MedGen

Pantothenate kinase-associated neurodegeneration (PKAN) is a type of neurodegeneration with brain iron accumulation (NBIA). The phenotypic spectrum of PKAN includes classic PKAN and atypical PKAN. Classic PKAN is characterized by early-childhood onset of progressive dystonia, dysarthria, rigidity, and choreoathetosis. Pigmentary retinal degeneration is common. Atypical PKAN is characterized by later onset (age >10 years), prominent speech defects, psychiatric disturbances, and more gradual progression of disease. [from GeneReviews]

Hypophosphatasia is characterized by defective mineralization of growing or remodeling bone, with or without root-intact tooth loss, in the presence of low activity of serum and bone alkaline phosphatase. Clinical features range from stillbirth without mineralized bone at the severe end to pathologic fractures of the lower extremities in later adulthood at the mild end. While the disease spectrum is a continuum, seven clinical forms of hypophosphatasia are usually recognized based on age at diagnosis and severity of features: Perinatal (severe): characterized by pulmonary insufficiency and hypercalcemia. Perinatal (benign): prenatal skeletal manifestations that slowly resolve into one of the milder forms. Infantile: onset between birth and age six months of clinical features of rickets without elevated serum alkaline phosphatase activity. Severe childhood (juvenile): variable presenting features progressing to rickets. Mild childhood: low bone mineral density for age, increased risk of fracture, and premature loss of primary teeth with intact roots. Adult: characterized by stress fractures and pseudofractures of the lower extremities in middle age, sometimes associated with early loss of adult dentition. Odontohypophosphatasia: characterized by premature exfoliation of primary teeth and/or severe dental caries without skeletal manifestations. [from GeneReviews]

Achondrogenesis type II (ACG2) is characterized by severe micromelic dwarfism with small chest and prominent abdomen, incomplete ossification of the vertebral bodies, and disorganization of the costochondral junction. ACG2 is an autosomal dominant trait occurring mostly as new mutations. However, somatic and germline mosaicism have been reported (summary by Comstock et al., 2010). [from OMIM]

Carnitine palmitoyltransferase II (CPT II) deficiency is a disorder of long-chain fatty-acid oxidation. The three clinical presentations are lethal neonatal form, severe infantile hepatocardiomuscular form, and myopathic form (which is usually mild and can manifest from infancy to adulthood). While the former two are severe multisystemic diseases characterized by liver failure with hypoketotic hypoglycemia, cardiomyopathy, seizures, and early death, the latter is characterized by exercise-induced muscle pain and weakness, sometimes associated with myoglobinuria. The myopathic form of CPT II deficiency is the most common disorder of lipid metabolism affecting skeletal muscle and the most frequent cause of hereditary myoglobinuria. Males are more likely to be affected than females. [from GeneReviews]

Free sialic acid storage disorders (FSASDs) are a spectrum of neurodegenerative disorders resulting from increased lysosomal storage of free sialic acid. Historically, FSASD was divided into separate allelic disorders: Salla disease, intermediate severe Salla disease, and infantile free sialic acid storage disease (ISSD). The mildest type was Salla disease, characterized by normal appearance and absence of neurologic findings at birth, followed by slowly progressive neurologic deterioration resulting in mild-to-moderate psychomotor delays, spasticity, athetosis, and epileptic seizures. Salla disease was named for a municipality in Finnish Lapland where a specific founder variant is relatively prevalent. However, the term Salla has been used in the literature to refer to less severe FSASD. More severe FSASD is historically referred to as ISSD, and is characterized by severe developmental delay, coarse facial features, hepatosplenomegaly, and cardiomegaly; death usually occurs in early childhood. [from GeneReviews]

The autosomal dominant TRPV4 disorders (previously considered to be clinically distinct phenotypes before their molecular basis was discovered) are now grouped into neuromuscular disorders and skeletal dysplasias; however, the overlap within each group is considerable. Affected individuals typically have either neuromuscular or skeletal manifestations alone, and in only rare instances an overlap syndrome has been reported. The three autosomal dominant neuromuscular disorders (mildest to most severe) are: Charcot-Marie-Tooth disease type 2C. Scapuloperoneal spinal muscular atrophy. Congenital distal spinal muscular atrophy. The autosomal dominant neuromuscular disorders are characterized by a congenital-onset, static, or later-onset progressive peripheral neuropathy with variable combinations of laryngeal dysfunction (i.e., vocal fold paresis), respiratory dysfunction, and joint contractures. The six autosomal dominant skeletal dysplasias (mildest to most severe) are: Familial digital arthropathy-brachydactyly. Autosomal dominant brachyolmia. Spondylometaphyseal dysplasia, Kozlowski type. Spondyloepiphyseal dysplasia, Maroteaux type. Parastremmatic dysplasia. Metatropic dysplasia. The skeletal dysplasia is characterized by brachydactyly (in all 6); the five that are more severe have short stature that varies from mild to severe with progressive spinal deformity and involvement of the long bones and pelvis. In the mildest of the autosomal dominant TRPV4 disorders life span is normal; in the most severe it is shortened. Bilateral progressive sensorineural hearing loss (SNHL) can occur with both autosomal dominant neuromuscular disorders and skeletal dysplasias. [from GeneReviews]

Hidrotic ectodermal dysplasia 2, or Clouston syndrome (referred to as HED2 throughout this GeneReview) is characterized by a triad of major clinical features including partial-to-complete alopecia, nail dystrophy, and palmoplantar hyperkeratosis. Sweating is preserved and there are usually no dental anomalies. Sparse scalp hair and dysplastic nails are seen early in life. In infancy, scalp hair is fine, sparse, and brittle. Progressive hair loss may lead to total alopecia by puberty. The nails may be milky white in early childhood; they gradually become dystrophic, thick, and distally separated from the nail bed. Palmoplantar keratoderma may develop during childhood and increases in severity with age. Associated features may include cutaneous hyperpigmentation (particularly over the joints) and finger clubbing. The clinical manifestations are highly variable even within the same family. [from GeneReviews]

Classic Joubert syndrome (JS) is characterized by three primary findings: A distinctive cerebellar and brain stem malformation called the molar tooth sign (MTS). Hypotonia. Developmental delays. Often these findings are accompanied by episodic tachypnea or apnea and/or atypical eye movements. In general, the breathing abnormalities improve with age, truncal ataxia develops over time, and acquisition of gross motor milestones is delayed. Cognitive abilities are variable, ranging from severe intellectual disability to normal. Additional findings can include retinal dystrophy, renal disease, ocular colobomas, occipital encephalocele, hepatic fibrosis, polydactyly, oral hamartomas, and endocrine abnormalities. Both intra- and interfamilial variation are seen. [from GeneReviews]

EXOSC3 pontocerebellar hypoplasia (EXOSC3-PCH) is characterized by abnormalities in the posterior fossa and degeneration of the anterior horn cells. At birth, skeletal muscle weakness manifests as hypotonia (sometimes with congenital joint contractures) and poor feeding. In persons with prolonged survival, spasticity, dystonia, and seizures become evident. Within the first year of life respiratory insufficiency and swallowing difficulties are common. Intellectual disability is severe. Life expectancy ranges from a few weeks to adolescence. To date, 82 individuals (from 58 families) with EXOSC3-PCH have been described. [from GeneReviews]

Christianson syndrome (referred to as CS in this GeneReview), an X-linked disorder, is characterized in males by cognitive dysfunction, behavioral disorder, and neurologic findings (e.g., seizures, ataxia, postnatal microcephaly, and eye movement abnormalities). Males with CS typically present with developmental delay, later meeting criteria for severe intellectual disability (ID). Behaviorally, autism spectrum disorder and hyperactivity are common, and may resemble the behaviors observed in Angelman syndrome. Hypotonia and oropharyngeal dysphagia in infancy may result in failure to thrive. Seizures, typically beginning before age three years, can include infantile spasms and tonic, tonic-clonic, myoclonic, and atonic seizures. Subsequently, regression (e.g., loss of ambulation and ability to feed independently) may occur. Manifestations in heterozygous females range from asymptomatic to mild ID and/or behavioral issues. [from GeneReviews]

Spinal muscular atrophy (SMA) is a hereditary neuromuscular disorder characterized by degeneration of spinal cord motor neurons resulting in muscle weakness. SMALED shows autosomal dominant inheritance with muscle weakness predominantly affecting the proximal lower extremities (Harms et al., 2010). The most common form of SMA (see, e.g., SMA1, 253300) shows autosomal recessive inheritance and is due to mutation in the SMN1 gene (600354) on chromosome 5q. Genetic Heterogeneity of Lower Extremity-Predominant Spinal Muscular Atrophy See also SMALED2A (615290) and SMALED2B (618291), both of which are caused by mutation in the BICD2 gene (609797) on chromosome 9q22. SMALED2A and SMALED2B differ in age at onset and severity, with SMALED2B being more severe. [from OMIM]

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. [from GeneReviews]

Progressive pseudorheumatoid dysplasia (PPD) is a skeletal dysplasia characterized by predominant involvement of articular cartilage with progressive joint stiffness and enlargement in the absence of inflammation. Onset – typically between ages three and six years – begins with the involvement of the interphalangeal joints. Over time, involvement of large joints and the spine causes significant joint contractures, gait disturbance, and scoliosis and/or kyphosis, resulting in abnormal posture and significant morbidity. Despite the considerable arthropathy, pain is not a major presenting feature of this condition. Initially height is normal; however, short stature (<3rd centile) becomes evident in adolescence as the skeletal changes progress. [from GeneReviews]

Pontocerebellar hypoplasia (PCH) refers to a group of severe neurodegenerative disorders affecting growth and function of the brainstem and cerebellum, resulting in little or no development. Different types were classified based on the clinical picture and the spectrum of pathologic changes. PCH type 1 is characterized by central and peripheral motor dysfunction associated with anterior horn cell degeneration resembling infantile spinal muscular atrophy (SMA; see SMA1, 253300); death usually occurs early. Genetic Heterogeneity of Pontocerebellar Hypoplasia Also see PCH1B (614678), caused by mutation in the EXOSC3 gene (606489); PCH1C (616081), caused by mutation in the EXOSC8 gene (606019); PCH1D (618065), caused by mutation in the EXOSC9 gene (606180); PCH1E (619303), caused by mutation in the SLC25A46 gene (610826); PCH1F (619304), caused by mutation in the EXOSC1 gene (606493); PCH2A (277470), caused by mutation in the TSEN54 gene (608755); PCH2B (612389), caused by mutation in the TSEN2 gene (608753); PCH2C (612390), caused by mutation in the TSEN34 gene (608754); PCH2D (613811), caused by mutation in the SEPSECS gene (613009); PCH3 (608027), caused by mutation in the PCLO gene (604918); PCH4 (225753), caused by mutation in the TSEN54 gene; PCH5 (610204), caused by mutation in the TSEN54 gene; PCH6 (611523), caused by mutation in the RARS2 gene (611524); PCH7 (614969), caused by mutation in the TOE1 gene (613931); PCH8 (614961), caused by mutation in the CHMP1A gene (164010); PCH9 (615809), caused by mutation in the AMPD2 gene (102771); PCH10 (615803), caused by mutation in the CLP1 gene (608757); PCH11 (617695), caused by mutation in the TBC1D23 gene (617687); PCH12 (618266), caused by mutation in the COASY gene (609855); PCH13 (618606), caused by mutation in the VPS51 gene (615738); PCH14 (619301), caused by mutation in the PPIL1 gene (601301); PCH15 (619302), caused by mutation in the CDC40 gene (605585); PCH16 (619527), caused by mutation in the MINPP1 gene (605391); and PCH17 (619909), caused by mutation in the PRDM13 gene (616741) on chromosome 6q16. [from OMIM]

Miller syndrome, or postaxial acrofacial dysostosis, is a rare autosomal recessive disorder characterized clinically by severe micrognathia, cleft lip and/or palate, hypoplasia or aplasia of the postaxial elements of the limbs, coloboma of the eyelids, and supernumerary nipples (summary by Ng et al., 2010). [from OMIM]

A rare hereditary motor and sensory neuropathy characterized by intermediate motor median nerve conduction velocities (usually between 25 and 60 m/s). It presents with moderately severe, slowly progressive usual clinical features of Charcot-Marie-Tooth disease (muscle weakness and atrophy of the distal extremities, distal sensory loss, reduced or absent deep tendon reflexes, feet deformities, extensor digitorum brevis atrophy). Findings in nerve biopsies include age-dependent axonal degeneration, reduced number of large myelinated fibers, segmental remyelination, and no onion bulbs. [from SNOMEDCT_US]

NMAN is an autosomal recessive neurologic disorder characterized by onset in the first or second decade of a peripheral axonal neuropathy predominantly affecting motor more than sensory nerves. The axonal neuropathy is reminiscent of Charcot-Marie-Tooth disease type 2 (see, e.g., CMT2A1, 118210) and distal hereditary motor neuropathy (see, e.g., HMND1, 182960). Individuals with NMAN also have delayed muscle relaxation and action myotonia associated with neuromyotonic discharges on needle EMG resulting from hyperexcitability of the peripheral nerves (summary by Zimon et al., 2012). [from OMIM]

Any brachydactyly type A1 in which the cause of the disease is a mutation in the BMPR1B gene. [from MONDO]

Van Maldergem syndrome is an autosomal recessive disorder characterized by intellectual disability, typical craniofacial features, auditory malformations resulting in hearing loss, and skeletal and limb malformations. Some patients have renal hypoplasia. Brain MRI typically shows periventricular nodular heterotopia (summary by Cappello et al., 2013). Genetic Heterogeneity of Van Maldergem Syndrome See also VMLDS2 (615546), caused by mutation in the FAT4 gene (612411) on chromosome 4q28. [from OMIM]

Congenital hypomyelinating neuropathy-3 is an autosomal recessive neurologic disorder characterized by onset of neurogenic muscle impairment in utero. Affected individuals present at birth with severe hypotonia, often causing respiratory insufficiency or failure and inability to swallow or feed properly. They have profoundly impaired psychomotor development and may die in infancy or early childhood. Those that survive are unable to sit or walk. Sural nerve biopsy shows hypomyelination of the nerve fibers, and brain imaging often shows impaired myelination and cerebral and cerebellar atrophy. Nerve conduction velocities are severely decreased (about 10 m/s) or absent due to improper myelination (summary by Vallat et al., 2016 and Low et al., 2018). For a discussion of genetic heterogeneity of CHN, see CHN1 (605253). [from OMIM]