Hereditary transthyretin amyloidosis mimicking ALS: First genetically proven case report from Saudi Arabia

Hereditary transthyretin amyloidosis (ATTRv) is a systemic disorder that may mimic motor neuron disease (MND), leading to misdiagnosis and delayed access to disease-modifying therapies.

We report the first genetically confirmed case of ATTRv mimicking amyotrophic lateral sclerosis (ALS) in Saudi Arabia. A 47-year-old male presented with progressive right-sided limb weakness (proximal > distal) and dysarthria over 18 months. Neurological examination revealed fasciculations, distal atrophy, and brisk reflexes with normal muscle tone and no spasticity. Electrophysiological studies demonstrated a length-dependent sensorimotor axonal neuropathy with widespread denervation changes involving bulbar, cervical, and lumbosacral regions. Brain and spine MRI, along with whole-body CT, excluded structural or paraneoplastic causes. Genetic testing identified a pathogenic heterozygous variant in the TTR gene: NM_000371.4:c.424G > A (p.Val142Ile). Transthoracic echocardiography revealed mild concentric left ventricular hypertrophy. There was no clinical evidence of autonomic, renal, or ocular involvement.

This case underscores the importance of considering ATTRv in patients presenting with atypical MND, particularly when clinically significant sensory symptoms, absent upper motor neuron signs, or unexplained cardiac abnormalities are present. Early diagnosis enables access to targeted therapies such as TTR stabilizers and gene-silencing agents, which can alter disease trajectory.