MedGen

Hereditary paraganglioma-pheochromocytoma (PGL/PCC) syndromes are characterized by paragangliomas (tumors that arise from neuroendocrine tissues distributed along the paravertebral axis from the base of the skull to the pelvis) and pheochromocytomas (paragangliomas that are confined to the adrenal medulla). Sympathetic paragangliomas cause catecholamine excess; parasympathetic paragangliomas are most often nonsecretory. Extra-adrenal parasympathetic paragangliomas are located predominantly in the skull base and neck (referred to as head and neck PGL [HNPGL]) and sometimes in the upper mediastinum; approximately 95% of such tumors are nonsecretory. In contrast, sympathetic extra-adrenal paragangliomas are generally confined to the lower mediastinum, abdomen, and pelvis, and are typically secretory. Pheochromocytomas, which arise from the adrenal medulla, typically lead to catecholamine excess. Symptoms of PGL/PCC result from either mass effects or catecholamine hypersecretion (e.g., sustained or paroxysmal elevations in blood pressure, headache, episodic profuse sweating, forceful palpitations, pallor, and apprehension or anxiety). The risk for developing metastatic disease is greater for extra-adrenal sympathetic paragangliomas than for pheochromocytomas. [from GeneReviews]

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. [from GeneReviews]

Hyperphosphatemic familial tumoral calcinosis (HFTC) is characterized by: Ectopic calcifications (tumoral calcinosis) typically found in periarticular soft tissues exposed to repetitive trauma or prolonged pressure (e.g., hips, elbows, and shoulders); and Painful swellings (referred to as hyperostosis) in the areas overlying the diaphyses of the tibiae (and less often the ulna, metacarpal bones, and radius). The dental phenotype unique to HFTC includes enamel hypoplasia, short and bulbous roots, obliteration of pulp chambers and canals, and pulp stones. Less common are large and small vessel calcifications that are often asymptomatic incidental findings on radiologic studies but can also cause peripheral vascular insufficiency (e.g., pain, cold extremities, and decreased peripheral pulses). Less frequently reported findings include testicular microlithiasis and angioid streaks of the retina. [from GeneReviews]

Tetrahydrobiopterin (BH4)-deficient hyperphenylalaninemia (HPA) D is an autosomal recessive disorder characterized by mild transient hyperphenylalaninemia often detected by newborn screening. Patients also show increased excretion of 7-biopterin. Affected individuals are asymptomatic and show normal psychomotor development, although transient neurologic deficits in infancy have been reported (Thony et al., 1998). Patients may also develop hypomagnesemia and nonautoimmune diabetes mellitus during puberty (summary by Ferre et al., 2014). For a general phenotypic description and a discussion of genetic heterogeneity of BH4-deficient hyperphenylalaninemia, see HPABH4A (261640). [from OMIM]

Malaria, a major cause of child mortality worldwide, is caused by mosquito-borne hematoprotozoan parasites of the genus Plasmodium. Of the 4 species that infect humans, P. falciparum causes the most severe forms of malaria and is the major cause of death and disease. Although less fatal, P. malariae, P. ovale, and, in particular, P. vivax infections are major causes of morbidity. The parasite cycle involves a first stage in liver cells and a subsequent stage at erythrocytes, when malaria symptoms occur. A wide spectrum of phenotypes are observed, from asymptomatic infection to mild disease, including fever and mild anemia, to severe disease, including cerebral malaria, profound anemia, and respiratory distress. Genetic factors influence the response to infection, as well as disease progression and severity. Malaria is the strongest known selective pressure in the recent history of the human genome, and it is the evolutionary driving force behind sickle-cell disease (603903), thalassemia (see 141800), glucose-6-phosphatase deficiency (300908), and other erythrocyte defects that together constitute the most common mendelian diseases of humans (Kwiatkowski, 2005; Campino et al., 2006). [from OMIM]

Vitamin D-dependent rickets type 2A (VDDR2A) is caused by a defect in the vitamin D receptor gene. This defect leads to an increase in the circulating ligand, 1,25-dihydroxyvitamin D3. Most patients have total alopecia in addition to rickets. VDDR2B (600785) is a form of vitamin D-dependent rickets with a phenotype similar to VDDR2A but a normal vitamin D receptor, in which end-organ resistance to vitamin D has been shown to be caused by a nuclear ribonucleoprotein that interferes with the vitamin D receptor-DNA interaction. For a general phenotypic description and a discussion of genetic heterogeneity of rickets due to disorders in vitamin D metabolism or action, see vitamin D-dependent rickets type 1A (VDDR1A; 264700). [from OMIM]

Any colorectal cancer in which the cause of the disease is a mutation in the GALNT12 gene. [from MONDO]

Autosomal dominant hypocalcemia-1 (HYPOC1) is associated with low or normal serum parathyroid hormone concentrations (PTH). Approximately 50% of patients have mild or asymptomatic hypocalcemia; about 50% have paresthesias, carpopedal spasm, and seizures; about 10% have hypercalciuria with nephrocalcinosis or kidney stones; and more than 35% have ectopic and basal ganglia calcifications (summary by Nesbit et al., 2013). Thakker (2001) noted that patients with gain-of-function mutations in the CASR gene, resulting in generally asymptomatic hypocalcemia with hypercalciuria, have low-normal serum PTH concentrations and have often been diagnosed with hypoparathyroidism because of the insensitivity of earlier PTH assays. Because treatment with vitamin D to correct the hypocalcemia in these patients causes hypercalciuria, nephrocalcinosis, and renal impairment, these patients need to be distinguished from those with other forms of hypoparathyroidism (see 146200). Thakker (2001) suggested the designation 'autosomal dominant hypocalcemic hypercalciuria' for this CASR-related disorder. Genetic Heterogeneity of Autosomal Dominant Hypocalcemia Autosomal dominant hypocalcemia-2 (HYPOC2; 615361) is caused by mutation in the GNA11 gene (139313) on chromosome 19p13. [from OMIM]

A familial syndrome characterized by gastrointestinal stromal tumors and paragangliomas, often at multiple sites. It is a very rare syndrome presenting at a young age. The gastric stromal sarcomas are multifocal and the paragangliomas are multicentric. The clinical spectrum of this syndrome varies widely, depending on the localization and the size of the tumors. The vast majority of cases are due to germline mutations of the succinate dehydrogenase (SDH) subunit genes SDHB, SDHC and SDHD. Predisposition to developing these tumors is inherited in an autosomal dominant manner with incomplete penetrance. [from SNOMEDCT_US]

Trisomy 13, also called Patau syndrome, is a chromosomal condition associated with severe intellectual disability and physical abnormalities in many parts of the body. Individuals with trisomy 13 often have heart defects, brain or spinal cord abnormalities, very small or poorly developed eyes (microphthalmia), extra fingers or toes, an opening in the lip (a cleft lip) with or without an opening in the roof of the mouth (a cleft palate), and weak muscle tone (hypotonia). Due to the presence of several life-threatening medical problems, many infants with trisomy 13 die within their first days or weeks of life. Only five percent to 10 percent of children with this condition live past their first year. [from MedlinePlus Genetics]

X-linked congenital stationary night blindness (CSNB) is characterized by non-progressive retinal findings of reduced visual acuity ranging from 20/30 to 20/200; defective dark adaptation; refractive error, most typically myopia ranging from low (-0.25 diopters [D] to -4.75 D) to high (=-10.00 D) but occasionally hyperopia; nystagmus; strabismus; normal color vision; and normal fundus examination. Characteristic ERG findings can help distinguish between complete X-linked CSNB and incomplete X-linked CSNB. [from GeneReviews]

Vitamin D3 (cholecalciferol), synthesized in the epidermis in response to UV radiation, and dietary vitamin D2 (ergocalciferol, synthesized in plants) are devoid of any biologic activity. Vitamin D hormonal activity is due primarily to the hydroxylated metabolite of vitamin D3, 1-alpha,25-dihydroxyvitamin D3 (calcitriol), the actions of which are mediated by the vitamin D receptor (VDR; 601769) (Koren, 2006; Liberman and Marx, 2001). In the liver, vitamin D 25-hydroxylase (CYP2R1; 608713) catalyzes the initial hydroxylation of vitamin D at carbon 25; in the kidney, 1-alpha-hydroxylase (CYP27B1; 609506) catalyzes the hydroxylation and metabolic activation of 25-hydroxyvitamin D3 into 1,25-dihydroxyvitamin D3. The active metabolite 1,25(OH)2D3 binds and activates the nuclear vitamin D receptor, with subsequent regulation of physiologic events such as calcium homeostasis and cellular differentiation and proliferation (Takeyama et al., 1997). Disorders of vitamin D metabolism or action lead to defective bone mineralization and clinical features including intestinal malabsorption of calcium, hypocalcemia, secondary hyperparathyroidism, increased renal clearance of phosphorus, and hypophosphatemia. The combination of hypocalcemia and hypophosphatemia causes impaired mineralization of bone that results in rickets and osteomalacia (Liberman and Marx, 2001). Genetic Heterogeneity of Vitamin D-Dependent Rickets Vitamin D-dependent rickets type 1A (VDDR1A) is due to an enzymatic defect in synthesis of the active form of vitamin D caused by mutation in the CYP27B1 gene. VDDR1B (600081) is a form of rickets due to mutation in the gene encoding a vitamin D 25-hydroxylase (CYP2R1; 608713), another enzyme necessary for the synthesis of active vitamin D. Vitamin D-dependent rickets type 2A (VDDR2A; 277440) is caused by end-organ unresponsiveness of active vitamin D due to mutation in the gene encoding the vitamin D receptor (VDR; 601769). VDDR2B (600785) is an unusual form of end-organ unresponsiveness to active vitamin D due to an abnormal protein (see HNRNPC, 164020) that interferes with the function of the VDR. VDDR3 (619073) is a dominant form of VDDR caused by accelerated inactivation of vitamin D metabolites due to mutation in the CYP3A4 gene (124010). Other Forms of Hypophosphatemic Rickets For a discussion of other forms of hypophosphatemic rickets, see ADHR (193100). [from OMIM]

Lynch syndrome is characterized by an increased risk for colorectal cancer (CRC) and cancers of the endometrium, ovary, stomach, small bowel, urinary tract, biliary tract, brain (usually glioblastoma), skin (sebaceous adenomas, sebaceous carcinomas, and keratoacanthomas), pancreas, and prostate. Cancer risks and age of onset vary depending on the associated gene. Several other cancer types have been reported to occur in individuals with Lynch syndrome (e.g., breast, sarcomas, adrenocortical carcinoma). However, the data are not sufficient to demonstrate that the risk of developing these cancers is increased in individuals with Lynch syndrome. [from GeneReviews]

Disorders of intracellular cobalamin metabolism have a variable phenotype and age of onset that are influenced by the severity and location within the pathway of the defect. The prototype and best understood phenotype is cblC; it is also the most common of these disorders. The age of initial presentation of cblC spans a wide range: In utero with fetal presentation of nonimmune hydrops, cardiomyopathy, and intrauterine growth restriction. Newborns, who can have microcephaly, poor feeding, and encephalopathy. Infants, who can have poor feeding and slow growth, neurologic abnormality, and, rarely, hemolytic uremic syndrome (HUS). Toddlers, who can have poor growth, progressive microcephaly, cytopenias (including megaloblastic anemia), global developmental delay, encephalopathy, and neurologic signs such as hypotonia and seizures. Adolescents and adults, who can have neuropsychiatric symptoms, progressive cognitive decline, thromboembolic complications, and/or subacute combined degeneration of the spinal cord. [from GeneReviews]

Vitamin D-dependent rickets is a disorder of bone development that leads to softening and weakening of the bones (rickets). There are several forms of the condition that are distinguished primarily by their genetic causes: type 1A (VDDR1A), type 1B (VDDR1B), and type 2A (VDDR2A). There is also evidence of a very rare form of the condition, called type 2B (VDDR2B), although not much is known about this form.

The signs and symptoms of vitamin D-dependent rickets begin within months after birth, and most are the same for all types of the condition. The weak bones often cause bone pain and delayed growth and have a tendency to fracture. When affected children begin to walk, they may develop abnormally curved (bowed) legs because the bones are too weak to bear weight. Impaired bone development also results in widening of the areas near the ends of bones where new bone forms (metaphyses), especially in the knees, wrists, and ribs. Some people with vitamin D-dependent rickets have dental abnormalities such as thin tooth enamel and frequent cavities. Poor muscle tone (hypotonia) and muscle weakness are also common in this condition, and some affected individuals develop seizures.

In vitamin D-dependent rickets, there is an imbalance of certain substances in the blood. An early sign in all types of the condition is low levels of the mineral calcium (hypocalcemia), which is essential for the normal formation of bones and teeth. Affected individuals also develop high levels of a hormone involved in regulating calcium levels called parathyroid hormone (PTH), which leads to a condition called secondary hyperparathyroidism. Low levels of a mineral called phosphate (hypophosphatemia) also occur in affected individuals. Vitamin D-dependent rickets types 1 and 2 can be grouped by blood levels of a hormone called calcitriol, which is the active form of vitamin D; individuals with VDDR1A and VDDR1B have abnormally low levels of calcitriol and individuals with VDDR2A and VDDR2B have abnormally high levels.

Hair loss (alopecia) can occur in VDDR2A, although not everyone with this form of the condition has alopecia. Affected individuals can have sparse or patchy hair or no hair at all on their heads. Some affected individuals are missing body hair as well. [from MedlinePlus Genetics]

A rare hereditary motor and sensory neuropathy with characteristics of intermediate motor median nerve conduction velocities (usually between 25 and 45 m/s) and signs of both axonal degeneration and demyelination without onion bulbs in nerve biopsies. It presents with usual Charcot-Marie-Tooth disease clinical features of variable severity (progressive muscle weakness and atrophy of the distal extremities, distal sensory loss, reduced or absent deep tendon reflexes, and feet deformities). Other findings in some of the families include debilitating neuropathic pain and mild postural/kinetic upper limb tremor. [from SNOMEDCT_US]

Vitamin D hydroxylation-deficient rickets type 1B (VDDR1B) is caused by a defect in vitamin D 25-hydroxylation (Molin et al., 2017). The major function of vitamin D is to maintain calcium and phosphate levels in the normal range to support metabolic functions, neuromuscular transmission, and bone mineralization. Disorders of vitamin D metabolism or action lead to defective bone mineralization and clinical features including intestinal malabsorption of calcium, hypocalcemia, secondary hyperparathyroidism, increased renal clearance of phosphorus, and hypophosphatemia. The combination of hypocalcemia and hypophosphatemia causes impaired mineralization of bone that results in rickets and osteomalacia (summary by Liberman and Marx, 2001). Rickets can occur because of inadequate dietary intake or sun exposure or because of genetic disorders. Vitamin D3 (cholecalciferol) is taken in the diet or synthesized in the skin from 7-dehydrocholesterol by ultraviolet irradiation. For vitamin D to be active, it needs to be converted to its active form, 1,25-dihydroxyvitamin D3. Vitamin D is transported in the blood by the vitamin D binding protein (DBP; 139200) to the liver, where vitamin D 25-hydroxylase (CYP2R1; 608713) is the key enzyme for 25-hydroxylation. Vitamin D 25(OH)D3, the major circulating form of vitamin D, is then transported to the kidney, where 25(OH)D3 is hydroxylated at the position of carbon 1 of the A ring, resulting in the active form of vitamin D, 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) (summary by Christakos et al., 2010). [from OMIM]

Familial hypercholanemia-1 (FHCA1) is an autosomal recessive disorder characterized by elevated concentrations of bile acids (usually conjugated), itching, and fat malabsorption, leading to poor overall growth and deficiencies of fat-soluble vitamins. Vitamin D deficiency results in rickets, and vitamin K deficiency results in a coagulopathy (Morton et al., 2000; Shneider et al., 1997; summary by Carlton et al., 2003). See also bile acid conjugation defect-1 (BACD1; 619232), which can also show increased bile acid levels, although the bile acids in BACD1 are unconjugated. Genetic Heterogeneity of FHCA See FHCA2 (619256), caused by mutation in the SLC10A1 gene (182396) on chromosome 14q24. [from OMIM]

Infantile hypercalcemia is characterized by severe hypercalcemia, failure to thrive, vomiting, dehydration, and nephrocalcinosis. An epidemic of idiopathic infantile hypercalcemia occurred in the United Kingdom in the 1950s after the implementation of an increased prophylactic dose of vitamin D supplementation; however, the fact that most infants receiving the prophylaxis remained unaffected suggested that an intrinsic hypersensitivity to vitamin D might be implicated in the pathogenesis (summary by Schlingmann et al., 2011). Genetic Heterogeneity Infantile hypercalcemia-2 (HCINF2; 616963) is caused by mutation in the SLC34A1 gene (182309) on chromosome 5q35. [from OMIM]