Vitamin D deficiency remains a major cause of rickets worldwide. Nutritional factors are the major cause and less commonly, inheritance causes. Recently, CYP2R1 has been reported as a major factor for 25-hydroxylation contributing to the inherited forms of vitamin D deficiency. We conducted a prospective cohort study at King Faisal Specialist Hospital & Research Centre, Riyadh, Saudi Arabia, to review cases with 25-hydroxylase deficiency and describe their clinical, biochemical, and molecular genetic features. We analyzed 27 patients from nine different families who presented with low 25-OH vitamin D and not responding to usual treatment. Genetic testing identified two mutations: c.367+1G>A (12/27 patients) and c.768dupT (15/27 patients), where 18 patients were homozygous for their identified mutation and 9 patients were heterozygous. Both groups had similar clinical manifestations ranging in severity, but none of the patients with the heterozygous mutation had hypocalcemic manifestations. Thirteen out of 18 homozygous patients and all the heterozygous patients responded to high doses of vitamin D treatment, but they regressed after decreasing the dose, requiring lifelong therapy. Five out of 18 homozygous patients required calcitriol to improve their biochemical data, whereas none of the heterozygous patients and patients who carried the c.367+1G>A mutation required calcitriol treatment. To date, this is the largest cohort series analyzing CYP2R1-related 25-hydroxylase deficiency worldwide, supporting its major role in 25-hydroxylation of vitamin D. It is suggested that a higher percentage of CYP2R1 mutations might be found in the Saudi population. We believe that our study will help in the diagnosis, treatment, and prevention of similar cases in the future.

Background: The use of exome sequencing (ES) has helped in detecting many variants and genes that cause primary adrenal insufficiency (PAI). The diagnosis of PAI is difficult and can be life‐threatening if not treated urgently. Consanguinity can impact the detection of recessively inherited genes. Here, we report families with PAI in a consanguineous population of Saudi Arabia.Materials and Methods: A cohort of 47 PAI patients (41 males and six females) representing 30 families was recruited. The cohort excluded congenital adrenal hyperplasia (CAH) cases and had a known consanguinity of 70%. Using ES, molecular genetic causes of PAI were investigated.Results: In 30 unrelated families with PAI, pathogenic/likely pathogenic variants were detected in 27 families with a diagnostic yield of (90%). Clinically associated variants of uncertain significance (VUS) were identified in a further two PAI families (7%). Hemizygous variants in ABCD1 were the most common cause of PAI in this cohort (16 families) leading to adrenoleukodystrophy. A total of six novel variants were detected, of which four were predicted to be pathogenic (P) / likely pathogenic (LP) and two were VUS. Four pathogenic variants in ABCD1, NR0B1, and MC2R were detected in 10 families suggesting founder mutations.Conclusion: In this cohort, ES detected a diagnostic molecular abnormality in 90% of patients with PAI phenotypes. X‐linked inheritance is the most common cause of PAI and founder mutations likely contributed to a high diagnostic yield.

The ADAT2/ADAT3 (ADAT) complex catalyses the adenosine to inosine modification at the wobble position of eukaryotic tRNAs. Mutations in ADAT3, the catalytically inactive subunit of the ADAT2/ADAT3 complex, have been identified in patients presenting with severe neurodevelopmental disorders. Yet, the physiological function of the ADAT2/ADAT3 complex during brain development remains totally unknown. Here, we investigated the role of the ADAT2/ADAT3 complex in cortical development. First, we report 21 neurodevelopmental disorders patients carrying biallelic variants in ADAT3. Second, we used structural, biochemical and enzymatic assays to deeply characterize the impact of those variants on the ADAT2/ADAT3 structure, biochemical properties, enzymatic activity, and tRNAs editing and abundance. Finally, in vivo complementation assays were performed to correlate functional deficits with neuronal migration defects in the developing mouse cortex. Our results showed that maintaining a proper level of ADAT2/ADAT3 catalytic activity is essential for radial migration of projection neurons in the developing mouse cortex. We demonstrated that the identified ADAT3 variants significantly impaired the abundance and, for some, the activity of the complex, leading to a substantial decrease in inosine 34 levels with direct consequence on tRNAs steady state. We correlated the severity of the migration phenotype with the degree of loss of function caused by the variants. Altogether, our results highlight the critical role of ADAT2/ADAT3 during cortical development and provide cellular and molecular insights into the pathogenic mechanisms underlying ADAT3-related neurodevelopmental disorders.

Hajdu-Cheney syndrome is a rare disorder caused by truncation mutations in exon 34 of the NOTCH2 gene. The main presentation includes acro-osteolysis, osteoporosis, and dysmorphism. This syndrome affects the other body systems as well. We report a case of a 6-year-old female that initially developed polyhydramnios and short upper limbs as a fetus. In addition, the patient had multiple anomalies as a neonate, including dysmorphism, congenital heart disease, hearing loss, recurrent respiratory tract infections, skeletal abnormalities, renal cysts, and hypertension. She continues to receive multidisciplinary care, and the finding of a C.7021C > T: P.Q2341x mutation in exon 34 of the NOTCH2 gene confirms the diagnosis. To our knowledge, this is the first case to report this variant in the literature. Because of the rarity of this syndrome and its diverse presentation, a high index of suspicion accompanied by genetic testing is paramount for diagnosing Hajdu-Cheney syndrome. We recommend a multidisciplinary approach for these patients to provide the highest possible quality of care.

Pycnodysostosis, a rare osteopetrosis subtype, is mainly caused by homozygous or compound heterozygous biallelic pathogenic mutation of the cathepsin K (CTSK) gene. The cohort included eight patients (four males and four females) with a mean current age of 13 years (SD ± 3.6) and a mean age at diagnosis of 5 years (SD ± 2). All patients had a positive family history of pycnodysostosis and were born to consanguineous parents. Genetic analysis revealed that all individuals carried the same mutation: NM_000396.3(CTSK):c.244-29A>G. Clinically, they exhibited characteristic craniofacial features and skeletal deformities consistent with the diagnosis. Bone fractures were reported in 7 out of 8 patients, highlighting a significant clinical burden. All affected individuals received growth hormone therapy(GHT), though response to treatment varied among the group. These findings emphasize the importance of early genetic screening, particularly in families with a known history of pycnodysostosis, to enable timely diagnosis and intervention. Although pycnodysostosis is typically described as a nonprogressive skeletal dysplasia, the presence of complications such as osteomyelitis and recurrent fractures may contribute to a more complex and progressive clinical course in some patients.

Summary: X-linked hypophosphatemic rickets (XLH), the most prevalent form of inherited hypophosphatemic rickets, is caused by loss-of-function mutations in the gene encoding phosphate-regulating endopeptidase homolog, X-linked (PHEX). This case series presents 14 cases of XLH from Gulf Cooperation Council (GCC) countries. The patients’ medical history, biochemical and radiological investigative findings, as well as treatment responses and side effects from both conventional and burosumab therapy, are described. Cases were aged 2–40 years at diagnosis. There were two male cases and 12 female cases. All cases were treated with conventional therapy which resulted in a lack of improvement in or worsening of the clinical signs and symptoms of rickets or biochemical parameters. Side effects of conventional therapy included nausea, diarrhea, abdominal pain, nephrocalcinosis, and hyperparathyroidism, which affected the patients’ quality of life and adherence to treatment. In the 10 patients treated with burosumab, there was a marked improvement in the biochemical markers of rickets, with a mean increase in serum phosphate of +0.56 mmol/L and tubular maximum phosphate reabsorption (TmP) to glomerular filtration rate (GFR) ratio (TmP/GFR) of +0.39 mmol/L at 12 months compared to baseline. Furthermore, a mean decrease in serum alkaline phosphatase (ALP) of −80.80 IU/L and parathyroid hormone (PTH) of −63.61 pmol/L at 12 months compared to baseline was observed in these patients. Additionally, patients treated with burosumab reported reduced pain, muscle weakness, and fatigue as well as the ability to lead more physically active lives with no significant side effects of treatment. Learning points: Conventional therapy resulted in a suboptimal response, with a lack of improvement of clinical signs and symptoms. Side effects of conventional therapy included nausea, diarrhea, abdominal pain, nephrocalcinosis, and hyperparathyroidism, which affected the patients’ quality of life and adherence to treatment. Burosumab demonstrated marked improvements in the biochemical markers of rickets, in addition to reducing pain, muscle weakness, and fatigue. There were no significant side effects associated with burosumab therapy.