New Single Nucleotide Deletion In the SMPD1 Gene Causes Niemann Pick Disease Type A in a Child from Southwest Iran: A Case Report
A 2.5 year-old male, the first born child from first cousin parents was attending our center for genetic counseling and genetic diagnostics. The patient showed typical signs of the Niemann Pick disease, such as hepatosplenomegaly, developmental delay, mental retardation, and foam cells in the bone marrow, hypotonia, and cherry red maculae. Seizure and anorexia at 5-6th month of life was observed. He died as results of his illness. Unfortunately, measurement of the ASM activity in the white blood cells failed and DNA test was the only chance to establish a definite diagnosis.\nAfter obtaining informed consent, blood samples were collected from patient and his parents.\nGenomic DNA was extracted from EDTA-anticoagulated whole blood by standard salting out procedures. Selective amplification of all 6 exons was performed in a volume of 25 µl reaction containing 10 pmol of each primer (TAG Copenhagen A/S, Fruebjergvej3, Denmark) and 50ng of genomic DNA. PCR was carried out by a set of designed primers using primer3out software (). Properties of primers are indicated in .\nTemperature profile of reactions were as follow: initial denaturation at 95°C for 3 min, 35 cycles of 95°C for 30s, 56-60°C for 30s and 72°C for 45s and a final extension at 72°C for 7 min. Direct sequencing of PCR products was carried out using ABI automated sequencer 3700 according to the manufacture's instruction (ABI 3700, PE Applied BioSystems, Foster City, CA, USA). Sequencing reactions were accomplished by the same primers that were used for exon amplification. Sequence analysis was performed with the software BioEdit (version 7.0.5.3). According to the human reference sequence NM_000543.4, a homozygous single guanine deletion, c.740delG, was observed in exon 2 of the SMPD1 gene, which results in a premature stop codon (CTG>TGA) between codons 256-257 (p.Gly247Alafs*9) (). Apparently healthy parents were heterozygous for the detected change. They are also obligate carrier. To confirm the pathogenic relevance of the detected deletion, 27 healthy individuals were tested.