A B C D E F G H I J K L M N O P Q R S T U V W X Y Z # |
(CTC) SMA Carrier Screen
Test Code718041C
Physician Attestation of Informed Consent
This germline genetic test requires physician attestation that patient consent has been received if ordering medical facility is located in AK, DE, FL, GA, IA, MA, MN, NV, NJ, NY, OR, SD or VT or test is performed in MA.
Preferred Specimen
4 mL whole blood collected in an EDTA (lavender-top) tube
Minimum Volume
Whole blood: 2 mL
Cultured cells: 2 flasks
Amniotic fluid: 10 mL
Cultured cells: 2 flasks
Amniotic fluid: 10 mL
Other Acceptable Specimens
Whole blood collected in an ACD solution (yellow-top) • 2 flasks Cultured cells from Amniotic fluid or CVS • 20 mL [x2] amniotic fluid in conical tube
Instructions
Whole blood: Normal phlebotomy procedure. Specimen stability is crucial. Store and ship ambient immediately. Do not freeze.
Transport Temperature
Room temperature
Specimen Stability
Whole blood
Room temperature: 8 days
Refrigerated: 14 days
Frozen: Unacceptable
Cultured cells or Amniotic fluid
Room temperature: 48 hours
Refrigerated: Unacceptable
Frozen: Unacceptable
Room temperature: 8 days
Refrigerated: 14 days
Frozen: Unacceptable
Cultured cells or Amniotic fluid
Room temperature: 48 hours
Refrigerated: Unacceptable
Frozen: Unacceptable
Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Samples received frozen • Clotted specimen
Methodology
Allele Specific Real-Time Polymerase Chain Reaction • ddCt Method
Setup Schedule
Night Sets up 7 days a week.
Report Available
Reports in 2 to 3 days.
Clinical Significance
Spinal Muscular Atrophy (SMA) is one of the most common
autosomal recessive diseases. SMA is characterized by the
degeneration of the anterior horn cells of the spinal cord
which leads to symmetric proximal muscle weakness. The
estimated incidence of SMA is 1/6,000 to 1/10,000 live
births with a carrier frequency of 1/40 to 1/60. Clinical
presentation, mainly based upon age of onset of symptoms,
is classified into 4 SMA subtypes: subtype I, onset before
6 months of age; subtype II, onset between 6 and 12 months
of age; subtype III, onset in childhood after 12 months of
age; and subtype IV, adult onset. Each subtype displays
significant variance of clinical prognosis, including
lifespan. The survival motor neuron 1 (SMN1) gene has been
shown to be responsible for 99% of SMA cases. An adjacent
homologous gene, SMN2, encodes a protein identical to that
of SMN1. SMA is caused by a critical reduction in the total
amount of functional SMN protein. Typically 80% to 90% of
SMN protein is derived from functional SMN1 genes, while
10% to 20% is derived from SMN2 genes. Therefore, SMN
protein expression, or dosage, is based largely upon SMN1
gene copy number, and to a much lesser extent, SMN2 gene
copy number. Loss of functional production of SMN protein
most commonly occurs by deletion of SMN1 and/or SMN2 genes,
either by homologous recombination or gene conversion (95%
of SMA alleles). The remaining 5% of SMA alleles harbor
point mutations in the SMN1 gene(s) that effectively
eliminates the production of functional SMN protein from
those gene copies. Although a diagnosis of SMA depends upon
SMN1 gene copy number, a less severe SMA phenotype may be
associated with an increased number (greater than or equal
to 3 copies) of functional SMN2 gene copies. Conversely, a
severe SMA phenotype may be associated with fewer (less
than or equal to 2) functional SMN2 gene copies.
autosomal recessive diseases. SMA is characterized by the
degeneration of the anterior horn cells of the spinal cord
which leads to symmetric proximal muscle weakness. The
estimated incidence of SMA is 1/6,000 to 1/10,000 live
births with a carrier frequency of 1/40 to 1/60. Clinical
presentation, mainly based upon age of onset of symptoms,
is classified into 4 SMA subtypes: subtype I, onset before
6 months of age; subtype II, onset between 6 and 12 months
of age; subtype III, onset in childhood after 12 months of
age; and subtype IV, adult onset. Each subtype displays
significant variance of clinical prognosis, including
lifespan. The survival motor neuron 1 (SMN1) gene has been
shown to be responsible for 99% of SMA cases. An adjacent
homologous gene, SMN2, encodes a protein identical to that
of SMN1. SMA is caused by a critical reduction in the total
amount of functional SMN protein. Typically 80% to 90% of
SMN protein is derived from functional SMN1 genes, while
10% to 20% is derived from SMN2 genes. Therefore, SMN
protein expression, or dosage, is based largely upon SMN1
gene copy number, and to a much lesser extent, SMN2 gene
copy number. Loss of functional production of SMN protein
most commonly occurs by deletion of SMN1 and/or SMN2 genes,
either by homologous recombination or gene conversion (95%
of SMA alleles). The remaining 5% of SMA alleles harbor
point mutations in the SMN1 gene(s) that effectively
eliminates the production of functional SMN protein from
those gene copies. Although a diagnosis of SMA depends upon
SMN1 gene copy number, a less severe SMA phenotype may be
associated with an increased number (greater than or equal
to 3 copies) of functional SMN2 gene copies. Conversely, a
severe SMA phenotype may be associated with fewer (less
than or equal to 2) functional SMN2 gene copies.