Penetrance

Penetrance is 100%; all individuals who have an FGFR3 heterozygous pathogenic variant associated with achondroplasia have the clinical manifestations of the disorder.

Source: GeneReviews — "Achondroplasia"

Diagnostic Criteria

The clinical and radiologic features that can establish the diagnosis of achondroplasia have been well defined .

Suggestive Findings

The diagnosis of achondroplasia should be suspected in a newborn with the following clinical features; characteristic radiographic features can confirm the diagnosis.

• Clinical features in a newborn

• Proximal shortening of the arms

• Large head

• Narrow chest

• Short fingers with a trident configuration

• Radiographic features in a newborn that can establish the diagnosis

• Square ilia and horizontal acetabula

• Narrow sacrosciatic notch

• Proximal radiolucency of the femurs

• Generalized metaphyseal abnormality including flaring

• Decreasing interpedicular distance caudally

Source: GeneReviews — "Achondroplasia"

Differential Diagnosis

While more than 700 skeletal dysplasias are recognized , many are extremely rare, and virtually all have clinical and radiographic features that readily distinguish them from achondroplasia. Conditions that may be confused with achondroplasia are listed in .

Table 3.

Achondroplasia: Differential Diagnosis

Gene(s) | Disorder | MOI | Clinical Characteristics

FGFR3

| Hypochondroplasia | AD | See .

Severe achondroplasia w/developmental delay acanthosis nigricans (SADDAN) (OMIM 616482)

Thanatophoric dysplasia

Source: GeneReviews — "Achondroplasia"

Management Guidelines

Recommendations for health supervision of children with achondroplasia were outlined by the American Academy of Pediatrics Committee on Genetics . These recommendations serve as guidelines and do not replace individual decision making. The review by also provides management recommendations. Specialized skeletal dysplasia clinics exist; their recommendations may vary slightly from these general guidelines. Evaluations Following Initial Diagnosis Clinical manifestations in achondroplasia vary modestly. In order to establish the extent of disease in an individual diagnosed with achondroplasia, the evaluations summarized (if not performed as part of the evaluation that led to the diagnosis) are recommended. Table 4. Achondroplasia: Recommended Evaluations Following Initial Diagnosis

Source: GeneReviews — "Achondroplasia"

Surveillance Guidelines

Recommendations for surveillance are incorporated into the American Academy of Pediatrics guidelines . To monitor existing manifestations, the individual's response to supportive care, and the emergence of new manifestations, the evaluations summarized in are recommended. Table 7. Achondroplasia: Recommended Surveillance

Source: GeneReviews — "Achondroplasia"