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Autosomal recessive spastic paraplegia (SPG30) with mild ataxia and sensory neuropathy maps to chromosome 2q37.3

Stephan Klebe, Hamid Azzedine, Alexandra Durr, Patrick Bastien, Naima Bouslam, Nizar Elleuch, Sylvie Forlani, Celine Charon, Michel Koenig, Judith Melki, Alexis Brice, Giovanni Stevanin
DOI: http://dx.doi.org/10.1093/brain/awl012 1456-1462 First published online: 24 January 2006

Summary

The hereditary spastic paraplegias (HSPs) are a clinically and genetically heterogeneous group of neurodegenerative diseases characterized by progressive spasticity in the lower limbs. Twenty-nine different loci (SPG) have been mapped so far, and 11 responsible genes have been identified. Clinically, one distinguishes between pure and complex HSP forms which are variably associated with numerous combinations of neurological and extra-neurological signs. Less is known about autosomal recessive forms (ARHSP) since the mapped loci have been identified often in single families and account for only a small percentage of patients. We report a new ARHSP locus (SPG30) on chromosome 2q37.3 in a consanguineous family with seven unaffected and four affected members of Algerian origin living in Eastern France with a significant multipoint lod score of 3.8. Ten other families from France (n = 4), Tunisia (n = 2), Algeria (n = 3) and the Czech Republic (n = 1) were not linked to the newly identified locus thus demonstrating further genetic heterogeneity. The phenotype of the linked family consists of spastic paraparesis and peripheral neuropathy associated with slight cerebellar signs confirmed by cerebellar atrophy on one CT scan.

  • SPG30
  • chromosome 2q37.3
  • autosomal recessive spastic paraplegia
  • linkage

Introduction

The hereditary spastic paraplegias (HSPs) are a clinically and genetically heterogeneous group of neurodegenerative diseases characterized by progressive spasticity in the lower limbs. The mode of inheritance may be autosomal dominant, autosomal recessive (ARHSP) or X-linked. Twenty-nine different loci (SPG) have been mapped so far, and 11 responsible genes identified. The corresponding proteins are often involved in axonal trafficking or mitochondrial metabolism (Reid, 2003).

Clinically, one distinguishes between pure and complex forms of HSP (Durr and Brice, 2000; Tallaksen et al., 2001). In pure forms, clinical features consist of isolated pyramidal signs, such as brisk reflexes, Babinski sign, spasticity and motor deficit, which can be associated with sphincter disturbances and deep sensory loss. In the complex forms of HSP, the disease is variably associated with numerous combinations of neurological and extra-neurological signs such as cerebellar ataxia, dysarthria, mental retardation, peripheral neuropathy, optic atrophy, retinitis pigmentosa, hearing loss or thin corpus callosum.

Approximately 40% of dominant cases are explained by the known loci. Less is known about ARHSP since the mapped loci have been identified in few, often single, families and account for only a small percentage of patients. ARHSP is usually associated with clinically complex phenotypes but SPG5, SPG24 and SPG28 are considered to be pure forms of the disease (Bouslam et al., 2005; Hodgkinson et al., 2002; Meijer et al., 2004; Wilkinson et al., 2003).

In this study we report a new ARHSP locus on chromosome 2q37.3 in a consanguineous family of Algerian origin.

Patients and methods

Patients

Eleven families with ARHSP were selected (eight with a pure form and three with a complex form of ARHSP). They included 64 individuals, 27 of whom were affected. After written consent, all individuals were examined by a neurologist. Standardized charts were used for the clinical evaluations of all participants. An Algerian family (FSP-546; Fig. 1), with seven unaffected and four affected members, was included in a genome-wide scan. The other ten families originated from France (n = 4), Tunisia (n = 2), Algeria (n = 3) and the Czech Republic (n = 1).

Fig. 1

Pedigree of Family FSP-546. Haplotype reconstruction for nine microsatellite markers spanning ∼13 cM on chromosome 2 is shown. The code numbers of all sampled individuals are given below the symbols. Closed circles (women) and squares (men) indicate affected members. The homozygous haplotype assumed to carry the disease allele is flanked by closed boxes. Mb = megabase; cM = centimorgan.

DNA was extracted from blood samples using a standard protocol. Mutations in the SPG7 gene (paraplegin) (Casari et al., 1998) were excluded in the index patients of all families by dHPLC screening (Elleuch et al., 2006).

Genotyping

Microsatellite markers were amplified with fluorescent primers and the fragments resolved on an ABI-3730 sequencer (Applied Biosystems, Foster City, CA, USA). Genotypes were determined with the GeneMapper 3.5 software (Applied Biosystems).

The genome-wide scan in family FSP-546 was performed using 400 microsatellites spaced ∼10 cM (centimorgans) apart on all chromosomes. Pairwise and multipoint linkage analyses were performed using Fastlink 3.0 (Cottingham et al., 1993) and Allegro 1.2c software (Gudbjartsson et al., 2000). The disease was considered to be a fully penetrant autosomal recessive trait, with a disease allele frequency of 0.00005 and equal recombination fractions for males and females. Genetic distances were those of the Marshfield Centre for Medical Genetics and map positions were verified on the human genome sequence draft (NCBI and Ensembl centres).

Candidate gene analysis

Direct sequencing of all coding exons, their flanking splice sites and at least 50 bp of intronic sequence on each side of the STK25 gene was done using the BigDye terminator chemistry on an ABI-3730 sequencer (Applied Biosystems). The chromatogram profiles were analysed using Seqscape 2.5 software (Applied Biosystems). PCR primers and annealing conditions are available upon request.

Results

Mapping of SPG30

After exclusion of linkage to several known loci for ARHSP (SPG5, SPG11, SPG21, SPG24, SPG27, SPG28) and amyotrophic lateral sclerosis (ALS2 and ALS5) and in the absence of mutations in the SPG7 gene, a genome-wide screen in family FSP-546 provided evidence of linkage at two consecutive markers on chromosome 2 with a multipoint lod score of 3.8. Six other possible locations with multipoint lod scores >1 were detected on chromosomes 2, 7, 10, 11, 12 and 20, but were excluded when 25 additional markers were used (data not shown).

Analysis of nine additional microsatellite markers on chromosome 2 generated significant pairwise lod scores >3 (Table 1) at markers D2S2285 (z = 3.1) and D2S125 (z = 3.2). A maximal and significant multipoint lod score of 3.8 was obtained in the D2S2338–D2S2585 interval (Fig. 2), in agreement with haplotype reconstruction showing that all markers in this 5.1 cM interval were homozygous in affected patients (Fig. 1). This new locus was named SPG30 according to the HUGO nomenclature. This interval spans a 4 Mb region and contains 62 genes, one of which, STK25, that encodes a protein kinase involved in the response to environmental stress and in protein transport, did not have mutations/polymorphisms in the coding exons, in patients.

Fig. 2

Multipoint linkage analysis. Lod scores are plotted according to the genetic map of chromosome 2q. In bold are indicated the markers used for the genome scan. cM = centimorgan.

View this table:
Table 1

Pairwise lod scores calculated in family FSP-546 between the disease locus and 9 microsatellite markers on chromosome 2

MarkerLOD score at θ
0.00.010.050.10.20.30.4
D2S338−2.77−0.88−0.230.150.160.05
D2S345−2.35−0.84−0.22−0.010.090.070.01
D2S2338−2.45−0.96−0.36−0.17−0.06−0.010.01
D2S22853.113.052.792.471.801.120.44
D2S1253.233.172.912.581.901.200.50
D2S3951.351.331.221.080.790.490.20
D2S13782.802.742.502.201.570.940.33
D2S1401.421.401.291.140.840.530.22
D2S25850.851.321.331.050.640.23
  • LOD: logarithm of odds.

The interval between markers D2S2338 and D2S2585 was excluded in the other 10 ARHSP families by haplotype reconstruction and/or linkage analysis with multipoint lod scores below the threshold of −2 (data not shown).

Clinical features in family FSP-546

In the nuclear family FSP-546 (Fig. 1), there were nine siblings (six men, three women) born of parents who were first cousins. All 11 members were examined and sampled for DNA extraction. Four of the siblings (three men, one woman) were clinically affected and neurological examination was normal in the remaining children and both parents. The mean age at onset was 17.5 ± 4 years (12–21 years).

The overall picture was spastic gait with variable associated distal wasting, sensory neuropathy and cerebellar ataxia (Table 2).

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Table 2

Clinical characteristics of the 4 patients in family FSP-546

Clinical featuresPatients
004009010011
Age at onset (years)20172112
Age at examination (years)35272624
Disease duration (years)1510512
Functional impairmentCannot runMildCannot runCannot run
Spasticity
    at gaitModerateModerateModerateSevere
    at restModerateModerateModerateModerate
Increased reflexes in the LLYesYesYesYes
Extensor plantar reflexNoYesYesYes
Impaired pin-prick, vibrationNoYesYesNo
Finger nose testNoMildly cerebellarCerebellar left sideMildly cerebellar
Sphincter disturbancesNoMildNoMild
Saccadic ocular pursuitNoYesNoYes
Brain CT scann.dMild diffuse cerebellar atrophyn.dn.d
  • LL = lower limb; n.d = not done.

The index patient (FSP-546-004) was a 35-year-old man who first noticed stiff legs at age 20. At age 25, he was unable to run and had difficulty going down the stairs. Examination showed increased reflexes in the lower limbs (LL) and flexor plantar responses. Reflexes were normal in the upper limbs. Spasticity was moderate on gait and at rest with moderate weakness in the proximal LL. Muscle wasting in both legs was evident. Vibration sense and pinprick sensation were normal, and there were no sphincter disturbances or cerebellar signs.

His brother (FSP-546-009) complained at age 17 of a pricking sensation in the upper limbs. When he was examined at age 27 he could not stand with his feet in tandem position. There was moderate spasticity in his lower limbs at gait and rest. He had increased reflexes in his knees but not in his ankles and plantar reflexes were extensor. There was mild distal wasting in the lower limbs and some distal weakness. The finger–nose test showed cerebellar clumsiness. The patient also described mild sphincter disturbances. Distal touch/pinprick sensitivity was decreased in the legs, but vibration sense at the ankles was observed. Ocular gaze was normal except for saccadic pursuit. Decreased sensory but physiological motor amplitudes were recorded during nerve conduction studies (Table 3). Needle EMG showed a reduced recruitment pattern with some potentials firing at an increased rate, which is a sign of denervation. Cerebral CT scan performed at age 29 showed mild diffuse cerebellar atrophy.

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Table 3

Nerve conduction study in patient FSP 546-009

RightLeft
AmplitudeVelocity (m/s)AmplitudeVelocity (m/s)
Sensory
    Radial nerve (sensory)27 µV595 µV49
    Sural nerve4 µV532 µV50
Motor
    Common peroneal nerve2.8 mV523 mV53
    Deep peroneal nerve8 mV477 mV54

Their sister (FSP-546-010) a 26-year-old woman, first remarked unsteadiness and stiff legs at age 21. She suffered of a painful knee and spasticity was moderate in her lower limbs predominantly in her left leg, on gait and at rest. Clinical examination revealed increased reflexes in all limbs and a plantar extensor reflex on both sides. Finger–nose test was slightly cerebellar on the left side. Vibration sense was described as normal at the ankles. Pinprick sensation was decreased in both feet.

The youngest brother (FSP-546-11) fell accidentally at age 11, and thereafter unsteady gait and stiff legs symptoms developed. At age 19, he was moderately impaired but unable to run. Spasticity was severe at gait and muscle tonus increased at rest. He had increased reflexes in all limbs with ankles clonus and bilateral extensor plantar reflexes. There was mild wasting in the upper limbs. He reported having mild urinary urgency and painful legs. Ocular pursuit was saccadic.

Discussion

We mapped a novel ARHSP locus (SPG30) on chromosome 2q37.3 in a consanguineous Algerian family living in Eastern France. After exclusion of candidate SPG and ALS loci and of the other regions with a lod score >1 in the genome-wide scan, a single candidate region remained on chromosome 2. Fine mapping using nine additional markers and haplotype reconstruction narrowed the candidate region to a 4 Mb interval. Linkage to SPG30 was also excluded in 10 other ARHSP families who did not carry mutations in the SPG7 gene.

This is the first ARHSP locus found on chromosome 2 where two forms of ADHSP, SPG4—the most frequent—and SPG13, have also been located (Durr et al., 1996; Hansen et al., 2002). ALS2 (Alsin) (Yang et al., 2001) and a genetic form of a spastic cerebral palsy (McHale et al., 1999) also map to chromosome 2, although to different regions and differ clinically from SPG30 by the occurrence of bulbar and pseudobulbar signs (ALS2), mental retardation, epilepsy and quadriplegia (spastic cerebral palsy). The refined region contains 62 genes, several of which encode proteins potentially involved in HSP according to their physiological function (proteins involved in the molecular trafficking and mitochondrial metabolism). Point mutations in the STK25 gene, which encodes serine/threonine kinase 25, were excluded by direct sequencing. The screening of other candidate genes is under way.

In contrast to autosomal dominant HSP where two genes, SPG3 encoding atlastin-1 and SPG4 encoding spastin, account for a significant proportion of patients, ARHSP seems to be caused by a multiplicity of genes, as suggested by a number of new ARHSP loci published recently (Hodgkinson et al., 2002; Meijer et al., 2004; Bouslam et al., 2005; Wilkinson et al., 2005). SPG7, the most frequent form of ARHSP reported so far, which encodes paraplegin, explains only part of the ARHSP cases (Elleuch et al., 2006).

The phenotype of the SPG30 family consists of early onset and slowly progressive spastic paraparesis associated with slight cerebellar signs, such as saccadic ocular pursuit, finger–nose clumsiness, difficulty with tandem standing and cerebellar atrophy on CT scan, when performed. In addition, electrophysiological examination in one patient showed the presence of a peripheral polyneuropathy which was found clinically in another patient. Finally, disease progression seemed slow as all patients were able to walk after disease durations up to 15 years.

Phenotypical variability is observed in several ARHSP and the phenotype of SPG30 might be larger than observed in this Algerian family. Most of the families tested in the present study showed a pure ARHSP phenotype, whereas most of the known ARHSP forms, including SPG30, are described as complicated with additional neurological or other clinical features (Table 4). This may explain why we did not find other families linked to the SPG30 locus. Both, pure and complicated forms may, however, be linked to the same locus, as shown for SPG4 (Heinzlef et al., 1998), SPG7 (De Michele et al., 1998) and SPG27 (Ribai et al., 2006).

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Table 4

Known recessive forms of spastic paraplegia, chromosomal localization, gene product and phenotype

Gene symbolChromosomal locationGene productPhenotypeAge at onset (years)Cerebellar signs and/or atrophyPNPAdditional signs
SPG5 (Hentati et al., 1994; Wilkinson et al., 2003)8q–11q13Pure1–40No
SPG7 (Casari et al., 1998; DeMichele et al., 1998; Wilkinson et al., 2004)16q24.3ParapleginPure, complex11–42YesYesPes cavus, optic atrophy
SPG11 (Martinez Murillo et al., 1999)15q13–q15Pure, complex1–50NoMental retardation, pes cavus, thin CC
SPG14 (Vazza et al., 2000)3q27–q28Complex∼30NoYesPes cavus, mental retardation, visual agnosia, memory deficiency
SPG15 (Hughes et al., 2001)14q22–q24Complex13-23YesIntellectual deterioration, pigmented macula, CC and brainstem atrophy
SPG20 (Patel et al., 2002)13q12.3SpartinComplexEarly childhoodYesMental retardation, shortness of stature
SPG21 (Simpson et al., 2003)15q21–q22MaspardinComplex20–40YesYesExtrapyramidal syndrome, dementia, thin CC, periventricular white matter hyperintensities, cataract, dystonia, chorea, hand muscle atrophy
SPG23 (Blumen et al., 2003)1q24–q32ComplexEarly childhoodNoAbnormalities of skin and hair pigmentation, facial and skeletal dysmorphism, postural tremor, cognitive impairment
SPG24 (Hodgkinson et al., 2002)13q14Pure1No
SPG25 (Zortea et al., 2002)6q23-q24.1Complex30–46NoYesMultiple disc herniation, bilateral cataract, congenital glaucoma
SPG26 (Wilkinson et al., 2005)12p11.1–12q14Complex22–42NoYesEmotional lability, tongue tremor, mild intellectual impairment
SPG27 (Meijer et al., 2004; Ribai et al., 2006)10–q22.1–q24.1Pure, complex2–45YesYesMental retardation, microcephaly, facial dysmorphia, blepharophimosis, skeletal dysmorphism
SPG28 (Bouslam et al., 2005)14q21.3–q22.3Pure6–15NoPes cavus and scoliosis in 1 patient
SPG302q37.3Complex12–21YesYes
Spastic cerebral palsy (McHale et al., 1999)2p24–25ComplexEarly childhoodMental retardation, epilepsy, microcephaly
  • CC = corpus callosum; PNP = peripheral polyneuropathy.

Although spastic paraparesis is clearly the major sign in SPG30, superficial examination could miss the associated neurological signs (e.g. cerebellar signs) leading to the initial diagnosis of pure and not complicated HSP. This finding is important in clinical practice since many forms of ARHSP present with additional cerebellar signs (6/14 ARHSP loci, Table 4) which may be overlooked when examining patients with prominent spasticity. The mild cerebellar involvement which was found in this new form of ARHSP is similar to that observed in patients with SPG7 (paraplegin) mutations, which was also initially thought to be a pure ARHSP (De Michele et al., 1998). Recent studies have shown, however, that mild cerebellar signs and/or cerebellar atrophy on brain imaging are almost constant in SPG7 (Elleuch et al., 2006). Several other forms of ARHSP are also associated with neuropathy (Table 4) and its association with cerebellar ataxia is not specific to SPG30 but can also be found in SPG7, SPG21 and SPG27.

In conclusion we have mapped a novel locus (SPG30) to chromosome 2q37.3 that is responsible for a new autosomal recessive form of complicated HSP. This is the first step towards the identification of a new gene crucial for understanding the underlying pathophysiology of HSP.

Electronic sources

Mashfield Centre for Medical Genetics: http://www.marshfieldclinic.org/genetics

National Centre of Biological Investigation (NCBI): http://www.ncbi.nlm.nih.gov

Ensembl genome browser: http://www.ensembl.org

Human Genome Organisation (HUGO): http://www.gene.ucl.ac.uk/hugo/

Acknowledgments

The technical help of the DNA and cell bank of the Federative Institute for Neuroscience is gratefully acknowledged and the authors thank Dr Merle Ruberg for critical review of the manuscript and Drs P. Couthino, A. Lossos, C. Tallaksen, M. Tazir and P. Vondracek for patient referral. This work was financially supported by the VERUM foundation (München, Germany) (to A.B.) and the GIS-Maladies Rares (to G.S. and A.D.). S.K. was supported by the post-doctoral programme of the German Academic Exchange Service (DAAD, Germany), the VERUM foundation and the Tom-Wahlig foundation (Münster, Germany). N.B. and N.E. received fellowships from the French association against Friedreich Ataxia (AFAF) and the association Connaître les Syndromes Cérébelleux (CSC, France), respectively.

References

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