Desbuquois Syndrome

Desbuquois syndrome (DBQD) is an osteochondrodysplasia characterized by severe micromelic dwarfism, facial dysmorphism, joint laxity with multiple dislocations, vertebral and metaphyseal abnormalities and advanced carpotarsal ossification. Two forms have been distinguished on the basis of the presence (type 1) or the absence (type 2) of characteristic hand anomalies. A variant form of DBQD, Kim variant (see these terms), has also been described and is characterized by short stature and articular, minor facial and significant hand anomalies.

Epidemiology

To date, less than 50 cases have been described in the literature.

Clinical description

DBQD is characterized by severe micromelic dwarfism, facial dysmorphism (round flat face, prominent eyes, midface hypoplasia, short nose, microstomia, long upper lip with flat philtrum, microretrognathia, often resulting in isolated Pierre Robin syndrome (see this term)), thoracic hypoplasia, kyphoscoliosis, severe joint laxity with dislocation, and osteopenia. Additional features include glaucoma, cardiac septal defects, lung hypoplasia, obesity and clubbed feet with rocker bottom appearance. Two forms have been distinguished on the basis of the presence (type 1) or the absence (type 2) of characteristic hand anomalies (accessory ossification center distal to the second metacarpal, bifid distal phalanx, or thumb with delta-shaped phalanx). A variant form of DBQD, Kim variant, has been described in 7 patients originating from Korea and Japan, and is characterized by short stature, articular and minor facial anomalies, together with significant hand anomalies including short metacarpals and elongated phalanges with advanced carpal bone age.

Etiology

DBQD type 1 and Kim variant are caused by mutation in the gene CANT1 (17q25.3). However, the function of CANT1 is still unknown. Mutations in the gene XYLT1 (16p12) has been reported to cause DBQD type 2. XYLT1 encodes xylosyltransferase 1 which is involved in proteoglycan synthesis. However not all DBQD type 2 have XYLT1 mutations supporting the involvement of other disease causing genes.

Diagnostic methods

'Diagnosis relies upon recognition of clinical and radiological features which include an advanced carpal and tarsal bone age; broad femoral neck with a spur-like projection and prominent lesser trochanter, producing characteristic ''monkey wrench'' (Swedish key) appearance; narrow thorax; coronal or sagittal clefting of the vertebrae and typical hand changes for DBQD type 1 that consist of small delta-shaped extraphalangeal bone, distal to the second metacarpal, leading to radial deviation of the index fingers (delta phalanx or bifid thumb),and horizontal acetabular roofs with dislocation of femoral heads. Diagnosis is confirmed by the genetic screening of CANT1 in type 1 and XYLT1 in type 2DBQD.'

Differential diagnosis

Differential diagnosis includes autosomal dominant or recessive Larsen syndrome, Reunion island's Larsen syndrome, Catel-Manzke syndrome, chondrodysplasia with joint dislocations, gPAPP type, CHST3-related skeletal dysplasia, spondyloepiphyseal dysplasia, Omani type, diastrophic dwarfism and humerospinal dysostosis (see these terms).

Antenatal diagnosis

Antenatal diagnosis is achieved by ultrasound during the second trimester of pregnancy, by the detection of hydramnios, hydrops fetalis (see this term), intrauterine growth retardation, vertebral abnormalities and characteristic dysmorphic features.

Genetic counseling

Transmission is autosomal recessive and genetic counseling is recommended.

Management and treatment

Management includes regular orthopedic survey with often a need for multiple surgeries (scoliosis, hip and knee dislocation), and eye and ear follow up.

Prognosis

Type 1 DBQD displays a high lethality rate of >33% due to respiratory failure. Survivors may have intellectual disability, developmental delay, generalized and progressive joint laxity with dislocated knees. Orthopedic complications often limit the ambulation in DBQD.