Table 3. [Selected Disorders in the Differential Diagnosis of Achondrogenesis Type 1B]. - GeneReviews®

Gene	MOI	Disorder	Key Features
Achondrogenesis ¹
TRIP11	AR	ACG1A (Houston-Harris type) (OMIM 200600)	Rib fractures & absence of ossification of vertebral pedicles may suggest ACG1A. Hands & fingers are less markedly shortened than in ACG1B. Cartilage matrix is normal & inclusions are present in chondrocytes.
COL2A1	AD	ACG2 (Langer-Saldino type) (See Type II Collagen Disorders Overview.)	Hands & fingers can be almost normal. ACG2 shows more severe underossification of vertebral bodies than ACG1B, & typical configuration of iliac bones w/concave medial & inferior borders, & nonossification of ischial & pubic bones. Cartilage is hypervascular & hypercellular w/↓ matrix & vacuoles ("Swiss cheese-like") but has roughly normal staining properties.
Osteochondrodysplasia
COL1A1 COL1A2	AD	Perinatally lethal osteogenesis imperfecta (OI) & progressively deforming OI (See COL1A1/2 OI.)	Typical signs: soft undermineralized skull & blue sclerae. Bones are bowed but not as short as in ACG. Multiple fractures are present.
FGFR3	AD	Thanatophoric dysplasia (TD)	The limbs are longer than in ACG & the thorax is narrow but elongated. Cloverleaf skull deformity is common in TD type II.
>20 genes ²	AR	Short-rib polydactyly syndromes (SRPS)	Extremely short limbs & ribs (severe narrow rib cage). Polydactyly is usually present; when absent, SRPS may be confused w/TD.
ESCO2	AR	Roberts syndrome (See ESCO2 Spectrum Disorder.)	Severe limb shortening w/only mildly affected axial skeleton may suggest Roberts syndrome.
COL11A1 COL11A2	AR AD	Fibrochondrogenesis (OMIM PS228520)	Distinguishing radiographic features: marked metaphyseal flaring of long bones & clefts of vertebral bodies

Gene

MOI

Disorder

Key Features

Achondrogenesis ¹

TRIP11

ACG1A (Houston-Harris type) (OMIM 200600)

Rib fractures & absence of ossification of vertebral pedicles may suggest ACG1A. Hands & fingers are less markedly shortened than in ACG1B. Cartilage matrix is normal & inclusions are present in chondrocytes.

COL2A1

ACG2 (Langer-Saldino type) (See Type II Collagen Disorders Overview.)

Hands & fingers can be almost normal. ACG2 shows more severe underossification of vertebral bodies than ACG1B, & typical configuration of iliac bones w/concave medial & inferior borders, & nonossification of ischial & pubic bones. Cartilage is hypervascular & hypercellular w/↓ matrix & vacuoles ("Swiss cheese-like") but has roughly normal staining properties.

Osteochondrodysplasia

COL1A1
COL1A2

Perinatally lethal osteogenesis imperfecta (OI) & progressively deforming OI (See COL1A1/2 OI.)

Typical signs: soft undermineralized skull & blue sclerae. Bones are bowed but not as short as in ACG. Multiple fractures are present.

FGFR3

Thanatophoric dysplasia (TD)

The limbs are longer than in ACG & the thorax is narrow but elongated. Cloverleaf skull deformity is common in TD type II.

>20 genes ²

Short-rib polydactyly syndromes (SRPS)

Extremely short limbs & ribs (severe narrow rib cage). Polydactyly is usually present; when absent, SRPS may be confused w/TD.

ESCO2

Roberts syndrome (See ESCO2 Spectrum Disorder.)

Severe limb shortening w/only mildly affected axial skeleton may suggest Roberts syndrome.

COL11A1
COL11A2

AR
AD

Fibrochondrogenesis (OMIM PS228520)

Distinguishing radiographic features: marked metaphyseal flaring of long bones & clefts of vertebral bodies

From: Achondrogenesis Type 1B

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