title: Unaffected patients with a homozygous absence of the SMN1 gene.
abstract: In this report, we present three families in which we identified asymptomatic carriers of a homozygous absence of the SMN1 gene. In the first family, the bialleleic deletion was found in three of four siblings: two affected brothers (SMA type 3a and 3b) and a 25-years-old asymptomatic sister. All of them have four SMN2 copies. In the second family, four of six siblings are affected (three suffer from SMA2 and one from SMA3a), each with three SMN2 copies. The clinically asymptomatic 47-year-old father has the biallelic deletion and four SMN2 copies. In the third family, the biallelic SMN1 absence was found in a girl affected with SMA1 and in her healthy 53-years-old father who had five SMN2 copies. Our findings as well as those of other authors show that an increased number of SMN2 copies in healthy carriers of the biallelic SMN1 deletion is an important SMA phenotype modifier, but probably not the only one.
authors.affiliation: Neuromuscular Unit, Mossakowski Medical Research Centre, Polish Academy of Sciences, Warsaw, Poland. mariaj@cmdik.pan.pl
authors.forename: Maria
authors.initials: M
authors.lastname: Jedrzejowska
authors.forename: Janina
authors.initials: J
authors.lastname: Borkowska
authors.forename: Janusz
authors.initials: J
authors.lastname: Zimowski
authors.forename: Anna
authors.initials: A
authors.lastname: Kostera-Pruszczyk
authors.forename: Michał
authors.initials: M
authors.lastname: Milewski
authors.forename: Marta
authors.initials: M
authors.lastname: Jurek
authors.forename: Danuta
authors.initials: D
authors.lastname: Sielska
authors.forename: Ewa
authors.initials: E
authors.lastname: Kostyk
authors.forename: Walenty
authors.initials: W
authors.lastname: Nyka
authors.forename: Jacek
authors.initials: J
authors.lastname: Zaremba
authors.forename: Irena
authors.initials: I
authors.lastname: Hausmanowa-Petrusewicz
mesh_terms: D000293:Adolescent; D000328:Adult; D002478:Cells, Cultured; D002648:Child; D017362:Cyclic AMP Response Element-Binding Protein / Q000235:genetics*; D005260:Female; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D018628:Gene Dosage; D006720:Homozygote; D006801:Humans; D007223:Infant; D008297:Male; D009134:Muscular Atrophy, Spinal / Q000235:genetics*; D009419:Nerve Tissue Proteins / Q000235:genetics*; D010375:Pedigree; D010641:Phenotype; D016601:RNA-Binding Proteins / Q000235:genetics*; D055532:SMN Complex Proteins; D055533:Survival of Motor Neuron 1 Protein; D055540:Survival of Motor Neuron 2 Protein
chemical_list: D017362:Cyclic AMP Response Element-Binding Protein; D009419:Nerve Tissue Proteins; D016601:RNA-Binding Proteins; D055532:SMN Complex Proteins; C526471:SMN1 protein, human; C526477:SMN2 protein, human; D055533:Survival of Motor Neuron 1 Protein; D055540:Survival of Motor Neuron 2 Protein