Congenital fiber type disproportion in identical twins

Area of Science:

• Neurology
• Muscle Histology
• Genetics

Background:

• Congenital fiber type disproportion (CFD) is a rare neuromuscular disorder characterized by hypotonic infants and muscle weakness.
• Histological analysis of muscle biopsies is crucial for diagnosing CFD, typically revealing smaller type 1 fibers compared to type 2 fibers.

Observation:

• This report details identical twins diagnosed with CFD at 18 months old.
• Muscle biopsy revealed significantly larger type 2 fibers than type 1 fibers, with type 2B fibers being the largest.
• One twin exhibited type 1 predominance due to a reduction in type 2B fibers (2B deficiency).

Findings:

• Both twins demonstrated muscle histological characteristics of congenital fiber type disproportion.
• Family members, including the probands, experienced transient delayed motor development, macrocephaly, and normal intelligence.
• A muscle biopsy from another family member did not show similar histological abnormalities, suggesting variable expressivity or a nonprogressive course.

Implications:

• The findings contribute to understanding the spectrum of congenital fiber type disproportion and its potential nonprogressive nature within families.
• This case highlights the importance of detailed muscle histology and family history in diagnosing and managing neuromuscular disorders.
• Further research may elucidate the genetic underpinnings and long-term outcomes of CFD, particularly in cases with 2B deficiency.