Spinal muscular atrophy (SMA) is the loss of motor nerve cells in the spinal cord because of a change in the SMN1 gene. It is a rare disease, affecting roughly 1 in every 10,000–11,000 births according to a literature review, but it is passed on by healthy carrier parents, who usually do not know they carry it. Over the past decade SMA has gone from an untreatable disease to a treatable one, and the outcome depends on one thing: how early the diagnosis is made.
Early signs in a baby (type 1)
- The legs move very little and stay in a "frog" position; the arms are relatively more active
- When you pick the baby up, the body seems to "slip through," and the head falls back with no head control
- Sucking is weak and tiring, and weight gain slows
- Small twitches in the tongue (fasciculations)
- Breathing with the belly, a weak cough, a weak cry; frequent respiratory infections
- Reflexes are absent
- The baby is alert and engages well, because thinking and awareness are not affected
In type 2, a baby learns to sit but does not walk; in type 3, a child walks but falls easily, has trouble on stairs, and the weakness increases over the years.
Diagnosis
When SMA is suspected, a genetic test for SMN1 is done on a blood sample; a biopsy and EMG/nerve conduction studies are no longer needed for the diagnosis. The number of SMN2 gene copies helps predict how severe the disease is likely to be and guides the treatment plan. In a number of countries SMA has been added to the newborn screening program so that treatment can begin before symptoms appear.
Treatment
There are three approaches that change the course of the disease: an antisense drug given into the spinal canal, a one-time intravenous gene therapy, and an oral drug. In a randomized trial in infantile-onset SMA, 51% of the babies who received the antisense treatment reached milestones such as head control, rolling and sitting, compared with none in the control group; the risk of death or permanent ventilation was cut roughly in half. In a systematic review of babies found through newborn screening and treated before symptoms, almost all children with three copies of the SMN2 gene went on to walk independently. The best results are seen in babies whose treatment starts before symptoms or in the first weeks.
Alongside the drugs, international standards call for physical therapy, positioning and orthoses, monitoring of spinal curvature and the hip joint, assessment of nutrition and swallowing, breathing support and full vaccination. A multidisciplinary team coordinates this work.
For the family
If SMA has occurred in the family, genetic counseling and carrier testing are possible before the next pregnancy. If a newborn has a worrying sign, a "wait and see" approach is not right in SMA: the test should be done right away. More detail: neuromuscular disorders, newborn neurological examination.
This article is for general information and does not replace an exam.
Scientific sources
The medical information on this page is based on the following peer-reviewed publications (PubMed).
- Verhaart IEC və b. (2017). Prevalence, incidence and carrier frequency of 5q-linked spinal muscular atrophy — a literature review Orphanet J Rare Dis. PMID 28676062
- Mercuri E və b. (2018). Diagnosis and management of spinal muscular atrophy: Part 1: Recommendations for diagnosis, rehabilitation, orthopedic and nutritional care Neuromuscul Disord. PMID 29290580
- Finkel RS və b. (2017). Nusinersen versus Sham Control in Infantile-Onset Spinal Muscular Atrophy N Engl J Med. PMID 29091570
- Aragon-Gawinska K və b. (2023). Spinal Muscular Atrophy Treatment in Patients Identified by Newborn Screening — A Systematic Review Genes (Basel). PMID 37510282
Medically reviewed by: Dr. Aynura IbrahimovaLast updated:
The information on this page is for education only and does not replace an examination by a doctor. If you are worried about your child, book an appointment. In an emergency, call 103.