Two cases of sideroblastic anemia with B-cell immunodeficiency, periodic fevers, and developmental delay (SIFD) syndrome in Chinese Han children caused by novel compound heterozygous variants of the TRNT1 gene

Alternative start codon selection shapes mitochondrial function during evolution, homeostasis, and disease

Mitochondrial endosymbiosis was a pivotal event in eukaryotic evolution, requiring core proteins to adapt to function both within the mitochondria and in the host cell. Here, we systematically profile the localization of protein isoforms generated by alternate start codon selection during translation. We identify hundreds of pairs of differentially-localized protein isoforms, many of which affect mitochondrial targeting and are essential for mitochondrial function. The emergence of dual-localized mitochondrial protein isoforms coincides with mitochondrial acquisition during early eukaryotic evolution. We further reveal that eukaryotes use diverse mechanisms-such as leaky ribosome scanning, alternative transcription, and paralog duplication-to maintain the production of dual-localized isoforms. Finally, we identify multiple isoforms that are specifically dysregulated by rare disease patient mutations and demonstrate how these mutations can help explain unique clinical presentations. Together, our findings illuminate the evolutionary and pathological relevance of alternative translation initiation, offering new insights into the molecular underpinnings of mitochondrial biology.

Comprehensive Genomic Analysis Identifies a Diverse Landscape of Sideroblastic and Nonsideroblastic Iron-Related Anemias with Novel and Pathogenic Variants in an Iron-Deficient Endemic Setting

Inherited iron metabolism defects are possibly missed or underdiagnosed in iron-deficient endemic settings because of a lack of awareness or a methodical screening approach. Hence, we systematically evaluated anemia cases (2019 to 2021) based on clinical phenotype, normal screening tests (high-performance liquid chromatography, α gene sequencing, erythrocyte sedimentation rate, C-reactive protein, and tissue transglutaminase), and abnormal iron profile by targeted next-generation sequencing (26-gene panel) supplemented with whole-exome sequencing, multiplex ligation probe amplification/mitochondrial DNA sequencing, and chromosomal microarray. Novel variants in ALAS2, STEAP3, and HSPA9 genes were functionally validated. A total of 290 anemia cases were screened, and 41 (14%) enrolled for genomic testing as per inclusion criteria. Comprehensive genomic testing revealed pathogenic variants in 23 of 41 cases (56%). Congenital sideroblastic anemia was the most common diagnosis (14/23; 61%), with pathogenic variations in ALAS2 (n = 6), SLC25A38 (n = 3), HSPA9 (n = 2) and HSCB, SLC19A2, and mitochondrial DNA deletion (n = 1 each). Nonsideroblastic iron defects included STEAP3-related microcytic anemia (2/23; 8.7%) and hypotransferrenemia (1/23; 4.3%). A total of 6 of 22 cases (27%) revealed a non-iron metabolism gene defect on whole-exome sequencing. Eleven novel variants (including variants of uncertain significance) were noted in 13 cases. Genotype-phenotype correlation revealed a significant association of frameshift/nonsense/splice variants with lower presentation age (0.8 months versus 9 years; P < 0.01) compared with missense variants. The systematic evaluation helped uncover an inherited iron defect in 41% (17/41) of cases, suggesting the need for active screening and awareness for these rare diseases in an iron-deficient endemic population.

Spontaneous, simultaneous bilateral osteonecrosis of the femoral heads in a patient with sideroblastic anaemia with B-cell immunodeficiency, periodic fever and developmental delay syndrome

Sideroblastic anaemia with B-cell immunodeficiency, periodic fever and developmental delay is a recently described, rare syndrome characterised by numerous manifestations underpinned by mutations in transfer RNA nucleotidyltransferase. The pathogenesis arises from mitochondrial dysfunction, with impaired intracellular stress response, deficient metabolism and cellular and systemic inflammation. This yields multiorgan dysfunction and early death in many patients with survivors suffering significant disability and morbidity. New cases, often youths, are still being described, expanding the horizon of recognisable phenotypes. We present a mature patient with spontaneous bilateral hip osteonecrosis that likely arises from the impaired RNA quality control and inflammation caused by this syndrome.

Thalidomide as an Effective Treatment in Sideroblastic Anemia, Immunodeficiency, Periodic Fevers, and Developmental Delay (SIFD)

PURPOSE

Sideroblastic anemia, immunodeficiency, periodic fevers, and developmental delay (SIFD) is an autosomal recessive syndrome caused by biallelic loss-of-function variant of tRNA nucleotidyl transferase 1 (TRNT1). Efficacious methods to treat SIFD are lacking. We identified two novel mutations in TRNT1 and an efficacious and novel therapy for SIFD.

METHODS

We retrospectively summarized the clinical records of two patients with SIFD from different families and reviewed all published cases of SIFD.

RESULTS

Both patients had periodic fever, developmental delay, rash, microcytic anemia, and B cell lymphopenia with infections. Whole-exome sequencing of patient 1 identified a previously unreported homozygous mutation of TRNT1 (c.706G > A/p.Glu236Lys). He received intravenous immunoglobulin (IVIG) replacement and antibiotics, but died at 1 year of age. Gene testing in patient 2 revealed compound heterozygous mutations (c.907C > G/p.Gln303Glu and c.88A > G/p.Met30Val) in TRNT1, the former of which is a novel mutation. Periodic fever was controlled in the first month after adalimumab therapy and IVIG replacement, but recurred in the second month. Adalimumab was discontinued and replaced with thalidomide, which controlled the periodic fever and normalized inflammatory markers effectively. A retrospective analysis of reported cases revealed 69 patients with SIFD carrying 46 mutations. The male: female ratio was 1: 1, and the mean age of onset was 3.0 months. The most common clinical manifestations in patients with SIFD were microcytic anemia (82.6%), hypogammaglobulinemia/B cell lymphopenia (75.4%), periodic fever (66.7%), and developmental delay (60.0%). In addition to the typical tetralogy, SIFD features several heterogeneous symptoms involving multiple systems. Corticosteroids, immunosuppressants, and anakinra have low efficacy, whereas etanercept suppressed fever and improved anemia in reports. Bone-marrow transplantation can be used to treat severe SIFD, but carries a high risk. In total, 28.2% (20/71) of reported patients died, mainly because of multi-organ failure. Biallelic mutations located in exon1-intron5 lead to more severe phenotypes and higher mortality. Furthermore, 15.5% (11/71) patients survived to adulthood. The symptoms could be resolved spontaneously in five patients.

CONCLUSIONS

Thalidomide can control the inflammation of SIFD and represents a new treatment for SIFD.

Case report: Sideroblastic anemia with B-cell immunodeficiency, periodic fevers, and developmental delay: Three cases and a literature review

Sideroblastic anemia with B-cell immunodeficiency, periodic fevers, and developmental delay (SIFD) is a serious autosomal recessive syndrome caused by biallelic mutations in cytosine-cytosine-adenosine tRNA nucleotidyltransferase 1 (TRNT1). The main clinical features of SIFD are periodic fevers, developmental delay, sideroblastic or microcytic anemia, and immunodeficiency. Herein, we report three cases of SIFD with compound heterozygous variants of TRNT1. Patients 1 and 2 were siblings; they presented with periodic fevers, arthritis, low immunoglobulin A, bilateral cataracts, anemia, and neurodevelopmental and developmental delay. Patient 3 had severed clinical features with recurrent fever and infections. She was treated with infliximab and symptomatic treatments but without therapeutic effect. She received a stem cell transplantation of umbilical cord blood but died of posttransplant infection and posttransplant graft-vs.-host disease 17 days after transplantation. Finally, a literature review revealed that TRNT1 variants differed among SIFD patients. Our cases and literature review further expand existing knowledge on the phenotype and TRNT1 variations of SIFD and suggest that the early genomic diagnosis of TRNT1 is valuable to promptly assess bone marrow transplantation and tumor necrosis factor inhibitor treatments, which might be effective for the immunodeficiency and inflammation caused by SIFD.

A Rare Autoinflammatory Disorder in a Pediatric Patient with Favorable Response to Etanercept: Sideroblastic Anemia with B Cell Immunodeficiency, Periodic Fevers, and Developmental Delay Syndrome

Introduction: Sideroblastic anemia with B cell immunodeficiency, periodic fevers, and developmental delay (SIFD) syndrome is caused by biallelic TRNT1 mutations. TRNT1 gene encodes a CCA-adding tRNA nucleotidyl transferase enzyme. Mutant TRNT1 results in immunodeficiency and anemia in various degrees, accompanied by several organ involvement. Case Presentation: We present here a 15-month old male, demonstrated brittle hair, growth hormone deficiency, recurrent fever, arthritis, recurrent infections, mild anemia, and hypogammaglobulinemia. The patient did not respond to colchicine treatment, and after establishing SIFD diagnosis with the presence of homozygote c.948-949delAAinsGG (p.Lys317Glu) mutation in TRNT1 gene, we commenced monthly intravenous immunoglobulin replacement and weekly subcutaneous etanercept. A rapid resolution of fever episodes and infections occurred after initiation of this treatment regimen. Afterward, both anemia and growth parameters have improved during follow-up. Conclusion: SIFD syndrome should be considered in patients with recurrent fever, arthritis, and growth retardation even in the absence of severe anemia and prominent hypogammaglobulinemia.