Allelic and nonallelic heterogeneity in dyschondrosteosis (Leri-Weill syndrome)

Identification of a novel 15.5 kb SHOX deletion associated with marked intrafamilial phenotypic variability and analysis of its molecular origin

Haploinsufficiency of the short stature homeobox contaning SHOX gene has been shown to result in a spectrum of phenotypes ranging from Leri-Weill dyschondrosteosis (LWD) at the more severe end to SHOX-related short stature at the milder end of the spectrum. Most alterations are whole gene deletions, point mutations within the coding region, or microdeletions in its flanking sequences. Here, we present the clinical and molecular data as well as the potential molecular mechanism underlying a novel microdeletion, causing a variable SHOX-related haploinsufficiency disorder in a three-generation family. The phenotype resembles that of LWD in females, in males, however, the phenotypic expression is milder. The 15523-bp SHOX intragenic deletion, encompassing exons 3-6, was initially detected by array-CGH, followed by MLPA analysis. Sequencing of the breakpoints indicated an Alu recombination-mediated deletion (ARMD) as the potential causative mechanism.

A Track Record on SHOX: From Basic Research to Complex Models and Therapy

SHOX deficiency is the most frequent genetic growth disorder associated with isolated and syndromic forms of short stature. Caused by mutations in the homeobox gene SHOX, its varied clinical manifestations include isolated short stature, Léri-Weill dyschondrosteosis, and Langer mesomelic dysplasia. In addition, SHOX deficiency contributes to the skeletal features in Turner syndrome. Causative SHOX mutations have allowed downstream pathology to be linked to defined molecular lesions. Expression levels of SHOX are tightly regulated, and almost half of the pathogenic mutations have affected enhancers. Clinical severity of SHOX deficiency varies between genders and ranges from normal stature to profound mesomelic skeletal dysplasia. Treatment options for children with SHOX deficiency are available. Two decades of research support the concept of SHOX as a transcription factor that integrates diverse aspects of bone development, growth plate biology, and apoptosis. Due to its absence in mouse, the animal models of choice have become chicken and zebrafish. These models, therefore, together with micromass cultures and primary cell lines, have been used to address SHOX function. Pathway and network analyses have identified interactors, target genes, and regulators. Here, we summarize recent data and give insight into the critical molecular and cellular functions of SHOX in the etiopathogenesis of short stature and limb development.

Enhancer elements upstream of the SHOX gene are active in the developing limb

Léri-Weill Dyschondrosteosis (LWD) is a dominant skeletal disorder characterized by short stature and distinct bone anomalies. SHOX gene mutations and deletions of regulatory elements downstream of SHOX resulting in haploinsufficiency have been found in patients with LWD. SHOX encodes a homeodomain transcription factor and is known to be expressed in the developing limb. We have now analyzed the regulatory significance of the region upstream of the SHOX gene. By comparative genomic analyses, we identified several conserved non-coding elements, which subsequently were tested in an in ovo enhancer assay in both chicken limb bud and cornea, where SHOX is also expressed. In this assay, we found three enhancers to be active in the developing chicken limb, but none were functional in the developing cornea. A screening of 60 LWD patients with an intact SHOX coding and downstream region did not yield any deletion of the upstream enhancer region. Thus, we speculate that SHOX upstream deletions occur at a lower frequency because of the structural organization of this genomic region and/or that SHOX upstream deletions may cause a phenotype that differs from the one observed in LWD.

Short stature homeoboxcontaining gene and idiopathic short stature

The term idiopathic short stature (ISS) refers to patients who are short due to various unknown reasons. Although it is clear that multiple factors contribute to final height, genetic factors play a crucial role. Mutations of a human homeobox gene, short stature homeobox-containing (SHOX) gene, have been shown to be associated with the short stature phenotype in patients with Turner syndrome, most patients with Leri-Weill dyschondrosteosis and some cases of ISS. The prevalence of SHOX anomalies in subjects previously recognized as having ISS has been estimated at 2.4% in a large series of ISS individuals. This review focuses on the functional properties of the SHOX gene and its linkage to ISS.

SHOX at a glance: from gene to protein

The Short Stature Homeobox-containing Gene SHOX was identified as the genetic cause of the short stature phenotype in patients with Turner Syndrome and in certain patients with idiopathic short stature. Shortly after, SHOX mutations were also associated with the growth failure and skeletal deformities seen in patients with Léri - Weill dyschondrosteosis and Langer mesomelic dysplasia. Today it is estimated that SHOX mutations occur with an incidence of roughly 1:1,000 in newborns, making mutations of this gene one of the most common genetic defects leading to growth failure in humans. This review summarises the involvement of SHOX in several short stature syndromes and describes recent advances in our understanding of SHOX functions and regulation. We also discuss the current evidence in the literature that points to a role of this protein in growth and bone development. These studies have improved our knowledge of the SHOX gene and protein functions, and have given insight into the etiopathogenesis of short stature. However, the exact role of SHOX in bone development still remains elusive and poses the next major challenge for researchers in this field.

Identification and characterization of different SHOX gene deletions in patients with Leri-Weill dyschondrosteosys by MLPA assay

Deletions of the SHOX gene (Xp22-Yp11.3) are associated with Leri-Weill dyschondrosteosys (LWD) and idiopathic short stature. It has been estimated that SHOX deletions occur in 1,000-2,000 individuals in the total population, suggesting that this alteration should be investigated in all cases with unexplained short stature. SHOX deletions are currently investigated using fluorescence in situ hybridization (FISH) or molecular analysis of intragenic CA repeats. However, both techniques show some limitations. In the present study, the use of the multiple ligation probe amplification (MLPA) assay for the identification and characterization of SHOX deletions in 15 LWD patients, 3 of which carriers of chromosome abnormalities involving the SHOX gene, is reported. MLPA analysis demonstrated the heterozygous deletion of SHOX in seven patients (46.6%), disclosing the presence of two different proximal breakpoints. In patients with abnormal karyotype, MLPA analysis was able to identify the chromosomal rearrangement, showing, in addition to the SHOX deletions, the gain or loss of other genes mapped on the X and Y chromosomes. Since MLPA analysis can be carried out on a simple buccal swab, avoiding invasive peripheral blood collection, this technique represents a fast, simple and high throughput approach in the screening of SHOX deletions, able to provide more information as compared to FISH and microsatellite analysis.

The phenotype of short stature homeobox gene (SHOX) deficiency in childhood: contrasting children with Leri-Weill dyschondrosteosis and Turner syndrome

OBJECTIVE

To evaluate the growth disorder and phenotype in prepubertal children with Leri-Weill dyschondrosteosis (LWD), a dominantly inherited skeletal dysplasia, and to compare the findings from girls with Turner syndrome (TS).

STUDY DESIGN

We studied the auxologic and phenotypic characteristics in 34 prepubertal LWD subjects (ages 1 to 10 years; 20 girls, 14 boys) with confirmed short stature homeobox-containing gene (SHOX) abnormalities. For comparative purposes, we evaluated similar physical and growth parameters in 76 girls with TS (ages 1 to 19 years) and 24 girls with LWD (ages 1 to 15 years) by using data collected from the postmarketing observational study, GeNeSIS.

RESULTS

In the clinic sample LWD subjects, height standard deviation score ranged from -5.5 to +0.1 (-2.3 +/- 1.3, girls and -1.8 +/- 0.6, boys). Wrist changes related to Madelung deformity were present in 18 of 34 (53%) LWD subjects. In comparing the LWD and TS populations in the GeNeSIS sample, Madelung deformity, increased carrying angle, and scoliosis were more prevalent in the LWD population, whereas high arched palate was similarly prevalent in the two populations.

CONCLUSIONS

Short stature is common in both LWD (girls and boys) and TS (girls). Clinical clues to the diagnosis of SHOX haploinsufficiency in childhood include short stature, short limbs, wrist changes, and tibial bowing.

Identification of a major recombination hotspot in patients with short stature and SHOX deficiency

Human growth is influenced not only by environmental and internal factors but also by a large number of different genes. One of these genes, SHOX, is believed to play a major role in growth, since defects in this homeobox-containing gene on the sex chromosomes lead to syndromal short stature (Leri-Weill dyschondrosteosis, Langer mesomelic dysplasia, and Turner syndrome) as well as to idiopathic short stature. We have analyzed 118 unrelated patients with Leri-Weill dyschondrosteosis and >1,500 patients with idiopathic short stature for deletions encompassing SHOX. Deletions were detected in 34% of the patients with Leri-Weill dyschondrosteosis and in 2% of the patients with idiopathic short stature. For 27 patients with Leri-Weill dyschondrosteosis and for 6 with idiopathic short stature, detailed deletion mapping was performed. Analysis was performed by polymerase chain reaction with the use of pseudoautosomal polymorphic markers and by fluorescence in situ hybridization with the use of cosmid clones. Here, we show that, although the identified deletions vary in size, the vast majority (73%) of patients tested share a distinct proximal deletion breakpoint. We propose that the sequence present within this proximal deletion breakpoint "hotspot" region predisposes to recurrent breaks.

Auxology is a valuable instrument for the clinical diagnosis of SHOX haploinsufficiency in school-age children with unexplained short stature

SHOX (short stature homeobox-containing gene) mutations causing haploinsufficiency have been reported in some individuals with idiopathic short stature and in many patients with Leri-Weill-dyschondrosteosis. Around 80% of SHOX mutations are complete gene deletions, whereas diverse point mutations account for the rest. The aim of this study was to estimate the prevalence of SHOX mutations in children with idiopathic short stature and to give an unbiased characterization of the haploinsufficiency phenotype of such children. We recruited 140 children (61 girls), in our clinic, with idiopathic short stature, which was defined by the presence of normal IGF-I and free T(4); a normal karyotype in females; the absence of endomysium antibodies, of chronic organic, psychological, or syndromatic disease; and by the lack of clear signs of any osteodysplasia. Height, arm span, and sitting height were recorded, and subischial leg length was calculated. Two highly polymorphic microsatellite markers located around the SHOX coding region (CA-SHOX repeat and DXYS233) were PCR-amplified with fluorescent primers and separated in an automatic sequencing machine. Analysis of parental DNA was performed in the probands who had only one fragment size of each of both markers. SHOX haploinsufficiency caused by a SHOX deletion was confirmed in three probands (2%), all females, who carried a de novo deletion through loss of the paternal allele. Their auxological data revealed a significant shortening of arms and legs in the presence of a low-normal sitting height, when compared with the other 137 children tested. Therefore, the extremities-trunk ratio (sum of leg length and arm span, divided by sitting height) for total height was significantly lower in the three SHOX haploinsufficient probands, in comparison with the whole group. This observation was confirmed with the auxological data of five additional patients (four females) previously diagnosed with SHOX haploinsufficiency; all but the youngest girl had height-adjusted extremities-trunk ratios more than 1 SD below the mean. All children with SHOX haploinsufficiency exhibited at least one characteristic radiological sign of Leri-Weill-dyschondrosteosis in their left-hand radiography, namely triangularization of the distal radial epiphysis, pyramidalization of the distal carpal row, or lucency of the distal ulnar border of the radius. Our observations suggest that it is rational to limit SHOX mutation screening to children with an extremities-trunk ratio less than 1.95 + 1/2 height (m) and to add a critical judgment of the hand radiography.