Novel locus for autosomal dominant hereditary spastic paraplegia, on chromosome 8q.

Hereditary spastic paraplegia (HSP) is a clinically and genetically heterogeneous group of disorders characterized by insidiously progressive spastic weakness in the legs. Genetic loci for autosomal dominant HSP exist on chromosomes 2p, 14q, and 15q. These loci are excluded in 45% of autosomal dominant HSP kindreds, indicating the presence of additional loci for autosomal dominant HSP. We analyzed a Caucasian kindred with autosomal dominant HSP and identified tight linkage between the disorder and microsatellite markers on chromosome 8q (maximum two-point LOD score 5.51 at recombination fraction 0). Our results clearly establish the existence of a locus for autosomal dominant HSP on chromosome 8q23-24. Currently this locus spans 6.2 cM between D8S1804 and D8S1774 and includes several potential candidate genes. Identifying this novel HSP locus on chromosome 8q23-24 will facilitate discovery of this HSP gene, improve genetic counseling for families with linkage to this locus, and extend our ability to correlate clinical features with different HSP loci.     

Hereditary spastic paraplegia: LOD-score considerations for confirmation of linkage in a heterogeneous trait.

Hereditary spastic paraplegia (HSP) is a degenerative disorder of the motor system, defined by progressive weakness and spasticity of the lower limbs. HSP may be inherited as an autosomal dominant (AD), autosomal recessive, or an X-linked trait. AD HSP is genetically heterogeneous, and three loci have been identified so far: SPG3 maps to chromosome 14q, SPG4 to 2p, and SPG4a to 15q. We have undertaken linkage analysis with 21 uncomplicated AD families to the three AD HSP loci. We report significant linkage for three of our families to the SPG4 locus and exclude several families by multipoint linkage. We used linkage information from several different research teams to evaluate the statistical probability of linkage to the SPG4 locus for uncomplicated AD HSP families and established the critical LOD-score value necessary for confirmation of linkage to the SPG4 locus from Bayesian statistics. In addition, we calculated the empirical P-values for the LOD scores obtained with all families with computer simulation methods. Power to detect significant linkage, as well as type I error probabilities, were evaluated. This combined analytical approach permitted conclusive linkage analyses on small to medium-size families, under the restrictions of genetic heterogeneity.     

NIPA1 gene mutations cause autosomal dominant hereditary spastic paraplegia (SPG6)

The hereditary spastic paraplegias (HSPs) are genetically heterogeneous disorders characterized by progressive lower-extremity weakness and spasticity. The molecular pathogenesis is poorly understood. We report discovery of a dominant negative mutation in the NIPA1 gene in a kindred with autosomal dominant HSP (ADHSP), linked to chromosome 15q11-q13 (SPG6 locus); and precisely the same mutation in an unrelated kindred with ADHSP that was too small for meaningful linkage analysis. NIPA1 is highly expressed in neuronal tissues and encodes a putative membrane transporter or receptor. Identification of the NIPA1 function and ligand will aid an understanding of axonal neurodegeneration in HSP and may have important therapeutic implications.     

Pure hereditary spastic paraparesis: an exclusion map covering more than 40% of the autosomal genome

Pure hereditary spastic paraparesis (HSP) is an upper motor neuron syndrome clinically characterized by slowly progressive weakness and spasticity of the legs. To determine the chromosomal location of the genetic defect, a five-generational Dutch family with autosomal dominant pure HSP was subjected to linkage studies. Analysis was carried out on 48 members spanning three generations, of whom 23 individuals are definitely affected. By screening the genome with a total of 167 microsatellite markers distributed over all autosomes, an exclusion map for HSP was constructed. Depending on the actual size of the human genome, our exclusion map covered between 40% and 65% of its autosomal length. Loci on chromosomes 1, 8, 13, 14, and 18 showed slightly positive lod scores. The areas around these loci were investigated more closely, but no conclusive evidence for, or against, linkage could be obtained.     

A new locus for autosomal recessive spastic paraplegia associated with mental retardation and distal motor neuropathy, SPG14, maps to chromosome 3q27-q28

Hereditary spastic paraplegias (HSPs), a group of neurodegenerative disorders that cause progressive spasticity of the lower limbs, are characterized by clinical and genetic heterogeneity. To date, three loci for autosomal recessive HSP have been mapped on chromosomes 8p, 16q, and 15q. After exclusion of linkage at these loci, we performed a genomewide search in a consanguineous Italian family with autosomal recessive HSP complicated by mild mental retardation and distal motor neuropathy. Using homozygosity mapping, we obtained positive LOD scores for markers on chromosome region 3q27-q28, with a maximum multipoint LOD score of 3.9 for marker D3S1601. Haplotype analysis allowed us to identify a homozygous region (4.5 cM), flanked by markers D3S1580 and D3S3669, that cosegregates with the disease. These data strongly support the presence, on chromosome 3q27-28, of a new locus for complicated recessive spastic paraplegia, which we have named "SPG14."     

The gene for Treacher Collins syndrome maps to the long arm of chromosome 5.

Treacher Collins syndrome (TCS) is an autosomal dominant disorder of craniofacial development, the features of which include conductive hearing loss and cleft palate. We have studied 12 unrelated TCS families with multiple affected individuals for linkage to five chromosome 5 markers. There is strong evidence demonstrating linkage to three of these markers. Multipoint linkage analysis places the mutation causing TCS in the interval between the gene for the glucocorticoid receptor and the anonymous marker D5S22, with a maximum multipoint lod score of 9.1.     

Genetic heterogeneity in multiple epiphyseal dysplasia.

Multiple epiphyseal dysplasia (MED) comprises a group of hereditary chondrodysplasias in which there are major anatomic abnormalities of the long tubular bones. The Fairbank and Ribbing types are the most frequently cited types of MED. They are primarily defined radiographically and are autosomal dominant conditions. Recently, MED in one family was shown to map to the pericentromeric region of chromosome 19 and is probably allelic to pseudoachondroplasia. We have tested linkage with six short tandem repeat markers from chromosome 19 to autosomal dominant MED in one four-generation family and to MED in a unique family with three of seven siblings affected and with unaffected parents. Autosomal dominant MED in family 1 was linked with a maximum LOD score, at D19S212, of 3.22 at a recombination fraction (theta) of .00. Linkage to chromosome 19 was excluded with MED in the other family, under both autosomal recessive and autosomal dominant, with either reduced-penetrance or germ line-mosaicism models. Linkage to candidate genes COL9A1, COL9A2, and COL11A2 was tested and excluded for both genetic models in this family. COL11A1 was excluded under a recessive model. We have confirmed linkage of autosomal dominant Fairbank MED to chromosome 19 and have demonstrated that MED is genetically heterogeneous.     

Genetic linkage of hereditary gingival fibromatosis to chromosome 2p21.

Gingival fibromatosis is characterized by a slowly progressive benign enlargement of the oral gingival tissues. The condition results in the teeth being partially or totally engulfed by keratinized gingiva, causing aesthetic and functional problems. Both genetic and pharmacologically induced forms of gingival fibromatosis are known. The most common genetic form, hereditary gingival fibromatosis (HGF), is usually transmitted as an autosomal dominant trait, although sporadic cases are common and autosomal recessive inheritance has been reported. The genetic basis of gingival fibromatosis is unknown. We identified an extended family (n=32) segregating an autosomal dominant form of isolated gingival fibromatosis. Using a genomewide search strategy, we identified genetic linkage (Zmax=5.05, straight theta=.00) for the HGF phenotype to polymorphic markers in the genetic region of chromosome 2p21 bounded by the loci D2S1788 and D2S441. This is the first report of linkage for isolated HGF, and the findings have implications for identification of the underlying genetic basis of gingival fibromatosis.     

Autosomal dominant familial spastic paraplegia: tight linkage to chromosome 15q.

Autosomal dominant, uncomplicated familial spastic paraplegia (FSP) is a genetically heterogeneous disorder characterized by insidiously progressive lower-extremity spasticity. Recently, a locus on chromosome 14q was shown to be tightly linked with the disorder in one of three families. We performed linkage analysis in a kindred with autosomal dominant uncomplicated FSP. After excluding the chromosome 14q locus, we observed tight linkage of the disorder to a group of markers on chromosome 15q (maximum two-point lod score 9.70; theta = .05). Our results clearly establish the existence of a locus for autosomal dominant FSP in the centromeric region of chromosome 15q. Comparing clinical and genetic features in FSP families linked to chromosome 14q with those linked to chromosome 15q may provide insight into the pathophysiology of this disorder.     

Resolution of the two loci for autosomal dominant aniridia, AN1 and AN2, to a single locus on chromosome 11p13.

Two distinct loci have been proposed for aniridia; AN1 for autosomal dominant aniridia on chromosome 2p and AN2 for the aniridia in the WAGR contiguous gene syndrome on chromosome 11p13. In this report, the kindred segregating for autosomal dominant aniridia, which suggested linkage to acid phosphatase-1 (ACP1) and led to the assignment of the AN1 locus on chromosome 2p, has been updated and expanded. Linkage analysis between the aniridia phenotype and ACP1 does not support the original linkage results, excluding linkage up to theta = 0.17 with Z = -2. Tests for linkage to other chromosome 2p markers. APOB, D2S71, D2S5, and D2S1, also excluded linkage to aniridia. Markers that have been isolated from the chromosome 11p13 region were then analyzed in this aniridia family. Two RFLPs at the D11S323 locus give significant evidence for linkage. The PvuII polymorphism detected by probe p5S1.6 detects no recombinants, with a maximum lod score of Z = 6.97 at theta = 0.00. The HaeIII polymorphism detected by the probe p5BE1.2 gives a maximum lod score of Z = 2.57 at theta = 0.00. Locus D11S325 gives a lod score of Z = 1.53 at theta = 0.00. These data suggest that a locus for aniridia (AN1) on chromosome 2p has been misassigned and that this autosomal dominant aniridia family is segregating for an aniridia mutation linked to markers in the 11p13 region.     

Human spastin has multiple microtubule-related functions

Hereditary spastic paraplegias (HSPs) are neurodegenerative diseases caused by mutations in more than 20 genes, which lead to progressive spasticity and weakness of the lower limbs. The most frequently mutated gene causing autosomal dominant HSP is SPG4, which encodes spastin, a protein that belongs to the family of ATPases associated with various cellular activities (AAAs). A number of studies have suggested that spastin regulates microtubule dynamics. We have studied the ATPase activity of recombinant human spastin and examined the effect of taxol-stabilized microtubules on this activity. We used spastin translated from the second ATG and provide evidence that this is the physiologically relevant form. We showed that microtubules enhance the ATPase activity of the protein, a property also described for katanin, an AAA of the same spastin subgroup. Furthermore, we demonstrated that human spastin has a microtubule-destabilizing activity and can bundle microtubules in vitro, providing new insights into the molecular pathogenesis of HSP.     

A new locus for autosomal recessive hereditary spastic paraplegia maps to chromosome 16q24.3.

Hereditary spastic paraplegia is a genetically and phenotypically heterogeneous disorder. Both pure and complicated forms have been described, with autosomal dominant, autosomal recessive, and X-linked inheritance. Various loci (SPG1-SPG6) associated with this disorder have been mapped. Here, we report linkage analysis of a large consanguineous family affected with autosomal recessive spastic paraplegia with age at onset of 25-42 years. Linkage analysis of this family excluded all previously described spastic paraplegia loci. A genomewide linkage analysis showed evidence of linkage to chromosome 16q24.3, with markers D16S413 (maximum LOD score 3.37 at recombination fraction [theta] of .00) and D16S303 (maximum LOD score 3.74 at straight theta=.00). Multipoint analysis localized the disease gene in the most telomeric region, with a LOD score of 4.2. These data indicate the presence of a new locus linked to pure recessive spastic paraplegia, on chromosome 16q24.3, within a candidate region of 6 cM.     

A locus for autosomal dominant "pure" hereditary spastic paraplegia maps to chromosome 19q13

Genetic loci for autosomal dominant pure hereditary spastic paraplegia (ADPHSP) have been mapped to chromosomes 2p, 8q, 12q, 14q, and 15q. We undertook a genomewide linkage screen of a large family with ADPHSP, for which linkage at all previously identified ADPHSP loci was excluded. Analysis of markers on chromosome 19q gave a peak pairwise LOD score of 3.72 at D19S420, allowing assignment of a novel ADPHSP locus (which we have termed "SPG12") to this region. Haplotype construction and analysis of recombination events narrowed the SPG12 locus to a 16.1-cM region between markers D19S868 and D19S902.     

Autosomal dominant aniridia linked to the chromosome 11p13 markers catalase and D11S151 in a large Dutch family

In a large pedigree with autosomal dominant aniridia, we found close linkage between the aniridia locus AN2 and the markers catalase (CAT) (zeta = 7.27 at theta = 0.00) and D11S151 (zeta = 3.86 at theta = 0.10) flanking the AN2 locus on 11p13. Positive lod scores were also obtained for the 11p13----11p14 markers D11S16 and FSHB with the linkage group CAT/AN2/D11S151. We conclude that the autosomal dominant aniridia in this family is due to a mutation at the AN2 locus on 11p13. We have excluded linkage (zeta less than -2 at theta less than 0.18) between the aniridia and the chromosome 2p25 marker D2S1 (linked to ACP1).     

Genetic localization of a newly recognized autosomal dominant limb-girdle muscular dystrophy with cardiac involvement (LGMD1B) to chromosome 1q11-21.

Limb-girdle muscular dystrophy (LGMD) constitutes a clinically and genetically heterogeneous group of myogenic disorders with a limb-girdle distribution of weakness. One autosomal dominant family, LGMD1A, has been linked to chromosome 5q, whereas in other autosomal dominant families linkage to this chromosome has been excluded. We studied 58 members of three families with a newly recognized autosomal dominantly inherited LGMD with cardiac involvement. A search with highly polymorphic microsatellite markers was carried out. The gene for this newly recognized dominant form of LGMD was located on chromosome 1q11-21, with a combined maximum two-point LOD score >12 at theta = 0.     

Hereditary spastic paraplegia SPG13 is associated with a mutation in the gene encoding the mitochondrial chaperonin Hsp60

SPG13, an autosomal dominant form of pure hereditary spastic paraplegia, was recently mapped to chromosome 2q24-34 in a French family. Here we present genetic data indicating that SPG13 is associated with a mutation, in the gene encoding the human mitochondrial chaperonin Hsp60, that results in the V72I substitution. A complementation assay showed that wild-type HSP60 (also known as "HSPD1"), but not HSP60 (V72I), together with the co-chaperonin HSP10 (also known as "HSPE1"), can support growth of Escherichia coli cells in which the homologous chromosomal groESgroEL chaperonin genes have been deleted. Taken together, our data strongly indicate that the V72I variation is the first disease-causing mutation that has been identified in HSP60.     

Genetic linkage studies with cleft lip and palate: report of two family studies

Genetic linkage studies are reported on two families with cleft lip +/- cleft palate. For the first family (LP01) the etiology of the clefting is unknown, and the linkage analyses were done assuming both autosomal dominant and autosomal recessive inheritance. Close linkage is rejected with the Duffy blood group under the dominant model and with four loci (Duffy, Kidd, and ABO blood groups and haptoglobin) under the recessive model. The second family (LP02) is a Mexican-American family segregating the van der Woude syndrome with lip pits. The linkage analyses for this autosomal dominant trait excluded close linkage with seven genetic markers, including three on chromosome one. The maximum lod scores were 0.6 with BF (chromosome 6) and 0.4 with the P blood group, which is not yet mapped.     

Refinement of the "Silver syndrome locus" on chromosome 11q12-q14 in four families and exclusion of eight candidate genes

Silver syndrome is a rare variant of autosomal dominant complicated hereditary spastic paraparesis (HSP), in which spasticity of the lower limbs is accompanied by amyotrophy of the hands and occasionally also the lower limbs. The disease locus has been mapped to chromosome 11q12-q14. We report four Austrian families presenting with the typical clinical features of Silver syndrome. Sixteen individuals were affected upon clinical and/or electrophysiological examination. Ten persons showed mild to severe spasticity of the lower limbs. Wasting of the small hand muscles was present in nine affected family members of whom three had also gait disturbance. Three further individuals were asymptomatic. Electrophysiological studies showed normal or slightly to moderately slowed motor nerve conduction velocities, reduced amplitudes and occasionally chronodispersion of compound motor action potentials. In one patient, conduction block was observed. Sensory nerve action potentials were usually normal. Molecular genetic studies demonstrate linkage to chromosome 11q12-q14. Haplotype analysis in affected individuals indicates a common ancestor in the four families. By recombination analysis in affected individuals the Silver syndrome candidate gene interval can be reduced from 13 to 5.9 cM and can now be placed between the markers D11S1765 and D11S987. By sequence analysis of affected individuals eight functional and positional candidate genes could be excluded. Our study confirms the existence of the Silver syndrome locus on chromosome 11q12-q14 and provides the first report of nerve conduction velocity studies in Silver syndrome, which demonstrate the presence of a peripheral predominantly motor neuropathy.     

Linkage of hereditary distal myopathy with desmin accumulation to 2q

We are investigating the genetics of a large family with an autosomal dominant form of hereditary distal myopathy. This slowly progressive myopathy begins during early adulthood in the distal leg muscles, producing a gait disturbance. Cardiomyopathy is also present in most affected family members, manifesting itself as conduction block or congestive heart failure. Histologically, an accumulation of the protein, desmin, occurs in the subsarcolemmal spaces of myofibers. We have performed linkage analyses of this family, and have mapped the location of the gene causing the myopathy to human chromosome 2q33. The gene is within a 17-cM segment of chromosome 2q bounded by the DNA markers D2S2248 and D2S401. The best candidate gene for this myopathy is desmin.     

Linkage to chromosome 2q36.1 in autosomal dominant Dandy-Walker malformation with occipital cephalocele and evidence for genetic heterogeneity

We previously reported a Vietnamese-American family with isolated autosomal dominant occipital cephalocele. Upon further neuroimaging studies, we have recharacterized this condition as autosomal dominant Dandy-Walker with occipital cephalocele (ADDWOC). A similar ADDWOC family from Brazil was also recently described. To determine the genetic etiology of ADDWOC, we performed genome-wide linkage analysis on members of the Vietnamese-American and Brazilian pedigrees. Linkage analysis of the Vietnamese-American family identified the ADDWOC causative locus on chromosome 2q36.1 with a multipoint parametric LOD score of 3.3, while haplotype analysis refined the locus to 1.1 Mb. Sequencing of the five known genes in this locus did not identify any protein-altering mutations. However, a terminal deletion of chromosome 2 in a patient with an isolated case of Dandy-Walker malformation also encompassed the 2q36.1 chromosomal region. The Brazilian pedigree did not show linkage to this 2q36.1 region. Taken together, these results demonstrate a locus for ADDWOC on 2q36.1 and also suggest locus heterogeneity for ADDWOC.