A genetic disorder is a health problem caused by one or more abnormalities in the genome. It can be caused by a mutation in a single gene (monogenic) or multiple genes (polygenic) or by a chromosome abnormality. Although polygenic disorders are the most common, the term is mostly used when discussing disorders with a single genetic cause, either in a gene or chromosome. The mutation responsible can occur spontaneously before embryonic development, or it can be inherited from two parents who are carriers of a faulty gene or from a parent with the disorder. When the genetic disorder is inherited from one or both parents, it is also classified as a hereditary disease. Some disorders are caused by a mutation on the X chromosome and have X-linked inheritance. Very few disorders are inherited on the Y chromosome or mitochondrial DNA.
Rickets, scientific nomenclature: rachitis, is a condition that results in weak or soft bones in children and is caused by either dietary deficiency or genetic causes. Symptoms include bowed legs, stunted growth, bone pain, large forehead, and trouble sleeping. Complications may include bone deformities, bone pseudofractures and fractures, muscle spasms, or an abnormally curved spine. The analogous condition in adults is osteomalacia.
Osteopetrosis, literally 'stone bone', also known as marble bone disease or Albers-Schönberg disease, is an extremely rare inherited disorder whereby the bones harden, becoming denser, in contrast to more prevalent conditions like osteoporosis, in which the bones become less dense and more brittle, or osteomalacia, in which the bones soften. Osteopetrosis can cause bones to dissolve and break.
Osteomalacia is a disease characterized by the softening of the bones caused by impaired bone metabolism primarily due to inadequate levels of available phosphate, calcium, and vitamin D, or because of resorption of calcium. The impairment of bone metabolism causes inadequate bone mineralization.
Alport syndrome is a genetic disorder affecting around 1 in 5,000–10,000 children, characterized by glomerulonephritis, end-stage kidney disease, and hearing loss. Alport syndrome can also affect the eyes, though the changes do not usually affect vision, except when changes to the lens occur in later life. Blood in urine is universal. Proteinuria is a feature as kidney disease progresses.
Hypophosphatemia is an electrolyte disorder in which there is a low level of phosphate in the blood. Symptoms may include weakness, trouble breathing, and loss of appetite. Complications may include seizures, coma, rhabdomyolysis, or softening of the bones.
Hypophosphatasia (; also called deficiency of alkaline phosphatase, phosphoethanolaminuria, or Rathbun's syndrome; sometimes abbreviated HPP) is a rare, and sometimes fatal, inherited metabolic bone disease. Clinical symptoms are heterogeneous, ranging from the rapidly fatal, perinatal variant, with profound skeletal hypomineralization, respiratory compromise or vitamin B6 dependent seizures to a milder, progressive osteomalacia later in life. Tissue non-specific alkaline phosphatase (TNSALP) deficiency in osteoblasts and chondrocytes impairs bone mineralization, leading to rickets or osteomalacia. The pathognomonic finding is subnormal serum activity of the TNSALP enzyme, which is caused by one of 388 genetic mutations identified to date, in the gene encoding TNSALP. Genetic inheritance is autosomal recessive for the perinatal and infantile forms but either autosomal recessive or autosomal dominant in the milder forms.
Albright's hereditary osteodystrophy is a form of osteodystrophy, and is classified as the phenotype of pseudohypoparathyroidism type 1A; this is a condition in which the body does not respond to parathyroid hormone.
Pseudohypoparathyroidism is a rare autosomal dominant genetic condition associated primarily with resistance to the parathyroid hormone. Those with the condition have a low serum calcium and high phosphate, but the parathyroid hormone level (PTH) is inappropriately high. Its pathogenesis has been linked to dysfunctional G proteins. Pseudohypoparathyroidism is a very rare disorder, with estimated prevalence between 0.3 and 1.1 cases per 100,000 population depending on geographic location.
Blue diaper syndrome is a rare, autosomal recessive or X linked recessive metabolic disorder characterized in infants by bluish urine-stained diapers. It is also known as Drummond's syndrome, and hypercalcemia.
Fibroblast growth factor 23 (FGF-23) is a protein and member of the fibroblast growth factor (FGF) family which participates in the regulation of phosphate in plasma and vitamin D metabolism. In humans it is encoded by the FGF23 gene. FGF-23 decreases reabsorption of phosphate in the kidney. Mutations in FGF23 can lead to its increased activity, resulting in autosomal dominant hypophosphatemic rickets.
X-linked hypophosphatemia (XLH) is an X-linked dominant form of rickets that differs from most cases of dietary deficiency rickets in that vitamin D supplementation does not cure it. It can cause bone deformity including short stature and genu varum (bow-leggedness). It is associated with a mutation in the PHEX gene sequence (Xp.22) and subsequent inactivity of the PHEX protein. PHEX mutations lead to an elevated circulating (systemic) level of the hormone FGF23 which results in renal phosphate wasting, and local elevations of the mineralization/calcification-inhibiting protein osteopontin in the extracellular matrix of bones and teeth. An inactivating mutation in the PHEX gene results in an increase in systemic circulating FGF23, and a decrease in the enzymatic activity of the PHEX enzyme which normally removes (degrades) mineralization-inhibiting osteopontin protein; in XLH, the decreased PHEX enzyme activity leads to an accumulation of inhibitory osteopontin locally in bones and teeth to block mineralization which, along with renal phosphate wasting, both cause osteomalacia and odontomalacia.
Jansen's metaphyseal chondrodysplasia (JMC) is a disease that results from ligand-independent activation of the type 1 (PTH1R) of the parathyroid hormone receptor, due to one of three reported mutations.
Dent's disease is a rare X-linked recessive inherited condition that affects the proximal renal tubules of the kidney. It is one cause of Fanconi syndrome, and is characterized by tubular proteinuria, excess calcium in the urine, formation of calcium kidney stones, nephrocalcinosis, and chronic kidney failure.
Phosphate-regulating endopeptidase homolog X-linked also known as phosphate-regulating gene with homologies to endopeptidases on the X chromosome or metalloendopeptidase homolog PEX is an enzyme that in humans is encoded by the PHEX gene. This gene contains 18 exons and is located on the X chromosome.
Oncogenic osteomalacia, also known as tumor-induced osteomalacia or oncogenic hypophosphatemic osteomalacia, is an uncommon disorder resulting in increased renal phosphate excretion, hypophosphatemia and osteomalacia. It may be caused by a phosphaturic mesenchymal tumor. Symptoms typically include crushing fatigue, severe muscle weakness and brain fog due to the low circulating levels of serum phosphate.
Fanconi syndrome or Fanconi's syndrome is a syndrome of inadequate reabsorption in the proximal renal tubules of the kidney. The syndrome can be caused by various underlying congenital or acquired diseases, by toxicity, or by adverse drug reactions. It results in various small molecules of metabolism being passed into the urine instead of being reabsorbed from the tubular fluid. Fanconi syndrome affects the proximal tubules, namely, the proximal convoluted tubule (PCT), which is the first part of the tubule to process fluid after it is filtered through the glomerulus, and the proximal straight tubule, which leads to the descending limb of loop of Henle.
Burosumab, sold under the brand name Crysvita, is a human monoclonal antibody medication approved 2018 for the treatment of X-linked hypophosphatemia and tumor-induced osteomalacia.
Phosphate diabetes is a rare, congenital, hereditary disorder associated with inadequate tubular reabsorption that affects the way the body processes and absorbs phosphate. Also named as X-linked dominant hypophosphatemic rickets (XLH), this disease is caused by a mutation in the X-linked PHEX gene, which encodes for a protein that regulates phosphate levels in the human body. phosphate is an essential mineral which plays a significant role in the formation and maintenance of bones and teeth, energy production and other important cellular processes. phosphate diabetes is a condition that falls under the category of tubulopathies, which refers to the pathologies of the renal tubules. The mutated PHEX gene causes pathological elevations in fibroblast growth factor 23 (FGF23), a hormone that regulates phosphate homeostasis by decreasing the reabsorption of phosphate in the kidneys.
Pisit Pitukcheewanont, also known as "Dr. Duke" is a Doctor of Medicine, a former professor of Clinical Pediatrics and a philanthropist. Currently, he is an adjunct professor of Clinical Pediatrics at Keck School of Medicine of the University of Southern California, the president of a nonprofit organization, The Human Growth Foundation and Senior Vice President of Global Clinical Development and Medical Affairs Lumos Pharmacy.
