Fabry disease is the most common of the lysosomal storage disorders and results from deficient activity of the enzyme alpha-galactosidase A (a-Gal A), leading to progressive lysosomal deposition of globotriaosylceramide and its derivatives in cells throughout the body. The classic form, occurring in males with less than 1% a-Gal A enzyme activity, usually has its onset in childhood or adolescence with periodic crises of severe pain in the extremities (acroparesthesia), the appearance of vascular cutaneous lesions (angiokeratomas), sweating abnormalities (anhidrosis, hypohidrosis, and rarely hyperhidrosis), characteristic corneal and lenticular opacities, and proteinuria. Gradual deterioration of kidney function to end-stage kidney disease (ESKD) usually occurs in men in the third to fifth decade. In middle age, most males successfully treated for ESKD develop cardiac and/or cerebrovascular disease, a major cause of morbidity and mortality. Heterozygous females typically have milder symptoms at a later age of onset than males. Rarely, females may be relatively asymptomatic throughout a normal life span or may have symptoms as severe as those observed in males with the classic phenotype. In contrast, late-onset forms occur in males with greater than 1% a-Gal A activity. Clinical manifestations include cardiac disease, which usually presents in the sixth to eighth decade with left ventricular hypertrophy, cardiomyopathy, arrhythmia, and proteinuria; kidney failure, associated with ESKD but without the skin lesions or pain; or cerebrovascular disease presenting as stroke or transient ischemic attack.

Following dietary exposure to fructose, sucrose, or sorbitol, untreated hereditary fructose intolerance (HFI) is characterized by metabolic disturbances (hypoglycemia, lactic acidemia, hypophosphatemia, hyperuricemia, hypermagnesemia, hyperalaninemia) and clinical findings (nausea, vomiting, and abdominal distress; chronic growth restriction / failure to thrive). While untreated HFI typically first manifested when fructose- and sucrose-containing foods were introduced in the course of weaning young infants from breast milk, it is now presenting earlier, due to the addition of fructose-containing nutrients in infant formulas. If the infant ingests large quantities of fructose, the infant may acutely develop lethargy, seizures, and/or progressive coma. Untreated HFI may result in renal and hepatic failure. If identified and treated before permanent organ injury occurs, individuals with HFI can experience a normal quality of life and life expectancy.

Familial lipoprotein lipase (LPL) deficiency usually presents in childhood and is characterized by very severe hypertriglyceridemia with episodes of abdominal pain, recurrent acute pancreatitis, eruptive cutaneous xanthomata, and hepatosplenomegaly. Clearance of chylomicrons from the plasma is impaired, causing triglycerides to accumulate in plasma and the plasma to have a milky (lactescent or lipemic) appearance. Symptoms usually resolve with restriction of total dietary fat to =20 g/day.

Ovarian hyperstimulation syndrome (OHSS) most often occurs as an iatrogenic complication of ovarian stimulation treatments for in vitro fertilization; the incidence of severe forms ranges from 0.5 to 5% (Delvigne and Rozenberg, 2002). The clinical manifestations vary from abdominal distention and discomfort to potentially life-threatening, massive ovarian enlargement and capillary leak with fluid sequestration. Pathologic features of the syndrome, whether spontaneous or iatrogenic, include the presence of multiple serous and hemorrhagic follicular cysts lined by luteinized cells, a condition called hyperreactio luteinalis (Scully et al., 1998).

A condition characterized by recurrent, self-limiting episodes of vomiting associated with intense nausea, pallor, and lethargy. It is commonly a migraine precursor.

An acute porphyria attack is characterized by a urine porphobilinogen (PBG)-to-creatinine ratio =10 times the upper limit of normal (ULN) and the presence of =2 porphyria manifestations (involving the visceral, peripheral, autonomic, and/or central nervous systems) persisting for >24 hours in the absence of other likely explanations. Onset of acute attacks typically occurs in the second or third decade of life. Acute attacks are more common in women than men. Although attacks in most individuals are typically caused by exposure to certain endogenous or exogenous factors, often no precipitating factor can be identified. The course of acute porphyria attacks is highly variable in an individual and between individuals. Recovery from acute porphyria attacks may occur within days; however, recovery from severe attacks that are not promptly recognized and treated may take weeks or months. The five categories of acute intermittent porphyria (AIP), caused by a heterozygous HMBS pathogenic variant, are based on the urine PBG-to-creatinine ratio and occurrence of acute attacks. Active (symptomatic) AIP: An individual who has experienced at least one acute attack within the last two years. Symptomatic high excreter: Urine PBG-to-creatinine ratio =4 times ULN and no acute attacks in the last two years but chronic long-standing manifestations of acute porphyria. Asymptomatic high excreter: Urine PBG-to-creatinine ratio =4 times ULN and no acute attacks in the last two years and no porphyria-related manifestations. Asymptomatic AIP: Urine PBG-to-creatinine ratio <4 times ULN and no acute attacks in the last two years but has had =1 acute attack in the past. Latent (inactive) AIP: Urine PBG-to-creatinine ratio <4 times ULN and no acute porphyria-related manifestations to date.

Choroid plexus tumors are of neuroectodermal origin and range from benign choroid plexus papillomas (CPPs) to malignant choroid carcinomas (CPCs). These rare tumors generally occur in childhood, but have also been reported in adults. Patients typically present with signs and symptoms of increased intracranial pressure including headache, hydrocephalus, papilledema, nausea, vomiting, cranial nerve deficits, gait impairment, and seizures (summary by Safaee et al., 2013).

NR0B1-related adrenal hypoplasia congenita includes both X-linked adrenal hypoplasia congenita (X-linked AHC) and Xp21 deletion (previously called complex glycerol kinase deficiency). X-linked AHC is characterized by primary adrenal insufficiency and/or hypogonadotropic hypogonadism (HH). Adrenal insufficiency is acute infantile onset (average age 3 weeks) in approximately 60% of affected males and childhood onset (ages 1-9 years) in approximately 40%. HH typically manifests in a male with adrenal insufficiency as delayed puberty (i.e., onset age >14 years) and less commonly as arrested puberty at about Tanner Stage 3. Rarely, X-linked AHC manifests initially in early adulthood as delayed-onset adrenal insufficiency, partial HH, and/or infertility. Heterozygous females very occasionally have manifestations of adrenal insufficiency or hypogonadotropic hypogonadism. Xp21 deletion includes deletion of NR0B1 (causing X-linked AHC) and GK (causing glycerol kinase deficiency), and in some cases deletion of DMD (causing Duchenne muscular dystrophy). Developmental delay has been reported in males with Xp21 deletion when the deletion extends proximally to include DMD or when larger deletions extend distally to include IL1RAPL1 and DMD.

Multiple acyl-CoA dehydrogenase deficiency (MADD) represents a clinical spectrum in which presentations can be divided into type I (neonatal onset with congenital anomalies), type II (neonatal onset without congenital anomalies), and type III (late onset). Individuals with type I or II MADD typically become symptomatic in the neonatal period with severe metabolic acidosis, which may be accompanied by profound hypoglycemia and hyperammonemia. Many affected individuals die in the newborn period despite metabolic treatment. In those who survive the neonatal period, recurrent metabolic decompensation resembling Reye syndrome and the development of hypertrophic cardiomyopathy can occur. Congenital anomalies may include dysmorphic facial features, large cystic kidneys, hypospadias and chordee in males, and neuronal migration defects (heterotopias) on brain MRI. Individuals with type III MADD, the most common presentation, can present from infancy to adulthood. The most common symptoms are muscle weakness, exercise intolerance, and/or muscle pain, although metabolic decompensation with episodes of rhabdomyolysis can also be seen. Rarely, individuals with late-onset MADD (type III) may develop severe sensory neuropathy in addition to proximal myopathy.

Lysinuric protein intolerance (LPI) typically presents after an infant is weaned from breast milk or formula; variable findings include recurrent vomiting and episodes of diarrhea, episodes of stupor and coma after a protein-rich meal, poor feeding, aversion to protein-rich food, failure to thrive, hepatosplenomegaly, and muscular hypotonia. Over time, findings include: poor growth, osteoporosis, involvement of the lungs (progressive interstitial changes, pulmonary alveolar proteinosis) and of the kidneys (progressive glomerular and proximal tubular disease), hematologic abnormalities (normochromic or hypochromic anemia, leukopenia, thrombocytopenia, erythroblastophagocytosis in the bone marrow aspirate), and a clinical presentation resembling the hemophagocytic lymphohistiocytosis/macrophagic activation syndrome. Hypercholesterolemia, hypertriglyceridemia, and acute pancreatitis can also be seen.

Migraine is a common complex disorder that shows strong familial aggregation. The disorder is generally characterized by chronic episodic headache usually associated with nausea and vomiting (summary by Nyholt et al., 1998). For a phenotypic description and discussion of genetic heterogeneity of migraine headaches, see MGR1 (157300).

Migraine is a complex and heterogeneous disorder characterized by recurrent attacks of headache associated with autonomic and neurologic symptoms. Two primary types of migraine can be distinguished: migraine without aura and migraine with aura. Usually, 1 type of migraine prevails intraindividually. Migraine without aura (MO) is the more common form and is characterized by unilateral pulsating headache of moderate to severe intensity, lasting 4 to 72 hours. The attacks are associated with nausea, vomiting, and photo- and phonophobia and are aggravated by physical activity. Frequency, severity, and duration vary substantially (summary by Soragna et al., 2003). For a phenotypic description and discussion of genetic heterogeneity of migraine headaches, see MGR1 (157300).

A rare form of hereditary episodic ataxia characterised by vestibular ataxia, vertigo, tinnitus, and interictal myokymia.

A rare form of hereditary episodic ataxia characterised by late-onset episodic ataxia, recurrent attacks of vertigo, and diplopia.

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.

Episodic ataxia type 6 (EA6) is an exceedingly rare form of hereditary episodic ataxia with varying degrees of ataxia and associated findings including slurred speech, headache, confusion and hemiplegia.

STAT3 hyper IgE syndrome (STAT3-HIES) is a primary immune deficiency syndrome characterized by elevated serum IgE, eczema, and recurrent skin and respiratory tract infections, together with several nonimmune features. This disorder typically manifests in the newborn period with a rash (often diagnosed as eosinophilic pustulosis) that subsequently evolves into an eczematoid dermatitis. Recurrent staphylococcal skin boils and bacterial pneumonias usually manifest in the first years of life. Pneumatoceles and bronchiectasis often result from aberrant healing of pneumonias. Mucocutaneous candidiasis is common. Nonimmune features may include retained primary teeth, scoliosis, bone fractures following minimal trauma, joint hyperextensibility, and characteristic facial appearance, which typically emerges in adolescence. Vascular abnormalities have been described and include middle-sized artery tortuosity and aneurysms, with infrequent clinical sequelae of myocardial infarction and subarachnoid hemorrhage. Gastrointestinal (GI) manifestations include gastroesophageal reflux disease, esophageal dysmotility, and spontaneous intestinal perforations (some of which are associated with diverticuli). Fungal infections of the GI tract (typically histoplasmosis, Cryptococcus, and Coccidioides) also occur infrequently. Survival is typically into adulthood, with most individuals now living into or past the sixth decade. Most deaths are associated with gram-negative (Pseudomonas) or filamentous fungal pneumonias resulting in hemoptysis. Lymphomas occur at an increased frequency.

Mitochondrial DNA depletion syndrome-11 is an autosomal recessive mitochondrial disorder characterized by onset in childhood or adulthood of progressive external ophthalmoplegia (PEO), muscle weakness and atrophy, exercise intolerance, and respiratory insufficiency due to muscle weakness. More variable features include spinal deformity, emaciation, and cardiac abnormalities. Skeletal muscle biopsies show deletion and depletion of mitochondrial DNA (mtDNA) with variable defects in respiratory chain enzyme activities (summary by Kornblum et al., 2013). For a discussion of genetic heterogeneity of autosomal recessive mtDNA depletion syndromes, see MTDPS1 (603041).

Migraine is the most common type of chronic, episodic headache, as summarized by Featherstone (1985). One locus for migraine with or without aura (MGR1) has been identified on chromosome 4q24. Other loci for migraine have been identified on 6p21.1-p12.2 (MGR3; 607498), 14q21.2-q22.3 (MGR4; 607501), 19p13 (MGR5; 607508), 1q31 (MGR6; 607516), 15q11-q13 (MGR7; 609179), 5q21 (with or without aura, MGR8, 609570; with aura, MGR9, 609670), 17p13 (MGR10; 610208), 18q12 (MGR11; 610209), 10q22-q23 (MGR12; 611706), and the X chromosome (MGR2; 300125). Mutation in the KCNK18 gene (613655) on chromosome 10q25 causes migraine with aura (MGR13; 613656). See also familial hemiplegic migraine-1 (FHM1; 141500), a subtype of autosomal dominant migraine with aura (MA).

Autosomal recessive progressive external ophthalmoplegia-6 (PEOB6) is characterized by ptosis and ophthalmoplegia as well as other clinical manifestations and multiple mtDNA deletions in muscle (Shintaku et al., 2022). For a discussion of genetic heterogeneity of autosomal recessive PEO, see PEOB1 (258450).