Gene Therapy for Spinal Muscular Atrophy (SMA): What Parents Need to Know

Spinal Muscular Atrophy (SMA) is a severe genetic condition affecting the nervous system and muscles. It leads to progressive muscle weakness and atrophy, significantly impacting a child’s development and quality of life.

Today, gene therapy offers a promising treatment option that can greatly improve outcomes for affected children.

 

What Is Spinal Muscular Atrophy (SMA)?

Spinal Muscular Atrophy is an autosomal recessive genetic disorder caused by mutations in the SMN1 gene on chromosome 5.

This mutation leads to reduced production of the SMN protein, resulting in degeneration of motor neurons in the spinal cord (anterior horn cells). As a result, patients lose control of muscle movement.

      ๐  Incidence: ~1 in 6,000 - 10,000 live births

      ๐  Carrier rate: ~1 in 40 - 60 individuals

      ๐  Severe cases in early infancy may lead to death within the first 2 years without treatment

Early treatment - especially before symptom onset or within the first 6 weeks of life - is critical for the best outcomes.

 

Types and Symptoms of SMA

SMA is classified into 4 types based on age of onset and severity:

      ๐  Type 0:
Severe symptoms at birth: often leads to respiratory failure shortly after birth

      ๐  Type 1 (most common and severe):
Onset at 2 - 6 months

        ๐  Muscle weakness and atrophy

        ๐  Cannot sit or hold head up

        ๐  Breathing difficulties

        ๐  High mortality within 2 years without ventilatory support

      ๐  Type 2 (moderate):
Onset at 6 - 18 months

        ๐  Can sit but cannot walk

        ๐  Swallowing and breathing difficulties

        ๐  Tremors in fingers

      ๐  Type 3 (mild):
Onset after 18 months

        ๐  Able to walk initially but progressively weakens

        ๐  Normal life expectancy

 

SMA Screening: When and How?

Early detection significantly improves treatment outcomes. Screening can be performed at multiple stages:

1. Carrier Screening Before Pregnancy

      ๐  Blood test using qRT - PCR

      ๐  Detects mutations in the SMN1 gene

      ๐  Helps couples assess risk before having children

2. Preimplantation Genetic Testing (PGT)

      ๐  Used during IVF/ICSI

      ๐  Embryos are tested at the blastocyst stage

      ๐  Only unaffected embryos are selected for implantation

3. Prenatal Screening

      ๐  Maternal blood testing in early pregnancy

      ๐  Confirmatory tests:

          ๐  Chorionic Villus Sampling (CVS)

          ๐  Amniocentesis

4. Newborn Screening

      ๐  Heel - prick blood test (Dried Blood Spot)

      ๐  Detects SMN1 mutations early

      ๐  Enables treatment before symptoms appear

 

Treatment Options for SMA

SMA cannot be completely cured, but treatments aim to improve outcomes:

      ๐  SMN - enhancing medications:
Delivered into the spinal canal

      ๐  Gene Therapy:
A one-time intravenous treatment replacing the defective gene

      ๐  Supportive care:

          ๐  Ventilatory support

          ๐  Physical therapy

          ๐  Nutritional support

 

What Is Gene Therapy?

Gene Therapy is an advanced treatment that replaces the defective gene at the root cause of the disease.

      ๐  Uses a viral vector to deliver a functional SMN1 gene

      ๐  Targets motor neurons directly

      ๐  Administered via a single intravenous infusion

      ๐  Must be performed in specialized medical centers

This therapy was approved by the U.S. FDA in 2019 and in Thailand in 2023.

 

Who Is Eligible for Gene Therapy?

Gene therapy is most effective for:

      ๐  Infants from birth to 24 months

Note:
Treatment after 24 months may have reduced effectiveness.

 

Pre - Treatment Evaluation

Before gene therapy, patients must undergo:

      ๐  Liver function tests

      ๐  Kidney function tests

      ๐  Immune status assessment

      ๐  Complete blood count (CBC)

      ๐  Cardiac screening (Troponin - I)

 

Benefits of Gene Therapy

      ๐  Pre-symptomatic children may achieve normal milestones (sitting, walking)

      ๐  Symptomatic children show improved motor function

      ๐  Increased survival rates, especially in SMA Type 1

      ๐  Reduced need for ventilators and long-term supportive care

 

Possible Side Effects

      ๐  Elevated liver enzymes

      ๐  Low platelet count

 

Prevention: Why Genetic Screening Matters

Since SMA is inherited in an autosomal recessive pattern:

      ๐  If both parents are carriers:

          ๐  25% chance the child will have SMA

          ๐  50% chance the child will be a carrier

Pre-pregnancy genetic screening is highly recommended to reduce the risk.

Preventive strategies include:

      ๐  Carrier screening in couples

      ๐  Prenatal testing

      ๐  Embryo screening (PGT) during IVF/ICSI

 

Why Early Gene Therapy Matters

A single early gene therapy treatment can provide long-term benefits and significantly better outcomes compared to other treatment approaches. However, care must be delivered under a multidisciplinary team of pediatric specialists in well - equipped hospitals.

 

Where to Get Treatment?

Bangkok Hospital Pediatric Center provides specialized care for children with SMA, supported by experienced pediatricians, multidisciplinary teams, and advanced medical technology to deliver effective gene therapy treatment.

 

Specialist Doctors

      ๐  Dr. Thianchai Bannalai - Pediatrician

      ๐  Dr. Suchawadee Hosasuwan - Pediatric Neurologist

 

Conclusion

Gene therapy represents a groundbreaking advancement in treating Spinal Muscular Atrophy. With early diagnosis and intervention, children with SMA now have a significantly improved chance of survival and a better quality of life.

 

Source : Bangkok Hospital

**Translated and compiled by ArokaGO Content Team