Clinical Guidance

Growth. The most common presenting feature of children with hypochondroplasia is short stature with disproportionate limbs and relative macrocephaly. Birth weight and length are often within the normal range and the disproportion in limb-to-trunk length is usually mild and easily overlooked during infancy. Typically, these children present to pediatricians or pediatric endocrinologists as toddlers or at early school age with decreased growth velocity leading to short stature. There is a lack of the pubertal growth spurt when the height difference from those with hypochondroplasia and those with average stature may increase.

Source: GeneReviews — "Hypochondroplasia"

Differential Diagnosis

Numerous forms of skeletal dysplasia with disproportionate limbs are recognized and are characterized by clinical and radiologic features that distinguish them from hypochondroplasia and achondroplasia. Many of these disorders are quite rare. The diagnosis of hypochondroplasia is seldom made at birth unless a prior family history exists. Most affected individuals present with short stature as toddlers or young school-age children. Inappropriate diagnoses of hypochondroplasia are often made because the disorder is considered to be relatively common and the radiologic features are variable and may be subtle. Conditions with a known genetic etiology that may be confused with hypochondroplasia are summarized in . Table 3. Genes of Interest in the Differential Diagnosis of Hypochondroplasia

Source: GeneReviews — "Hypochondroplasia"

Management Guidelines

Management of children with hypochondroplasia usually does not differ significantly from that of children with average stature except for genetic counseling issues and dealing with parental concerns about short stature. However, because the phenotype of FGFR3-related hypochondroplasia may overlap with that of achondroplasia, recommendations for the management of achondroplasia as outlined by the American Academy of Pediatrics Committee on Genetics should be considered in children with hypochondroplasia who exhibit more severe phenotypic features.

Evaluations Following Initial Diagnosis

To establish the extent of disease and needs in an individual diagnosed with hypochondroplasia, the evaluations summarized (if not performed as part of the evaluation that led to the diagnosis) are recommended.

Table 4.

Hypochondroplasia: Recommended Evaluations Following Initial Diagnosis

System/Concern | Evaluation | Comment

Growth

| Measurement of height, weight, head circumference | Plot growth parameters on hypochondroplasia-standardized growth curves (full text).

Musculoskeletal

| Clinical assessment for truncal weakness or evidence of thoracolumbar kyphosis | Lateral spine radiographs to evaluate for thoracolumbar kyphosis if indicated

Clinical assessment for genu varum | Referral to orthopedist if bowing interferes w/walking

Narrow craniocervical junction

| • Assess for signs/symptoms of sleep apnea; refer for polysomnography if needed.

Source: GeneReviews — "Hypochondroplasia"