PubMed · 3627056
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M Stura, S Boero, C Origo, V Tarantino. 1987-06-30. [Audiologic problems in achondroplastics].. https://pubmed.ncbi.nlm.nih.gov/3627056/
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Achondrogenesis type II is a lethal skeletal dysplasia caused by new dominant mutations within the type II collagen gene (COL2A1). Here we report on two pregnancies of a healthy, nonconsanguineous young couple. In the first pregnancy, severe micromelia and generalized edema were noted on ultrasound at 21 weeks' gestation. Clinical, radiological, and histological evaluation of the fetus after termination of the pregnancy showed typical findings of achondrogenesis type II. In the second pregnancy, fetal hygroma was noted at 11 weeks' gestation. Similar clinical, radiographic, and histologic findings were observed in the second fetus, suggesting the recurrence of achondrogenesis II within this family. Molecular analysis of genomic DNA extracted from amniotic cells of the second fetus revealed heterozygosity for a 1340G > A missense mutation (G316D) in the COL2A1 gene. This mutation was not found in the parents. Although, we could not evaluate the presence of this mutation in the first fetus, we strongly believe that our data are in favor of germline mosaicism as the most likely explanation for the recurrence of type II achondrogenesis in both sibs.
A 13-year-old male achondroplastic dwarf with fixed thoracolumbar kyphosis was treated by segmental pedicle screw fixation, posterolateral fusion combined with one stage two level posterior column resection. Preoperative and postoperative kyphosis angles were 97 and 32 degrees, respectively. Combination of segmental pedicle instrumentation with posterior column resection is a treatment option even in immature achondroplastic patients.
We generated transgenic mice that express a constitutively active mutant of MEK1 in chondrocytes. These mice showed a dwarf phenotype similar to achondroplasia, the most common human dwarfism, caused by activating mutations in FGFR3. These mice displayed incomplete hypertrophy of chondrocytes in the growth plates and a general delay in endochondral ossification, whereas chondrocyte proliferation was unaffected. Immunohistochemical analysis of the cranial base in transgenic embryos showed reduced staining for collagen type X and persistent expression of Sox9 in chondrocytes. These observations indicate that the MAPK pathway inhibits hypertrophic differentiation of chondrocytes and negatively regulates bone growth without inhibiting chondrocyte proliferation. Expression of a constitutively active mutant of MEK1 in chondrocytes of Fgfr3-deficient mice inhibited skeletal overgrowth, strongly suggesting that regulation of bone growth by FGFR3 is mediated at least in part by the MAPK pathway. Although loss of Stat1 restored the reduced chondrocyte proliferation in mice expressing an achondroplasia mutant of Fgfr3, it did not rescue the reduced hypertrophic zone, the delay in formation of secondary ossification centers, and the achondroplasia-like phenotype. These observations suggest a model in which Fgfr3 signaling inhibits bone growth by inhibiting chondrocyte differentiation through the MAPK pathway and by inhibiting chondrocyte proliferation through Stat1.