Genetic basis of osteogenesis imperfecta from a single tertiary centre in South Africa

Osteogenesis imperfecta (OI) is a clinically heterogeneous disorder characterised by skeletal fragility and an increased fracture incidence. It occurs in approximately one in every 15-20,000 births and is known to vary considerably in its severity. This report aimed to use next-generation sequencing (NGS) technology to identify disease genes and causal variants in South African patients with clinical-radiological features of OI. A total of 50 affected individuals were recruited at Tygerberg Hospital's Medical Genetics clinic. Patients were selected for a gene panel test (n = 39), a single variant test (n = 1) or exome sequencing (ES) (n = 12, 7 singletons, 1 affected duo, and 1 trio), depending on funding eligibility. An in-house genomic bioinformatics pipeline was developed for the ES samples using open-source software and tools. This study's 100% diagnostic yield was largely attributable to an accurate clinical diagnosis. A causal variant in COL1A1 or COL1A2 was identified in 94% of this patient cohort, which is in line with previous studies. Interestingly, this study was the first to identify the common South African pathogenic FKBP10 variant in a patient of mixed ancestry, adding to what was previously known about this variant in our population. Additionally, a recurrent variant in COL1A2: c.1892G>T was discovered in 27 individuals (25 from three large unrelated families and two further individuals), facilitating the establishment of local testing for this variant in South African patients.