Clinical Manifestations Associated with the Domain-Containing Protein 2 Gene Mutation in an Iranian Family with Spastic Paraplegia 54.

INTRODUCTION: Spastic paraplegia type 54 (SPG54) is an autosomal recessive disorder caused by bi-allelic mutations in the DDHD-domain-containing protein 2 (DDHD2) gene. Worldwide, over 24 SPG54 families and 24 pathogenic variants have been reported. Our study aimed to describe the clinical and molecular findings of a pediatric patient from a consanguineous Iranian family with significant motor development delay, walking problems, paraplegia, and optic atrophy. METHODS: The patient was a 7-year-old boy with severe neurodevelopmental and psychomotor problems. Neurological examinations, laboratory tests, electroencephalography, computed tomography scan, and brain magnetic resonance scan (MRI) were carried out for clinical evaluation. Whole-exome sequencing and in silico analysis were undertaken to identify the genetic cause of the disorder. RESULTS: The neurological examination showed developmental delay, spasticity in the lower extremities, ataxia, foot contractures, and deep tendon reflexes in the extremities. The computed tomography scan was normal, but MRI revealed corpus callosum thinning with atrophic changes in the white matter. The genetic study reported a homozygous variant (c.856 C>T, p.Gln286Ter) in the DDHD2 gene. The homozygous state was confirmed by direct sequencing in the proband and his 5-year-old brother. This variant was not reported as a pathogenic variant in the literature or genetic databases and was predicted to affect the function of the DDHD2 protein. CONCLUSION: The clinical symptoms in our cases were similar to the previously reported phenotype of SPG54. Our results deepen the molecular and clinical spectrum of SPG54 to facilitate future diagnoses.

Radiation-Induced Endothelial Ferroptosis Accelerates Atherosclerosis via the DDHD2-Mediated Nrf2/GPX4 Pathway.

This study sought to explore potential roles of endothelial ferroptosis in radiation-associated atherosclerosis (RAA) and molecular mechanisms behind this phenomenon. Here, an in vivo RAA mouse model was used and treated with ferroptosis inhibitors. We found that the RAA group had a higher plaque burden and a reduction in endothelial cells with increased lipid peroxidation compared to the control group, while ameliorated by liproxstatin-1. In vitro experiments further confirmed that radiation induced the occurrence of ferroptosis in human artery endothelial cells (HAECs). Then, proteomics analysis of HAECs identified domain-containing protein 2 (DDHD2) as a co-differentially expressed protein, which was enriched in the lipid metabolism pathway. In addition, the level of lipid peroxidation was elevated in DDHD2-knockdown HAECs. Mechanistically, a significant decrease in the protein and mRNA expression of glutathione peroxidase 4 (GPX4) was observed in HAECs following DDHD2 knockdown. Co-immunoprecipitation assays indicated a potential interaction between DDHD2 and nuclear factor erythroid 2-related factor 2 (Nrf2). The downregulation of Nrf2 protein was also detected in DDHD2-knockdown HAECs. In conclusion, our findings suggest that radiation-induced endothelial ferroptosis accelerates atherosclerosis, and DDHD2 is a potential regulatory protein in radiation-induced endothelial ferroptosis through the Nrf2/GPX4 pathway.

Identification and analyses of exonic and copy number variants in spastic paraplegia.

Hereditary spastic paraplegias are a diverse group of degenerative disorders that are clinically categorized as isolated; with involvement of lower limb spasticity, or symptomatic, where spastic paraplegia is complicated by further neurological features. We sought to identify the underlying genetic causes of these disorders in the participating patients. Three consanguineous families with multiple affected members were identified by visiting special schools in the Punjab Province. DNA was extracted from blood samples of the participants. Exome sequencing was performed for selected patients from the three families, and the data were filtered to identify rare homozygous variants. ExomeDepth was used for the delineation of the copy number variants. All patients had varying degrees of intellectual disabilities, poor speech development, spasticity, a wide-based gait or an inability to walk and hypertonia. In family RDHR07, a homozygous deletion involving multiple exons and introns of SPG11 (NC000015.9:g.44894055_449028del) was found and correlated with the phenotype of the patients who had spasticity and other complex movement disorders, but not those who exhibited ataxic or indeterminate symptoms as well. In families ANMD03 and RDFA06, a nonsense variant, c.985C > T;(p.Arg329Ter) in DDHD2 and a frameshift insertion‒deletion variant of AP4B1, c.965-967delACTinsC;p.(Tyr322SerfsTer14), were identified which were homozygous in the patients while the obligate carriers in the respective pedigrees were heterozygous. All variants were ultra-rare with none, or very few carriers identified in the public databases. The three loss of function variants are likely to cause nonsense-mediated decay of the respective transcripts. Our research adds to the genetic variability associated with the SPG11 and AP4B1 variants and emphasizes the genetic heterogeneity of hereditary spastic paraplegia.

Case report: Novel compound heterozygous missense mutations in the DDHD2 gene in a Chinese patient associated with spastic paraplegia type 54.

Background: Spastic paraplegia type 54 (SPG54) is a rare inherited autosomal recessive disorder, and a complex hereditary spastic paraplegia (HSP) caused by mutations in the phospholipase DDHD2 gene. SPG54 is characterized by early onset of spastic paraplegia, intellectual disability and dysplasia of corpus callosum. Case presentation: We report a 9 years and 5 months old Chinese girl with progressive spasm of the lower limbs, muscle weakness and intellectual disability. Brain magnetic resonance imaging (MRI) showed periventricular leukomalacia and thinning of the corpus callosum. According to the Wechsler Intelligence Scale, her IQ is 42. By whole exome sequencing, novel compound heterozygous missense mutations in the DDHD2 gene [c.168G>C, p.(Trp56Cys) and c.1505T>C, p.(Phe502Ser)] were identified in the proband. Comparative amino acid sequence alignment across different species revealed that Trp56 and Phe502 in the DDHD2 protein were highly conserved during evolution. And multiple in silico prediction tools suggested that both mutations were deleterious. Conclusions: Our study reports a very rare case of complicated HSP caused by two novel compound heterozygous mutations in the DDHD2 gene. Our findings expand the genetic spectrum of SPG54.

Coinheritance of novel mutations in NAGLU causing mucopolysaccharidosis type IIIB and in DDHD2 causing spastic paraplegia54 in a Turkish family.

Mucopolysaccharidosis type IIIB (MPSIIIB) is one of the lysosomal storage diseases, clinically related to developmental delay in the early phase and loss of skills in the late phases of the disease. The disease is caused by homozygous mutations in the NAGLU gene. Spastic paraplegia54 (SPG54) is a neurodegenerative disorder caused by homozygous mutations in the DDHD2 gene. Clinical features are progressive spasticity and weakness in the lower limbs and corpus callosum agenesis. We report on two siblings in a consanguineous family, presenting both the clinical and molecular diagnoses of MPSIIIB and SPG54 with novel mutations by using whole exome sequencing (WES). This interesting finding shows that we should be aware of the importance of using WES for diagnosing rare diseases in consanguineous families.

Enzymatic characterization of recombinant rat DDHD2: a soluble diacylglycerol lipase.

DDHD2 has been reported to exhibit phospholipase A1, triacylglycerol (TG) lipase and diacylglycerol (DG) lipase activities. However, the detailed enzymatic properties of DDHD2 have not yet been elucidated. In the current study, the substrate specificity of DDHD2 towards DG, TG and phosphatidic acid (PA) has been examined using highly purified recombinant rat DDHD2 (rDDHD2) with a liquid chromatography mass spectrometer. The k cat/Km value for DG (18:0/20:4) was much higher than those for TG (18:1/18:1/18:1), and PA (18:0/20:4) in the presence of sodium deoxycholate. The enzyme activity of rDDHD2 towards DG (18:0/20:4) was highest among all of the substrates tested. In addition, rDDHD2 was highly specific to DG substrates with a polyunsaturated fatty acid at their sn-2 position. The levels of 2-arachidonoylglycerol (2-AG) in CHO cells were quantified by gas chromatography-tandem mass spectrometry, showing that CHO cells expressing recombinant rDDHD2 contained higher levels of 2-AG when cells were treated with a monoacylglycerol lipase inhibitor, URB602. These results therefore support the idea that DDHD2 functions as a DG lipase in vivo and produces 2-AG.