What is the best course of action for a newborn with poor feeding, tongue fasciculations, and decreased deep tendon reflexes, suggestive of a potential neuromuscular disorder such as spinal muscular atrophy (SMA)?

Spinal Muscular Atrophy Type 1: Early Disease-Modifying Therapy is Critical

The correct answer is D: There is a new therapy that is more effective if started early. This newborn's clinical presentation—tongue fasciculations, poor feeding, and decreased deep tendon reflexes—is pathognomonic for spinal muscular atrophy (SMA) type 1, and FDA-approved disease-modifying therapies (nusinersen, onasemnogene abeparvovec, risdiplam) dramatically improve outcomes when initiated before irreversible motor neuron loss occurs. 1, 2, 3

Why This Clinical Triad Demands Urgent Action

The combination of tongue fasciculations, hypotonia, and absent/decreased deep tendon reflexes in a newborn is pathognomonic for lower motor neuron disease, with SMA type 1 being the most common cause. 1

Key distinguishing features:

• Tongue fasciculations are highly specific for peripheral (lower motor neuron) hypotonia and distinguish this from central causes of hypotonia 1
• Decreased or absent deep tendon reflexes indicate lower motor neuron or peripheral nerve involvement, not upper motor neuron disease 1
• This triad differentiates SMA from congenital myopathies (which have preserved reflexes) and cerebral palsy (which has increased reflexes) 4, 5

Why Each Answer is Right or Wrong

Option A is dangerously incorrect: SMA type 1 is the most common genetic cause of infant mortality, with high mortality within the first year if untreated. 6, 7 This is not a benign condition that resolves spontaneously. Attributing symptoms to "benign congenital hypotonia" without evaluating for tongue fasciculations and deep tendon reflexes results in missed diagnosis and preventable death. 1

Option B is incorrect: While muscle biopsy is the gold standard for congenital myopathies 4, SMA diagnosis is achieved through DNA-based testing demonstrating homozygous deletion of SMN1 exon 7, which has up to 95% sensitivity and nearly 100% specificity. 6, 2 Muscle biopsy is not needed for SMA diagnosis and delays life-saving treatment.

Option C is misleading and inadequate: While nutritional optimization through gastrostomy tube feeding may improve quality of life, it does not address the underlying motor neuron degeneration and will not extend life expectancy without disease-modifying therapy. 1 Good nutrition alone cannot prevent respiratory failure or progressive motor neuron loss in untreated SMA type 1. 1 Focusing solely on feeding support without addressing the underlying neuromuscular disease represents inadequate care. 1

Option D is correct: Three FDA-approved disease-modifying therapies are now available:

• Nusinersen (antisense oligonucleotide increasing SMN protein expression) 2
• Onasemnogene abeparvovec (gene therapy using AAV9 vector) 2
• Risdiplam (small molecule altering SMN2 splicing) 2

Newborn screening for SMA has demonstrated that treating infants before motor neuron loss results in dramatically improved clinical outcomes. 2, 3 Early treatment can significantly modify the natural course of the disease. 3

Immediate Management Algorithm

Step 1: Urgent referral to pediatric neurology and genetics 1

• Do not delay for confirmatory testing
• Same-day or next-day consultation is appropriate given the time-sensitive nature of treatment

Step 2: Genetic testing for SMN1 deletion 6, 2

• Homozygous deletion of SMN1 exon 7 confirms diagnosis in 95% of cases
• Results typically available within days to 1-2 weeks

Step 3: Initiate disease-modifying therapy as soon as diagnosis is confirmed 2, 3

• Treatment efficacy is highest when started before irreversible motor neuron loss
• Delay of even weeks can result in permanent disability

Step 4: Concurrent supportive care 1

• Nutritional support (nasogastric or gastrostomy tube as needed) should be viewed as adjunct to, not substitute for, disease-modifying therapy 1
• Pulmonary, gastroenterology/nutrition, and orthopedic care coordination 6

Critical Pitfall to Avoid

The most dangerous error is reassuring parents that this will resolve with supportive care alone or delaying specialist referral. Without disease-modifying therapy, SMA type 1 has high mortality within the first year of life. 6, 7 The window for optimal treatment is narrow—every day counts in preserving motor neurons.