Neuromuscular Disorders, Vol. 1, No. 5, pp. 327-331, 1991 0960-8966/91 $3.00 + 0.00 Printed in Great Britain ~t" 1992 Pergamon Press pie MAPPING OF DYSTROPHIN BRAIN PROMOTER: A DELETION OF THIS REGION IS COMPATIBLE WITH NORMAL INTELLECT JOHANT. DENDUNNEN,* t LETIZIA CASULA, *+ ADINAMAKOVER,§ BERT BAKKER,* DAVIDYAFFE,§URI NUDEL§ and GERT-JAN B. VANOMMEN* *Department of Human Genetics,LeidenUniversity,Leiden,The Netherlands; and, §:~Departmentof Cell Biology, The Weizmann Institute of Science,Rehovot,Israel (Received2 August 1991; revised24 September1991) Abstract--Using a mouse genomic fragment containing the brain-specific promoter region of the dystrophin gene, we have located the brain promoter 75-300 kb proximal of the muscle promoter. Within our DMD-families we detected a patient who lacks both the brain-specific and muscle-specific promoter sequences. The normal intellectual capabilities of the patient argue against an indispensable role of the brain-specific first exon in mental functioning. The possibility exists that a NH2-terminally truncated dystrophin has taken over the function of the normal dystrophins in brain and/or muscle. Key words: Duchenne muscular dystrophy (DMD), Becker muscular dystrophy (BMD), brain promoter, mental retardation. INTRODUCTION The Duchenne muscular dystrophy (DMD) gene has been shown to measure 2.3 million base pairs (Mb) [1]. It encodes a 427 kiloDalton cyto- skeletal protein, dystrophin [2], located at the sarcolemma of skeletal, smooth and heart mus- cle. An isoform of dystrophin, a product of the same gene, is present in the brain [2~,]. Studies have demonstrated that expression of the gene in the brain [5-10] and in neuronal cultures [7, 8], is driven by a different promoter. The amino- terminal amino acids of the brain and muscle dystrophin differ due to the splicing of two different first exons, to a common second exon [5, 6]. In addition to the severe muscle degeneration, some 30% of the patients suffer from mental retardation [11]. The molecular basis of this association is not understood yet. The discovery of dystrophin in the brain has raised the possibility that its absence or malfunction is causally related to mental retardation. We have used the brain-specific probe to locate the brain-specific promoter region 5' of the muscle-specific promoter of the human dystrophin tAuthor to whom correspondence should be addressed at: Department of Human Genetics,State University of Leiden, Wassenaarseweg 72, 2333 AL Leiden,The Netherlands. SPresent address: Istituto di Clinica e Biologiadell 'eta' Evolutiva, UniversityCagliari, Cagliari, Italy. gene. The existence of two promoters in the human dystrophin gene implies the possibility of deletion mutations affecting one or both promo- ters. Using the appropriate probes, we have screened our Duchenne and Becker muscular dystrophy (BMD) patients and found one in- teresting case; a patient who had normal intellectual capabilities despite a deletion of both promoters [12]. MATERIALS AND METHODS DNA probes Probe Pb was a subcloned 1462 base pair (bp) mouse genomic NdeI-fragment containing the promoter region, the first exon, and sequences from intron 1 of the brain-specific dystrophin gene transcript [10]. Dystrophin specific cDNA sequences have been described by Koenig et al. [13]. PCR detection of the muscle-specific exon 1 sequences (Pro) was performed according to Beggs et aL [14]. Patient data Patient DL52.6 was diagnosed as suffering from DMD. The first signs of his disease ap- peared when he was 15 months old. He became wheelchair bound at the age of 11. At that time, CPK-levels showed a 10-fold increase, the EMG was myopathic and the muscle biopsy showed severe atrophy but no necrosis. Subsequently he 327