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Pseudoachondroplasia (PsACH) is a rare, autosomal dominant skeletal dysplasia characterized by disproportionate short stature, ligamentous laxity, and epiphyseal and metaphyseal abnormalities, but normal facial features and intelligence.
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Genetic basis:
| Feature | Description |
|---|---|
| Gene involved | COMP (Cartilage Oligomeric Matrix Protein) |
| Inheritance | Autosomal dominant (often de novo mutations) |
| Pathophysiology | Abnormal COMP disrupts cartilage matrix and endochondral ossification, especially in epiphyses and metaphyses |
| Domain | Manifestations |
|---|---|
| Stature | Disproportionate short-limbed dwarfism; presents at 2–3 years |
| Face | Normal facial features (unlike achondroplasia) |
| Limbs | Rhizomelic shortening, genu varum/valgum, limb bowing |
| Joints | Ligamentous laxity, hypermobility, early-onset osteoarthritis |
| Spine | Scoliosis, lumbar lordosis, and platyspondyly (mild to moderate) |
| Hands | Brachydactyly, short metacarpals and phalanges |
| Motor development | Delayed walking, waddling gait due to instability and joint pain |
| Intelligence | Normal |
Skeletal features change with age: a. A pseudoachondroplasia patient aged 6. Short-limbed short stature resembling achondroplasia, but the patient is of normal facies. b. Lateral radiograph of the spine aged 6 showing the “anterior tongue-like protrusion” appearance (red arrow). c. The same patient aged 17. The short stature and deformity of extremities have become more conspicuous. d. Lateral radiograph of the spine aged 17. The characteristic feature has disappeared.
Ikegawa, S. Genetic analysis of skeletal dysplasia: recent advances and perspectives in the post-genome-sequence era. J Hum Genet 51, 581–586 (2006). https://doi.org/10.1007/s10038-006-0401-x
Differences between pseudoachondroplasia and achondroplasia: https://doi.org/10.4329/wjr.v6.i10.808
| Features | Pseudoachondroplasia | Achondroplasia |
|---|---|---|
| Skull | Normal “Achondroplasia with normal face” | Abnormal |
| ‣ | + | – |
| Interpedicular distance | Normal | Decreased in lumbar spine |
| Long bones | Epiphyses and metaphyses abnormal | Only metaphyses abnormal |
| ‣ & ‣ | - | + |
A. Long Bones
| Feature | Description |
|---|---|
| Short, irregular metaphyses | Especially in femur and humerus |
| “Trumpeting” of femur | Metaphyseal flaring |
| Irregular, fragmented epiphyses | Delayed and irregular ossification in multiple joints |
B. Spine
| Region | Findings |
|---|---|
| Spine | Mild ‣, anterior beaking |
| Odontoid | Hypoplasia (risk of atlantoaxial instability) |
Pseudoachondroplasia.
A 9‐year‐old female patient 1. Notice the disproportionate short‐limb short stature. Mark the arm and thigh shortening (rhizomelic shortening), bow legs, and broadening of distal ends of forearm and tibias (a). AP radiograph of both legs (b) demonstrating metaphyseal flaring and cupping (hollow white arrows), epiphyseal irregularities (solid white arrows), and dense sclerotic lines of the distal metaphyses (black arrows). All these changes are known as “rachitic‐like changes”. Similar changes can be appreciated in the AP radiograph of both arms
(c). A 9‐year‐old male with “hypophosphatemic rickets” patient 2. Hand and wrist radiographs (d) show typical rachitic changes in metaphyses of the distal radiuses and ulnae (hollow arrows). Note the small for age distal radial epiphyses (solid arrows). Notice the deceptive resemblance between these rachitic changes and the “rachitic‐like changes” observed in the pseudoachondroplasia radiographs. Note the symmetry of epimetaphyseal lesions (b‐d).
AP radiograph of the hips (e) of an 8‐year‐old male patient 3 demonstrates the absence of ossification in the proximal femoral epiphyses and greater trochanteric apophyses, the characteristic medial beaking of the neck (arrows) and coxa vara.
A 4‐year‐old male patient 4. Cervical spine radiographs (f) depict the characteristic platyspondyly (uniformly reduced vertebral height) in anteroposterior view and atypical bullet‐shaped/oval vertebrae (convexity of superior border with mild anterior and central beaking) in lateral view. Lumbar spine radiograph lateral view (g) depicts typical bullet‐shaped/oval vertebrae (convexity of both the superior and inferior vertebral borders with clear anterior and central beaking)
El-Sobky TA, Shawky RM, Sakr HM, Elsayed SM, Elsayed NS, Ragheb SG, Gamal R. A systematized approach to radiographic assessment of commonly seen genetic bone diseases in children: A pictorial review. J Musculoskelet Surg Res 2017;1:25-32
C. Pelvis and Hips
