Fukuyama congenital muscular dystrophy

Fukuyama congenital muscular dystrophy (FCMD) is a form of congenital muscular dystrophy.

Epidemiology

FCMD is almost exclusively found in Japan where it has an incidence of 2-4 per 100,000 infants and is the second most common muscular dystrophy after Duchenne muscular dystrophy ^1,2. However, it has also been reported as far as Netherlands and Australia in patients without Japanese ancestry ¹.

Clinical presentation

Affected infants are hypotonic and have generalized symmetric weakness affecting proximal, distal, and facial muscles by 9 months of age ^1,3. These features ultimately progress into childhood, and are accompanied by developmental delay and intellectual disability ^1,3. Other features such as skeletal muscle pseudohypertrophy, joint contractures, and epilepsy are also seen in most patients ^1,3.

Pathology

FCMD is inherited in an autosomal recessive pattern, and is due to a mutation in the fukutin-related protein (FKTN) gene ^1-3. This gene is located on the q arm of chromosome 9 and as its name suggests encodes for the protein fukutin, which has a role in protecting skeletal muscle and organizing early brain development ^1-3.

Radiographic features

Brain MR features are most commonly described, and include:

• polymicrogyria
  • cerebral polymicrogyria is seen in nearly all patients, typically in the frontal and parietal lobes ^4,5
  • cerebellar polymicrogyria is seen in approximately 90% of patients, typically in the superior semilunar lobule ^4,5
• pachygyria (type II (cobblestone complex) lissencephaly): in approximately half of patients, typically involving the temporal and occipital lobes ^4,5
• white matter changes: most commonly diffuse prolonging of T1 and T2 signal in the white matter, but may also be patchy, spotty or equivocal ^4-6

Unlike Walker-Warburg syndrome, one of its main differentials, cerebellar dysplasia, retinal dysplasia and gyral malformations are not commonly appreciated in FCMD ⁷.

Treatment and prognosis

No disease-modifying therapy is available (as of 2017), and management relies on input from allied health services. 

History and etymology

This disorder is named after Yukio Fukuyama (1928-2014), a Japanese pediatric neurologist, who first described the condition in his 1960 seminal paper ^1,8.