Only seven people with TEFM-related disease have been reported so far, and their symptoms varied widely. Some people have a very severe form of the disease, while others have a milder course.
Reported symptoms include:
- Severe cases (early infancy):
o Life-threatening illness soon after birth
o Low blood sugar
o High levels of lactic acid in the blood
o Seizures
o Liver failure
o Early death (within the first few months of life)
- Moderate cases (infancy to early childhood):
o Progressive epilepsy with muscle jerks
o Delayed development or loss of developmental milestones
o Eye movement problems (like drooping eyelids or trouble moving the eyes)
o Vomiting and feeding difficulties
o Death in early toddler years
- Milder cases:
o Developmental delay
o Autism spectrum disorder
o Mild learning difficulties
o Muscle weakness that may come and go
o Balance problems (ataxia)
o Vision issues (like optic atrophy)
o Some may have seizures, others may not
o Two children in the study showed symptoms similar to a congenital myasthenic syndrome, which affects how nerves interact with muscles. These children improved with a medication called salbutamol.