{
 "topic": "Achondroplasia",
 "slug": "achondroplasia",
 "category_id": 14973,
 "summary": "FGFR3-driven skeletal dysplasia causing disproportionate short stature, its characteristic radiographic findings, and the structured health-supervision surveillance it requires.",
 "written_by": "claude-sonnet",
 "references": [
  {
   "title": "Pediatric Clinical Practice Guidelines and Policies",
   "author": "American Academy of Pediatrics (AAP);",
   "pages": [
    854,
    855,
    870,
    871,
    872,
    1295
   ]
  },
  {
   "title": "Diagnostic Imaging: Pediatrics",
   "author": "A. Carlson Merrow Jr. MD",
   "pages": [
    973
   ]
  },
  {
   "title": "Kliegman R. Nelson Textbook of Pediatrics 2-Volume Set 22ed 2024",
   "author": null,
   "pages": [
    4387,
    4388,
    4389
   ]
  },
  {
   "title": "MedStudy Pediatrics Core 11th Edition 2024-2025",
   "author": null,
   "pages": [
    971
   ]
  },
  {
   "title": "Netters Pediatrics (Florin \u0422., Ludwig St.)",
   "author": null,
   "pages": [
    786
   ]
  }
 ],
 "short": [
  {
   "title": "In short",
   "content": "- Achondroplasia is the most common skeletal dysplasia causing disproportionate short stature; birth incidence estimates range from about 1 in 10,000 to 1 in 40,000 (commonly cited as roughly 1 in 20,000\u201330,000), with no ethnic or sex predisposition.\n- Caused by a gain-of-function mutation in FGFR3 (fibroblast growth factor receptor 3) on chromosome 4p16.3, found in about 99% of affected patients; inheritance is autosomal dominant, but most cases are de novo, and the mutation rate rises with advancing paternal age. The mutation decreases endochondral ossification, chondrocyte proliferation, and cartilage matrix production.\n- Classic features: rhizomelic (proximal) limb shortening, macrocephaly with frontal bossing, midface hypoplasia, trident-configuration hands, a long/near-normal-length trunk, exaggerated lumbar lordosis, and hyperextensible joints except the elbow (extension is restricted there).\n- A thoracolumbar gibbus (kyphosis) is typical in infancy and resolves without intervention in about 90% of cases once the child begins walking \u2014 though it can become fixed and angular if not monitored, so it is considered probably preventable with appropriate positioning guidance.\n- Radiographic findings: square pelvis with small sacrosciatic notch, short vertebral pedicles with progressive interpedicular narrowing from lower thoracic through lumbar spine, proximal femoral radiolucency, chevron-shaped distal femoral epiphyses, relatively long fibula compared to the tibia, and rounded iliac bones with a horizontal acetabular roof.\n- Intelligence and lifespan are generally normal, though one source notes lifespan may run about 10 years shorter than the general population on average; infants show hypotonia and delayed gross/fine motor milestones that typically improve with age.\n- Serious complications to actively screen for: cervicomedullary compression (from a small foramen magnum), hydrocephalus (possibly related to intracranial venous hypertension), obstructive and (more rarely) central sleep apnea, middle-ear dysfunction/conductive hearing loss, thoracolumbar kyphosis, and lower-extremity long-bone bowing.\n- Obesity is common and can be disabling in older children with achondroplasia; standard population BMI curves are not appropriate for monitoring growth in these children, since achondroplasia has its own growth/weight-for-height standards.\n- Because of respiratory and cervicomedullary risks, perioperative and anesthetic management requires specific expertise, and dedicated best-practice guidelines exist for perioperative care of patients with skeletal dysplasias."
  }
 ],
 "long": [
  {
   "title": "Definition",
   "content": "Achondroplasia is the prototype chondrodysplasia and the most common skeletal dysplasia causing disproportionate short stature. It is additionally marked by rhizomelia (limb shortening greatest in the proximal segments), macrocephaly, midface hypoplasia, and \u2014 importantly for counseling \u2014 normal cognition. Clinically it typically manifests at birth with short limbs, a long narrow trunk, and a large head with a prominent forehead and midfacial hypoplasia."
  },
  {
   "title": "Epidemiology",
   "content": "Achondroplasia is the most common condition associated with severe, disproportionate short stature, with an estimated birth incidence ranging from about 1 in 10,000 to 1 in 40,000 live births across cited sources (commonly quoted as roughly 1 in 20,000\u201330,000). There is no recognized ethnic or sex predisposition."
  },
  {
   "title": "Etiology",
   "content": "Achondroplasia is an autosomal dominant disorder in which most affected individuals carry a de novo mutation in FGFR3 (fibroblast growth factor receptor 3) on chromosome 4p16.3; achondroplasia-specific FGFR3 mutations (most commonly the recurrent G380R substitution) are identified in about 99% of affected patients. The mutation rate increases with advancing paternal age. Because inheritance is autosomal dominant, an affected parent has a 50% chance of transmitting the condition to each child, but most cases arise as new mutations in families with no prior history."
  },
  {
   "title": "Pathophysiology",
   "content": "The FGFR3 mutation in achondroplasia is a gain-of-function mutation that results in decreased endochondral ossification, decreased chondrocyte proliferation, and decreased cartilage matrix production. Because endochondral ossification is the process by which long bones normally grow in length, impairing it selectively shortens the long bones (most severely at their proximal segments) while sparing membranous bone growth, which is why the skull and facial skeleton show a distinct pattern of macrocephaly, frontal bossing, and midface hypoplasia rather than uniform smallness."
  },
  {
   "title": "Clinical features",
   "content": "At birth, infants show macrocephaly, frontal bossing, midface hypoplasia, a small chest, rhizomelic shortening of all limbs, redundant skinfolds, and extreme joint laxity, with a trident-shaped hand (short fingers in a characteristic spread configuration) and abducted hips; birth length is often slightly reduced but frequently still plots in the low-normal range. Most joints are hyperextensible, but elbow extension is characteristically restricted. A thoracolumbar gibbus is typically present in the newborn period and improves without intervention in about 90% of cases once the child begins walking, though exaggerated lumbar lordosis, a prominent buttocks, and a protuberant abdomen become apparent after walking begins. Infants show hypotonia and delayed gross and fine motor milestones, which improve over time; by around age 3, redundant skinfolds resolve and joint laxity improves, while rhizomelic limb shortening becomes more pronounced and may be accompanied by tibial bowing. Intelligence is normal throughout life. Obesity is a common and potentially disabling problem in older children with achondroplasia and requires dedicated, condition-specific growth references rather than standard population BMI curves."
  },
  {
   "title": "Diagnostics",
   "content": "Diagnosis is usually made on the basis of clinical features together with characteristic radiographic findings: a square-shaped pelvis with a small sacrosciatic notch, short vertebral pedicles with progressive interpedicular narrowing from the lower thoracic through lumbar spine, rhizomelic long-bone shortening, proximal femoral radiolucency, and a characteristic chevron shape of the distal femoral epiphyses. Additional imaging findings include a relatively long fibula compared with the tibia, rounded iliac bones, a horizontal acetabular roof, and short ribs with normal vertebral body height. Molecular confirmation of the characteristic FGFR3 mutation is available and identifies the mutation in about 99% of affected individuals when clinical uncertainty exists."
  },
  {
   "title": "Complications",
   "content": "Beyond the skeletal phenotype, achondroplasia carries specific, actively monitored medical risks: lower-extremity long-bone bowing, middle-ear dysfunction with associated hearing loss, and obstructive sleep apnea are relatively common, while cervicomedullary compression (from a small foramen magnum, with risk assessed prospectively in infancy), hydrocephalus (possibly related to intracranial venous hypertension), thoracolumbar kyphosis that can become fixed and angular if unmonitored, and central sleep apnea occur more rarely but carry serious consequences, including increased risk of death in infancy from spinal cord compression or upper airway obstruction. Obesity becomes an increasing and potentially disabling problem with age. Because of the airway and cervicomedullary risks, perioperative management requires dedicated expertise, and consensus best-practice guidelines exist specifically for the perioperative care of patients with skeletal dysplasias."
  }
 ],
 "clinical": [
  {
   "title": "Health supervision and monitoring",
   "content": "Children with achondroplasia require structured, condition-specific health supervision rather than standard well-child monitoring alone, per American Academy of Pediatrics guidance developed and twice revised specifically for this population. Use achondroplasia-specific growth curves rather than standard population curves to track height, weight, and head circumference, and monitor weight-for-height carefully given how common and disabling obesity becomes in older children with this condition.\n\nScreen proactively for the serious but less common complications rather than waiting for symptoms: assess infants for risk of cervicomedullary-junction compression, since this is a recognized cause of increased infant mortality in achondroplasia; monitor for hydrocephalus; and evaluate the thoracolumbar spine for kyphosis, intervening with positioning guidance early since fixed, angular kyphosis is considered probably preventable if caught before it becomes structural (most infantile gibbus resolves spontaneously by walking age without intervention). Screen for obstructive sleep apnea and, less commonly, central sleep apnea, and arrange hearing screening given the frequency of middle-ear dysfunction and associated hearing loss in this population. If surgery is needed for any reason, involve a team experienced in the specific perioperative considerations for skeletal dysplasia, given the airway and cervicomedullary risks described above. Reassure families that cognitive development and life expectancy are generally normal, while being clear and proactive about the orthopedic, respiratory, and neurologic surveillance this condition specifically requires."
  }
 ]
}