SCN9A neuropathic pain syndromes (SCN9A-NPS) comprise SCN9A erythromelalgia (EM), SCN9A paroxysmal extreme pain disorder (PEPD), and SCN9A small fiber neuropathy (SFN). SCN9A-EM is characterized by recurrent episodes of bilateral intense, burning pain, and redness, warmth, and occasionally swelling. While the feet are more commonly affected than the hands, in severely affected individuals the legs, arms, face, and/or ears may be involved. SCN9A-PEPD is characterized by neonatal or infantile onset of autonomic manifestations that can include skin flushing, harlequin (patchy or asymmetric) color change, tonic non-epileptic attacks (stiffening), and syncope with bradycardia. Later manifestations are episodes of excruciating deep burning rectal, ocular, or submandibular pain accompanied by flushing (erythematous skin changes). SCN9A-SFN is characterized by adult-onset neuropathic pain in a stocking and glove distribution, often with a burning quality; autonomic manifestations such as dry eyes, mouth, orthostatic dizziness, palpitations, bowel or bladder disturbances; and preservation of large nerve fiber functions (normal strength, tendon reflexes, and vibration sense).

Gitelman syndrome (GTLMNS) is an autosomal recessive renal tubular salt-wasting disorder characterized by hypokalemic metabolic alkalosis with hypomagnesemia and hypocalciuria. It is the most common renal tubular disorder among Caucasians (prevalence of 1 in 40,000). Most patients have onset of symptoms as adults, but some present in childhood. Clinical features include transient periods of muscle weakness and tetany, abdominal pains, and chondrocalcinosis (summary by Glaudemans et al., 2012). Gitelman syndrome is sometimes referred to as a mild variant of classic Bartter syndrome (607364). For a discussion of genetic heterogeneity of Bartter syndrome, see 607364.

Gelatinous drop-like corneal dystrophy is an autosomal recessive disorder characterized by severe corneal amyloidosis leading to blindness. Clinical manifestations, which appear in the first decade of life, include blurred vision, photophobia, and foreign-body sensation. By the third decade, raised, yellowish-gray, gelatinous masses severely impair visual acuity, and lamellar keratoplasty is required for most patients (summary by Tsujikawa et al., 1999).

Episodic ataxia type 1 (EA1) is a potassium channelopathy characterized by constant myokymia and dramatic episodes of spastic contractions of the skeletal muscles of the head, arms, and legs with loss of both motor coordination and balance. During attacks individuals may experience a number of variable symptoms including vertigo, blurred vision, diplopia, nausea, headache, diaphoresis, clumsiness, stiffening of the body, dysarthric speech, and difficulty in breathing, among others. EA1 may be associated with epilepsy. Other possible associations include delayed motor development, cognitive disability, choreoathetosis, and carpal spasm. Usually, onset is in childhood or early adolescence.

Keratoendotheliitis fugax hereditaria (KEFH) is an autosomal dominant corneal disease that periodically and fleetingly affects the corneal endothelium, stroma, and vision, eventually resulting in central corneal stromal opacities in some patients. The disease is characterized by episodes of unilateral ocular pain, pericorneal injection, and photophobia. The acute symptoms vanish in 1 to 2 days, but vision remains blurry for several weeks. Onset occurs between ages 3 and 12 years, and may involve either eye. Episodes generally decrease in frequency and become more mild with age (summary by Turunen et al., 2018).

Familial hemiplegic migraine (FHM) falls within the category of migraine with aura. In migraine with aura (including FHM) the neurologic symptoms of aura are unequivocally localizable to the cerebral cortex or brain stem and include visual disturbance (most common), sensory loss (e.g., numbness or paresthesias of the face or an extremity), and dysphasia (difficulty with speech). FHM must include motor involvement, such as hemiparesis (weakness of an extremity). Hemiparesis occurs with at least one other symptom during FHM aura. Neurologic deficits with FHM attacks can be prolonged for hours to days and may outlast the associated migrainous headache. FHM is often earlier in onset than typical migraine, frequently beginning in the first or second decade; the frequency of attacks tends to decrease with age. Approximately 40%-50% of families with CACNA1A-FHM have cerebellar signs ranging from nystagmus to progressive, usually late-onset mild ataxia.

Any sarcoidosis in which the cause of the disease is a mutation in the HLA-DRB1 gene.

The designation 'antiphospholipid syndrome' was proposed for the association of arterial and venous thrombosis, recurrent fetal loss, and immune thrombocytopenia with a spectrum of autoantibodies directed against cellular phospholipid components. Anticardiolipin antibodies may react with cardiolipin and with other negatively charged phospholipids, including beta-2-glycoprotein I (B2GPI, APOH; 138700). The term 'lupus anticoagulant' refers to a heterogeneous group of antibodies, most commonly of the IgG type, that are detected by their inhibitory effect on coagulant-active phospholipid components of in vitro coagulation tests (summary by Matthey et al., 1989). Shoenfeld et al. (2008) noted that antiphospholipid syndrome is characterized by up to 30 different autoantibodies, including those against platelets, glycoproteins, coagulation factors, lamins, mitochondrial antigens, and cell surface markers. Some of these may have an additive effect on the prothrombotic tendency of the syndrome. Ruiz-Irastorza et al. (2010) reviewed pathophysiologic, clinical, diagnostic, and therapeutic advances related to the antiphospholipid syndrome. Various autoimmune disorders that cluster in families, including autoimmune thrombocytopenia (188030), are discussed elsewhere (e.g., 109100, 269200).

A retinitis pigmentosa that has material basis in variation in the chromosome region 6q23.

Any retinitis pigmentosa in which the cause of the disease is a mutation in the HGSNAT gene.

SOST-related sclerosing bone dysplasias include sclerosteosis and van Buchem disease, both disorders of progressive bone overgrowth due to increased bone formation. The major clinical features of sclerosteosis are progressive skeletal overgrowth, most pronounced in the skull and mandible, and variable syndactyly, usually of the second (index) and third (middle) fingers. Affected individuals appear normal at birth except for syndactyly. Facial distortion due to bossing of the forehead and mandibular overgrowth is seen in nearly all individuals and becomes apparent in early childhood with progression into adulthood. Hyperostosis of the skull results in narrowing of the foramina, causing entrapment of the seventh cranial nerve (leading to facial palsy) with other, less common nerve entrapment syndromes including visual loss (2nd cranial nerve), neuralgia or anosmia (5th cranial nerve), and sensory hearing loss (8th cranial nerve). In sclerosteosis, hyperostosis of the calvarium reduces intracranial volume, increasing the risk for potentially lethal elevation of intracranial pressure. Survival of individuals with sclerosteosis into old age is unusual, but not unprecedented. The manifestations of van Buchem disease are generally milder than sclerosteosis and syndactyly is absent; life span appears to be normal.

The spectrum of clinical manifestations of MAPT-related frontotemporal dementia (MAPT-FTD) has expanded from its original description of frontotemporal dementia and parkinsonian manifestations to include changes in behavior, motor function, memory, and/or language. A recent retrospective study suggested that the majority of affected individuals have either behavioral changes consistent with a diagnosis of behavioral variant FTD (bvFTD) or, less commonly, a parkinsonian syndrome (i.e., progressive supranuclear palsy, corticobasal syndrome, or Parkinson disease). Fewer than 5% of people with MAPT-FTD have primary progressive aphasia or Alzheimer disease. Clinical presentation may differ between and within families with the same MAPT variant. MAPT-FTD is a progressive disorder that commonly ends with a relatively global dementia in which some affected individuals become mute. Progression of motor impairment in affected individuals results in some becoming chairbound and others bedbound. Mean disease duration is 9.3 (SD: 6.4) years but is individually variable and can be more than 30 years in some instances.

The spectrum of COL4A1-related disorders includes: small-vessel brain disease of varying severity including porencephaly, variably associated with eye defects (retinal arterial tortuosity, Axenfeld-Rieger anomaly, cataract) and systemic findings (kidney involvement, muscle cramps, cerebral aneurysms, Raynaud phenomenon, cardiac arrhythmia, and hemolytic anemia). On imaging studies, small-vessel brain disease is manifest as diffuse periventricular leukoencephalopathy, lacunar infarcts, microhemorrhage, dilated perivascular spaces, and deep intracerebral hemorrhages. Clinically, small-vessel brain disease manifests as infantile hemiparesis, seizures, single or recurrent hemorrhagic stroke, ischemic stroke, and isolated migraine with aura. Porencephaly (fluid-filled cavities in the brain detected by CT or MRI) is typically manifest as infantile hemiparesis, seizures, and intellectual disability; however, on occasion it can be an incidental finding. HANAC (hereditary angiopathy with nephropathy, aneurysms, and muscle cramps) syndrome usually associates asymptomatic small-vessel brain disease, cerebral large vessel involvement (i.e., aneurysms), and systemic findings involving the kidney, muscle, and small vessels of the eye. Two additional phenotypes include isolated retinal artery tortuosity and nonsyndromic autosomal dominant congenital cataract.