Familial dysautonomia, which affects the development and survival of sensory, sympathetic, and parasympathetic neurons, is a debilitating disorder present from birth. Neuronal degeneration progresses throughout life. Affected individuals have gastrointestinal dysfunction, autonomic crises (i.e., hypertensive vomiting attacks), recurrent pneumonia, altered pain sensitivity, altered temperature perception, and blood pressure instability. Hypotonia contributes to delay in acquisition of motor milestones. Optic neuropathy results in progressive vision loss. Older individuals often have a broad-based and ataxic gait that deteriorates over time. Developmental delay / intellectual disability occur in about 21% of individuals. Life expectancy is decreased.

Hereditary congenital facial paresis (HCFP) is the isolated dysfunction of the facial nerve (CN VII). HCFP is considered to be distinct from Moebius syndrome (157900), which shares some of the same clinical features. Genetic Heterogeneity of Hereditary Congenital Facial Paresis One locus for HCFP (HCFP1) has been mapped to chromosome 3q. Another locus (HCFP2; 604185) has been mapped to chromosome 10q. HCFP3 (614744) is caused by mutation in the HOXB1 gene (142968) on chromosome 17q21.

Hereditary sensory and autonomic neuropathy type II (HSAN2) is characterized by progressively reduced sensation to pain, temperature, and touch. Onset can be at birth and is often before puberty. The sensory deficit is predominantly distal with the lower limbs more severely affected than the upper limbs. Over time sensory function becomes severely reduced. Unnoticed injuries and neuropathic skin promote ulcerations and infections that result in spontaneous amputation of digits or the need for surgical amputation. Osteomyelitis is common. Painless fractures can complicate the disease. Autonomic disturbances are variable and can include hyperhidrosis, tonic pupils, and urinary incontinence in those with more advanced disease.

Marsili syndrome (MARSIS) is an autosomal dominant pain insensitivity disorder characterized by a lowered ability to sense pain, to experience temperature, and to sweat. Affected individuals do not perceive broken bones and burns as painful, and have lowered sensitivity to capsaicin. However, visceral pain (e.g., childbirth-related) and light touch are perceived (summary by Habib et al., 2018).