ABSTRACT

Genetic skeletal disorders (GSDs) are heritably and clinically varied classes of bone and cartilage anomalies, characterized by irregular growth/development of the skeleton. They are rare, but their cases may be upraised with endogamy as it increases homozygosity. Pakistan has the highest rate (55%-60%) of consanguinity, which is quite worrying. Still, Pakistan has no reliable data (geographical prevalence, clinical, and epidemiological data) associated with GSDs and other rare genetic disorders. Unfortunately, due to the lack of adequate clinical/diagnostic resources and genetic knowledge, the suspected cases of genetic disorders are misdiagnosed and hence mistreated, thus, causing psycho-socioeconomic problems. The present study reviewed current literature, published on several Internet databases including the “Nosology of GSDs: (2023 Revision)” from Pakistan. GSDs such as acromesomelic dysplasia, mucopolysaccharidosis, polydactyly, synpolydactyly, and split hand/split foot malformation were reported in several families and have 55.04% of all the reported GSDs from Pakistan. To date, in the literature, 72 different mutated genes have been reported from the Pakistani community. This review will help clinicians and researchers in understanding, diagnosis, and management of GSDs and will offer a descriptive approach to carry out fruitful molecular genetic research in genetically vulnerable and low-resource regions. Moreover, it will also speed up the possible therapy development and may insist the stakeholders to establish a multi-level network to find a path towards the healthcare challenges of GSDs from Pakistan.

Keywords:

Prevalence, genetic skeletal disorders, skeletal dysplasia, Pakistani population.

Background

Genetic/hereditary skeletal disorders (GSDs) represent a diverse set of clinical/genetical conditions that arise from the mutations in different candidate genes resulting in disturbances of complex skeletal pathways of growth, development, and homeostasis. In contrast to the prevalent diseases, GSDs are rare and affect a very small fraction of people. However, due to the advent of next-generation sequencing (NGS) technologies, novel candidate genes are reported on a daily basis which has increased the number of rare genetic disorders (RGDs) and is thus currently recognized as one of the most significant global public health issues (1).

In developing countries, there are a number of difficulties like limited advanced clinical resources, and no or far localized genetic services centers, which hampered research and managing studies for GSDs. The proper diagnosis of GSDs is always a challenge because a variety of syndromic and nonsyndromic forms of GSDs affect a large number of people around the world, resulting in substantial healthcare costs and low quality of life (2,3). Despite numerous international initiatives to address the GSDs-associative problems, considerable work still needs to be done to deal with this ignored health sector, especially in Pakistan (4).

In recent times, advanced high-throughput, sequencing technologies such as whole genome sequencing and whole-exome sequencing have greatly increased our understanding of GSDs. The majority of the variants/mutations listed in Table 1 are identified by using recent advanced technology like NGS and with parallel Sanger sequencing method. Though 80% of rare disorders have a genetic origin and significant advances/discoveries are made every day, but still, approximately 65%-70% of causing genes/factors still need to be identified (5).

The nosology classification-2023 revision has classified the 771 different GSDs into 41 groups, on the basis of clinical, molecular, and radiographic diagnostics criteria, while only 552 genes have been associated with RGDs. The entire number of GSDs increased to 771 from 461 and the number of genes to 552 from 437; however, groups decreased from 42 to 41 due to regrouping and restructuring in the review of nosology-2023 classification (86).

Table 1. Up-to-date reported mutations and their candidate genes causing GSDs within the Pakistani community.

Table 2. Province-wise number of GSDs reported and published from each province of Pakistan.

The nosology classification-2023 revision is more helpful in the identification of novel skeletal disorders and provides an excellent framework for a better understanding of the underlying mechanisms essential for regular skeletal growth, maintenance, and development (86). Based on the nosology classification-2023 revision, this is our second effort at population research studies to display the prevalence and pervasiveness of GSDs in Pakistan (10).

The reasons that stimulate us to compile and publish a second revision of GSDs is to facilitate research and diagnosis by sharing fresh knowledge about the growing number and variety of GSDs. Commonly in Pakistani society, GSD has an autosomal dominant or recessive mode of inheritance.

Skeletal dysplasia

Skeletal dysplasia is the heterogeneous camp of RGDs occurrence rate of 1 in every 5,000 live births (87). Mutations in several genes are associated with skeletal disorders that might affect the development, structure, or function of the skeletal system. They may have autosomal dominant, autosomal recessive, X-linked dominant, or X-linked recessive or as a de novo mode of inheritance (87). GSDs display varied clinical conditions ranging from a particular organ to multisystematic disorder and are due to defects/mutations in a variety of gene families, including genes encoding transcription factors, extracellular matrix proteins, tumor suppressors, ligands, channel proteins, receptors, enzymes, cellular transporters, intracellular binding and morphogenic proteins, chaperones, RNA processing molecules, cytoplasmic proteins, cilia, and others. Moreover, exposure to teratogen, somatic mosaicism, and imprinting errors may lead to GSDs (87).

In practice, the distinction between different types of skeletal disorders is often implausible due to analogous disease patterns including radiographic and molecular findings and clinical manifestation. GSDs may be classified as skeletal dysplasia or dysostoses on the basis of anomalies in pattern, differentiation, linear development, and maintenance of skeletal tissues (88,89). Skeletal dysplasia is a broad term referring to abnormalities of bone and cartilage that result in unbalanced stature, size, and shape of the skeleton. They primarily affect the development of cartilage and bone (due to the mutation in genes regulating the development, growth, and maintenance of bone/cartilage) but muscles, tendons, and ligaments may also be affected (89,90). On the other hand, dysostosis refers to anomalies in the ossification of one or more bones due to mutation of genes involved in skeletal patterning. They often occur in conjunction with other inherited disorders in the form of spondylocostal dysostosis, cleidocranial dysostosis, and limb deformities such as polydactyly, brachydactyly, and syndactyly (91,92).

To categorize the newly reported genes and disorders, the International Skeletal Dysplasia Society completed its most recent revision in 2023, which revealed a novel molecular and pathological concept of GSDs. In their recent analysis, Unger et al. (86) divide 771 disorders into 41 groups with only 552 known associated candidates’ genes.

The present study is coping with sufficient and to-date information on GSD phenotypes reported by the Pakistani community and has systematically evaluated them. The appraisal also comprehensively analyzed, explored, and emphasized all the challenges and concerns associated with accurate diagnosis and proper treatment of GSDs, especially life-threatening GSDs.

Methodology

The current study covered and reported all 552 known GSD candidates’ genes, which were grouped into 41 categories in the “Nosology of GSDs (2023 revision).”

Research approaches

All reported GSD genes were obtained from the “Nosology of GSDs (2023 revision).” The search was conducted by entering the mesh “gene name” and “Pakistan” by using various online accessible databases and search browsers such as OMIM, Google Scholar, PubMed, HMGD, and Research Gate.

Results

In the existing literature, 559 cases of GSDs are documented in 21 different groups of the “Nosology of GSDs (2023 revision)” from the Pakistani community. Table 1 lists details of all the pathogenic mutations reported from the Pakistani community till now. SHFM, Synpolydactyly, Polydactyly, Acromesomelic dysplasia/short-limb dwarfism (AMDH, AMDG, AMDM), and Glycosaminoglycans (Mucopolysaccharidosis) are five most reported GSDs, accounting for 14.19%, 13.18%, 11.51%, 7.8%, and 5.5%, respectively (Tables 1 and 2). Figure 1A and B illustrates the geographical prevalence of GSDs in Pakistan. However, this time a significantly higher number of cases were reported from the Punjab province (40.56%), compared to the GSD 2019, in which Sindh province was at the top with 40.38% GSD cases and Punjab was second with 39.04 of all the cases. All the numbers and details of GSDs reported so far from each province (Pakistan) have been listed in Table 2.

Figure 1. (A) Provinces-wise percent prevalence of hereditary skeletal disorders reported and published from Pakistan. (B) Number-wise graphical representation of different GSDs reported from Pakistani provinces. Punjab province is showing the highest reports.

Discussion

The term GSD is commonly used to describe bone and cartilage abnormalities. It is a very heterogeneous class of anomalies that result from the mutations of numerous genes, causing disruption in the organization and function of the growth plate. It can range from mild (polydactyly, and so on) to severe/lethal (thoracic hypoplasia, and so on) and from nonsyndromic to syndromic. Genotypically, GSD has both dominant (autosomal/X-linked) and recessive (autosomal/X-linked) forms of inheritance. Keeping in mind the challenges of the precise diagnosis and evaluation of the GSDs, it is important to obtain family history, physical examination, a full set of skeletal radiographs/photographs, audiogram, magnetic resonance imaging, and complete medical records (93).

Currently, Pakistan is the 5th most populous country in the world (241.49 million with a growth rate of 2.55% (census 2023); having five provinces (Balochistan, Gilgit-Baltistan, Khyber Pakhtunkhwa Punjab, and Sindh), and Pakistan administered territories of Azad Jammu and Kashmir (4.045 million populations (census 2017). All GSD cases reported from Pakistan to date include Punjab (40.56%), Sindh (35.96%), KPK (19.05%), Balochistan (1.31%), and Kashmir (3.12%), while from Gilgit-Baltistan still no case has been reported (Figure 1A and B).

Although very little information is available about the prevalence of genetic disorders in Pakistan, the statistics from Europe and golf countries point to a concerning situation for Pakistan, as cousin marriage drastically increases genetic disorders and Pakistan has the highest rate of cousin marriage. For example, Europe has less than 1% cousin marriages with 1/5,000 live births affected by a genetic disorder, while Qatar has 54% consanguinity with 1/1,300 affected birth individuals (94).

According to studies, cousins marry each other in about 55%-60% of marriages in the nation. Numerous cultural, social, and economic factors contribute to this high prevalence. The prevailing cultural and societal norms in Pakistan that encourage cousin marriages are a major contributing factor to the high number of these marriages. In many cultures, getting married within the extended family is seen as a means of preserving inherited wealth and ties to the family. Cousin marriages are also frequently viewed as the best option because of their apparent compatibility and shared morals. However, there are certain negative consequences associated with the prevalence of cousin marriages in Pakistan, including economic burdens. Consanguineous marriages can lead to an increased risk of genetic disorders and disabilities in offspring. Research has shown that the children of cousin marriages are more likely to suffer from birth defects, developmental delays, and other hereditary conditions (85). In addition, the majority of mutations found in the Pakistani population are biallelic; however, heterozygous mutations are also common.

According to Umair (5), 65%-70% of casual genes of RGDs have to be identified; moreover, recently the “Nosology of GSDs (2023)” has reported many novel GSDs worldwide. Developing countries like Pakistan, where 60% of people are below the line in poverty, have no concept of proper testing and have no database or any other organization for the entry and registration of RGDs including GSDs. Even though, the Pakistani population has a high rate of consanguineous marriage, researchers and physicians have little to no documented information.

The current analysis reveals that in the last two decades number and kind of GSDs in Pakistan have rapidly increased due to the powerful NGS screening technologies. Especially, in the last 10 years publications and reports about genetic rare disorders have increased by 99%. That is why GSDs and their causing genes/mutations have a relatively high novelty rate reporting from Pakistan. The aim of this revision is to provide bridges among clinicians, scientists, and genetics interested in GSDs and in skeletal biology, through the list of GSDs and their causative genes, mutations, pathways, and other associated spectrums. Moreover, it will also ensure a proper diagnosis, as this review holds the treasure of detail and novel information on GSDs (95).

GSDs are a complicated and diverse set of disorders caused by 552 different genes, making it very challenging to identify the exact disorder (5). Monogenetic disorders are very rare but it is helpful to identify the specific gene function and to track down its associated molecular pathways. Studying the pathogenicity of various mutations that occur in different genes sheds light on the potential prevention measures, diagnostic tools, treatment, and a necessary step for providing correct genetic counseling. In modern times, there has been significant progress in molecular/genetic diagnosis (such as NGS, and so on) to confirm clinical/radiographic diagnosis and to predict the risk level of a family for GSDs. Moreover, targeting these molecular pathways has encouraging results both in vitro and in vivo even though these therapies are still under the research and developmental stage (84).

Despite the paucity of research on GSDs in Pakistan, efforts have been made to comprehend, diagnose, and treat these severe conditions. Pakistan’s medical community has been actively involved in the diagnosis, treatment, and management of patients with skeletal dysplasias and other genetic conditions. A significant obstacle in carrying out investigations on GSDs in Pakistan is their uncommon occurrence, which makes it hard to locate enough afflicted people for thorough examinations. Precise diagnosis and treatment of these disorders are further complicated by the fact that certain areas of the nation lack access to specialized genetic testing facilities and knowledge.

The future management of GSDs is likely to be influenced by advancements in genetics, molecular biology, and medical technology. Potential developmental areas that can improve our understanding include precision medicine, CRISPR-Cas9-based gene therapy, stem cell therapies, pre-genetic testing, and early interventions (83,94).

Future studies may focus on the discovery of therapy for GSDs by finding new therapeutic drugs that more specifically affect this integrated signaling network and enhance the delivery of therapeutics to the growth plate. Moreover, in Pakistan, a sound medical policy and establishing robust collaborative partnerships abroad is required. At each big city, a department for genetic counseling through the multidisciplinary approach (including orthopedists, rheumatologists, otolaryngologists, gynecologists, neurologists, ophthalmologists, and so on, having genetically knowledge and experience) should be established for RGDs. This would considerably reduce the likelihood of misdiagnosis and will make it easy to enhance treatment for patients of RGDs.

Conclusion

In conclusion, the main goal of the present systematic revision is to summarize the detailed information on the rare and ultra-rare GSDs on the number, geographic, and molecular genetic bases affecting the Pakistani community. Thus, updating the current literature of GSDs in Pakistan according to the recent nosology classification 2023 (5). Where, it will provide an exact roadmap to proper diagnosis, awareness, and approaches to successful molecular research, as well as it will elaborate on the pathological mechanism of GSDs. Furthermore, it will also accelerate understanding of the potential therapy development and will urge researchers, geneticists, clinicians, and other policymakers to establish a multilevel network organization that might offer a proper solution to diagnosis, treatment, and care to patients suffering from GSDs in Pakistan.

Acknowledgment

The author would like to thank UMT for its support.

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