FGFR3-related condition: a skeletal dysplasia with similarities to thanatophoric dysplasia and SADDAN due to Lys650Met

Achondroplasia: a comprehensive clinical review

Achondroplasia is the most common of the skeletal dysplasias that result in marked short stature (dwarfism). Although its clinical and radiologic phenotype has been described for more than 50 years, there is still a great deal to be learned about the medical issues that arise secondary to this diagnosis, the manner in which these are best diagnosed and addressed, and whether preventive strategies can ameliorate the problems that can compromise the health and well being of affected individuals. This review provides both an updated discussion of the care needs of those with achondroplasia and an exploration of the limits of evidence that is available regarding care recommendations, controversies that are currently present, and the many areas of ignorance that remain.

Perinatal imaging findings and molecular genetic analysis of thanatophoric dysplasia type 1 in a fetus with a c.2419T>G (p.Ter807Gly) (X807G) mutation in FGFR3

OBJECTIVE

We present perinatal imaging findings and molecular genetic analysis of thanatophoric dysplasia type I (TD1) in a fetus.

CASE REPORT

A 28-year-old woman was referred for genetic counseling at 22 weeks of gestation because of abnormal prenatal ultrasound findings. Level II ultrasound examination revealed a narrow chest, shortened and curved long limbs, protrusion of the abdomen, and macrocephaly. A tentative diagnosis of TD1 was made. After genetic counseling, the pregnancy was terminated and a malformed fetus was delivered. Postnatal radiography findings were consistent with the diagnosis of TD1, with additional findings of short ribs, platyspondyly, and horizontal acetabular roofs. Molecular genetic analysis using umbilical cord tissue revealed a heterozygous mutation of c.2419T>G (p.Ter807Gly) (X807G) in the fibroblast growth factor receptor 3 gene (FGFR3).

CONCLUSION

A second-trimester fetus with a heterozygous c.2419T>G mutation in FGFR3 may present characteristic ultrasound and X-ray findings of TD1.

Achondroplasia: Development, pathogenesis, and therapy

Autosomal dominant mutations in fibroblast growth factor receptor 3 (FGFR3) cause achondroplasia (Ach), the most common form of dwarfism in humans, and related chondrodysplasia syndromes that include hypochondroplasia (Hch), severe achondroplasia with developmental delay and acanthosis nigricans (SADDAN), and thanatophoric dysplasia (TD). FGFR3 is expressed in chondrocytes and mature osteoblasts where it functions to regulate bone growth. Analysis of the mutations in FGFR3 revealed increased signaling through a combination of mechanisms that include stabilization of the receptor, enhanced dimerization, and enhanced tyrosine kinase activity. Paradoxically, increased FGFR3 signaling profoundly suppresses proliferation and maturation of growth plate chondrocytes resulting in decreased growth plate size, reduced trabecular bone volume, and resulting decreased bone elongation. In this review, we discuss the molecular mechanisms that regulate growth plate chondrocytes, the pathogenesis of Ach, and therapeutic approaches that are being evaluated to improve endochondral bone growth in people with Ach and related conditions. Developmental Dynamics 246:291-309, 2017. © 2016 Wiley Periodicals, Inc.

Mild achondroplasia/hypochondroplasia with acanthosis nigricans, normal development, and a p.Ser348Cys FGFR3 mutation

Pathogenic allelic variants in the fibroblast growth factor receptor 3 (FGFR3) gene have been associated with a number of phenotypes including achondroplasia, hypochondroplasia, thanatophoric dysplasia, Crouzon syndrome with acanthosis nigricans (Crouzonodermoskeletal syndrome), and SADDAN (severe achondroplasia with developmental delay and acanthosis nigricans). Crouzon syndrome with acanthosis nigricans is caused by the pathogenic variant c.1172C>A (p.Ala391Glu) in the FGFR3 gene. The p.Lys650Thr pathogenic variant in FGFR3 has been linked to acanthosis nigricans without significant craniofacial or skeletal abnormalities. Recently, an infant with achondroplasia and a novel p.Ser348Cys FGFR3 mutation was reported. We describe the clinical history of an 8-year-old child with a skeletal dysplasia in the achondroplasia-hypochondroplasia spectrum, acanthosis nigricans, typical development, and the recently described p.Ser348Cys FGFR3 mutation.

Protein-losing enteropathy with intestinal lymphangiectasia in skeletal dysplasia with Lys650Met mutation

Protein-losing enteropathy is a primary or secondary manifestation of a group of conditions, and etiologies which are broadly divisible into those with mucosal injury on the basis of inflammatory and ulcerative conditions, mucosal injury without erosions or ulcerations, and lymphatic abnormalities. We describe the first case of protein-losing enteropathy in a pediatric patient, with severe skeletal dysplasia consistent with thanatophoric dysplasia type I and DNA analysis that revealed a c.1949A>T (p.Lys650Met) in exon 15 of the FGFR3 gene. She presented with protein-losing enteropathy in her 6th month. Post-mortem examination revealed lymphangiectasia in the small intestine. To our knowledge, this is the first report of intestinal lymphangiectasia as a complication of skeletal dysplasia resulting in severe protein-losing enteropathy. © 2016 Wiley Periodicals, Inc.