Evidence‑Based Summary of Nemaline Myopathy

Genetics

• NEB (nebulin) mutations are the most common genetic cause of nemaline myopathy, while RYR1 mutations represent the most frequent overall cause among congenital myopathies, occurring in approximately 1 in 90,000 individuals【1】.
• The estimated prevalence of nemaline myopathy in the general population is about 1 in 26,000 – 28,000【1】.

Clinical Presentation

Neonatal and Early‑Childhood Features

• Affected infants typically present with generalized hypotonia and weakness from birth【1】.
• Prominent facial weakness, which may include ptosis, is frequently observed【1】.
• Reduced deep tendon reflexes and diminished muscle bulk are common findings【1】.
• Proximal muscle weakness accompanied by impaired respiratory and bulbar muscle function characterizes the early disease course【1】.

Severity Spectrum

• The severe congenital form manifests as life‑threatening generalized weakness in the neonatal period, often associated with ACTA1 mutations【1】.
• The mild form presents later with subtle proximal muscle weakness in older children or adults【1】.

Distinguishing Features

• Cognitive function and sensory perception are generally preserved, helping to differentiate nemaline myopathy from congenital muscular dystrophies and other hypotonic disorders【1】.

Cardiac Involvement

• Cardiac disease is uncommon in nemaline myopathy but has been documented【1】.
• In a cohort of 143 patients, six neonates experienced transient heart failure and one infant developed left‑ventricular dysfunction associated with congenital long‑QT syndrome【1】.
• Reported cardiac phenotypes include hypertrophic, dilated, and left‑ventricular non‑compaction cardiomyopathy【1】.
• Sudden cardiac death has been reported in this population【1】.

Recommendations for Cardiac Assessment

• A cardiac evaluation should be performed before any anesthesia or sedation in individuals with nemaline myopathy; if cardiac symptoms are present, re‑evaluation should occur within 3–6 months of the procedure【1】.
• Neurologists caring for patients with nemaline myopathy should collaborate with a cardiologist experienced in neuromuscular disorders (or at minimum an electrophysiologist or heart‑failure specialist)【1】.
• For pediatric‑onset cases, referral to a pediatric heart‑failure specialist is advisable【1】.
• During major surgery, cardiac monitoring by an anesthesiologist familiar with neuromuscular disease should be provided at centers equipped with appropriate intensive‑care facilities【1】.

Management and Prognosis

• The overall disease trajectory is typically static or slowly progressive【1】.

Nutritional Management and Pubertal Considerations in Type 2 Nemaline Myopathy

Energy Requirements in Neuromuscular Disease

• Calculate daily energy needs at 30–35 kcal per kilogram of body weight for individuals with neuromuscular disorders, adjusting upward only if acute hypermetabolic complications arise. 2

Growth and Anthropometric Monitoring

• Perform serial measurements of weight, height, and BMI at each clinic visit and plot them on growth charts to identify early signs of growth deceleration or weight loss. 3
• Conduct annual Tanner staging to verify that pubertal progression follows the expected tempo for the age group. 3

Pubertal Nutritional Demands

• During mid‑adolescence (approximately ages 12–16), puberty‑related insulin resistance and a surge in growth‑hormone secretion raise caloric requirements, making adequate nutrition essential. 4
• The increase in appetite and overall nutrition needs that accompanies rapid growth in puberty must be met to support normal development. 5

Endocrine Impact of Nemaline Myopathy

• Nemaline myopathy (type 2) does not produce primary hormonal dysfunction and does not directly interfere with the hypothalamic‑pituitary‑gonadal axis. 6

Nutritional Intervention Thresholds

• If weight gain is insufficient or BMI percentile declines over a 6–12‑month period, first increase the caloric density of meals and add oral nutritional supplements before proceeding to enteral feeding. 7
• When bulbar weakness compromises oral intake, initiate enteral feeding support early (e.g., nasogastric or gastrostomy tube) rather than waiting for overt malnutrition. 7
• Prior to tube placement, trial oral modifications such as soft foods, thickened liquids, or smaller, more frequent meals to maximize safe oral intake. 7

Respiratory Muscle Weakness and Energy Balance

• Respiratory muscle involvement can raise the work of breathing, thereby increasing total energy expenditure and potentially creating a negative energy balance even when apparent intake seems adequate. 2