Analysis of point mutations in the SMN1 gene in SMA patients bearing a single SMN1 copy.
Spinal muscular atrophy (SMA) is caused by homozygous deletion of the SMN1 gene in approximately 96% of cases. Four percent of SMA patients have a combination of the deletion or conversion on one allele and an intragenic mutation on the second one. We performed analysis of point mutations in a set of our patients with suspicion of SMA and without homozygous deletion of the SMN1 gene. A quantitative test determining SMN1 copy number (using real-time PCR and/or MLPA analysis) was performed in 301 patients and only 1 SMN1 copy was detected in 14 of them. When these 14 patients were screened for the presence of point mutations we identified 6 mutations, p.Y272C (in three patients) and p.T274I, p.I33IfsX6, and p.A188S (each in one case). The mutations p.I33IfsX6 and p.A188S were found in two SMAI patients and were not detected previously. Further, evaluation of the relationship between mutation type, copy number of the SMN2 gene and clinical findings was performed. Among our SMA patients with a SMN1 homozygous deletion, we found a family with two patients: the son with SMAII possesses 3 SMN2 copies and the nearly asymptomatic father has a homozygous deletion of SMN1 exon 7 and carries 4 SMN2 copies. Generally, our results illustrate that an increased SMN2 gene copy number is associated with a milder SMA phenotype.
Zapletalová
Eva
E
University Hospital Brno, Centre of Molecular Biology and Gene Therapy, Brno, Czech Republic.
Hedvicáková
Petra
P
Kozák
Libor
L
Vondrácek
Petr
P
Gaillyová
Renata
R
Maríková
Tat'ána
T
Kalina
Zdenek
Z
Jüttnerová
Vera
V
Fajkus
Jirí
J
Fajkusová
Lenka
L
D000293:Adolescent; D000328:Adult; D002675:Child, Preschool; D017362:Cyclic AMP Response Element-Binding Protein / Q000235:genetics*; D004247:DNA / Q000235:genetics; D005091:Exons / Q000235:genetics; D017353:Gene Deletion; D018628:Gene Dosage; D006720:Homozygote; D006801:Humans; D009134:Muscular Atrophy, Spinal / Q000235:genetics*; D009419:Nerve Tissue Proteins / Q000235:genetics*; D021141:Nucleic Acid Amplification Techniques; D010641:Phenotype; D017354:Point Mutation / Q000235:genetics*; D016601:RNA-Binding Proteins / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D055532:SMN Complex Proteins; D055533:Survival of Motor Neuron 1 Protein; D055540:Survival of Motor Neuron 2 Protein
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; D004247:DNA