SHOX gene deficiency is one of the single gene disorders of the bone resulting in highly variable osteodysplasia and hence affecting the overall height in children. However, as the knowledge of the gene and allelic alterations in the gene have evolved over time, it is now well known that isolated deficiency of either the SHOX gene or its modifiers up and down the Par region are responsible in a spectrum of disorders ranging from simple idiopathic short stature to more severe spectrum of disorders like “Leri–Weill dyschondrosteosis (LWD, MIM 127300) and Langer Mesomelic dysplasia (LMD, MIM 249700)”. In present study, SHOX gene variation was found in 12.9% cases in the study (7 out of 54 children) using MLPA and Sanger sequencing, wherein heterozygous deletion of exons was seen in 4 children (7.4%), and duplications in SHOX gene was noticed in 3 children (5.5%).
The skeletal findings in Leri–Weill dyschondrosteosis are characteristic, however, in one of our subjects, multiple exostosis was observed around the knee joints. It’s rare and was observed in some members in a multigenerational non-consanguineous North African family, reported by Al Kaissi A et al. 2016.
In studies conducted earlier, and as mentioned in SHOX database, this value ranges from 2-15% among children with Idiopathic short stature (Huber et al., 2006; Jorge et al., 2007; Hirschfeldova et al., 2012; Binder et al., 2011). In study by Hirschfeldova et al, MLPA analysis detected a total of 13.7% of SHOX gene anomalies including 4 deletions, 1 duplication with an “ambiguous effect” and 2 SHOX gene point variations (Hirschfeldova et al., 2012). In the same study single isolated enhancer duplication was also observed in LWD group. In our study, 3 duplications (5.5%) are observed, with no enhancer effect noticed, and was found in children with short stature. In present study, SHOX gene association was seen significantly to be related to gender, with predominance in female sex (P value: 0.047), and had no significant age correlation. Short arms and forearms were the only trait seen in 51.85% of the children and was found to be significantly related to SHOX gene variation in the study (P value: 0.024) and the rest of phenotypic traits were not found to be significantly associated. Seven children who had SHOX gene mutated were thoroughly studied for the phenotypic- genotypic correlation.
For the better delineation of the clinical expression in our cohort, the Rappold scoring was done for the investigated patients. Interestingly, all patients had varied scores with a median value of 3 (range 0-10). Short forearm was the most observed feature (62.5%), while cubitus valgus was observed in 2 patients. All the reported BMI were less than 50th percentile. Unexpectedly, arm span/height ratio was uncommon (28.5%), whereas bowing of forearm and tibia was present in only 1 patient. Sitting height/height ratio (>55.5%), dislocation of ulna at the elbow and muscular hypertrophy were absent in all the subject (Table 1).
In different studies conducted in different populations, the prevalence of SHOX variations in ISS children represent a wide array. The study conducted by Suppia et al., 2003 showed around 7% patients with ISS having SHOX gene deletion, while Musebeck et al., 2001 conducted a study over 35 patients of ISS, none of whom had the gene deletion.
This meta-analysis aimed to investigate the association between the SHOX variation and ISS in Asia. Data was included from 11 selected studies, which involved 979 ISS cases. Overall prevalence of SHOX variation in Asia was found to be 14.3%. These results indicate the implication and the association of these variations with ISS in Asia. For comparison, the participants were divided into South, West and East Asian sub-groups. In South Asia, the results indicated the presence of SHOX variations in 10.4% of the patients with ISS.
Among South Asians, Kumar et al., 2020 reported pathogenic heterozygous variants in 4 children (6.5%). Variations included exon 5 duplication, splice site point variant c.278-1G>C in exon 3, partial deletion and complete deletion. Singh et al., 2018 showed SHOX haploinsufficiency in two patients, while one patient had mosaic gain in SHOX.
In West Asian population, Dalil et al., 2016 found one patient (2.6%) with SHOX variation. Contrarily, Bakir et al., 2018 has not found any variation in the exonic sequences and exon/intron boundaries of the SHOX gene. Alharthi et al., 2017 found only one variation in exon 4 of SHOX gene while rest of patients had polymorphisms in exons 1, 2, 4, and 6. Gursoy et al., 2020 showed three different point variations and one whole SHOX gene deletion 15 patients from four different families. Overall prevalence in West Asia came around 7.5%.
In Eastern Asia, Fukami et al., 2015 reported six rare CNVs in PAR1 in 245 patients. Lee et al., 2021 have confirmed SHOX deficiency in 23 patients from 15 unrelated families. In a study by Tung et al., 2018 SHOX gene intragenic deletions were found in five patients, one deletion in the regulatory region, and a missense variation at exon 5. Prevalence of variation in SHOX gene varied in between different geographical regions of Asia, being highest in South Asia. While Shima et al., 2016 stated SHOX abnormalities in 3.8% of ISS and 50% of LWD cases. These results indicate the difference in the prevalence of the SHOX variations according to the selection criteria, used methods, sample size, and population.
The meta-analysis is a compilation of findings from the last decade and an updated picture of overall prevalence of SHOX variations in Asians, underscoring its potential as a main target in ISS patients. Further investigations of higher quality, large cohort size with functional validation are warranted to validate this association.