• Central core disease
  
  
• Nemaline myopathy
  
  
• Centronuclear Myopathy
  
  

Central core disease: It is a rare disorder. It is so named because of the metabolically inactive cores present in the muscle fibres. Patients have decreased fetal movements and breech presentation. They have hypotonia and delay in motor milestones with increased proximal weakness. In childhood, they have difficulty in climbing stairs and getting up from the floor. Legs are more affected than arms. Investigations reveal increased CPK levels. EMG shows myopathic pattern and muscle biopsy shows fibres with single or multiple central or eccentric discrete zones devoid of oxidative enzymes.

Respiratory system: There is distinctive presence of rods or thread-like structures in the muscle fibres. A severe neonatal form presents with hypotonia and feeding difficulties leading to early death. Older children present with delayed motor milestones. The physical appearance is striking. Patients have long narrow facies, high-arched palate, open-mouthed appearance due to prognathous jaw, skeletal abnormalities and facial and generalised muscle weakness. Investigations reveal increase in CPK levels. EMG shows myopathic pattern with occasional fibrillation potentials. Muscle biopsy shows cluster of small rods. The muscle often shows Type 1 fibre predominance.

Centronuclear myopathy: It is of 3 types:

• Neonatal form: Presents with severe hypotonia and weakness at birth. Respiratory assistance may be required.
  
  
• Late infancy - Early childhood: Presents with delayed milestones, marfanoid features (slender body habitus, long narrow
  face, high arched palate), scoliosis, club feet, progressive Ophthalmoplegia (may have ptosis) and varying degrees of
  extraocular muscle impairment.
  
  
• Late childhood - Adult type: Present in the 2nd or 3rd decade with full extraocular muscle involvement (rarely ptosis).
  Scoliosis and clubfeet may be present.
  
  

*All myopathies may have varying degrees of cardiac involvement. Central core disease is especially prone to cardiomyopathies.