[1][2] They include amyotrophic lateral sclerosis (ALS),[3][4] progressive bulbar palsy (PBP), pseudobulbar palsy, progressive muscular atrophy (PMA), primary lateral sclerosis (PLS), spinal muscular atrophy (SMA) and monomelic amyotrophy (MMA), as well as some rarer variants resembling ALS.

[5] While each motor neuron disease affects patients differently, they all cause movement-related symptoms, mainly muscle weakness.

[2] Studies into these inherited forms have led to discoveries of various genes (e.g. SOD1) that are thought to be important in understanding how the disease occurs.

Emotional disturbance (e.g. pseudobulbar affect) and cognitive and behavioural changes (e.g. problems in word fluency, decision-making, and memory) are also seen.

[2] Those that affect children tend to be inherited or familial, and their symptoms are either present at birth or appear before learning to walk.

[11] Motor neuron diseases with both UMN and LMN findings include both familial and sporadic ALS.

[2] TAR DNA-binding protein 43 (TDP-43), is a critical component of the non-homologous end joining (NHEJ) enzymatic pathway that repairs DNA double-strand breaks in pluripotent stem cell-derived motor neurons.

In TDP-43 depleted human neural stem cell-derived motor neurons, as well as in sporadic ALS patients' spinal cord specimens there is significant double-strand break accumulation and reduced levels of NHEJ.

[2] Differential diagnosis can be challenging due to the number of overlapping symptoms, shared between several motor neuron diseases.

[17] All types of MND can be differentiated by two defining characteristics:[6] Sporadic or acquired MNDs occur in patients with no family history of degenerative motor neuron disease.

[2][5][23] In the United Kingdom and Australia, the term motor neuron(e) disease is used for amyotrophic lateral sclerosis,[3][4] although is not uncommon to refer to the entire group.