Hereditary sensory and autonomic neuropathy (HSAN) or hereditary sensory neuropathy (HSN) is a condition used to describe any of the types of this disease which inhibit sensation.

They are less common than Charcot-Marie-Tooth disease.

Five different clinical entities have been described under hereditary sensory and autonomic neuropathies – all characterized by progressive loss of function that predominantly affects the peripheral sensory nerves. Their incidence has been estimated to be about 1 in 25,000.

FHM signs overlap significantly with those of migraine with aura. In short, FHM is typified by migraine with aura associated with hemiparesis and, in FHM1, cerebellar degeneration. This cerebellar degeneration can result in episodic or progressive ataxia. FHM can also present with the same signs as benign familial infantile convulsions (BFIC) and alternating hemiplegia of childhood. Other symptoms are altered consciousness (in fact, some cases seem related to head trauma), gaze-evoked nystagmus and coma. Aura symptoms, such as numbness and blurring of vision, typically persist for 30–60 minutes, but can last for weeks and months. An attack resembles a stroke, but unlike a stroke, it resolves in time. These signs typically first manifest themselves in the first or second decade of life.

The most distinctive clinical feature is the absence of overflow tears with emotional crying after age 7 months. This symptom can manifest less dramatically as persistent bilateral eye irritation. There is also a high prevalence of breech presentation. Other symptoms include weak or absent suck and poor tone, poor suck and misdirected swallowing, and red blotching of skin.

Symptoms in an older child with familial dysautonomia might include:

1. Delayed speech and walking

2. Unsteady gait

3. Spinal curvature

4. Corneal abrasion

5. Less perception in pain or temperature with nervous system.

6. Poor growth

7. Erratic or unstable blood pressure.

8. Red puffy hands

9. Dysautonomia crisis: a constellation of symptoms in response to physical and emotional stress; usually accompanied by vomiting, increased heart rate, increase in blood pressure, sweating, drooling, blotching of the skin and a negative change in personality.

Notalgia paraesthetica (NP) or notalgia paresthetica (also known as "Hereditary localized pruritus", "Posterior pigmented pruritic patch", and "Subscapular pruritus") is a chronic sensory neuropathy. Notalgia paraesthetica is a common localized itch, affecting mainly the area between the shoulder blades (especially the T2–T6 dermatomes) but occasionally with a more widespread distribution, involving the shoulders, back, and upper chest. The characteristic symptom is pruritus (itch or sensation that makes a person want to scratch) on the back, usually on the left hand side below the shoulder blade (mid to upper back). It is occasionally accompanied by pain, paresthesia (pins and needles), or hyperesthesia (unusual or pathologically increased sensitivity of the skin to sensory stimuli, such as pain, heat, cold, or touch), which results in a well circumscribed hyperpigmentation of a skin patch in the affected area.

Hemiplegic migraine or Hemiplegic migraine headache is a rare and serious subtype of classical migraine that typically includes weakness of half the body which can last for hours, days or weeks. It can be accompanied by other symptoms, such as ataxia, coma and paralysis.

The correlation of notalgia paraesthetica localization with corresponding degenerative changes in the spine suggest that spinal nerve impingement may be a contributing cause. According to Plete and Massey, "The posterior rami of spinal nerves arising in T2 through T6 are unique in that they pursue a right-angle course through the multifidus spinae muscle, and this particular circumstance may predispose them to harm from otherwise innocuous insults of a varied nature." Patients may have other conditions that predispose them to peripheral neuropathies (nerve damage).

The causes of this condition have not yet been completely defined. Patients are usually older persons.

HIDS is one of a number of periodic fever syndromes. It is characterised by attacks of fever, arthralgia, skin lesions including cyclical mouth ulcers, and diarrhea. Laboratory features include an acute phase response (elevated CRP and ESR) and markedly elevated IgD (and often IgA), although cases with normal IgD have been described.

It has mainly been described in the Netherlands and France, although the international registry includes a number of cases from other countries.

The differential diagnosis includes fever of unknown origin, familial Mediterranean fever (FMF) and familial Hibernian fever (or TNFα reception associated periodic syndrome/TRAPS).

The ICHD classification and diagnosis of migraine distinguish 6 subtypes of hemiplegic migraine. FHM can be loosely divided into two categories: with and without cerebellar signs. Cerebellar signs refer to ataxia, sometimes episodic and other times progressive, that can accompany FHM1 mutations and is caused by degeneration of the cerebellum. These cerebellar signs result in a phenotypic overlap between FHM and both episodic ataxia and spinocerebellar ataxia. This is unsurprising as subtypes of these disorders (FHM1, EA2 and SCA6) are allelic, i.e., they result from mutations in the same gene. The other forms of FHM seem to be distinguishable only on the basis of their genetic cause.

Reported symptoms include:

- Sensorineural hearing loss

- Vestibular areflexia

- Hearing impairment

- Vertigo

- Nausea and vomiting

- Head movement-dependent oscillopsia

Hyperimmunoglobulinemia D with recurrent fever (HIDS) is a periodic fever syndrome originally described in 1984 by the internist Jos van der Meer, then at Leiden University Medical Centre. No more than 300 cases have been described worldwide.

The entire distribution of the nerve is rarely affected. Usually, the unpleasant sensation(s) affect only part of the skin supplied by the nerve.

Vertigo is a medically recognized term for the symptom of vestibular system disturbance. It may include a feeling of rotation or illusory sensations of motion or both. The general term dizziness is used by nonmedical people for those symptoms but often refers to a feeling of light-headedness, giddiness, drowsiness, or faintness, all of which must be differentiated from true vertigo, since the latter symptoms might have other causes.

Motion sickness occurs more frequently in migraine patients (30–50% more than in controls). Benign paroxysmal vertigo of childhood is an example of migraine-associated vertigo in which headache does not often occur. Basilar artery migraine (BAM) consists of two or more symptoms (vertigo, tinnitus, decreased hearing, ataxia, dysarthria, visual symptoms in both hemifields or both eyes, diplopia, bilateral paresthesias, paresis, decreased consciousness and/or loss of consciousness) followed by throbbing headache. Auditory symptoms are rare. However, a study showed a fluctuating low-tone sensorineural hearing loss in more than 50% of patients with BAM with a noticeable change in hearing just before the onset of a migraine headache. The attacks of vertigo are usually concurrent with the headache and the family history is usually positive. The diagnostician must rule out: TIAs, and paroxysmal vestibular disorder accompanied by headache.

There is also a familial vestibulopathy, familial benign recurrent vertigo (fBRV), where episodes of vertigo occur with or without migraine headache. Testing may show profound vestibular loss. The syndrome responds to acetazolamide. Familial hemiplegic migraine (FHM) has been linked to mutations in the calcium channel gene. (Ophoff et al. 1966 cf. Lempert et al.)

Familial dysautonomia (FD), sometimes called Riley–Day syndrome and hereditary sensory and autonomic neuropathy type III (HSAN-III), is a disorder of the autonomic nervous system which affects the development and survival of sensory, sympathetic and some parasympathetic neurons in the autonomic and sensory nervous system resulting in variable symptoms, including insensitivity to pain, inability to produce tears, poor growth, and labile blood pressure (episodic hypertension and postural hypotension). People with FD have frequent vomiting crises, pneumonia, problems with speech and movement, difficulty swallowing, inappropriate perception of heat, pain, and taste, as well as unstable blood pressure and gastrointestinal dysmotility. FD does not affect intelligence. Originally reported by Drs. Conrad Milton Riley (1913–2005) and Richard Lawrence Day (1905–1989) in 1949, FD is one example of a group of disorders known as hereditary sensory and autonomic neuropathies (HSAN). All HSAN are characterized by widespread sensory dysfunction and variable autonomic dysfunction caused by incomplete development of sensory and autonomic neurons. The disorders are believed to be genetically distinct from each other.

Meralgia paresthetica or meralgia paraesthetica (or Bernhardt-Roth syndrome), is numbness or pain in the outer thigh not caused by injury to the thigh, but by injury to a nerve that extends from the spinal column to the thigh.

This chronic neurological disorder involves a single nerve—the lateral cutaneous nerve of thigh, which is also called the lateral femoral cutaneous nerve (and hence the syndrome lateral femoral cutaneous neuropathy). The term "meralgia paraesthetica" combines four Greek roots to mean "thigh pain with anomalous perception". The disorder has also been nicknamed skinny pants syndrome, in reference to a rise in teenagers wearing skin-tight pants.

Vestibulocochlear dysfunction progressive familial, known also as familial progressive vestibulocochlear dysfunction is an autosomal dominant disease that results in sensorineural hearing loss and vestibular areflexia. Patients report feelings of vague dissiness, blurred vision, dysequilibrium in the dark, and progressive hearing impairment.

Familial hemiplegic migraine (FHM) is an autosomal dominant type of hemiplegic migraine that typically includes weakness of half the body which can last for hours, days or weeks. It can be accompanied by other symptoms, such as ataxia, coma and paralysis. There is clinical overlap in some FHM patients with episodic ataxia type 2 and spinocerebellar ataxia type 6, benign familial infantile epilepsy, and alternating hemiplegia of childhood. There are 3 known loci for FHM. FHM1, which accounts for approximately 50% of FHM patients, is caused by mutations in a gene coding for the P/Q-type calcium channel α subunit, CACNA1A. FHM1 is also associated with cerebellar degeneration. FHM2, which accounts for <25% of FHM cases, is caused by mutations in the /-ATPase gene ATP1A2. FHM3 is a rare subtype of FHM and is caused by mutations in a sodium channel α-subunit coding gene, SCN1A. These three subtypes do not account for all cases of FHM, suggesting the existence of at least one other locus (FHM4). Many of the non-familial cases of hemiplegic migraine (sporadic hemiplegic migraine) are also caused by mutations at these loci. A fourth gene that has been associated with this condition is the proline rich transmembrane protein 2 (PRRT2) - an axonal protein associated with the exocytosis complex. A fifth gene associated with this condition is SLC4A4 which encodes the electrogenic NaHCO3cotransporter NBCe1.

There are also non-familial cases of hemiplegic migraine, termed sporadic hemiplegic migraine. These cases seem to have the same causes as the familial cases and represent de novo mutations. Sporadic cases are also clinically identical to familial cases with the exception of a lack of family history of attacks.

Lipomatosis is believed to be an autosomal dominant condition in which multiple lipomas are present on the body. Many discrete, encapsulated lipomas form on the trunk and extremities, with relatively few on the head and shoulders. In 1993, a genetic polymorphism within lipomas was localized to chromosome 12q15, where the HMGIC gene encodes the high-mobility-group protein isoform I-C. This is one of the most commonly found mutations in solitary lipomatous tumors but lipomas often have multiple mutations. Reciprocal translocations involving chromosomes 12q13 and 12q14 have also been observed within.

Although this condition is benign, it can sometimes be very painful depending on location of the lipomas. Some patients who are concerned with cosmetics seek removal of individual lipomas. Removal can include simple excision, endoscopic removal, or liposuction.

Other entities which are accompanied by multiple lipomas include Proteus syndrome, Cowden syndrome and related disorders due to PTEN gene mutations, benign symmetric lipomatosis (Madelung disease),Dercum's Disease, familial lipodystrophy, hibernomas, epidural steroid injections with epidural lipomatosis, and familial angiolipomatosis.

Henri Gougerot and Alexandre Carteaud originally described the condition in 1927. The cause remains unknown, but the observation that the condition may clear with Minocycline turned attention to an infectious agent. "Actinomycete Dietzia" strain X was isolated from one individual. Other antibiotics found useful include azithromycin, fusidic acid, clarithromycin, erythromycin, tetracycline and cefdinir.

SCA6 is typified by progressive and permanent cerebellar dysfunction. These cerebellar signs include ataxia and dysarthria, likely caused by cerebellar atrophy. Prior to diagnosis and the onset of major symptoms, patients often report a feeling of "wooziness" and momentary imbalance when turning corners or making rapid movements. The age at which symptoms first occur varies widely, from age 19 to 71, but is typically between 43 and 52. Other major signs of SCA6 are the loss of vibratory and proprioceptive sensation and nystagmus.

While most patients present with these severe progressive symptoms, others, sometimes within the same family, display episodic non-progressive symptoms more similar to episodic ataxia. Still others present with symptoms common to both SCA6 and familial hemiplegic migraine.

Benign paroxysmal positional vertigo - Migraine is commonly associated with BPPV, the most common vestibular disorder in patients presenting with dizziness. The two may be linked by genetic factors or by vascular damage to the labyrinth.

Ménière's disease - There is an increased prevalence of migraine in patients with Ménière's disease and migraine leads to a greater susceptibility of developing Ménière’s disease. But they can be distinguished. Ménière's disease may go on for days or even years, while migraines typically do not last longer than 24 hours.

Motion sickness is more prevalent in patients with migraine.

Psychiatric syndromes Dizziness and spinning vertigo are the second most common symptom of panic attacks, and they can also present as a symptom of major depression. Migraine is a risk factor for developing major depression and panic disorder and vice versa.

The familial amyloid neuropathies (or familial amyloidotic neuropathies, neuropathic heredofamilial amyloidosis, familial amyloid polyneuropathy) are a rare group of autosomal dominant diseases wherein the autonomic nervous system and/or other nerves are compromised by protein aggregation and/or amyloid fibril formation.

PAPA syndrome usually begins with arthritis at a young age, with the skin changes more prominent from the time of puberty.

The arthritis is the predominant feature, noted by its juvenile onset and destructive course. Individuals often recall episodes of arthritis precipitated by a traumatic event. With repeated episodes the joints become damaged with multiple joint replacements required. Hopefully, with improved treatment options, the damage will be limited in new cases.

Pyoderma gangrenosum is variably expressed, which means that it is not always present in all individuals with the disease. It presents as poorly healing ulcers with undermined edges. Pathergy is an important feature (this term refers to the tendency of ulcers to arise at points of injury). There are reports of lesions developing at the site of a joint replacement wound, central venous line and intravenous drip insertion.

Acne affects most individuals with PAPA syndrome but to a variable degree. It is usually of a severe nodulocystic type which if untreated results in scarring.

May–White syndrome is a rare familial progressive myoclonus epilepsy with lipomas, deafness, and ataxia. This syndrome is probably a familial form of mitochondrial encephalomyopathy.

Reactive perforating collagenosis is a rare, familial, nonpuritic skin disorder characterized by papules that grow in a diameter of 4 to 6mm and develop a central area of umbilication to which keratinous material is lodged. The cause of reactive perforating collagenosis is unknown.