The following summary is from Orphanet, a European reference portal for information on rare diseases and orphan drugs.

Blomstrand lethal chondrodysplasia (BLC) is a neonatal osteosclerotic dysplasia (see this term) characterized by advanced endochondral bone maturation, very short limbs, dwarfism and prenatal lethality.

To date, less than 10 cases have been described in the literature.

BLC is a congenital disorder characterized by a low birth weight, facial dysmorphism (widely spaced and protruding eyes (which typically show cataract), depressed nasal bridge, short columella, long philtrum, macroglossia, protruding tongue, severe micrognathia), short trunk, narrow thorax and severe rhizo-meso-acromelic shortness of the limbs. Other anomalies also observed include tooth and mammary gland development defects, hypoplastic lungs, aorta coarctation (see this term), and bowel malrotation. Two forms of BCL, have been described: type I which is the severe, classical form and type II which has less severe features (such as absence of short trunk or, severely shortened arms but moderately shortened legs).

BLC is caused by inactivating homozygous or compound heterozygous mutations in PTH1R (3p22-p21.1) which encodes the parathyroid hormone (PTH)/parathyroid-hormone-related peptide (PTHrP) receptor (PTH1R). These mutations result in the decrease in binding or response to PTH and PTHrP.

Diagnosis is based on the clinical and radiological characteristics which show generalized increase in bone density with advanced ossification, severe shortness of the long bones with wide metaphyses and club-shaped distal ends, long narrow thorax, calcified hyoid bone and laryngeal cartilage and underdeveloped viscerocranium. Histopathological examination shows an important acceleration of the endochondral ossification in tubular bones, narrow cartilages of the epiphyses and large epiphyseal ossification centers. Diagnosis is confirmed by the genetic screening of PTH1R.

Differential diagnosis includes primary failure of tooth eruption (see this term) and other lethal short limbed dwarfisms.

Prenatal diagnosis is achieved by sonographic examination showing polyhydramnios, hydrops fetalis (see this term) and a fetus with very short limbs, nuchale dema, macroglossia, a protuberant abdomen, internal anomalies and markedly advanced endochondral bone formation.

Transmission is autosomal recessive. Genetic counseling should be offered to at-risk couples (both individuals are carriers of a disease-causing mutation) informing them of the 25% chance of having an affected child.

Both forms of BLC are lethal either prenatally or shortly after birth.

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