Molecular analysis of LPIN1 in Jordanian patients with rhabdomyolysis

Systemic corticosteroids for the treatment of acute episodes of rhabdomyolysis in lipin-1-deficient patients

Mutations in the LPIN1 gene constitute a major cause of severe rhabdomyolysis (RM). The TLR9 activation prompted us to treat patients with corticosteroids in acute conditions. In patients with LPIN1 mutations, RM and at-risk situations that can trigger RM have been treated in a uniform manner. Since 2015, these patients have also received intravenous corticosteroids. We retrospectively compared data on hospital stays by corticosteroid-treated patients vs. patients not treated with corticosteroids. Nineteen patients were hospitalized. The median number of admissions per patient was 21 overall and did not differ when comparing the 10 corticosteroid-treated patients with the 9 patients not treated with corticosteroids. Four patients in the non-corticosteroid group died during a RM (mean age at death: 5.6 years). There were no deaths in the corticosteroid group. The two groups did not differ significantly in the number of RM episodes. However, for the six patients who had RM and occasionally been treated with corticosteroids, the median number of RM episodes was significantly lower when intravenous steroids had been administered. The peak plasma creatine kinase level and the area under the curve were or tended to be higher in patients treated with corticosteroids-even after the exclusion of deceased patients or focusing on the period after 2015. The median length of stay (10 days overall) was significantly longer for corticosteroid-treated patients but was similar after the exclusion of deceased patients. The absence of deaths and the higher severity of RM observed among corticosteroid-treated patients could suggest that corticotherapy is associated with greater survival.

LPIN1 rhabdomyolysis: A single site cohort description and treatment recommendations

Individuals with LPIN1 deficiency have early recurrent, life-threatening rhabdomyolysis but the full phenotypic spectrum and optimal treatment of the disorder remains unknown. Here we report the clinical details and treatment outcomes of 6 patients from our health system. The average age of presentation in our cohort was 23.8 months ±11.6 months (range 15–46 months). The average number of days for each hospitalization for this cohort is 11.7±13.2 days. Creatinine kinase (CK) levels peak during our care averaged 607,725 units/L (range 157,000-1,100,000 units/L). We observed that aspartate aminotransferase levels paralleled the CK levels in its elevation and resolution (Pearson's correlation R = 0.995); while alanine aminotransferase paralleled the elevation but lagged in the resolution of CK levels (R = 0.728). Unlike historical accounts, in our patient population, rhabdomyolysis was sometimes seen without inciting viral or traumatic events. We also cared for multiple individuals that had received treatment at other centers. This allowed us to compare multiple practice approaches and led to a standardized Care Recommendations.

Acute recurrent rhabdomyolysis in a Chinese boy associated with a novel compound heterozygous LPIN1 variant: a case report

Background

LPIN1-related acute recurrent rhabdomyolysis (RM), first reported in 2008, is an autosomal recessive inherited metabolic disease. In recent years, LPIN1 gene variants have been identified as one of the main causes of severe RM in children in Western countries. The disease is extremely rare in China, and we report a case of acute recurrent RM caused by a novel compound heterozygous LPIN1 variant.

Case presentation

A 15-year-old Chinese boy presented with myalgia after strenuous exercise, accompanied by transient increases in serum creatine kinase and myoglobin and persistent hyperuricaemia and hyperbilirubinaemia. Genetic analysis using high-throughput genomic sequencing and Sanger sequencing revealed that there was a compound heterozygous variant in the LPIN1 gene of the proband: the paternal c.2047A > G(p.I683V) was an unreported missense variant, and the maternal c.2107_2108 insAGG(p.Q703delin sQE) was an unreported in-frame variant.

Conclusions

In children with RM, LPIN1 variants should always be considered in the differential diagnosis. The clinical features of our case are atypical, which highlights the importance of an accurate diagnosis by genetic testing. If detected early, the condition may be controlled, and the prognosis may be improved.

Lipin 1 deficiency causes adult-onset myasthenia with motor neuron dysfunction in humans and neuromuscular junction defects in zebrafish

Lipin 1 is an intracellular protein acting as a phosphatidic acid phosphohydrolase enzyme controlling lipid metabolism. Human recessive mutations in LPIN1 cause recurrent, early-onset myoglobinuria, a condition normally associated with muscle pain and weakness. Whether and how lipin 1 deficiency in humans leads to peripheral neuropathy is yet unclear. Herein, two novel compound heterozygous mutations in LPIN1 with neurological disorders, but no myoglobinuria were identified in an adult-onset syndromic myasthenia family. The present study sought to explore the pathogenic mechanism of LPIN1 in muscular and neural development.

Methods: The clinical diagnosis of the proband was compared to the known 48 cases of LPIN1 recessive homozygous mutations. Whole-exome sequencing was carried out on the syndromic myasthenia family to identify the causative gene. The pathogenesis of lipin 1 deficiency during somitogenesis and neurogenesis was investigated using the zebrafish model. Whole-mount in situ hybridization, immunohistochemistry, birefringence analysis, touch-evoke escape response and locomotion assays were performed to observe in vivo the changes in muscles and neurons. The conservatism of the molecular pathways regulated by lipin 1 was evaluated in human primary glioblastoma and mouse myoblast cells by siRNA knockdown, drug treatment, qRT-PCR and Western blotting analysis.

Results: The patient exhibited adult-onset myasthenia accompanied by muscle fiber atrophy and nerve demyelination without myoglobinuria. Two novel heterozygous mutations, c.2047A>C (p.I683L) and c.2201G>A (p.R734Q) in LPIN1, were identified in the family and predicted to alter the tertiary structure of LPIN1 protein. Lipin 1 deficiency in zebrafish embryos generated by lpin1 morpholino knockdown or human LPIN1 mutant mRNA injections reproduced the myotomes defects, a reduction both in primary motor neurons and secondary motor neurons projections, morphological changes of post-synaptic clusters of acetylcholine receptors, and myelination defects, which led to reduced touch-evoked response and abnormalities of swimming behaviors. Loss of lipin 1 function in zebrafish and mammalian cells also exhibited altered expression levels of muscle and neuron markers, as well as abnormally enhanced Notch signaling, which was partially rescued by the specific Notch pathway inhibitor DAPT.

Conclusions: These findings pointed out that the compound heterozygous mutations in human LPIN1 caused adult-onset syndromic myasthenia with peripheral neuropathy. Moreover, zebrafish could be used to model the neuromuscular phenotypes due to the lipin 1 deficiency, where a novel pathological role of over-activated Notch signaling was discovered and further confirmed in mammalian cell lines.

Lipin-1 Deficiency-Associated Recurrent Rhabdomyolysis and Exercise-Induced Myalgia Persisting into Adulthood: A Case Report and Review of Literature

Phosphatidate phosphatase-1 (lipin-1) is encoded by LPIN1 gene. Lipin-1 deficiency has been reported as the second most common cause of early-onset rhabdomyolysis after primary fatty acid oxidation disorders. We report a case of a 32-year-old Sri Lankan female with a history of more than 10 episodes of rhabdomyolysis and exercise intolerance since childhood. These episodes were triggered by infections and exercise. A temporal relationship between the acute episodes and use of drugs such as theophylline, mefenamic acid, co-trimoxazole, and combined oral contraceptive pills was also noted. There was marked elevation of serum creatine kinase and transaminases during acute episodes. Family history revealed parental consanguinity and an affected sibling who died of an acute episode associated with muscle weakness, dark coloured urine, and cyanosis, at the age of 2 years. The histochemical findings of the patient under discussion were consistent with a metabolic myopathy affecting membrane integrity. A homozygous, likely pathogenic variant c.1684G>T encoding p.(Glu562∗) was identified by clinical exome sequencing. Even though the studies to date give no convincing evidence of a possible causal or contributory relationship between the drugs under discussion and lipin-1 related rhabdomyolysis, this case highlights the importance of pharmacovigilance and reporting adverse drug reactions in patients with lipin-1 deficiency.

A rare case of pediatric recurrent rhabdomyolysis with compound heterogenous variants in the LPIN1

Background

Lipin-1, encoded by LPIN1 gene, serves as an enzyme and a transcriptional co-regulator to regulate lipid metabolism and mitochondrial respiratory chain. Autosomal recessive mutations in LPIN1 were recognized as one of the most common causes of pediatric recurrent rhabdomyolysis in western countries. However, to date, there were only a few cases reported in Asian group. This study aims to report the first pediatric case of recurrent rhabdomyolysis with a novel LPIN1 mutation in China mainland in order to raise the awareness of both pediatricians and patients.

Case presentations

Here we report a Chinese pediatric case of recurrent rhabdomyolysis with compound heterozygous variants (p.Arg388* and p.Arg810Cys) in the LPIN1 gene. The c.2428C > T was a novel missense variant involved Arg-to-Cys substitution at position 810 (p.Arg810Cys), located in the highly conserved region which predicted to be damaging by multiple algorithms. The patient manifested as cola-colored urine, muscle weakness and tenderness, as well as acute kidney injury with peak blood creatine kinase level 109,570 U/l in 19-month old. In his second episode of 9 years old, the symtoms were relatively milder with peak creatine kinase level 50,948 U/l. He enjoyed quite normal life between the bouts but slightly elevation of serum creatine kinase level during the fever or long-term exercises. Prolonged weight training combined with calorie deprivation were speculated to be the triggers of his illness. Prompt symptomatic therapy including fluid therapy and nutritional support was given and the patient recovered soon.

Conclusions

LPIN1-related rhabdomyolysis is still quite new to physicians due to its seemly low-incidence especially in Asian countries. In the future, more active genetic test strategy and detailed prophylactic care education should be taken in patients with severe recurrent rhabdomyolysis, who are the high risk group of LPIN1 genetic defects.

Crystal structure of a lipin/Pah phosphatidic acid phosphatase

Lipin/Pah phosphatidic acid phosphatases (PAPs) generate diacylglycerol to regulate triglyceride synthesis and cellular signaling. Inactivating mutations cause rhabdomyolysis, autoinflammatory disease, and aberrant fat storage. Disease-mutations cluster within the conserved N-Lip and C-Lip regions that are separated by 500-residues in humans. To understand how the N-Lip and C-Lip combine for PAP function, we determined crystal structures of Tetrahymena thermophila Pah2 (Tt Pah2) that directly fuses the N-Lip and C-Lip. Tt Pah2 adopts a two-domain architecture where the N-Lip combines with part of the C-Lip to form an immunoglobulin-like domain and the remaining C-Lip forms a HAD-like catalytic domain. An N-Lip C-Lip fusion of mouse lipin-2 is catalytically active, which suggests mammalian lipins function with the same domain architecture as Tt Pah2. HDX-MS identifies an N-terminal amphipathic helix essential for membrane association. Disease-mutations disrupt catalysis or destabilize the protein fold. This illustrates mechanisms for lipin/Pah PAP function, membrane association, and lipin-related pathologies.

Lipin/Pah phosphatidic acid phosphatases generate diacylglycerol to regulate triglyceride synthesis and cellular signaling. Here authors determine structures of Tetrahymena thermophila Pah2 and identify an N-terminal amphipathic helix essential for membrane association.

A rare case of adult onset LPIN1 associated rhabdomyolysis

Pathogenic variants in LPIN1 are a recognised cause of severe and often fatal rhabdomyolysis in childhood. We present a rare case of adult onset recurrent rhabdomyolysis due to compound heterozygous variants in LPIN1. Despite first presenting with rhabdomyolysis in his twenties and having undergone extensive investigations, the patient did not receive a diagnosis until he was 46 years of age. DNA sequencing revealed a pathogenic deletion involving exon 18 of LPIN1 in conjunction with a c.2410G>A missense variant in exon 19. Whilst LPIN1 variants are a noteworthy cause of severe recurrent rhabdomyolysis in childhood, this is the first detailed description and only the second reported case of adult onset rhabdomyolysis. Variants in LPIN1 should be considered as a cause of recurrent severe rhabdomyolysis in adults when other more common causes have been excluded.

Loss of lipin 1-mediated phosphatidic acid phosphohydrolase activity in muscle leads to skeletal myopathy in mice

Lipin 1 regulates glycerolipid homeostasis by acting as a phosphatidic acid phosphohydrolase (PAP) enzyme in the triglyceride-synthesis pathway and by regulating transcription factor activity. Mutations in human lipin 1 are a common cause of recurrent rhabdomyolysis in children. Mice with constitutive whole-body lipin 1 deficiency have been used to examine mechanisms connecting lipin 1 deficiency to myocyte injury. However, that mouse model is confounded by lipodystrophy not phenocopied in people. Herein, 2 muscle-specific mouse models were studied: 1) Lpin1 exon 3 and 4 deletion, resulting in a hypomorphic protein without PAP activity, but which preserved transcriptional coregulatory function; and 2) Lpin1 exon 7 deletion, resulting in total protein loss. In both models, skeletal muscles exhibited a chronic myopathy with ongoing muscle fiber necrosis and regeneration and accumulation of phosphatidic acid and, paradoxically, diacylglycerol. Additionally, lipin 1-deficient mice had abundant, but abnormal, mitochondria likely because of impaired autophagy. Finally, these mice exhibited increased plasma creatine kinase following exhaustive exercise when unfed. These data suggest that mice lacking lipin 1-mediated PAP activity in skeletal muscle may serve as a model for determining the mechanisms by which lipin 1 deficiency leads to myocyte injury and for testing potential therapeutic approaches.-Schweitzer, G. G., Collier, S. L., Chen, Z., McCommis, K. S., Pittman, S. K., Yoshino, J., Matkovich, S. J., Hsu, F.-F., Chrast, R., Eaton, J. M., Harris, T. E., Weihl, C. C., Finck, B. N. Loss of lipin 1-mediated phosphatidic acid phosphohydrolase activity in muscle leads to skeletal myopathy in mice.

Lipin proteins and glycerolipid metabolism: Roles at the ER membrane and beyond

The regulation of glycerolipid biosynthesis is critical for homeostasis of cellular lipid stores and membranes. Here we review the role of lipin phosphatidic acid phosphatase enzymes in glycerolipid synthesis. Lipin proteins are unique among glycerolipid biosynthetic enzymes in their ability to transit among cellular membranes, rather than remain membrane tethered. We focus on the mechanisms that underlie lipin protein interactions with membranes and the versatile roles of lipins in several organelles, including the endoplasmic reticulum, mitochondria, endolysosomes, lipid droplets, and nucleus. We also review the corresponding physiological roles of lipins, which have been uncovered by the study of genetic lipin deficiencies. We propose that the growing body of knowledge concerning the biochemical and cellular activities of lipin proteins will be valuable for understanding the physiological functions of lipin proteins in health and disease. This article is part of a Special Issue entitled: Membrane Lipid Therapy: Drugs Targeting Biomembranes edited by Pablo V. Escribá.