Refinement of the SPG9 locus on chromosome 10q23.3-24.2 and exclusion of candidate genes E. Panza a , T. Pippucci a , R. Cusano b , C. Lo Nigro c , L. Pradella a , S. Contardi d , G. A. Rouleau e , G. Stevanin f , R. Ravazzolo g , R. Liguori d , P. Montagna d , G. Romeo a and M. Seri a a Laboratory of Medical Genetics, Department of Internal Medicine, Cardioangiology and Hepatology, University of Bologna, Bologna; b Department of Oncology, Biology and Genetics (DOBiG), University of Genoa, Genoa; c Laboratory of Oncology, S. Croce e Carle Hospital, Cuneo; d Department of Neurological Science, University of Bologna, Bologna, Italy; e CHUM Research Center, Notre Dame Hospital, Montreal, East Montreal, Canada; f INSERM, UMR679, Pitie ´-Salpe ˆtrie `re Hospital, Paris Cedex, France; and g Laboratory of Molecular Genetics, Giannina Gaslini Institute, Genoa, Italy Keywords: positional candidate gene approach, refinement of candidate chromosomal region, SPG27, SPG33, SPG9 Received 23 October 2007 Accepted 8 February 2008 Background and purpose: The hereditary spastic paraplegias (HSPs) are a hetero- geneous group of neurodegenerative disorders, characterized by a progressive spas- ticity of the lower limbs. So far, 33 different loci (SPGs) have been mapped and the 15 genes responsible have been identified. We mapped a locus responsible for a form of spastic paraplegia, complicated by bilateral cataracts, gastroesophageal reflux with persisting vomiting and amyotrophy to chromosome 10q23.3–q24.2, in an Italian family. The critical region was in a 12 cm chromosomal interval between markers D10S564 and D10S603 (SPG9, MIM601162). In the same region, two other forms of HSP have been recently mapped: SPG27 and SPG33. In the latter case, the gene responsible has been identified. Materials and methods: To better characterize this region, we genotyped individuals from SPG9-linked families using additional markers and reduced the candidate region to a 4.8 Mb, excluding several genes by positional cloning. Results: The refined SPG9 locus is positioned completely within SPG27 and does not include the SPG33 gene. Discussion: Fifty-two transcripts are present in the refined critical region and 25 strong candidates have been excluded as disease causing genes by direct sequencing. Six of them were also excluded as responsible for SPG27. Introduction The hereditary spastic paraplegias (HSPs) are a clinically and genetically heterogeneous group of dis- orders characterized by progressive spastic weakness in the legs. They may be subclassified into pure (or uncomplicated) and complicated forms, according to the presence of additional neurological or non-neuro- logical features [1,2]. Autosomal dominant (AD), autosomal recessive (AR) and X-linked recessive forms of HSP have been recognized and the existence of multiple recessive and dominant types have been demonstrated. The complicated forms of HSP consist of a large number of rare conditions and they can be characterized by the presence of optic nerve involve- ment, pigmentary retinopathy, extra-pyramidal signs, distal amyotrophy, dementia, ataxia, skin lesions, oligophrenia, neuropathy, deafness and cone-shaped epiphyses [1–4]. To date, 33 HSP loci have been iden- tified. Despite the large and increasing number of autosomal HSP loci mapped, only 13 autosomal genes have been identified to date and a clear molecular basis for most forms of HSP remains elusive [5–7] (Table S1 in Supplementary Material). In 1999, we mapped the first genetic AD, complicated form of HSP, to chromosome 10q23.3–10q24.2 in a large Italian family. These patients presented congenital bilateral cataracts and developed later spasticity of the lower limbs. Other minor features included persistent vomiting, amyotrophy and peripheral neuropathy [8]. As we have described in a previous paper, we were able to confirm the linkage to SPG9 in another small British pedigree we had collected [9,10]. Two other forms of HSP have been mapped in the same region: SPG27 (MIM 609041) and SPG33 (MIM 610244). SPG27 is an AR uncomplicated form of HSP with adult onset, and it has been mapped by linkage analysis on chromosome 10q22.1–q24.1, overlapping the SPG9 locus [11]. Later, another family with an AR complicated form of HSP linked to SPG27 was described, possibly refining the critical region [12]. In 2006, through a two hybrid ap- proach, a new interactor of spastin termed ZFYVE27 Correspondence: Dr Emanuele Panza, Department of Internal Med- icine, Cardioangiology and Hepatology, University of Bologna, UO Medical Genetics, S. Orsola Malpighi General Hospital, Via Massarenti 9, 40138 Bologna, Italy (tel: +39-051-4294724; fax: +39-051-6364004; e-mail: emanuele.panza2@.unibo.it). 520 Ó 2008 The Author(s) Journal compilation Ó 2008 EFNS European Journal of Neurology 2008, 15: 520–524 doi:10.1111/j.1468-1331.2008.02117.x