Spinal Muscular Atrophy (SMA)

This test looks for genetic changes in the SMN1 gene, which are the main cause of spinal muscular atrophy (SMA). SMA is an inherited condition that affects the nerves controlling movement, leading to progressive muscle weakness. Most cases are caused by a missing (deleted) copy of the SMN1 gene. This test analyses the SMN1 gene for deletions and copy number changes, helping to identify whether someone is a carrier of SMA or affected by it.

What it can help assess

• Carrier status: identifying whether you carry an SMA gene change, which is important for family planning, as SMA is one of the more common inherited conditions
• Supporting a diagnosis: helping to confirm or investigate SMA in someone with symptoms
• Understanding family risk: particularly relevant if you have a family history of SMA or a known carrier in the family

Understanding the results

SMA is usually inherited in a recessive pattern, meaning a person typically needs to inherit two faulty copies of the SMN1 gene, one from each parent, to be affected. This test examines the number of working copies of the gene and can typically identify:

• No change detected: the expected working copies of SMN1 are present
• Carrier: one working copy is missing, meaning you carry SMA but are not affected by it. If your partner is also a carrier, there is a chance of having a child with SMA
• Affected: consistent with a diagnosis of SMA, which would be confirmed and managed clinically

An important note on interpretation

This test detects the deletions and copy number changes that cause the great majority of SMA, but a small proportion of cases are caused by other, rarer changes that this test may not detect. This means a negative carrier result greatly reduces, but does not completely remove, the chance of being a carrier. Because this is a genetic test with lifelong implications for you and your relatives, your referring clinician will interpret your result in context, and where appropriate, genetic counselling can help explain what it means for you and your family.

Why it matters

Spinal muscular atrophy is one of the more common serious inherited conditions, and carrier testing is valuable for anyone planning a family, particularly where there is a family history. Knowing your carrier status allows for informed decisions and, where relevant, access to counselling and support. Importantly, treatments for SMA have advanced significantly in recent years, so early identification can also be important where the condition is present.