Achondrogenesis.

In this issue of Pediatric and Developmental Pathology, Aigner and colleagues report a detailed investigation of cartilage matrix changes in a 14-week fetus with achondrogenesis type IA. The changes reported differ from matrix alterations observed in achondrogenesis types IB or II and provide insight into the phenotypic and genotypic differences within this group of skeletal dysplasias.

Survival to adulthood and dominant inheritance of platyspondylic skeletal dysplasia, Torrance-Luton type.

We present a second family with survival to adulthood and dominant transmission of the Torrance-Luton type of platyspondylic chondrodysplasia, and demonstrate the radiographs at different ages together with radiographs and further data of the first family which was published in the Journal of Pediatrics (J Pediatr 136:411-413). Two families are described with survival to adulthood and dominant transmission of the Torrance-Luton type of platyspondylic chondrodysplasia. Although lethality is increased in patients with this disorder, mild expressions of the genetic defect are compatible with survival into adulthood. The heterogeneous group of platyspondylic lethal skeletal dysplasias (PLSD) originally included thanatophoric dysplasias (TD1/2: MIM 187600, 187100) as the most common forms of this condition, as well as TD variants San Diego type (PLSD-SD: MIM 270230) and Torrance-Luton type (PLSD-TL: MIM 151210). Fibroblast growth factor receptor 3 ( FGFR3) gene mutations have been detected in TD1/2 and PLSD-SD. Molecular studies in one of our two families with the Torrance-Luton type did not disclose mutations in the FGFR3 coding region, suggesting that this type of platyspondylic chondrodysplasia is not a thanatophoric dysplasia variant. In contrast to TD1/2 and PLD-SD, the Torrance-Luton type platyspondylic dysplasia is compatible with survival to adulthood.

Clinical and biochemical findings of a patient with thanatophoric dysplasia type I: additional finding of dicarboxylic aciduria.

OBJECTIVE: A long-surviving thanatophoric dysplasia type I patient to age of 6 years is presented. RESULTS AND CONCLUSIONS: Molecular studies revealed a heterozygous point mutation, S249C in the fibroblast growth factor receptor 3 gene. Most of the clinical course was similar to previous reports, including hearing loss and acanthosis nigricans. Abnormal urinary excretion of dicarboxylic acids and 3-hydroxydicarboxylic acids was observed. We hypothesize that this was a consequence of the FGFR3 mutation.

Molecular, radiologic, and histopathologic correlations in thanatophoric dysplasia.

Various mutations in the fibroblast growth factor receptor 3 (FGFR3) gene have recently been reported in thanatophoric dysplasia (TD). We examined the clinical, radiographic, and histologic findings in 91 cases from the International Skeletal Dysplasia Registry and correlated them with the specific FGFR3 mutation. Every case of TD examined had an identifiable FGFR3 mutation. Radiographically, all of the cases with the Lys650Glu substitution demonstrated straight femora with craniosynostosis, and frequently a cloverleaf skull (CS) was demonstrated. In all other cases, the femora were curved, and CS was infrequently present but was occasionally as severe as TD with the Lys650Glu substitution. Histopathologically, all of the cases shared similar abnormalities, but cases with the Lys650Glu substitution had better preservation of the growth plate. Cases with the Tyr373Cys substitution tended to have more severe radiographic manifestations than the Arg248Cys cases, but there was overlap in the phenotypic spectrum between them. One common classification of TD distinguishes affected infants based on the presence or absence of CS. In contrast, and as originally proposed by Langer et al. [1987: Am J Med Genet 3: 167-179], our data suggest that TD can be divided into at least two groups (TD1 and TD2) based on the presence of straight or curved femora. The variable presence of CS and severity of the radiologic and histologic findings in the other substitutions may be due to other genetic, environmental, or stochastic factors.

Thanatophoric dysplasia type I: new radiologic, morphologic, and histologic aspects toward the exact definition of the disorder.

A comprehensive seven-step study on THANATOPHORIC DYSPLASIA without cloverleaf skull (TD Type I) was carried out postmortem on three aborted fetuses of 19, 26-27, and 34 weeks and one preterm neonate of 35 weeks gestation, respectively. The characteristic x-ray configuration of the spine in TD Type I presenting with H-, U- or reversed U-shape vertebrae were shown to correlate with the inclination or reclination of the vertebral bodies within a kyphotic or lordotic segment. The bowing of the tubular bones in TD Type I is explained by a diminished mechanical stability that is causally related to a specific cartilage structure. The perichondral spurs are defined by their morphologic structure, and their origin is attributed to a normal perichondral ossification in the presence of an impaired enchondral ossification. Impairment of enchondral ossification was more evident in the periphery than in the center of the metaphyses leading to a tongue-shaped osseous cone directed toward the epiphysis. The perichondral spurs and the linguiform enchondral growth plate resulted in a three-phase maple leaf-like contour of the metaphyses of tubular bones and acetabular roof. The nature of the perichondral fibrous bands, the fibrovascular bundles, and the fibrovascular bands of the growth plate and their significance in atypical ossification processes are discussed in detail. It is suggested that the diminished longitudinal growth of the skeleton is caused by a reduced mitotic activity of cartilage cells in the proliferative zone leading to a reduction of cell numbers in the columnar zone transversely oriented spongiosa bars resulting from desmal ossification of the metaphyseal fibrovascular structures.

Thanatophoric dysplasia type II: new entity?

There is some question about whether the two forms of thanatophoric dysplasia (TD), Type II with and Type I without cloverleaf skull, belong to the same entity. Thus, we investigated one 6-day-old TD with cloverleaf skull using examination of the external phenotype, radiology, autopsy, skeleton preparation, large section histology, detailed section histology, and ultrastructure. The loss of the three-phase contours-characteristics for Type I (54)--in certain metaphyses, the absence of the perichondral spurs to some extent, and their substitution by a structure similar to the perichondral "ring of Lacroix" have a suggested origin in normal cartilage-bone tissue. The same mechanism is postulated (a) for the appearance of less bent or normally shaped tubular bones compared with TD Type I, and their corresponding increased mechanical stability, and (b) for the less amount of platyspondyly in Type II than in Type I. We suggest that the malformation of the cloverleaf skull has its origin in the promontory growth of the relatively normal cartilage-bone tissues at the skull base resulting in an early synostosis and a consecutive fusion of the cranial sutures. The ultrastructural analysis of chondrocytes demonstrates the significant contribution of electron microscopy for TD studies. We suggest that pathologically altered light chondrocytes accounts for plump cross-striated collagen fibrils, the reduced cellular proliferation, and the impaired formation of columnar and hypertrophic zones. It is clear that normal cartilage-bone tissue distributed among "thanatophoric" tissue is the reason for the differences between Type I and Type II. Hypotheses are presented that explain this tissue mosaicism. Thus, TD Type I and TD Type II do not represent two different entities but the same entity with varying features due to mutational events occurring at different times.

Thanatophoric dysplasia (types I and II) caused by distinct mutations in fibroblast growth factor receptor 3.

Thanatophoric dysplasia (TD), the most common neonatal lethal skeletal dysplasia, affects one out of 20,000 live births. Affected individuals display features similar to those seen in homozygous achondroplasia. Mutations causing achondroplasia are in FGFR3, suggesting that mutations in this gene may cause TD. A sporadic mutation causing a Lys650Glu change in the tyrosine kinase domain of FGFR3 was found in 16 of 16 individuals with one type of TD. Of 39 individuals with a second type of TD, 22 had a mutation causing an Arg248Cys change and one had a Ser371Cys substitution, both in the extracellular region of the protein. None of these mutations were found in 50 controls showing that mutations affecting different functional domains of FGFR3 cause different forms of this lethal disorder.

Some variants of lethal neonatal short-limbed platyspondylic dysplasia: a radiological ultrasonographic, neuropathological and histopathological study of 22 cases.

Data on twenty-two infants with lethal neonatal short-limbed platyspondylic dysplasia are reported. Thanatophoric dysplasia (TD) is the most frequent diagnosis in this group. TD combined with a cloverleaf skull (CS), has been variably classified. TD type 1 with curved femora is rarely combined with CS; TD type 2 with straight femora is almost always associated with CS. Other varieties of TD, known as 'Torrance', 'San Diego' or 'Luton' types, are separate entities. Apart from the differences in radiography and osteochondrohistology, the temporal-lobe abnormalities seen in TD were absent in one of the cases of the 'Torrance' variety. There were also differences in the composition of the cartilage glycosaminoglycans between this case and TD. Nearly all of the cases of these different types mentioned in the literature, including those of this study group, have been sporadic and may result from new dominant mutations. Documentation and classification by full (postmortem) radiography and osteochondrohistology is essential for two reasons. It will be the foundation for the clinical geneticist to inform the parents about the risk of recurrence. It will also be the basis for a biochemical or molecular-biological classification in the near future.

Thanatophoric dysplasia of the straight-bone type (type 2).

We describe two cases of type 2 thanatophoric dysplasia. Cloverleaf skull and relatively straight, shortened long bones distinguish this condition from the more common type 1 thanatophoric dysplasia.

[Fatal nanism: 3 different entities]. / Enanismos letales: tres entidades diferentes.

Three cases of congenital dwarfism are presented. All of them are lethal and represent the three better known nonviable nosologic entities: Achondrogenesis I, Achondrogesis II and Thanatophoric dwarfism. According to clinical features and radiologic data it is possible to approach the diagnosis accurately. We comment genetic, clinic, radiologic and histologic aspects of these processes. It is important to establish a differential diagnosis as these entities have different genetic basis, what influences genetic counsel.

Histopathology of the temporal bones in thanatophoric dysplasia.

The pathological findings of temporal bone in two cases of thanatophoric dysplasia were reported. Thanatophoric dysplasia is classified into type 1 and type 2, each of which has been reported to show specific clinical and radiographic-findings. The present study revealed that each type also showed specific characteristic in the structure of the temporal bones. The developmental mechanisms of hearing impairment in this disease were also discussed on the basis of the pertinent literature.

Thanatophoric dysplasia and cloverleaf skull.

Nine infants with thanatophoric dysplasia (TD) and cloverleaf skull (CS) are reported. Twenty-two previously published CSTD cases are reviewed. These CSTD cases are compared to cases of TD without CS. It is concluded that there are two types of TD: type 1, with curved femora and very flat vertebral bodies; and type 2, with straight femora and taller vertebral bodies. Consistent but subtle histopathological characteristics differentiate the two types. Only a very few type 1 cases have CS, and the CS is mild. Almost all type 2 cases have severe CS.

A new type of achondrogenesis.

A new type of neonatal death dwarfism, resembling the achondrogenesis syndromes on clinical examination but presenting distinctive radiographic and microscopic features has been described. It presents another, new form of achondrogenesis.