHD phenotype may be due to very small 4q35 deletions. On the whole, estimating a prevalence rate of 44 x 10(-6), our survey confirmed FSHD as one of the most frequent neuromuscular disorders in Western populations.

Rare Risk Variants Identification by Identity-by-Descent Mapping and Whole-Exome Sequencing Implicates Neuronal Development Pathways in Schizophrenia and Bipolar Disorder.

Schizophrenia (SCZ) and bipolar disorder (BPD) are highly heritable disorders with an estimated co-heritability of 68%. Hundreds of common alleles have been implicated, but recently a role for rare, high-penetrant variants has been also suggested in both disorders. This study investigated a familial cohort of SCZ and BPD patients from a closed population sample, where the high recurrence of the disorders and the homogenous genetic background indicate a possible enrichment in rare risk alleles. A total of 230 subjects (161 cases, 22 unaffected relatives, and 47 controls) were genetically investigated through an innovative strategy that integrates identity-by-descent (IBD) mapping and whole-exome sequencing (WES). IBD analysis allowed to track high-risk haplotypes (IBDrisk) shared exclusively by multiple patients from different families and possibly carrying the most penetrant alleles. A total of 444 non-synonymous sequence variants, of which 137 disruptive, were identified in IBDrisk haplotypes by WES. Interestingly, gene sets previously implicated in SCZ (i.e., post-synaptic density (PSD) proteins, voltage-gated calcium channels (VGCCs), and fragile X mental retardation protein (FMRP) targets) were found significantly enriched in genes carrying IBDrisk variants. Further, IBDrisk variants were preferentially affecting genes involved in the extracellular matrix (ECM) biology and axon guidance processes which appeared to be functionally connected in the pathway-derived meta-network analysis. Results thus confirm rare risk variants as key factors in SCZ and BPD pathogenesis and highlight a role for the development of neuronal connectivity in the etiology of both disorders.

A novel 9-bp insertion in the GJB1 gene causing a mild form of X-linked CMT with late onset.

X-linked Charcot-Marie-Tooth disease is the second most common variant of CMT. CMTX1 is caused by mutations in the GJB1 gene encoding for connexin 32. We describe an Italian family with an intermediate CMTX phenotype with late onset. Mutation screening of the GJB1 gene revealed a 9-bp duplication leading to the insertion of three aminoacids (Thr-Val-Phe) between the end of the second extracellular domain and the beginning of the fourth transmembrane domain. This is the third in-frame insertion in the GJB1 gene identified so far and, like the previous ones, it consists in the duplication of the flanking sequence which is repeated in tandem in the wild-type gene.

Cardiac involvement in Becker muscular dystrophy.

OBJECTIVES: The purpose of this study was to assess the incidence of myocardial involvement and the relation of cardiac disease to the molecular defect at the deoxyribonucleic acid (DNA) or protein level in Becker muscular dystrophy. BACKGROUND: Dystrophin gene mutations produce clinical manifestations of disease in the heart and skeletal muscle of patients with Becker muscular dystrophy. METHODS: Thirty-one patients underwent electrocardiographic and echocardiographic examination and 24-h Holter monitoring. The diagnosis was established by neurologic examination, dystrophin immunohistochemical assays or Western blot on muscle biopsy, or both, and DNA analysis. RESULTS: Electrocardiographic and echocardiographic findings were abnormal in 68% and 62% of the patients, respectively. Right ventricular involvement was detected in 52%. Left ventricular impairment was observed either as an isolated phenomenon (10%) or in association with right ventricular dysfunction (29%). Right ventricular disease was manifested in the teenagers, and an impairment of the left ventricle was observed in older patients. Right ventricular end-diastolic volumes were significantly increased compared with those in a control group. The left ventricular ejection fraction was significantly lower in older patients than in control subjects or younger patients. Life-threatening ventricular arrhythmias were detected in four patients. No correlations were found between skeletal muscle disease, cardiac involvement and dystrophin abnormalities. In our patients, exon 49 deletion was invariably associated with cardiac involvement. Exon 48 deletion was associated with cardiac disease in all but two patients. CONCLUSIONS: The cardiac manifestation of Becker muscular dystrophy is characterized by early right ventricular involvement associated or not with left ventricular impairment. Exon 49 deletion is associated with cardiac disease.

Genetic mapping of a susceptibility locus for disc herniation and spastic paraplegia on 6q23.3-q24.1.

It has been suggested that a genetic factor(s) or a familial predisposition may contribute to the clinical manifestations of disc herniation; moreover, no genetic linkage between spinal disc herniation and spastic paraplegia has ever been described. A family with consanguineous parents and four of eight sibs affected by multiple disc herniations and spastic paraplegia was clinically and genetically analysed. Surgery caused partial improvement in all of them. After the exclusion of type II collagen and vitamin D receptor genes and the recessive loci for HSPs, a genome wide search was performed with about 500 fluorescent markers. Positive lod score values were obtained for chromosome 6q22.31-q24.1, with evidence of three homozygous intervals. The maximum multipoint lod score of 3.28 was obtained in only one interval, between markers D6S1699 and D6S314. On the whole, a susceptibility locus for disc herniation and autosomal recessive spastic paraplegia was found on chromosome 6q23.3-q24.1. This is the first time that disc herniation and the associated neurological syndrome has been linked to a human chromosomal region.

Charcot-Marie-Tooth disease type I and related demyelinating neuropathies: Mutation analysis in a large cohort of Italian families.

Charcot-Marie-Tooth neuropathy type 1 (CMT1), the most common hereditary neurological disorder in humans, is characterized by clinical and genetic heterogeneity. It is caused mainly by a 1.5 Mb duplication in 17p11.2, but also by mutations in the myelin genes PMP22 (peripheral myelin protein 22), MPZ (myelin protein zero), Cx32 (connexin 32; also called GJB1), and EGR2 (early growth response 2). In this study, we have screened 172 index cases of Italian families in which there was at least one subject with a CMT1 diagnosis for the duplication on 17p11.2 and mutations in these genes. Among 170 informative unrelated patients, the overall duplication frequency was 57.6%. A difference could be observed between the duplication frequency in familial cases (71.6%) and that observed in non-familial cases (36.8%). Among the non-duplicated patients, 12 were mutated in Cx32, four in MPZ, two in PMP22, and none in the EGR2. In the non-duplicated cases, the overall point mutation frequency for these genes was 25.0%. We describe the mutations identified, and consider possible genotype-phenotype correlation.

Estimation of the mutation frequencies in Charcot-Marie-Tooth disease type 1 and hereditary neuropathy with liability to pressure palsies: a European collaborative study.

A European collaboration on Charcot-Marie-Tooth type 1 (CMT1) disease and hereditary neuropathy with liability to pressure palsies (HNPP) was established to estimate the duplication and deletion frequency, respectively, on chromosome 17p11.2 and to make an inventory of mutations in the myelin genes, peripheral myelin protein 22 (PMP22), myelin protein zero (MPZ) and connexin 32 (Cx32) located on chromosomes 17p11.2, 1q21-q23 and Xq13.1, respectively. In 70.7% of 819 unrelated CMT1 patients, the 17p11.2 duplication was present. In 84.0% of 156 unrelated HNPP patients, the 17p11.2 deletion was present. In the nonduplicated CMT1 patients, several different mutations were identified in the myelin genes PMP22, MPZ and Cx32.

Identification and characterization of C3orf6, a new conserved human gene mapping to chromosome 3q28.

This study reports the characterization of a novel human gene, chromosome 3 open reading frame 6 (C3orf6), mapped to chromosome 3q28, within the critical region of hereditary spastic paraplegia SPG14 locus. Based on computational "spliced" EST alignment and RT-PCR, two C3orf6 transcript variants were identified. The longer C3orf6 transcript contains a 1449-nt ORF, encoding a protein of 482 aa, while the shorter variant contains a 921-nt ORF, encoding for a protein of 306 aa. C3orf6 gene is organised on 12 exons and the shorter transcript comes from an alternative splicing event skipping exon 6. The two mRNA are differentially expressed in brain and in several other human tissues with a predominant level for the shorter transcript. By database analysis, EST assembling and RT-PCR, we identified the transcripts of mouse and rat C3orf6 orthologous genes. The involvement of C3orf6 in the spastic paraplegia was investigated by sequencing all coding exons and flanking sequences in the SPG14 family, excluding the presence of causative mutations.

Hereditary spastic paraplegia associated with peripheral neuropathy: a distinct clinical and genetic entity.

Hereditary motor and sensory neuropathy type V is a very rare disease in which hereditary spastic paraplegia is associated with peripheral motor and sensory neuropathy. The symptomatic onset of the disorder is usually in the second decade of life or later and the course is progressive over many years. Hereditary motor and sensory neuropathy type V is inherited as an autosomal dominant trait usually showing incomplete penetrance. So far, no molecular data are available in the literature about this disease. In our study we present clinical and molecular data from a large Italian family displaying hereditary motor and sensory neuropathy type V. Taking into account the clinical features in this family, we have performed a linkage analysis for markers strictly associated with all the known loci for autosomal dominant and autosomal recessive forms of hereditary spastic paraplegia and hereditary motor and sensory neuropathy type II, and have found no linkage to these loci. Our study suggests that hereditary motor and sensory neuropathy type V is not only a distinct clinical entity but also a distinct genetic entity.

Multipoint linkage mapping of the Emery-Dreifuss muscular dystrophy gene.

The clinical features to establish the diagnosis of X-linked Emery-Dreifuss muscular dystrophy (EMD) were recently redefined at the European EMD workshop in Baarn 1991. These criteria were used to select families from the literature and two new families for linkage analysis with the DNA markers F9, DX52, DXS15, F8C and DXS115. Recombinations are observed with the DNA markers F9, DXS52 and DXS15. No recombinations were found with F8C and DXS115. Multipoint linkage analysis indicates with a maximum location score of 73.9 that the EMD locus maps very close to F8C.

Discordant clinical outcome in type III spinal muscular atrophy sibships showing the same deletion pattern.

Three type III spinal muscular atrophy (SMA) families are described in which the same deletion pattern for SMN gene and flanking loci is apparent in both affected and unaffected siblings. Deletions extending to include the NAIP gene are reported in one sibship. All three individuals in which SMN and/or NAIP deletions were detected showed the same haplotypes for SMA linked microsatellite markers as their affected sibs. The three index cases had a SMA III with early onset (1.5-2 yr) and became chairbound at the age 4, 5 and 20 yr. The three haploidentical sibs were given a clinical severity score. One of them showed no sign of the disease at the age of 4 yr and was considered "unaffected"; a 35-yr-old female, who had no symptoms but showed tongue fasciculations and hand tremor was considered "asymptomatic"; a 34-yr-old female, who had mild muscular weakness since the age of 24, was rated "mild". These observations demonstrate the presence of a continuum of clinical variability within SMA III families. These data suggest that, in these three families at least, the SMA phenotype is caused or influenced by another gene(s) additional to SMN.

Problems in genetic counseling in a family with an "atypical" centronuclear myopathy.

Genetic counseling often deals with a rare disease the inheritance of which is not clearly established or in which genetic heterogeneity is reported. In addition, relevant parameters such as penetrance, gene frequency, and mutation rate may not be available. In this situation, establishing the risk may be very difficult. An example is presented in which Bayesian risk calculation proved to be of great help in providing precise risk estimates in a family in which an "atypical" centronuclear myopathy was segregating.

Genetic epidemiology of hereditary motor sensory neuropathies (type I).

Patients affected with hereditary motor sensory neuropathy (HMNS) type I were traced through hospital records. Each case was re-examined, a family history was drawn, and EMG examination was performed in those members of the family who could have inherited the trait. In the prevalence year 1987, in a population of 1,067,130 inhabitants of 2 contiguous provinces of northeast Italy, 100 living cases were recorded in 30 families, giving a minimal prevalence rate estimate of 9.37/100,000. HMSN I is inherited as an autosomal dominant trait, when clinical evaluation includes EMG. No difference may be established clinically between the 2 subtypes (Ia, linked to chromosome 1 and Ib, linked to chromosome 17). Sporadic cases are very rare and the mutation rate, including both the subtypes, is estimated between 3 and 6 X 10(-6).

Double missense mutation in exon 41 of the human dystrophin gene detected by double strand conformation analysis.

Development of late-onset Becker muscular dystrophy is reported in a patient whose two healthy brothers showed high serum creatine kinase level. No cases of neuromuscular disorders had been previously reported in this family. The analysis of the dystrophin gene showed that the three brothers had A-->C transversion at nucleotide 6092 in exon 41, a missense mutation which converts lysine into glutamine. The symptomatic patient showed an additional mutation in the same exon, a T-->C transition at nucleotide 6119, converting a phenylalanine to leucine. The possible pathogenic role of this mutation is discussed.

Occurrence of two different intragenic deletions in two male relatives affected with Duchenne muscular dystrophy.

The occurrence of 2 different intragenic deletions (exons 10-44 and exon 45, respectively) is reported in 2 male relatives affected with Duchenne muscular dystrophy, both showing the same haplotype for DNA markers not included in the deleted segment. The 2 different deletions seem to have occurred independently in the same X chromosome. This finding, together with other reports, suggests possibly an increased predisposition to mutations within the DMD locus in some families. Therefore, when dealing with prenatal diagnosis, the investigation on fetal DNA cannot be restricted only to the region in which a mutation was previously identified in the family.

Prediction of myotonic dystrophy clinical severity based on the number of intragenic [CTG]n trinucleotide repeats.

We carried out a genotype-phenotype correlation study, based on clinical findings in 465 patients with myotonic dystrophy (DM), in order to assess [CTG] repeat number as a predictive test of disease severity. Our analysis showed that the DM subtypes defined by strict clinical criteria fall into three different classes with a log-normal distribution. This distribution is useful in predicting the probability of specific DM phenotypes based on triplet [CTG] number. This study demonstrates that measurement of triplet expansions in patients' lymphocyte DNA is highly valuable and accurate for prognostic assessment.

High prevalence of chitotriosidase deficiency in Peruvian Amerindians exposed to chitin-bearing food and enteroparasites.

The human genome encodes a gene for an enzymatically active chitinase (CHIT1) located in a single copy on Chromosome 1, which is highly expressed by activated macrophages and in other cells of the innate immune response. Several dysfunctional mutations are known in CHIT1, including a 24-bp duplication in Exon 10 causing catalytic deficiency. This duplication is a common variant conserved in many human populations, except in West and South Africans. Thus it has been proposed that human migration out of Africa and the consequent reduction of exposure to chitin from environmental factors may have enabled the conservation of dysfunctional mutations in human chitinases. Our data obtained from 85 indigenous Amerindians from Peru, representative of populations characterized by high prevalence of chitin-bearing enteroparasites and intense entomophagy, reveal a very high frequency of the 24-bp duplication (47.06%), and of other single nucleotide polymorphisms which are known to partially affect enzymatic activity (G102S: 42.7% and A442G/V: 25.5%). Our finding is in line with a founder effect, but appears to confute our previous hypothesis of a protective role against parasite infection and sustains the discussion on the redundancy of chitinolytic function.