Spinal Muscular Atrophy: HINE-2 Staging, Gene Therapy and Motor Rehabilitation
In short
Novel gene therapies (Zolgensma, Spinraza) have transformed Spinal Muscular Atrophy. Learn HINE-2 motor milestone tracking and physiotherapy protocols.
In this guide (4 sections)
The Transforming Landscape of Spinal Muscular Atrophy (SMA)
Spinal Muscular Atrophy (SMA) is an autosomal recessive motor neuron disease caused by deletion or mutation of the survival motor neuron 1 (SMN1) gene on chromosome 5q. Loss of SMN protein leads to progressive degeneration of anterior horn cells in the spinal cord, resulting in proximal, symmetrical muscle weakness and generalized hypotonia.
With disease-modifying therapies (nusinersen, risdiplam, and onasemnogene abeparvovec / Zolgensma gene therapy), infants who previously had a life expectancy under 2 years are now surviving and acquiring unprecedented gross motor milestones.
SMA Clinical Classification and HINE-2 Motor Tracking
The Hammersmith Infant Neurological Examination Section 2 (HINE-2) evaluates 8 motor milestone categories: head control, sitting, voluntary grasp, kicking, rolling, crawling, standing, and walking.
| SMA Type | Age of Onset | SMN2 Copy Count | Traditional Prognosis | Post-Gene Therapy Potential | |
|---|---|---|---|---|---|
| Type 1 (Werdnig-Hoffmann) | Before 6 months | Typically 2 copies | Never sit unsupported; respiratory failure before age 2. | Achieve independent sitting; many achieve supported standing. | |
| Type 2 (Dubowitz Disease) | 6 to 18 months | Typically 3 copies | Achieve sitting; never walk independently. | Maintain independent sitting; potential for household ambulation. | |
| Type 3 (Kugelberg-Welander) | After 18 months | 3 to 4 copies | Achieve walking; may lose ambulation in adolescence. | Preserve long-term community ambulation and stair climbing. | |
| Type 4 (Adult-Onset) | Adulthood | 4 to 6 copies | Mild muscle weakness; normal lifespan. | Maintained independent mobility with strength preservation. |
Physiotherapy Framework Post-Treatment
Gene therapy preserves motor neurons, but physiotherapy is essential to teach newly re-innervated muscles how to coordinate and execute motor milestones.
- Trunk and Postural Alignment: Provide external trunk support (such as supportive adaptive seating or soft spinal orthoses) to prevent progressive collapsing neuromuscular scoliosis while training active head turning.
- Aquatic Physiotherapy: Warm water therapy allows infants with weak anti-gravity muscles to achieve active limb movement, rolling, and reaching in an unweighted environment.
- Standing Frames and Weight-Bearing: Introduce standing devices once head control is achieved, targeting 60 minutes daily to promote bone mineral accretion and prevent knee and hip flexion contractures.
Frequently Asked Questions
What is the CHOP INTEND assessment in SMA?
The Children Hospital of Philadelphia Infant Test of Neuromuscular Disorders (CHOP INTEND) is a 16-item scale (max score 64) specifically designed to measure motor skills in weak infants with Type 1 SMA.
Why are contractures common even after gene therapy?
Imbalance between stronger flexor muscle groups and weaker extensor groups leads to joint contractures. Daily passive stretching and orthotic splinting remain necessary.
How does physiotherapy support respiratory function in SMA?
Therapists train families in manual cough assistance, chest expansion techniques, and postural drainage to prevent atelectasis and pneumonia.
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