Genetic prion disease generally manifests with cognitive difficulties, ataxia, and myoclonus (abrupt jerking movements of muscle groups and/or entire limbs). The order of appearance and/or predominance of these features and other associated neurologic and psychiatric findings vary. The three major phenotypes of genetic prion disease are genetic Creutzfeldt-Jakob disease (gCJD), fatal familial insomnia (FFI), and Gerstmann-Sträussler-Scheinker (GSS) syndrome. Although these phenotypes display overlapping clinical and pathologic features, recognition of these phenotypes can be useful when providing affected individuals and their families with information about the expected clinical course. The age at onset typically ranges from 50 to 60 years. The disease course ranges from a few months in gCJD and FFI to a few (up to 4, and in rare cases up to 10) years in GSS syndrome.

Lipoid proteinosis (LP) is characterized by deposition of hyaline-like material in various tissues resulting in a hoarse voice from early infancy, vesicles and hemorrhagic crusts in the mouth and on the face and extremities, verrucous and keratotic cutaneous lesions on extensor surfaces (especially the elbows), and moniliform blepharosis (multiple beaded papules along the eyelid margins and inner canthus). Extracutaneous manifestations may include epilepsy, neuropsychiatric disorders, spontaneous CNS hemorrhage, and asymptomatic multiple yellowish nodules throughout the gastrointestinal tract. Generally, the disease course is chronic and fluctuating. Males and females are affected equally. Affected individuals have a normal life span unless they experience laryngeal obstruction.

A psychotic syndrome caused by damage to the brain by lack of thiamine (vitamin B1). Signs and symptoms include anterograde and retrograde amnesia, confabulation, apathy, ataxia, and coma.

Genetic prion disease generally manifests with cognitive difficulties, ataxia, and myoclonus (abrupt jerking movements of muscle groups and/or entire limbs). The order of appearance and/or predominance of these features and other associated neurologic and psychiatric findings vary. The three major phenotypes of genetic prion disease are genetic Creutzfeldt-Jakob disease (gCJD), fatal familial insomnia (FFI), and Gerstmann-Sträussler-Scheinker (GSS) syndrome. Although these phenotypes display overlapping clinical and pathologic features, recognition of these phenotypes can be useful when providing affected individuals and their families with information about the expected clinical course. The age at onset typically ranges from 50 to 60 years. The disease course ranges from a few months in gCJD and FFI to a few (up to 4, and in rare cases up to 10) years in GSS syndrome.

CHMP2B frontotemporal dementia (CHMP2B-FTD) has been described in a single family from Denmark, in one individual with familial FTD from Belgium, and in one individual with FTD and no family history. It typically starts between ages 46 and 65 years with subtle personality changes and slowly progressive behavioral changes, dysexecutive syndrome, dyscalculia, and language disturbances. Disinhibition or loss of initiative is the most common presenting symptom. The disease progresses over a few years into profound dementia with extrapyramidal symptoms and mutism. Several individuals have developed an asymmetric akinetic rigid syndrome with arm and gait dystonia and pyramidal signs that may be related to treatment with neuroleptic drugs. Symptoms and disease course are highly variable. Disease duration may be as short as three years or longer than 20 years.

FMR1 disorders include fragile X syndrome (FXS), fragile X-associated tremor/ataxia syndrome (FXTAS), and fragile X-associated primary ovarian insufficiency (FXPOI). Fragile X syndrome occurs in individuals with an FMR1 full mutation or other loss-of-function variant and is nearly always characterized in affected males by developmental delay and intellectual disability along with a variety of behavioral issues. Autism spectrum disorder is present in 50%-70% of individuals with FXS. Affected males may have characteristic craniofacial features (which become more obvious with age) and medical problems including hypotonia, gastroesophageal reflux, strabismus, seizures, sleep disorders, joint laxity, pes planus, scoliosis, and recurrent otitis media. Adults may have mitral valve prolapse or aortic root dilatation. The physical and behavioral features seen in males with FXS have been reported in females heterozygous for the FMR1 full mutation, but with lower frequency and milder involvement. FXTAS occurs in individuals who have an FMR1 premutation and is characterized by late-onset, progressive cerebellar ataxia and intention tremor followed by cognitive impairment. Psychiatric disorders are common. Age of onset is typically between 60 and 65 years and is more common among males who are hemizygous for the premutation (40%) than among females who are heterozygous for the premutation (16%-20%). FXPOI, defined as hypergonadotropic hypogonadism before age 40 years, has been observed in 20% of women who carry a premutation allele compared to 1% in the general population.

Alzheimer's disease can be classified as early-onset or late-onset. The signs and symptoms of the early-onset form appear between a person's thirties and mid-sixties, while the late-onset form appears during or after a person's mid-sixties. The early-onset form of Alzheimer's disease is much less common than the late-onset form, accounting for less than 10 percent of all cases of Alzheimer's disease.\n\nIndividuals with Alzheimer's disease usually survive 8 to 10 years after the appearance of symptoms, but the course of the disease can range from 1 to 25 years. Survival is usually shorter in individuals diagnosed after age 80 than in those diagnosed at a younger age. In Alzheimer's disease, death usually results from pneumonia, malnutrition, or general body wasting (inanition).\n\nAs the disorder progresses, some people with Alzheimer's disease experience personality and behavioral changes and have trouble interacting in a socially appropriate manner. Other common symptoms include agitation, restlessness, withdrawal, and loss of language skills. People with Alzheimer's disease usually require total care during the advanced stages of the disease.\n\nMemory loss is the most common sign of Alzheimer's disease. Forgetfulness may be subtle at first, but the loss of memory worsens over time until it interferes with most aspects of daily living. Even in familiar settings, a person with Alzheimer's disease may get lost or become confused. Routine tasks such as preparing meals, doing laundry, and performing other household chores can be challenging. Additionally, it may become difficult to recognize people and name objects. Affected people increasingly require help with dressing, eating, and personal care.\n\nAlzheimer's disease is a degenerative disease of the brain that causes dementia, which is a gradual loss of memory, judgment, and ability to function. This disorder usually appears in people older than age 65, but less common forms of the disease appear earlier in adulthood.

The spectrum of GRN frontotemporal dementia (GRN-FTD) includes the behavioral variant (bvFTD), primary progressive aphasia (PPA; further subcategorized as progressive nonfluent aphasia [PNFA] and semantic dementia [SD]), and movement disorders with extrapyramidal features such as parkinsonism and corticobasal syndrome (CBS). A broad range of clinical features both within and between families is observed. The age of onset ranges from 35 to 87 years. Behavioral disturbances are the most common early feature, followed by progressive aphasia. Impairment in executive function manifests as loss of judgment and insight. In early stages, PPA often manifests as deficits in naming, word finding, or word comprehension. In late stages, affected individuals often become mute and lose their ability to communicate. Early findings of parkinsonism include rigidity, bradykinesia or akinesia (slowing or absence of movements), limb dystonia, apraxia (loss of ability to carry out learned purposeful movements), and disequilibrium. Late motor findings may include myoclonus, dysarthria, and dysphagia. Most affected individuals eventually lose the ability to walk. Disease duration is three to 12 years.

Spastic paraplegia 7 (SPG7) is characterized by insidiously progressive bilateral leg weakness and spasticity. Most affected individuals have decreased vibration sense and cerebellar signs. Onset is mostly in adulthood, although symptoms may start as early as age 11 years and as late as age 72 years. Additional features including ataxia (gait and limbs), spastic dysarthria, dysphagia, pale optic disks, ataxia, nystagmus, strabismus, ptosis, hearing loss, motor and sensory neuropathy, amyotrophy, scoliosis, pes cavus, and urinary sphincter disturbances may be observed.

Alzheimer's disease is a degenerative disease of the brain that causes dementia, which is a gradual loss of memory, judgment, and ability to function. This disorder usually appears in people older than age 65, but less common forms of the disease appear earlier in adulthood.\n\nMemory loss is the most common sign of Alzheimer's disease. Forgetfulness may be subtle at first, but the loss of memory worsens over time until it interferes with most aspects of daily living. Even in familiar settings, a person with Alzheimer's disease may get lost or become confused. Routine tasks such as preparing meals, doing laundry, and performing other household chores can be challenging. Additionally, it may become difficult to recognize people and name objects. Affected people increasingly require help with dressing, eating, and personal care.\n\nAs the disorder progresses, some people with Alzheimer's disease experience personality and behavioral changes and have trouble interacting in a socially appropriate manner. Other common symptoms include agitation, restlessness, withdrawal, and loss of language skills. People with Alzheimer's disease usually require total care during the advanced stages of the disease.\n\nIndividuals with Alzheimer's disease usually survive 8 to 10 years after the appearance of symptoms, but the course of the disease can range from 1 to 25 years. Survival is usually shorter in individuals diagnosed after age 80 than in those diagnosed at a younger age. In Alzheimer's disease, death usually results from pneumonia, malnutrition, or general body wasting (inanition).\n\nAlzheimer's disease can be classified as early-onset or late-onset. The signs and symptoms of the early-onset form appear between a person's thirties and mid-sixties, while the late-onset form appears during or after a person's mid-sixties. The early-onset form of Alzheimer's disease is much less common than the late-onset form, accounting for less than 10 percent of all cases of Alzheimer's disease.

Huntington disease-like 2 (HDL2) typically presents in midlife with a relentless progressive triad of movement, emotional, and cognitive abnormalities which lead to death within ten to 20 years. HDL2 cannot be differentiated from Huntington disease clinically. Neurologic abnormalities include chorea, hypokinesia (rigidity, bradykinesia), dysarthria, and hyperreflexia in the later stages of the disease. There is a strong correlation between the duration of the disease and the progression of the motor and cognitive disorder.

Spinocerebellar ataxia type 14 (SCA14) is characterized by slowly progressive cerebellar ataxia, dysarthria, and nystagmus. Axial myoclonus, cognitive impairment, tremor, and sensory loss may also be observed. Parkinsonian features including rigidity and tremor have been described in some families. Findings seen in other ataxia disorders (e.g., dysphagia, dysphonia) may also occur in SCA14. The average age of onset is in the 30s, with a range from childhood to the seventh decade. Life span is not shortened.

An Alzheimer's disease that is characterized by an associated with variation in the region 7q36.

Spastic paraplegia 4 (SPG4; also known as SPAST-HSP) is characterized by insidiously progressive bilateral lower-limb gait spasticity. More than 50% of affected individuals have some weakness in the legs and impaired vibration sense at the ankles. Sphincter disturbances are very common. Onset is insidious, mostly in young adulthood, although symptoms may start as early as age one year and as late as age 76 years. Intrafamilial variation is considerable.

Hereditary spastic ataxia comprises a heterogeneous group of progressive neurodegenerative disorders characterized by lower-limb spasticity and generalized ataxia with dysarthria, impaired ocular movements, and gait disturbance. Spastic ataxia-1 (SPAX1) is an autosomal dominant form of the disorder with onset between the ages of 10 and 20 years. Other clinical features are supranuclear gaze palsy, hyperreflexia, hypertonicity, dystonia, pes cavus, mild ptosis, and decreased vibration sense in the lower limbs. Symptom severity is variable, but neither life span nor cognition is affected (summary by Meijer et al., 2002 and Bourassa et al., 2012). Genetic Heterogeneity of Spastic Ataxia See also SPAX2 (611302), caused by mutation in the KIF1C gene (603060) on chromosome 17p13; SPAX3 (611390), caused by rearrangements of the MARS2 gene (609728) on chromosome 2q33; SPAX4 (613672), caused by mutation in the MTPAP gene (613669) on chromosome 10p11; SPAX5 (614487), caused by mutation in the AFG3L2 gene (604581) on chromosome 18p11; SPAX6 (270550), caused by mutation in the SACS gene (604490) on chromosome 13q12; SPAX7 (108650); SPAX8 (617560), caused by mutation in the NKX6-2 gene (605955) on chromosome 8q21; SPAX9 (618438), caused by mutation in the CHP1 gene (606988) on chromosome 15q15; and SPAX10 (620666), caused by mutation in the COQ4 gene (612898) on chromosome 9q34.

A heterozygous deletion of chromosome 15q11.2 may increase the susceptibility to neuropsychiatric or neurodevelopmental problems, including delayed psychomotor development, speech delay, autism spectrum disorder, attention deficit-hyperactivity disorder, obsessive-compulsive disorder, and possibly seizures (summary by Doornbos et al., 2009 and Burnside et al., 2011). See also chromosome 15q11.2 duplication syndrome (608636).

DNMT1-related disorder is a degenerative disorder of the central and peripheral nervous systems comprising a phenotypic spectrum that includes hereditary sensory and autonomic neuropathy type 1E (HSAN1E) and autosomal dominant cerebellar ataxia, deafness, and narcolepsy (ADCA-DN). DNMT1 disorder is often characterized by moderate-to-severe sensorineural hearing loss beginning in the teens or early 20s, sensory impairment, sudomotor dysfunction (loss of sweating), and dementia usually beginning in the mid-40s. In some affected individuals, narcolepsy/cataplexy syndrome and ataxia are predominant findings.

ADCADN is an autosomal dominant neurologic disorder characterized by adult onset of progressive cerebellar ataxia, narcolepsy/cataplexy, sensorineural deafness, and dementia. More variable features include optic atrophy, sensory neuropathy, psychosis, and depression (summary by Winkelmann et al., 2012).

Primary familial brain calcification (PFBC) is a neurodegenerative disorder with characteristic calcium deposits in the basal ganglia and other brain areas visualized on neuroimaging. Most affected individuals are in good health during childhood and young adulthood and typically present in the fourth to fifth decade with a gradually progressive movement disorder and neuropsychiatric symptoms. The movement disorder first manifests as clumsiness, fatigability, unsteady gait, slow or slurred speech, dysphagia, involuntary movements, or muscle cramping. Neuropsychiatric symptoms, often the first or most prominent manifestations, range from mild difficulty with concentration and memory to changes in personality and/or behavior, to psychosis and dementia. Seizures of various types occur frequently, some individuals experience chronic headache and vertigo; urinary urgency or incontinence may be present.

Primary familial brain calcification (PFBC) is a neurodegenerative disorder with characteristic calcium deposits in the basal ganglia and other brain areas visualized on neuroimaging. Most affected individuals are in good health during childhood and young adulthood and typically present in the fourth to fifth decade with a gradually progressive movement disorder and neuropsychiatric symptoms. The movement disorder first manifests as clumsiness, fatigability, unsteady gait, slow or slurred speech, dysphagia, involuntary movements, or muscle cramping. Neuropsychiatric symptoms, often the first or most prominent manifestations, range from mild difficulty with concentration and memory to changes in personality and/or behavior, to psychosis and dementia. Seizures of various types occur frequently, some individuals experience chronic headache and vertigo; urinary urgency or incontinence may be present.

Primary familial brain calcification (PFBC) is a neurodegenerative disorder with characteristic calcium deposits in the basal ganglia and other brain areas visualized on neuroimaging. Most affected individuals are in good health during childhood and young adulthood and typically present in the fourth to fifth decade with a gradually progressive movement disorder and neuropsychiatric symptoms. The movement disorder first manifests as clumsiness, fatigability, unsteady gait, slow or slurred speech, dysphagia, involuntary movements, or muscle cramping. Neuropsychiatric symptoms, often the first or most prominent manifestations, range from mild difficulty with concentration and memory to changes in personality and/or behavior, to psychosis and dementia. Seizures of various types occur frequently, some individuals experience chronic headache and vertigo; urinary urgency or incontinence may be present.

CADASIL (cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy) is characterized by mid-adult onset of recurrent ischemic stroke, cognitive decline progressing to dementia, a history of migraine with aura, mood disturbance, apathy, and diffuse white matter lesions and subcortical infarcts on neuroimaging.

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.

Polycystic lipomembranous osteodysplasia with sclerosing leukoencephalopathy (PLOSL) is characterized by fractures (resulting from radiologically demonstrable polycystic osseous lesions), frontal lobe syndrome, and progressive presenile dementia beginning in the fourth decade. The clinical course of PLOSL can be divided into four stages: 1. The latent stage is characterized by normal early development. 2. The osseous stage (3rd decade of life) is characterized by pain and tenderness, mostly in ankles and feet, usually following strain or injury. Fractures are typically diagnosed several years later, most commonly in the bones of the extremities. 3. In the early neurologic stage (4th decade of life), a change of personality begins to develop insidiously. Affected individuals show a frontal lobe syndrome (loss of judgment, euphoria, loss of social inhibitions, disturbance of concentration, and lack of insight, libido, and motor persistence) leading to serious social problems. 4. The late neurologic stage is characterized by progressive dementia and loss of mobility. Death usually occurs before age 50 years.

Polycystic lipomembranous osteodysplasia with sclerosing leukoencephalopathy-2 (PLOSL2), or Nasu-Hakola disease, is a recessively inherited presenile frontal dementia with leukoencephalopathy and basal ganglia calcification. In most cases the disorder first manifests in early adulthood as pain and swelling in ankles and feet, followed by bone fractures. Neurologic symptoms manifest in the fourth decade of life as a frontal lobe syndrome with loss of judgment, euphoria, and disinhibition. Progressive decline in other cognitive domains begins to develop at about the same time. The disorder culminates in a profound dementia and death by age 50 years (summary by Klunemann et al., 2005). For a discussion of genetic heterogeneity of polycystic lipomembranous osteodysplasia with sclerosing leukoencephalopathy, see 221770.

Progressive myoclonic epilepsy-6 (EPM6) is an autosomal recessive neurologic disorder characterized by onset of ataxia in the first years of life, followed by action myoclonus and seizures later in childhood, and loss of independent ambulation in the second decade. Cognition is not usually affected, although mild memory difficulties may occur in the third decade (summary by Corbett et al., 2011). For a discussion of genetic heterogeneity of progressive myoclonic epilepsy, see EPM1A (254800).

Autosomal recessive idiopathic basal ganglia calcification-7 is a neurologic disorder characterized by onset of symptoms in adulthood. Patients present with dysarthria, gait abnormalities, various movement abnormalities, and often cognitive decline. Brain imaging shows abnormal accumulation of calcium deposits in deep brain regions, including the basal ganglia, thalamus, dentate nuclei, cerebellum, and sometimes other areas of the brain and spinal cord. Some patients with brain imaging abnormalities may be clinically asymptomatic (summary by Yao et al., 2018). For a detailed phenotypic description and a discussion of genetic heterogeneity of IBGC, see IBGC1 (213600).

Frontotemporal dementia and/or amyotrophic lateral sclerosis-8 (FTDALS8) is an autosomal dominant neurodegenerative disorder characterized by adult-onset dementia manifest as memory impairment, executive dysfunction, and behavioral or personality changes. Some patients may develop ALS or parkinsonism. Neuropathologic studies show frontotemporal lobar degeneration (FTLD) with tau (MAPT; 157140)- and TDP43 (605078)-immunoreactive inclusions (summary by Dobson-Stone et al., 2020). For a discussion of genetic heterogeneity of FTDALS, see FTDALS1 (105550).

Amyotrophic lateral sclerosis-26 with or without frontotemporal dementia (ALS26) is an autosomal dominant neurodegenerative disorder characterized by adult onset of upper and low motor neuron disease causing bulbar dysfunction and limb weakness (ALS). Patients may also develop frontotemporal dementia (FTD) manifest as primary progressive aphasia, memory impairment, executive dysfunction, and behavioral or personality changes. Although patients may present with 1 or the other diseases, all eventually develop ALS. Neuropathologic studies of the brain and spinal cord show TDP43 (605078)-immunoreactive cytoplasmic inclusions that correlate with clinical features and Lewy body-like cytoplasmic inclusions in lower motor neurons (summary by Mackenzie et al., 2017). For a discussion of genetic heterogeneity of amyotrophic lateral sclerosis, see ALS1 (105400).

CSF1R-related adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP) is characterized by executive dysfunction, memory decline, personality changes, motor impairments, and seizures. A frontal lobe syndrome (e.g., loss of judgment, lack of social inhibitors, lack of insight, and motor persistence) usually appears early in the disease course. The mean age of onset is usually in the fourth decade. Affected individuals eventually become bedridden with spasticity and rigidity. The disease course ranges from two to 30 or more years (mean: 8 years).

Combined oxidative phosphorylation deficiency-54 (COXPD54) is an autosomal recessive disorder with pleiotropic multisystem presentations resulting from a disruption in mitochondrial transcription and translation. The phenotype is highly variable. Many patients have early-onset sensorineural hearing loss, sometimes in isolation, and sometimes associated with global developmental delay or primary ovarian failure. Other features may include peripheral hypertonia, seizures, muscle weakness, behavioral abnormalities, and leukoencephalopathy on brain imaging. Serum lactate may or may not be elevated (summary by Hochberg et al., 2021). For a discussion of genetic heterogeneity of combined oxidative phosphorylation deficiency, see COXPD1 (609060).

Autosomal recessive intellectual developmental disorder-75 with neuropsychiatric features and variant lissencephaly (MRT75) is characterized by global developmental delay apparent from infancy or early childhood and moderate to profoundly impaired intellectual development. Most affected individuals have behavioral abnormalities, including aggression and ADHD; a few have psychiatric manifestations, including psychosis. More variable additional features include well-controlled seizures and dysmorphic facial features. Brain imaging often shows frontal predominant pachygyria or other gyri/sulci abnormalities, consistent with a variant of lissencephaly and a malformation of cortical development (MCD) (summary by Zaki et al., 2021).

Spinocerebellar ataxia-50 (SCA50) is an autosomal dominant neurologic disorder characterized by cerebellar ataxia, oculomotor apraxia and other eye movement abnormalities, and cerebellar atrophy on brain imaging. Most patients develop symptoms as adults, although childhood onset has rarely been reported. Additional more variable features may include tremor, dysarthria, dysphagia, and cognitive impairment with executive dysfunction (Coutelier et al., 2022; Schoggl et al., 2022).

Any leukoencephalopathy with vanishing white matter in which the cause of the disease is a variation in the EIF2B1 gene.

Leukoencephalopathy with vanishing white matter-2 (VWM2) is a chronic and progressive autosomal recessive leukoencephalopathy characterized by neurologic deterioration with cerebellar ataxia, spasticity, and relatively mild mental decline. Severity ranges from onset at birth with death in infancy to mild cases with later and even adult onset. Initial development may be normal. Episodes of rapid deterioration occur following febrile infection or minor head trauma. Death occurs after a variable period usually of a few years to a few decades, usually following an episode of fever and coma. Affected females may have ovarian failure manifest as primary or secondary amenorrhea. Magnetic resonance imaging (MRI) and magnetic resonance spectroscopy are diagnostic and show a diffuse abnormality of the cerebral white matter beginning in the presymptomatic stage, with increasing amounts of the abnormal white matter vanishing and being replaced by cerebrospinal fluid; autopsy confirms these findings (summary by Leegwater et al., 2001, van der Knaap et al., 2003). For a discussion of genetic heterogeneity of VWM, see 603896.