Achondrogenesis-hypochondrogenesis: the spectrum of chondrogenesis imperfecta. A radiological, ultrasonographic, and histopathologic study of 23 cases

Obstetric complications in pregnancies with life-limiting malformations

PURPOSE OF REVIEW

The implementation of palliative care at birth has led to a significant rise in the number of couples who choose to continue with pregnancies complicated by life-limiting malformations (LLMs). Prenatal counselling and appropriate antenatal/perinatal management in these cases are poorly studied and may pose significant challenges. The purpose of this review is to outline specific obstetric risks and to suggest management for mothers who choose to continue with pregnancies with the most common LLMs.

RECENT FINDINGS

In pregnancies complicated by LLMs where parents opt for expectant management, clinicians should respect parental wishes, whilst openly sharing potential serious maternal medical risks specific for the identified abnormalities. The focus of both antenatal and perinatal care should be maternal wellbeing rather than foetal survival. Follow-up ultrasound examinations and maternal surveillance should be aimed at achieving timely diagnosis and effective management of obstetric complications. A clear perinatal plan, agreed with the couples by a multi-disciplinary team including a foetal medicine specialist, a neonatologist and a geneticist, is crucial to reduce maternal morbidity.

SUMMARY

This review provides a useful framework for clinicians who face the challenges of counselling and managing cases complicated by LLMs where parents opt for pregnancy continuation.

Pathologic diagnosis of achondrogenesis type 2 in a fragmented fetus: case report and evidence-based differential diagnostic approach in the early midtrimester

As a group, lethal genetic skeletal disorders (GSDs) usually result in death within the perinatal period. Because lethal GSDs are often ultrasonographically detectible by early midtrimester, dilation and evacuation (D&E) is the method of choice for elective termination of pregnancy in many institutions. However, because the diagnosis of the lethal GSDs relies heavily upon radiologic examination of fetal remains, reaching an accurate diagnosis in this setting can be challenging. We report an autopsy case of a fetus delivered by D&E at 15 4/7 weeks gestation with radiologic, histologic, and genetic findings compatible with achondrogenesis type 2 and discuss an evidence-based differential diagnostic approach to lethal GSDs terminated by early midtrimester D&E.

Extensive cervical spine and foregut anomaly in 'serpentine syndrome'

INTRODUCTION

We report an extremely rare and challenging combination of congenital anomalies. Only five similar cases have been described in the English language medical literature to date.

PRESENTATION OF CASE

A male infant was born at 30(+5) weeks gestation by emergency caesarian section. Cervical spine rachischisis, shortened oesophagus, intrathoracic stomach, atretic duodenum and absent spleen were noted, in addition to respiratory insufficiency. Gastrointestinal re-anastomosis, particularly oesophageal lengthening, was not feasible at the initial thoracotomy. Surgical stabilization of the cervical spine was unlikely to be successful until two years of age. Asplenia predisposed the infant to sepsis from encapsulated organisms, and recurrent respiratory infections occurred.

DISCUSSION

A close relationship exists between the upper gastrointestinal tract and cervical spine during embryonic development. An embryonic aberration at this level could account for all the deformities present in this infant. Tethering of the embryonic cervical oesophagus to the somites in the first trimester, preventing foregut elongation, and producing ischaemia at the coeliac axis, is suggested as the aetiology.

CONCLUSION

This case presented a challenge to the multi-disciplinary team involved in his management and prompted extensive consultation with international experts. After considerable counseling of the parents, care was directed towards palliation.

Prenatal diagnosis of achondrogenesis type I: a case report

Introduction

Achondrogenesis is a lethal osteochondrodysplasia characterized by hypoplasia of the bones and is associated with various anomalies varying in severity. Based on clinical, radiologic, and histopathologic features, two types are distinguished.

Case presentation

The prenatal ultrasound examination of a 32-year-old Turkish woman who was referred to our clinic at 33 weeks and 6 days of gestation revealed fetal micromelia together with several other anomalies. The female baby died shortly after birth and was diagnosed with achondrogenesis type I based on the clinical and radiographic findings.

Conclusion

Ultrasonography is important in prenatal diagnosis and for distinguishing lethal skeletal dysplasias in order to counsel the parents about future recurrent risks. As it is a uniformly lethal disease, a definitive prenatal diagnosis of achondrogenesis may be an indication for pregnancy termination.

Visceral manifestations of hypochondrogenesis

Autopsy of a stillborn neonate with hypochondrogenesis revealed severe cardiac abnormalities and extensive diverticulosis of the proximal region of the small intestine. Visceral ramifications are unusual in hypochondrogenesis; they may reflect heterogeneity of the intramolecular defect in the COL2A1 gene that codes for the achondrogenesis type II-hypochondrogenesis spectrum of disorders.

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.

Achondrogenesis type II with normally developed extremities: a case report

We present a case of achondrogenesis type II with normally developed extremities that was confirmed with postmortem ultrasonographic and radiographic examination. The length of the long bones may vary and the diagnosis of achondrogenesis should not be ruled out with normally developed extremities. Intrauterine sonographic examination of the vertebrae is very important and the absence of vertebral body ossification may be the unique finding of achondrogenesis type II. Axial ultrasonographic images and postmortem plain radiographs are useful to clarify the pathology.

Achondrogenesis type IB: agenesis of cartilage interterritorial matrix as the link between gene defect and pathological skeletal phenotype

Achondrogenesis type IB is a lethal osteochondrodysplasia caused by mutations in the diastrophic dysplasia sulfate transporter gene. How these mutations lead to the skeletal phenotype is not known. Histology of plastic-embedded skeletal fetal achondrogenesis type IB samples suggested that interterritorial epiphyseal cartilage matrix was selectively missing. Cartilage was organized in "chondrons" separated by cleft spaces; chondrocyte seriation, longitudinal septa, and, in turn, mineralized cartilaginous septa were absent. Agenesis of interterritorial matrix as the key histologic change was confirmed by immunohistology using specific markers of territorial and interterritorial matrix. Biglycan-enriched territorial matrix was preserved; decorin-enriched interterritorial areas were absent, although immunostaining was observed within chondrocytes. Thus, in achondrogenesis type IB: (1) a complex derangement in cartilage matrix assembly lies downstream of the deficient sulfate transporter activity; (2) the severely impaired decorin deposition participates in the changes in matrix organization with lack of development of normal interterritorial matrix; and (3) this change determines the lack of the necessary structural substrate for proper endochondral bone formation and explains the severe skeletal phenotype.

Mutations in the diastrophic dysplasia sulfate transporter (DTDST) gene (SLC26A2): 22 novel mutations, mutation review, associated skeletal phenotypes, and diagnostic relevance

Mutations in the DTDST gene can result in a family of skeletal dysplasia conditions which comprise two lethal disorders, achondrogenesis type 1B (ACG1B) and atelosteogenesis type 2 (AO2); and two non-lethal disorders, diastrophic dysplasia (DTD) and recessive multiple epiphyseal dysplasia (rMED). The gene product is a sulfate-chloride exchanger of the cell membrane. Inactivation of the sulfate exchanger leads to intracellular sulfate depletion and to the synthesis of undersulfated proteoglycans in susceptible cells such as chondrocytes and fibroblasts. Genotype-phenotype correlations are recognizable, with mutations predicting a truncated protein or a non-conservative amino acid substitution in a transmembrane domain giving the severe phenotypes, and non-transmembrane amino acid substitutions and splice site mutations giving the milder phenotypes. The clinical phenotype is modulated strictly by the degree of residual activity. Over 30 mutations have been observed, including 22 novel mutations reported here. The most frequent mutation, 862C>T (R279W), is a mild mutation giving the rMED phenotype when homozygous and mostly DTD when compounded; occurrence at a CpG dinucleotide and its panethnic distribution suggest independent recurrence. Mutation IVS1+2T>C is the second most common mutation, but is very frequent in Finland. It produces low levels of correctly spliced mRNA, and results in DTD when homozygous. Two other mutations, 1045-1047delGTT (V340del) and 558C>T (R178X), are associated with severe phenotypes and have been observed in multiple patients. Most other mutations are rare. Heterozygotes are clinically unaffected. When clinical samples are screened for radiologic and histologic features compatible with the ACG1B/AO2/DTD/rMED spectrum prior to analysis, the mutation detection rate is high (over 90% of alleles), and appropriate genetic counseling can be given. The sulfate uptake or sulfate incorporation assays in cultured fibroblasts have largely been replaced by mutation analysis, but may still be useful in cases where mutation analysis is not informative. Although supplementation of patients' cultured cells with thiols may bypass the transporter defect and enhance sulfation of proteoglycans, therapeutic approaches are not yet available. Mouse models for this and other disorders of sulfate metabolism are being developed to help in developing therapeutic treatments.

New form of bone dysplasia with multiple fractures associated with monosomy X

We report on the clinical, radiologic, and pathologic findings in a 20-week-old fetus with monosomy X and severe hydrops associated with fetal dwarfism. The fetus presented with osteoporosis, bent bones, multiple fractures, and distinctive symmetric submetaphyseal transverse bone interruptions or pseudofractures. We excluded by radiologic and histopathologic examination the diagnoses of osteogenesis imperfecta, hypophosphatasia, campomelic dysplasia, achondrogenesis, hypochondrogenesis, and other types of bone dysplasia. To our knowledge, this is a previously undescribed bone dysplasia associated with monosomy X. This bone dysplasia may be inherited as an X-linked recessive disorder.

Achondrogenesis type 1B

Images

Undersulfation of proteoglycans synthesized by chondrocytes from a patient with achondrogenesis type 1B homozygous for an L483P substitution in the diastrophic dysplasia sulfate transporter

Achondrogenesis type 1B is an autosomal recessive, lethal chondrodysplasia caused by mutations in the gene encoding a sulfate/chloride antiporter of the cell membrane (Superti-Furga, A., Hästbacka, J., Wilcox, W. R., Cohn, D. H., van der Harten, J. J., Rossi, A., Blau, N., Rimoin, D. L., Steinmann, B., Lander, E. S., and Gitzelmann, R.(1996) Nat. Genet. 12, 100-102). To ascertain the consequences of the sulfate transport defect on proteoglycan synthesis, we studied the structure and sulfation of proteoglycans in cartilage tissue and in fibroblast and chondrocyte cultures from a fetus with achondrogenesis 1B. Proteoglycans extracted from epiphyseal cartilage and separated on agarose gels migrated more slowly than controls and stained poorly with alcian blue. The patient's cultured cells showed reduced incorporation of [35S]sulfate relative to [3H]glucosamine, impaired uptake of sulfate, and higher resistance to chromate toxicity compared to control cells. Epiphyseal chondrocytes cultured in alginate beads synthesized proteoglycans of normal molecular size as judged by gel filtration chromatography, but undersulfated as judged by ion exchange chromatography and by the amount of nonsulfated disaccharide. High performance liquid chromatography analysis of chondroitinase-digested proteoglycans showed that sulfated disaccharides were present, although in reduced amounts, indicating that at least in vitro, other sources of sulfate can partially compensate for sulfate deficiency. A t1475c transition causing a L483P substitution in the eleventh transmembrane domain of the sulfate/chloride antiporter was present on both alleles in the patient who was the product of a consanguineous marriage. The results indicate that the defect of sulfate transport is expressed in both chondrocytes and fibroblasts and results in the synthesis of proteoglycans bearing glycosaminoglycan chains which are poorly sulfated but of normal length.

A chondrodysplasia family produced by mutations in the diastrophic dysplasia sulfate transporter gene: genotype/phenotype correlations

Achondrogenesis type 1B (ACG-1B), atelosteogenesis type 2 (AO-2), and diastrophic dysplasia (DTD) are recessively inherited chondrodysplasias of decreasing severity caused by mutations in the diastrophic dysplasia sulfate transporter (DTDST) gene on chromosome 5. In these conditions, sulfate transport across the cell membrane is impaired which results in insufficient sulfation of cartilage proteoglycans and thus in an abnormally low sulfate content of cartilage. The severity of the phenotype correlates well with the predicted effect of the underlying DTDST mutations: homozygosity or compound heterozygosity for stop codons or transmembrane domain substitutions mostly result in achondrogenesis type 1B, while other structural or regulatory mutations usually result in one of the less severe phenotypes. The chondrodysplasias arising at the DTDST locus constitute a bone dysplasia family with recessive inheritance.

Collagen type II in Langer-Saldino achondrogenesis: absence of major abnormalities in a less severe case

Collagen extracted either from cartilage or synthesized in vitro was analyzed to identify possible molecular defects in the cartilaginous matrix of a male fetus suffering from a mild form of type II achondrogenesis (Langer-Saldino). The tissue architecture of the patient's cartilage was markedly altered and showed numerous fibrous vascular canals which were focally stained by antibodies against collagens I and III. Collagen II was present, although heterogenously distributed throughout the cartilaginous matrix. Upon electrophoretic separation, however, the patient's femoral head cartilage showed the presence of collagens II, IX and XI only, which was similar to an age-matched control. The hydroxyproline/hydroxylysine ratio of collagen II of the patient was not significantly different from that of the control. Likewise, the compositions of collagens synthesized by cultured chondrocytes as well as fibroblasts were similar in the patient and the control. The results provide strong evidence that, in the present mild case of Langer-Saldino achondrogenesis, collagen II is expressed and regularly hydroxylated at its lysyl residues. This may indicate that cartilage components other than collagen II may be responsible for the altered tissue organization observed. Along with previous observations, our data suggest that the degree of biochemical matrix alterations may be related to the severity of the clinical phenotype.

Ratios between growth parameters for the prenatal ultrasonographic diagnosis of skeletal dysplasias

The clinical applicability and usefulness of nine ratios that express the relation between particular fetal growth parameters were tested in ten fetuses affected by skeletal dysplasia. The results were compared with the ratios calculated from five growth-retarded fetuses without structural anomalies. Femur/foot, femur/head circumference, head circumference/thoracic circumference and abdominal circumference/thoracic circumference ratios are useful additional parameters for the prenatal ultrasonographic diagnosis of skeletal dysplasias. They reduce the problem of an unknown gestational age and help to distinguish between fetal skeletal dysplasia and intra-uterine growth-retardation caused by other factors.

The prenatal development of the normal human skeleton: a combined ultrasonographic and post-mortem radiographic study

Post-mortem radiography of fetuses with skeletal dysplasia is essential for diagnostic classification. Interpretation of the radiographs should be based on the knowledge of morphology and dimensions of the normal skeleton in all stages of development. A retrospective post-mortem radiographic study is presented with measurements of the lengths of the long bones and thoracic and lumbar spine. The study included 69 fetuses and neonates with a normal skeleton, whose gestational age ranged from 13-42 weeks and who died perinatally or lived for less than one week. The measurements of the long bones were plotted on growth curves obtained from a prospective longitudinal ultrasonographic investigation of another group of 63 normal fetuses from 12-40 weeks of gestation. Thoracic and lumbar spine measurements by ultrasonography were not available. The radiographic data of thoracic and lumbar spine were, therefore, compared to radiographic studies from the literature. No disagreement with these studies was found. It can be concluded that measurements of bones from standardized post-mortem radiographs in cases of questionable gestational age or defects of bone development can be compared with ultrasonographic measurements. To illustrate the usefulness of the graphs, 13 fetuses with various types of skeletal dysplasia were evaluated retrospectively.