Campomelic dysplasia: evidence of autosomal dominant inheritance

Campomelic Dysplasia

Campomelic dysplasia is a rare congenital skeletal disorder. It is an autosomal dominant condition caused by mutation of the SOX9 gene on chromosome 17. Many different body systems can be harmfully affected, resulting in a variety of skeletal and extraskeletal anomalies attributable to the gene mutation. The most evident characteristics of the condition are symmetrical shortening and anterior bowing of the femurs and tibias. For most affected fetuses, death occurs in the fetal period or in the neonatal period shortly after birth. The primary cause of death is respiratory distress due to many possible factors such as micrognathia and hypoplastic chest cavity, lungs, or airways. Fetal sonography is fundamental in the detection of related defects and the ultimate diagnosis of the disorder.

Campomelic dysplasia

Campomelic dysplasia is a rare hereditary congenital osteochondral dysplasia characterized by abnormal bowing of the lower limbs, sex reversal in males, and other skeletal and extraskeletal abnormalities. It is usually fatal in the neonatal period because of respiratory insufficiency. The diagnosis is usually difficult because of its rare presentation and the prognosis is poor. We present such a case in a 1-month-old child with typical skeletal abnormalities, whose presentation was unusual because of later presentation of respiratory distress and lack of genitourinary abnormalities.

Familial acampomelic form of campomelic dysplasia caused by a 960 kb deletion upstream of SOX9

Campomelic dysplasia (CD) is a rare autosomal dominant osteochondrodysplasia with or without XY disorders of sexual development (DSD). Campomelia is absent in about 10% of the cases, referred to as the acampomelic form of CD (ACD). Most CDs are caused by mutations within the SOX9 coding region. Several CD patients with balanced chromosome rearrangements involving the 17q24 region have been reported suggesting the presence of cis-regulatory elements upstream and/or downstream of the gene. Deletions upstream of SOX9 represent a third mechanism of mutation. To date, a 1.5 Mb de novo deletion in the SOX9 upstream region has been identified in a single 46,XY patient with ACD and DSD. We report here for the first time on a familial ACD caused by an inherited deletion mapping upstream of the SOX9 gene. Using high-density oligoarray comparative genomic hybridization (CGH), we showed that the size of the deletion was 960 kb in the XY-DSD child and her mother, both affected. The deletion lying from 517 kb to 1.477 Mb upstream of SOX9 remove several highly conserved elements and reduce the minimum critical size and therefore the number of highly conserved sequence elements responsible for ACD.

Findings from aCGH in patients with congenital diaphragmatic hernia (CDH): a possible locus for Fryns syndrome

Congenital diaphragmatic hernia (CDH) is a common and often devastating birth defect that can occur in isolation or as part of a malformation complex. Considerable progress is being made in the identification of genetic causes of CDH. We applied array-based comparative genomic hybridization (aCGH) of approximately 1Mb resolution to 29 CDH patients with prior normal karyotypes who had been recruited into our multi-site study. One patient, clinically diagnosed with Fryns syndrome, demonstrated a de novo 5Mb deletion at chromosome region 1q41-q42.12 that was confirmed by FISH. Given prior reports of CDH in association with cytogenetic abnormalities in this region, we propose that this represents a locus for Fryns syndrome, a Fryns syndrome phenocopy, or CDH.

Fine mapping of chromosome 17 translocation breakpoints > or = 900 Kb upstream of SOX9 in acampomelic campomelic dysplasia and a mild, familial skeletal dysplasia

Previously, our group reported a five-generation family in which a balanced t(13;17) translocation is associated with a spectrum of skeletal abnormalities, including Robin sequence, hypoplastic scapulae, and a missing pair of ribs. Using polymerase chain reaction (PCR) with chromosome-specific markers to analyze DBA from somatic cell hybrids containing the derivative translocation chromosomes, we narrowed the breakpoint on each chromosome. Subsequent sequencing of PCR products spanning the breakpoints identified the breaks precisely. The chromosome 17 breakpoint maps approximately 932 kb upstream of the sex-determining region Y (SRY)-related high-mobility group box gene (SOX) within a noncoding transcript represented by two IMAGE cDNA clones. A growing number of reports have implicated chromosome 17 breakpoints at a distance of up to 1 Mb from SOX9 in some cases of campomelic dysplasia (CD). Although this multigeneration family has a disorder that shares some features with CD, their phenotype is significantly milder than any reported cases of (nonmosaic) CD. Therefore, this case may represent an etiologically distinct skeletal dysplasia or may be an extremely mild familial example of CD, caused by the most proximal translocation breakpoint from SOX9 reported to date. In addition, we have refined the breakpoint in a acampomelic CD case described elsewhere and have found that it lies approximately 900 kb upstream of SOX9.

The molecular action and regulation of the testis-determining factors, SRY (sex-determining region on the Y chromosome) and SOX9 [SRY-related high-mobility group (HMG) box 9]

Despite 12 yr since the discovery of SRY, little is known at the molecular level about how SRY and the SRY-related protein, SOX9 [SRY-related high-mobility group (HMG) box 9], initiate the program of gene expression required to commit the bipotential embryonic gonad to develop into a testis rather than an ovary. Analysis of SRY and SOX9 clinical mutant proteins and XX mice transgenic for testis-determining genes have provided some insight into their normal functions. SRY and SOX9 contain an HMG domain, a DNA-binding motif. The HMG domain plays a central role, being highly conserved between species and the site of nearly all missense mutations causing XY gonadal dysgenesis. SRY and SOX9 are architectural transcription factors; their HMG domain is capable of directing nuclear import and DNA bending. Whether SRY and SOX9 activate testis-forming genes, repress ovary-forming genes, or both remains speculative until downstream DNA target genes are identified. However, factors that control SRY and SOX9 gene expression have been identified, as have a dozen sex-determining genes, allowing some of the pieces in this molecular genetic puzzle to be connected. Many genes, however, remain unidentified, because in the majority of cases of XY females and in all cases of XX males lacking SRY, the mutated gene is unknown.

Orthopaedic manifestations of campomelic dysplasia

Campomelic dysplasia is a rare form of congenital dwarfism associated with potentially fatal respiratory insufficiency. There are several types of campomelic dysplasia; however, it is characterized by the presence of anteriorly bowed tibias with cutaneous dimpling, anterolaterally bowed femurs, thoracic kyphoscoliosis, hypoplastic scapulas, and absence or delayed ossification of thoracic pedicles. With improving treatment of respiratory insufficiency, the survival rate of affected infants has increased, thereby necessitating treatment of the musculoskeletal malformations to prevent additional morbidity. In an attempt to increase awareness of the presentation of infants with campomelic dysplasia and to emphasize the difficulties of treating associated developmental dislocation of the hip early, the current authors report the case of a 2-year-old girl with campomelic dysplasia who was treated for dislocation of the right hip. The postoperative course of this child was complicated seriously by several apneic episodes secondary to tracheobronchial malacia for which she required admission to the pediatric intensive care unit.

Compound effects of point mutations causing campomelic dysplasia/autosomal sex reversal upon SOX9 structure, nuclear transport, DNA binding, and transcriptional activation

Human mutations in the transcription factor SOX9 cause campomelic dysplasia/autosomal sex reversal. Here we identify and characterize two novel heterozygous mutations, F154L and A158T, that substitute conserved "hydrophobic core" amino acids of the high mobility group domain at positions thought to stabilize SOX9 conformation. Circular dichroism studies indicated that both mutations disrupt alpha-helicity within their high mobility group domain, whereas tertiary structure is essentially maintained as judged by fluorescence spectroscopy. In cultured cells, strictly nuclear localization was observed for wild type SOX9 and the F154L mutant; however, the A158T mutant showed a 2-fold reduction in nuclear import efficiency. Importin-beta was demonstrated to be the nuclear transport receptor recognized by SOX9, with both mutant proteins binding importin-beta with wild type affinity. Whereas DNA bending was unaffected, DNA binding was drastically reduced in both mutants (to 5% of wild type activity in F154L, 17% in A158T). Despite this large effect, transcriptional activation in cultured cells was only reduced to 26% in F154L and 62% in A158T of wild type activity, suggesting that a small loss of SOX9 transactivation activity could be sufficient to disrupt proper regulation of target genes during bone and testis formation. Thus, clinically relevant mutations of SOX9 affect protein structure leading to compound effects of reduced nuclear import and reduced DNA binding, the net effect being loss of transcriptional activation.

Acampomelic campomelic dysplasia: further radiographic variations

Acampomelic campomelic dysplasia (ACD) is a rare genetic syndrome affecting bone and connective tissue. This syndrome is a variant of the more commonly encountered campomelic dysplasia but is characterized by the absence of long bone curvature (acampomelia). Affected children have a characteristically flat facial profile and present with respiratory distress. They all have markedly hypoplastic scapulae. We present two sisters with ACD between whom there were some clinical and radiographic differences and also variations from the classic CD. We describe shallow orbits, a radiographic finding that has not been previously documented in this dysplasia.

A clinical and genetic study of campomelic dysplasia

Campomelic dysplasia (CMD) is a rare skeletal disorder that is usually lethal. It is characterised by bowing of the lower limbs, severe respiratory distress, and many of the chromosomal (XY) males show sex reversal. Because of a number of reports of familial campomelic dysplasia it is considered to be inherited in an autosomal recessive manner. In this study, details of 36 patients with campomelic dysplasia were collected from genetic centres, radiologists, and pathologists in the United Kingdom. The chromosomal sex ratio was approximately 1:1. There was a preponderance of phenotypic females owing to sex reversal. Three quarters of the chromosomal males were sex reversed or had ambiguous genitalia. Three cases are still alive, two with chromosomal rearrangements involving chromosome 17q. The majority of the others died in the neonatal period. The 36 index cases had 41 sibs of whom only two were affected. Formal segregation analysis gave a segregation ratio of 0.05 (95% CI approximately 0.00 to 0.11). This excludes an autosomal recessive mode of inheritance. The data suggest a sporadic, autosomal dominant mode of inheritance. Patients with a chromosomal rearrangement involving 17q (q23.3-q25.1) show a milder phenotype. The molecular mechanism for the difference is still unknown.

Acampomelic campomelic syndrome and sex reversal associated with de novo t(12;17) translocation

The association of rare chromosomal rearrangements involving a specific 17q breakpoint with campomelic syndrome (CMPS) and/or sex reversal (SR) has led to an assignment of the CMPS1/SRA1 locus to 17q24.3-->q25.1. We describe a patient with multiple anomalies and SR, who had a de novo t(12;17) translocation. The phenotype was consistent with that of CMPS except for the lack of lower limb bowing and talipes equinovarus. Chromosome painting indicated that the breakpoints appeared to have occurred at 12q21.32 and 17q24.3 or q25.1. This study suggests that acampomelic CMPD with SR represents a variant of the CMPS1/SRA1 locus disorder. We emphasize the likelihood that CMPS may be a contiguous gene syndrome.

Autosomal sex reversal and campomelic dysplasia are caused by mutations in and around the SRY-related gene SOX9

A human autosomal XY sex reversal locus, SRA1, associated with the skeletal malformation syndrome campomelic dysplasia (CMPD1), has been placed at distal 17q. The SOX9 gene, a positional candidate from the chromosomal location and expression pattern reported for mouse Sox9, was isolated and characterized. SOX9 encodes a putative transcription factor structurally related to the testis-determining factor SRY and is expressed in many adult tissues, and in fetal testis and skeletal tissue. Inactivating mutations on one SOX9 allele identified in nontranslocation CMPD1-SRA1 cases point to haploinsufficiency for SOX9 as the cause for both campomelic dysplasia and autosomal XY sex reversal. The 17q breakpoints in three CMPD1 translocation cases map 50 kb or more from SOX9.

Campomelic dysplasia and autosomal sex reversal caused by mutations in an SRY-related gene

Induction of testis development in mammals requires the presence of the Y-chromosome gene SRY. This gene must exert its effect by interacting with other genes in the sex-determination pathway. Cloning of a translocation chromosome breakpoint from a sex-reversed patient with campomelic dysplasia, followed by mutation analysis of an adjacent gene, indicates that SOX9, an SRY-related gene, is involved in both bone formation and control of testis development.