Table 1.

Parkinsonian features in IMDs.

IMD	Parkinsonian features	References
Gaucher Disease	Earlier age of diagnosis Asymmetric resting tremor is the most common feature Severe motor impairment Impairment in memory, executive function, visuospatial abilities, accelerated cognitive decline Greater risk of dementia, cognitive decline, global cognitive impairment Non-motor symptoms: anosmia, dysautonomia, REM sleep disorder, depression, anxiety, psychotic features Increase in mortality risk	(6–15)
Niemann-Pick Disease	Motor symptoms: Dysarthria, tremor, rigidity, bradykinesia, postural instability, stooped posture, festinating gait, impaired fine motor skills, hypomimia Autonomic dysfunction: orthostatic hypotension, constipation, urinary urgency and impotence Sensory symptoms: hyposmia, Difficulty with concentration	(16, 17)
GM1 Gangliosidosis	Akinetic-rigid parkinsonism Features of immobile face, bradykinesia, short-stepped gait	(18–20)
Neuronal Ceroid-Lipofuscinoses	Bilateral rigidity Rigidity, bradykinesia, tremor	(21, 22)
Disorders of metal metabolism
Wilson's Disease	Rigidity, bradykinesia, shuffling gait, hypophonic speech, hypomimia, micrographia Tremor may be resting, intentional, postural, or action-induced Most common form of tremor is an irregular, jerky, dystonic tremor	(23–26)
Hemochromatosis	Resting tremor, bradykinesia, rigidity Asymmetric onset Mixed resting and action tremor	(27–29)
Disorders of amino acid metabolism
Phenylketonuria	Rigidity and bradykinesia Tremor presenting both at rest and on action	(30, 31)
Maple Syrup Urine Disease	Bradykinesia on finger tapping No resting tremor	(32)
Methylmalonic acidemia	• Positive correlation between serum MMA and severity of neuropathic pain	(33)
Inherited mitochondrial disorders
Masked faces, rigidospasticity, slowed movements, gait disturbances Mental impairment		(34)

IMD, inherited metabolic disorder; REM, rapid eye movement; MMA, Methylmalonic acid.