Genetics of Achondroplasia 

Updated: Sep 17, 2018
Author: Germaine L Defendi, MD, MS, FAAP; Chief Editor: Maria Descartes, MD 

Overview

Background

Achondroplasia, a nonlethal form of chondrodysplasia, is the most common type of short-limb dwarfism. This skeletal dysplasia is inherited as a Mendelian autosomal dominant trait with complete penetrance. Approximately 80% of cases are due to a new (de novo) dominant mutation, with the mutation rate estimated to be 1.4 x 10-5 per gamete per generation.[1] Salient phenotypic features include disproportionate short stature, megalencephaly, a prominent forehead (frontal bossing), midface hypoplasia, a normal trunk length, rhizomelic (proximal) shortening of the arms and legs, prominent lumbar lordosis, genu varum (bowed legs), and a trident-hand configuration.[2] Graphs illustrating linear growth (height), growth velocity, upper and lower segment length, and head circumference (occipitofrontal circumference [OFC]), for both females and males diagnosed with achondroplasia, are shown below.

Height for females with achondroplasia (mean/stand Height for females with achondroplasia (mean/standard deviation [SD]) compared to normal standard curves. The graph is based on information from 214 females. Adapted from Horton WA, Rotter JI, Rimoin DL, et al. Standard growth curves for achondroplasia. J Pediatr. 1978 Sep; 93(3): 435-8.
Height for males with achondroplasia (mean/2 stand Height for males with achondroplasia (mean/2 standard deviations [SDs]) compared to normal standard curves. The graph is based on information from 189 males. Adapted from Horton WA, Rotter JI, Rimoin DL, et al: Standard growth curves for achondroplasia. J Pediatr. 1978 Sep; 93(3): 435-8.
Mean growth velocities (solid line) for males (top Mean growth velocities (solid line) for males (top) and females (bottom) with achondroplasia compared to normal growth velocity curves. Dashed lines indicate third percentile, mean, and 97th percentile. Data are from 26 males and 35 females. Adapted from Horton WA, Rotter JI, Rimoin DL, et al. Standard growth curves for achondroplasia. J Pediatr. 1978 Sep; 93(3): 435-8.
Upper and lower segment lengths for males (top) an Upper and lower segment lengths for males (top) and (bottom) with achondroplasia (mean/standard deviation [SD]). Data are from 75 males and 95 females. Adapted from Horton WA, Rotter JI, Rimoin DL, et al. Standard growth curves for achondroplasia. J Pediatr. 1978 Sep; 93(3): 435-8.
Head circumference for females with achondroplasia Head circumference for females with achondroplasia compared to normal curves (dashed lines). Data are from 145 females. Adapted from Horton WA, Rotter JI, Rimoin DL, et al. Standard growth curves for achondroplasia. J Pediatr. 1978 Sep; 93(3): 435-8.
Head circumference for males with achondroplasia c Head circumference for males with achondroplasia compared to normal curves (dashed lines). Data are from 114 females. Adapted from Horton WA, Rotter JI, Rimoin DL, et al. Standard growth curves for achondroplasia. J Pediatr. 1978 Sep; 93(3): 435-8.

Pathophysiology

Achondroplasia is caused by mutations in the fibroblast growth factor receptor-3 (FGFR3) gene.[2, 3, 4, 5, 6, 7, 8, 9] Mutations within FGFR3 are the only genetic changes known to cause achondroplasia.[10] FGFR3 has been mapped to the short arm of chromosome 4, p16.3 (4p16.3).[11, 12] All causal mutations occur at the exact same location within the gene; hence, molecular testing by targeted mutational analysis is easily done and interpreted. The two mutations, G1138A and G1138C, cause increased function of the FGFR3 gene. These mutations cause decreased endochondral ossification, decreased cellular hypertrophy, decreased cartilage matrix production, and inhibited proliferation of chondrocytes in growth plate cartilage.

G1138A and G1138C mutations of FGFR3 account for 99% of the mutational changes in patients with achondroplasia. A specific point mutation results; hence, an amino acid substitution occurs.[13] About 98% of diagnosed patients have the G1138A mutation, resulting in a G-to-A DNA nucleotide point change. One percent of cases have a G-to-C DNA point change at nucleotide 1138, causing the G1138C mutation. A rare missense mutation (Lys650Met) in the tyrosine kinase region of FGFR3 causes a disorder termed severe achondroplasia with developmental delay and acanthosis nigricans (SADDAN).[14] See Differentials.

A study by Di Rocco et al using murine and human subjects indicated that FGFR3 mutations in achondroplasia also affect membranous ossification. The investigators analyzed the calvaria and skull base in mice with an achondroplasia-like mutation, as well as in humans with achondroplasia or FGFR3-related craniosynostoses. Their evaluation revealed abnormal cartilage and premature fusion of the synchondroses, which changed the size and shape of the foramen magnum.[15]

Epidemiology

Frequency

United States

Frequency has not been documented for births in the United States.

International

Frequency is believed to be 1 case per 15,000-40,000 births worldwide, with an average worldwide frequency of 1 in 25,000 live births. However, there is a wide range, with the frequency of achondroplasia estimated to be 1 in 6400 live births in Denmark, and 1 in 10,000 live births in Latin America.

In 1986, Orioli et al reported on the frequency of all skeletal dysplasias in a study population of 349,470 live births and stillbirths.[16] Based on this study, the prevalence rate for achondroplasia was estimated to be 0.5-1.5 cases per 10,000 births (1 in 20,000 to 1 in 6,666 births) and the mutation rate to be 1.72-5.57 x 10-5 per gamete per generation.

Mortality/Morbidity

Central nervous system

Sudden death within the first year of life is attributed to abnormalities at the craniocervical junction leading to spinal cord compression. Central apnea occurs as a result of arterial compression at the cervical level of the foramen magnum. A small foramen magnum present in these patients may also cause a high cervical myelopathy.

The risk of sudden death for infants with achondroplasia is 2-5%. This risk can be minimized with appropriate assessment of the craniocervical junction, which includes a thorough neurological history and examination, neuroimaging (either computed tomography [CT] scanning or magnetic resonance imaging [MRI]), and polysomnography (sleep study). The presence of neurological abnormalities necessitates referral to a medical center with neurosurgical consultation services.

Cervical instability is present in a large number of patients. Great care must be taken with manipulation of the neck, as would occur for preparation of intubation in general anesthesia. Uncontrolled neck movements can cause significant neurological compromise with spinal cord compression.

Parents and caregivers should use an infant carrier with a firm back that affords good neck support and use a rear-facing car seat for travel as long as possible. Use of mechanical swings and carrying slings should be avoided to prevent uncontrolled head movement.

Thoracolumbar kyphosis occurs in most infants with achondroplasia. Severe kyphosis is related to unsupported sitting of the infant before adequate trunk muscle strength has developed.[17] Angular deformities of the extremities, premature degenerative joint disease, and spinal disorders are seen in these patients.

School-aged children with achondroplasia have shown head CT-scan findings of neuroanatomic abnormalities consistent with arrested hydrocephalus. In addition, enlarged ventricles and hypoplasia of the corpus callosum have been noted. These CT-scan findings are similar to those observed in children with compensated, unshunted hydrocephalus. The hydrocephalus may be due to increased intracranial venous pressure secondary to stenosis of the sigmoid sinus at the level of the narrowed jugular foramina.

Pulmonology and apnea

Respiratory disorders are seen frequently, including apnea and abnormalities of pulmonary gas exchange. Up to 75% of children with achondroplasia demonstrate a pathologic apnea index (> 30 episodes). Brainstem compression may contribute to central apnea. Obstructive sleep apnea may be due to midface hypoplasia and high body mass index.[18, 19] See Nutrition and body mass index (BMI) below.

Severe upper airway obstruction occurs in less than 5% in children with achondroplasia. For these children, tonsillectomy and adenoidectomy do not markedly resolve this obstruction. Adenotonsillar hypertrophy, hypotonicity, and a narrow trunk with a small thoracic cage all contribute to confining the airway and causing upper airway obstruction.

Children with achondroplasia who have respiratory dysfunction and obstructive sleep apnea (OSA) detected by polysomnography have associated cognitive deficits, as reported in children with OSA within the general population. Restrictive pulmonary disease, with or without restrictive airway disease, occurs in less than 5% of young children (< 3 y). This risk increases for patients who live at higher elevations.

Development

Children with achondroplasia have cognitive scores within normal; however, they may have mild deficits in visual-spatial tasks. This deficit has also been identified in children with arrested hydrocephalus.

Motor milestones typically are delayed for the first year of life due to a large cranium and poor overall muscle tone (hypotonia). Language development is normal, if no conductive hearing loss is present.[20]

Nutrition and body mass index (BMI)

Obesity, when present, aggravates the morbidity related to lumbar stenosis, nonspecific joint problems, and cardiovascular and apnea risks. Based on the weight/height (W/H) curves developed by Hunter et al for boys and girls with achondroplasia, the mean W/H curve in children with achondroplasia matches the control curve until the children reach 75 cm in height. Beyond 75 cm, the weight in children with achondroplasia increases disproportionately to height.

The Quetelet index or body mass index (BMI=W/H2) can be used to estimate weight excess in children aged 3-6 years. After that, the Rohrer index (RI=W/H3) should be used for children and adolescents aged 6-18 years; this index can be further extrapolated to adults.

Race

No documented race predilection is noted.

Sex

Males and females are equally affected, as the FGFR3 gene is located on chromosome 4 (an autosome) and not on a sex chromosome.

 

Presentation

History

Achondroplasia is primarily due to a de novo mutational event; however, there may be parents of an affected child who are affected themselves and are heterozygous for either the G1138A or G1138C mutation. Identifying family members at risk aids in addressing medical treatment plans, offering genetic counseling with options for genetic testing, and providing educational materials and emotional support.

Once the diagnosis of achondroplasia is made, obtain the following history to avoid serious complications:

  • A history of lower back numbness or pain, apnea, ataxia, and incontinence may be due to cervicomedullary compression. Cord compression can lead to respiratory arrest and progressive quadriparesis. Surgical indicators to release this compression include a small foramen magnum, central hypopnea, and brisk reflexes.

  • Obtain a careful history for recurrent otitis media to prevent conductive hearing loss, a factor related to speech delay.

  • A history of sleep disturbances[21] and increased head size may indicate neurologic and respiratory complications.

Physical

Neurologic findings are as follows:

  • Hypotonia in infancy and early childhood

  • Delayed motor milestones

  • Normal intelligence with possible minor deficits in visual-spatial tasks

Craniofacial features are as follows:

  • Large calvarial bones in contrast to the small cranial base and facial bones

  • True megalencephaly (large head) with frontal bossing

  • Midface hypoplasia

  • Dental malocclusion and crowding

Skeletal features are as follows:

  • Disproportionate short stature: Male average adult height 131 ± 5.6 cm; female average adult height 124 ± 5.9 cm; average adult height for both approximately 4 feet

  • Normal trunk length that appears long and narrow

  • Small thoracic cage

  • Rhizomelic shortening of the proximal limbs (arms and legs) with redundant skin folds

  • Brachydactyly

  • Trident hand configuration: Marked separation between the ring and middle fingers, giving the hand a 3-pronged appearance

  • Thoracolumbar gibbus (lumbar kyphosis) in infancy, which is replaced by an exaggerated lumbar lordosis once ambulation begins

  • Hyperextensibility of joints, especially the knee joint

  • Limited elbow extension and rotation

  • Genu varum (bowed legs)

In a study of adult males with achondroplasia, Sims et al found the patellar tendons to be more compliant in these individuals than in controls; the investigators suggested this to be a factor behind lower relative knee extensor force production seen in achondroplasia. The investigators reported a 47% reduction in stiffness and a 51% lower Young’s modulus, in achondroplastic patellar tendons, with the stress produced through isometric maximal voluntary contraction (iMVC) in subjects with achondroplasia being 54% below that of controls. In addition, the achondroplastic patellar tendons demonstrated 22% less maximal excursion at iMVC than did the controls’ tendons.[22]

Causes

Advanced paternal age (> 35 y) is identified as a risk factor for de novo cases of autosomal dominant syndromes. Achondroplasia is part of this category and suggests that factors influencing DNA replication or repair during spermatogenesis may predispose to the occurrence of G1138A or G1138C FGFR3 mutations in older men.

 

DDx

Diagnostic Considerations

The phenotype and radiographic findings of achondroplasia are distinctive; diagnosis of affected children should not be difficult. However, there are other types of short-limb dwarfism associated with mutations within FGFR3. Diagnostic testing by genetic molecular studies is available for confirmation.

Hypochondroplasia

This chondrodysplasia occurs less often than achondroplasia. Hypochondroplasia differs from achondroplasia in its lack of craniofacial involvement and milder phenotypic changes in the spine and hands. Inheritance is autosomal dominant, and the gene has been mapped to 4p16.3, but with a different mutational change within FGFR3. A study by Xue et al suggests that significant overlap exists between the genotypes and phenotypes of achondroplasia and hypochondroplasia, indicating that when either disorder is suspected, molecular genetic testing for both should be performed.[23]

SADDAN (severe achondroplasia with developmental delay and acanthosis nigricans)

Extremely short stature, profound developmental delay, marked tibial bowing, and acanthosis nigricans characterize this rare genetic disorder.

Thanatophoric dysplasia

This is a skeletal dysplasia with significant newborn mortality due to a small thoracic cage and pulmonary insufficiency. Patients who survive beyond the neonatal period have profound developmental delay and severe growth deficiency. It is inherited as an autosomal dominant trait; all cases are due to a de novo mutation.

Differential Diagnoses

 

Workup

Laboratory Studies

Commercially available direct DNA analysis for FGFR3 mutations identifies the G1138A (known as point mutation G380R) in patients with achondroplasia and the novel missense mutation (Lys650Met) in tyrosine kinase. Direct DNA analysis of FGFR3 mutations is used for prenatal screening in families at risk (ie, parents who are heterozygous for either the G1138A or the G1138C mutation). Transgenic mice with achondroplastic skeletal dysplasia have been developed, which can potentially speed the research and development of drugs and provide animal models for gene therapy trials.

Epiphyseal growth plate cartilage findings are histologically, immunohistochemically, biochemically, and electron microscopically normal.

Imaging Studies

Diagnosis is assisted with imaging studies and their findings. Confirmation of achondroplasia using these diagnostic tools helps exclude other types of skeletal dysplasias.

Ultrasonography

Fetal ultrasonography is recommended to assist in prenatal diagnosis, if there is concern for achondroplasia. Perform fetal ultrasonography to evaluate skeletal anomalies and to measure the long bones for size, shape, bowing, symmetry, and quality of calcification.

Perform serial ultrasonography starting at the second trimester to plot on growth curves the fetal (intrauterine) femoral length. This can aid in distinguishing a fetus with a skeletal dysplasia from an unaffected fetus; note that the characteristic features of achondroplasia may not be evident before this time. Also use fetal ultrasonography to evaluate the skull for size and shape.

Perform cranial ultrasonography at birth and at age 2 months, 4 months, and 6 months, to monitor ventricular size for hydrocephalus and/or an intracranial bleed.[24] In addition, perform ultrasonography if the following conditions are present:

  • If the fontanelle is unusually large and full

  • If the occipitofrontal circumference (OFC) increases disproportionately over time

  • If clinical symptoms of hydrocephalus are present

Radiography

Plain radiography performed at birth can identify achondroplasia. With the findings of disproportionately short limbs on fetal ultrasonography, plain film radiographs of the neonate may help distinguish achondroplasia from other skeletal dysplasias.[25]

Perform a skeletal survey. Radiographic findings include a contracted skull base, normal trunk length, rhizomelic shortening of the long bones, trident hands, a square-shaped pelvis with small sacrosciatic notch, and proximal femoral radiolucency. In older children, a chevron-shaped (V-shaped) distal femoral epiphyses is seen and growth plates are shortened.

Additional radiographic findings are as follows:

  • Progressive interpedicular narrowing in the lumbar spine 

  • Short pedicles, which can cause spinal stenosis

  • Short femoral neck and metaphyseal flaring

  • Dysplastic ilium, narrow sacroiliac groove, and flat-roofed acetabula

Pregnancy

Prior to pregnancy for a woman with achondroplasia, radiographic evaluation of the pelvis is recommended to assess for a narrow pelvis. Delivery options need to be discussed, especially with regard to defining difficulties associated with vaginal delivery.

CT scanning

Head CT-scan findings define neuroanatomic abnormalities consistent with arrested hydrocephalus. Enlarged cranial ventricles and changes in the corpus callosum are seen.

MRI

Craniocervical MRI findings include narrowing of the foramen magnum and stenosis in the lumbar spine.[26]

 

Treatment

Medical Care

Closely monitor body growth in patients with achondroplasia using achondroplasia-specific growth charts. Weight, height, and head circumference should be measured and plotted monthly for the first year of life. Measure and record the upper-to-lower segment ratio.

Monitor developmental milestones in gross and fine motor skills, language, and social/adaptive development.

Perform thorough neurologic examinations.

Diagnose and treat middle ear infections, as recurrence can lead to conductive hearing loss.

Orthodontic evaluation should be performed to assess for dental malocclusion and crowding.

Weight management should be instituted to prevent obesity and its associated comorbidities.

Recombinant human growth hormone (r-hGH or HGH) therapy should be administered to foster linear growth. Treatment with r-hGH therapy effectively increases the bone growth rate, especially for the first year of use. Initiating therapy at age 1-6 years is recommended to achieve maximum growth benefit. Long-term studies to determine final height and randomized, controlled studies to justify prolonged treatment with r-hGH in patients with short stature are presently not available.[27]

Anti-inflammatory agents, such as nonsteroidal anti-inflammatory drugs (NSAIDs), are useful to decrease pain and inflammation in patients with degenerative joint disease.

Consultations

Immediately refer patients to a neurologist and/or neurosurgeon for reflex asymmetry, profound hypotonia, early hand preference, or significant head circumference growth.

Depending on clinical concerns, referrals to pediatric specialists, such as an otolaryngologist, orthopedist, and pulmonologist, may be needed. 

A pediatric endocrinologist, with knowledge of r-hGH treatment protocol, can give guidance to parents about r-hGH as a therapeutic option to increase linear height. 

Dietary guidance by a nutritionist to maintain healthy weight goals may be helpful.

Refer to geneticists and genetic counselors for prenatal consultations, options for genetic testing, and resources for support organizations.

Offer psychological support and educational tools to patients and their caregivers to assist in coping with disproportionate short stature.

Diet

Hunter et al recommend that children with achondroplasia remain within 1 standard deviation of the mean weight/height (W/H) curve for people with achondroplasia. 

Sex- and age-specific body mass index (BMI) curves are available and should be used for patients with achondroplasia (birth to age 16 y) for health surveillance and nutritional guidance. Dietary guidance by a nutritionist to help maintain healthy weight goals is helpful.

Patients with elevated BMIs have increased risk of comorbidities as associated with their skeletal dysplasia and impact of excess weight (eg, cardiovascular disease, sleep apnea, diabetes, and skeletal burden).[28]

Surgical Options

Leg-lengthening procedures using distraction osteogenesis have been performed successfully. These procedures are lengthy, traumatic, and very demanding for both the patient and his or her family. Complications include bone infection, injury to nerves/blood vessels, injury to muscles/tendons, poor bone healing, and unequal lengthening.

An average leg-length gain of about 18 cm and an average increase in arm length of about 10 cm has been reported. Combining both r-hGH therapy and lengthening surgery may provide optimal benefit for patients in achieving near-normal stature and proportions. Successful height increase is reported to be 12-14 inches. Good outcomes are reported with the use of the Orthofix Garches lengthening device, along with tenotomy of the Achilles tendon and syndesmosis. This procedure has fewer complications and demonstrates healing indices similar to those of other operative protocols. Another procedure associated with few complications in children and adolescents (< 14 y) is tibia lengthening, rather than femur lengthening.

Children with signs of craniomedullary compression may require surgical treatment to release this compression to improve neurologic, cognitive, and respiratory functions.[29] Medical indications for suboccipital decompression include lower limb hyperreflexia or clonus on neurologic examination, central hypopnea demonstrated by polysomnography, and foramen magnum measurements lower than the mean values.

Lumbar laminectomy can be performed for spinal stenosis, which is a condition that tends to occur in early adulthood.

Spinal fusion can be performed for persistent kyphosis not improved with bracing and sitting modification.

 

Medication

Hormones

Class Summary

Human growth hormone (HGH) has been used for more than 10 years to treat patients with achondroplasia.[30, 31, 32] A study of 35 children with achondroplasia showed an increase in growth velocity in the first 2 years of treatment with HGH and demonstrated the safety of HGH use for a 5-year period.[33]

Growth hormone, human (Nutropin, Genotropin, Humatrope)

HGH stimulates growth of linear bone, skeletal muscle, and organs. It also stimulates erythropoietin, which increases red blood cell mass.

 

Follow-up

Further Outpatient Care

The following recommendations for the medical management and follow-up care of patients with achondroplasia were presented at the First International Symposium on Human Achondroplasia held in Rome, Italy, in 1986:

  • Height, weight, and head circumference measurements plotted on growth curves standardized for achondroplasia

  • Thorough neurologic examinations for clinical assessment; CT scanning, MRI, somatosensory-evoked potentials, and polysomnography as indicated for clinical findings of concern

  • Appropriate medical care for recurrent middle ear infections; referral to otolaryngologist if concern for conductive hearing loss due to chronic serous otitis media

  • Dentistry and orthodontics to address dental crowding associated with the craniofacial features seen in achondroplasia

Complications

Complications include cervicomedullary compression, spinal stenosis, restrictive and obstructive lung disease, otitis media, and tibial bowing. Other possible complications include the development of thoracolumbar kyphosis, symptomatic hydrocephalus, and symptomatic upper cord compression.

Prognosis

Most patients diagnosed with achondroplasia have normal intelligence, lead independent and productive lives, and have a normal life expectancy. However, infants and children below age 2 years have some increased risk for early death when compared with the general population. Without proper assessment and medical care, 2-5% of children with achondroplasia will die. Most of this increased risk is due to craniocervical junction abnormalities. 

 

Patient Education

Genetic counseling is recommended to discuss the genetics of cause, recurrence risk, and prenatal diagnosis with families.

Patient education guidelines

Age-related care guidelines have been provided in "Health Supervision for Children with Achondroplasia" by the American Academy of Pediatrics, Committee on Genetics, published in September 2005.[34]

Prenatal visits

Geneticists (genetic counselors and medical geneticists), obstetricians, and pediatricians should be consulted to educate parents regarding the disorder, inheritance, and prognosis for offspring.

Infants (0-12 mo)

Review the personal support available to the family.

Review contact information for support groups.

Review the increased risk of serous otitis media due to shortened eustachian tubes. Instruct that otic examination is needed with any upper respiratory tract infection.

Avoid infant carriers that place the infant in a curled-up position. Car safety seats should always be used during automobile travel.

Early childhood (1-5 y)

Discuss adapting the home so that the child can become independent (lower the height of light switches and supply step stools).

Discuss adapting age-appropriate clothing with snapless easy-opening fasteners and tuckable loops.

Discuss adaptation of toys, especially tricycles, to accommodate for shorter limbs.

Discuss adaptation of toilets to allow comfortable independent use, with an extended wand to clean soiled areas.

Discuss the use of a foot-support stool during sitting so that the child's feet are not hanging. Foot support is needed while the child is sitting in a chair. A cushion behind the child's back may be required for good posture.

Discuss orthodontics and the possible need for braces in children older than 5 years.

Encourage the family to develop activities in which the affected child can take part; avoid gymnastics, high diving, acrobatics, and collision sports.

Discuss how to talk with the child, friends, and family members about short stature.

Encourage preschool attendance so that the child can learn to socialize in an age-appropriate way.

Discuss with school staff, toileting procedures and special preparations as needed, due to the child's short stature

Discourage the child from high jump activity to minimize stress on the joints and spine.

Late childhood (5-13 y)

Children with achondroplasia usually have normal intelligence and are matriculated in the regular education program.

Discuss the need to prepare school personnel and to supply proper furnishings to accommodate for the child's stature.

Prepare the child for psychosocial situations, and teach the child how to address these issues.

Help children explain their short stature to their peers and encourage them to ask for assistance, if needed. 

Suggest adaptive aids in the school to help the child cope with heavy doors, high doorknobs, blackboard use, and a regular-sized desk, and stress the need for proper foot support.

Ensure that the child can use the restroom independently.

Adolescence to early adulthood (13-21 y)

Revisit the patient’s diagnosis to ensure that the adolescent has an understanding of his or her diagnosis and of the genetic etiology of achondroplasia.

Discuss contraception and the options available. Women of reproductive age with achondroplasia are fertile, and, as such, potential for pregnancy complications and outcomes should be addressed.

Continue nutritional counseling to address the importance of weight management. Stress eating habits that minimize the risk of obesity and the comorbid complications associated with excessive weight gain.

Assist the patient to establish an independent lifestyle. Fostering the ability to obtain a driver's license can help. Drivers require certain vehicle modifications, such as pedal extenders. The Association for Driver Rehabilitation Specialists (ADED) helps those who have certain transportation needs and vehicle adaptations.

Support organizations

Support groups may help (1) provide practical information to address potential problems in daily living and having disproportionate short stature and (2) provide emotional and psychosocial support to patients, parents, and caregivers living with achondroplasia.

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International Skeletal Dysplasia Registry

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Web site: www.csmc.edu