Intranuclear inclusions, neuronal loss and CAG mosaicism in two patients with Machado–Joseph disease E. Mun ˜oz a , M.J. Rey b , M. Mila ` c , A. Cardozo b , T. Ribalta b , E. Tolosa a,b , I. Ferrer b, * a Neurology Service, Hospital Clinic and University of Barcelona, Institut d’Investigacions Biome `diques August Pi i Sunyer (IDIBAPS), Barcelona, Spain b Neurological Tissues Bank, Hospital Clinic and University of Barcelona, Institut d’Investigacions Biome `diques August Pi i Sunyer (IDIBAPS), Barcelona, Spain c Genetics Service, Hospital Clinic and University of Barcelona, Institut d’Investigacions Biome `diques August Pi i Sunyer (IDIBAPS), Barcelona, Spain Received 10 October 2001; received in revised form 19 April 2002; accepted 22 April 2002 Abstract The presence of neuronal intranuclear inclusions (NIIs) and neuronal mosaicism has been described in some autosomal dominant spinocerebellar ataxias (SCA), but their implication in neurodegenerative mechanisms still remains unclear. Objective: To investigate the correlation between neuronal loss and NIIs, and the size of CAG triplet expansion in selected areas of the CNS in two SCA3 patients. Material and methods: Postmortem neuropathological study was carried out, and the regional distribution of neuronal loss was compared with NIIs. CAG expansion was analysed by PCR amplification in the same regions. Results: Marked neuronal loss was seen in the anterior horn of the spinal cord, pontine nuclei and motor nuclei of the brain stem. Moderate neurone loss was found in the locus ceruleus, colliculus and substantia nigra. Loss of granule and Purkinje cells was found in the cerebellum, mainly in the vermis. NIIs were present in neurones of the involved nuclei of the anterior horn of the spinal cord, medulla oblongata and pons, but not in the locus ceruleus, substantia nigra and cerebellum. A few NIIs were found in the striatum. The number of CAG repeats was 27/70 in the first patient and 21/74 in the second patient. The variation of the expanded allele size among different cerebral areas was F 1 – 3 CAG repeats. Conclusion: The partial correlation between neuronal loss and NIIs suggests that other factors distinct from NII formation may be involved in the neuronal death. Moreover, the low degree of mosaicism between regions without neuronal loss and regions with marked neuronal loss points to the existence of selective cellular vulnerability to the genetic defect. D 2002 Elsevier Science B.V. All rights reserved. Keywords: CAG; Neuronal loss; SCA 1. Introduction Spinocerebellar ataxias (SCA) constitute a heterogeneous group of diseases clinically characterised by a progressive cerebellar syndrome, but also with symptoms and signs suggesting involvement of the brain stem, spinal cord, basal ganglia or peripheral nerves in many cases. The CAG repeat expansion in a specific locus in different chromosomes is the mutation responsible for autosomal dominant ataxias such as SCA1, SCA2, SCA3, SCA6, SCA7, dentato– rubro–pallido–luysian atrophy (DRPLA) and SCA12. The CAG expansion is translated except in SCA12 into a protein that is expanded in polyglutamine residues. The number of CAG repeats influences the age at onset and the disease severity in many cases. SCA3 or Machado–Joseph disease is associated with the CAG expansion on the chromosome 14q32.1 [1] that results in the abnormal expression of the polyglutamine-expanded mutant protein ataxin-3. Both the normal and mutant ataxin-3 are widely expressed in all regions of the brain [2,3]. It has been proposed that this abnormal expanded protein is the cause of the neuronal death in vitro and in vivo [4]. However, the mechanism of mutant ataxin-3-induced cell death is poorly understood. It has been suggested that the formation of neuronal intra- nuclear inclusions (NIIs) is a common pathogenic mecha- nism involved in the neurodegeneration in most of the CAG triplet-repeat disorders [5], including SCA3 [6,7]. The corresponding expanded and normal protein and ubiquitin are components of NIIs [6]. The formation of NIIs still remains unclear, but the presence of the mutated protein in 0022-510X/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII:S0022-510X(02)00110-7 * Corresponding author. Institut de Neuropatologia, Servei Anatomia Patolo `gica, Hospital Princeps d’Espanya, Universitat de Barcelona, carrer Feixa Llarga sn, 08907 Hospitalet de Llobregat, Spain. Tel.: +34-93-403- 5808; fax: +34-93-204-5065. E-mail address: iferrer@sakma.es (I. Ferrer). www.elsevier.com/locate/jns Journal of the Neurological Sciences 200 (2002) 19 – 25