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Hypogonadism
Hypogonadism, or male testosterone deficiency, is failure of the testes to produce normal testosterone or sperm due to hypothalamic, pituitary, or testicular disease; diagnosed by symptoms plus repeated low morning testosterone, treated with testosterone replacement therapy.
Hypohidrosis
Hypohidrosis, also called anhidrosis, is abnormally diminished or absent sweating, focal or generalized, caused by skin injury, rheumatic disease, drugs, neurologic disorders, or genetic conditions such as ectodermal dysplasia.
Hypohidrosis-electrolyte imbalance-lacrimal gland dysfunction-ichthyosis-xerostomia syndrome
HELIX syndrome (hypohidrosis-electrolyte imbalance-lacrimal gland dysfunction-ichthyosis-xerostomia syndrome) is a rare autosomal recessive CLDN10 claudinopathy causing salt-losing nephropathy with hypermagnesemia, hypokalemia, hypocalciuria, reduced sweating, tears, and saliva, ichthyosis, and enamel wear.
Hypohidrotic ectodermal dysplasia
Hypohidrotic ectodermal dysplasia (HED, Christ-Siemens-Touraine syndrome) is a hereditary disorder causing sparse hair, reduced sweating, and missing teeth, usually X-linked via EDA mutations; prenatal EDA1 protein replacement is under trial.
Hypohidrotic ectodermal dysplasia with immunodeficiency
Hypohidrotic ectodermal dysplasia with immunodeficiency (HED-ID, EDA-ID) is a rare primary immunodeficiency with sparse hair, hypodontia, and hypohidrosis, caused by IKBKG (NEMO) or NFKBIA mutations impairing NF-κB signaling.
Hypokalemic periodic paralysis
Hypokalemic periodic paralysis, also called Westphall disease, is a rare inherited muscle ion channel disorder causing recurrent attacks of weakness with low blood potassium, usually beginning in childhood or adolescence.
Hypokaluria
Hypokaluria, also spelled hypokaliuria, is a decreased concentration of potassium in the urine, measured in 24-hour collections to tell renal potassium wasting apart from poor intake or gastrointestinal loss.
Hypolipoproteinaemia
Hypolipoproteinaemia (ICD-11 5C81), abnormally low plasma lipoproteins; primary forms include abetalipoproteinemia (MTTP), familial hypobetalipoproteinemia (APOB), chylomicron retention disease (SAR1B), PCSK9 and ANGPTL3 defects; also secondary causes.
Hypomagnesuria
Hypomagnesuria (ICD-11 MF98.5) is abnormally low urinary magnesium excretion, usually signaling magnesium depletion with intact renal conservation; normal excretion is 6-10 mEq/24 h, distinguishing it from renal magnesium wasting.
Hypomandibular faciocranial dysostosis
Hypomandibular faciocranial dysostosis (ORPHA1790, OMIM 241310) is an ultra-rare cranial malformation with severe mandibular and tongue hypoplasia, microstomia, laryngeal hypoplasia, and craniosynostosis; inheritance unknown, fewer than 1 in 1,000,000.
Hypomania
Hypomania: a mild manic-type mood episode (elevated, expansive, or irritable mood plus increased energy, at least 4 days, no marked impairment, hospitalization, or psychosis) defining bipolar II disorder; term coined by Erich Mendel in 1881.
Hypomenorrhea
Hypomenorrhea, or scanty/light menstrual periods, is decreased menstrual blood flow lasting two days or less for several months. Causes include stress, weight loss, hyperthyroidism, PMOS, perimenopause, and cervical stenosis; pooled prevalence in Iran was 5.25%.
Hypomyelination of early myelinating structures
Hypomyelination of early myelinating structures (HEMS) is a rare X-linked genetic disorder in which early-myelinating brain regions stay poorly myelinated, presenting in infancy with nystagmus and ataxia.
Hypomyelination with atrophy of basal ganglia and cerebellum
H-ABC (hypomyelination with atrophy of basal ganglia and cerebellum) is a rare TUBB4A- or UFM1-related leukodystrophy with hypomyelination, putamen and cerebellar atrophy, dystonia, spasticity, and ataxia, onset in infancy.
Hypomyelination with brain stem and spinal cord involvement and leg spasticity
HBSL (hypomyelination with brain stem and spinal cord involvement and leg spasticity), also called aspartyl-tRNA synthetase deficiency, is an autosomal recessive DARS1 leukodystrophy causing leg spasticity, nystagmus, and hypomyelination on MRI.
Hyponatremia
Hyponatremia, a serum sodium below 135 mmol/L, is the most common electrolyte disorder, affecting 15–30% of hospitalized patients; classified by volume status and treated with hypertonic saline, fluid restriction, or vaptans.
Hypoparathyroidism
Hypoparathyroidism, low PTH with hypocalcemia, is a rare endocrine disorder, about 75% postsurgical, treated with calcium and vitamin D; palopegteriparatide (Yorvipath) is the first PTH replacement approved.
Hypoparathyroidism-sensorineural deafness-renal disease syndrome
Hypoparathyroidism-sensorineural deafness-renal disease syndrome, also called Barakat or HDR syndrome, is a rare autosomal dominant inherited disorder from GATA3 gene variants, first described in 1977.
Hypophosphatasia
Hypophosphatasia (HPP) is a rare inherited metabolic bone disease caused by ALPL gene variants that impair bone and tooth mineralization, causing rickets, osteomalacia, and premature tooth loss.
Hypophosphatemia
Hypophosphatemia: serum phosphate below 2.5 mg/dL (0.81 mmol/L). Also called low phosphate. Causes include refeeding, alcohol use disorder, DKA recovery, diuretics, hyperparathyroidism; severe cases cause weakness, rhabdomyolysis, seizures.
Hypophosphaturia
Hypophosphaturia (低リン酸尿症), ICD-11 MF98.6, is abnormally low urinary phosphate, a lab finding distinct from hypophosphatemia; it indicates nonrenal causes such as poor absorption or cellular shift rather than renal phosphate wasting.
Hypophysectomy
Hypophysectomy is the surgical removal of the pituitary gland, evolved from open craniotomy to endoscopic endonasal surgery, most often to treat pituitary adenomas; the first transsphenoidal resection was by Hermann Schloffer in 1907.
Hypopigmentation-punctate palmoplantar keratoderma syndrome
Hypopigmentation-punctate palmoplantar keratoderma syndrome, or Cole disease (OMIM 615522), is a rare autosomal dominant ENPP1-related skin disorder with punctate palmoplantar keratoderma, extremity hypopigmentation, and occasional ectopic calcification.
Hypopituitarism
Hypopituitarism: deficiency of one or more pituitary hormones, also called Simmonds' disease; causes include pituitary adenoma, surgery, radiation, and Sheehan's syndrome; treated with hormone replacement.
Hypoplasia of pancreas
Hypoplasia of pancreas (ICD-11 LB21.5), also called partial pancreatic agenesis, is congenital underdevelopment of the pancreas, usually of the dorsal anlage. It causes exocrine insufficiency and neonatal diabetes, most often from GATA6, PDX1, PTF1A, or HNF1B mutations.
Hypoplasminogenemia
Hypoplasminogenemia (plasminogen deficiency type 1) is a rare autosomal recessive PLG disorder causing ligneous fibrin-rich mucosal lesions, chiefly ligneous conjunctivitis; treated with plasma-derived plasminogen concentrate Ryplazim, FDA approved 2021.
Hypoplastic left heart syndrome
Hypoplastic left heart syndrome (HLHS) is a critical congenital heart defect with underdeveloped left ventricle, mitral and aortic valves, and ascending aorta; treated with Norwood, Glenn, and Fontan staged surgery.
Hypoplastic right heart syndrome
Hypoplastic right heart syndrome (HRHS) is a rare cyanotic congenital defect with underdeveloped tricuspid valve, right ventricle, pulmonary valve, and pulmonary artery, treated with prostaglandin, shunts, and Glenn/Fontan palliation.
Hypopnea
Hypopnea: a sleep-related breathing event of reduced (not absent) airflow lasting at least 10 seconds, scored by AASM rules (30% airflow drop with 3% desaturation or arousal) and counted in the apnea-hypopnea index for obstructive sleep apnea diagnosis.
Hypopyon
Hypopyon (anterior chamber pus level, ICD-11 MC20.2) is a gravity-dependent layer of white blood cells in the eye's anterior chamber, signaling severe intraocular inflammation from causes such as HLA-B27 uveitis, Behçet disease, endophthalmitis, and keratitis.