A rare cause of nephrotic syndrome-sphingosine-1-phosphate lyase (SGPL1) deficiency: 6 cases and a review of the literature

[Research progress on monogenic inherited glomerular diseases with central nervous system symptoms]

To date, approximately 500 monogenic inherited kidney diseases have been reported, with more than 50 genes associated with the pathogenesis of monogenic isolated or syndromic nephrotic syndrome. Most of these genes are expressed in podocytes of the glomerulus. Neurological symptoms are common extrarenal manifestations of syndromic nephrotic syndrome, and various studies have found connections between podocytes and neurons in terms of morphology and function. This review summarizes the genetic and clinical characteristics of monogenic inherited diseases with concomitant glomerular and central nervous system lesions, aiming to enhance clinicians' understanding of such diseases, recognize the importance of genetic diagnostic techniques for comorbidity screening, and reduce the rates of missed diagnosis and misdiagnosis.

AAV-SPL 2.0, a Modified Adeno-Associated Virus Gene Therapy Agent for the Treatment of Sphingosine Phosphate Lyase Insufficiency Syndrome

Sphingosine-1-phosphate lyase insufficiency syndrome (SPLIS) is an inborn error of metabolism caused by inactivating mutations in SGPL1, the gene encoding sphingosine-1-phosphate lyase (SPL), an essential enzyme needed to degrade sphingolipids. SPLIS features include glomerulosclerosis, adrenal insufficiency, neurological defects, ichthyosis, and immune deficiency. Currently, there is no cure for SPLIS, and severely affected patients often die in the first years of life. We reported that adeno-associated virus (AAV) 9-mediated SGPL1 gene therapy (AAV-SPL) given to newborn Sgpl1 knockout mice that model SPLIS and die in the first few weeks of life prolonged their survival to 4.5 months and prevented or delayed the onset of SPLIS phenotypes. In this study, we tested the efficacy of a modified AAV-SPL, which we call AAV-SPL 2.0, in which the original cytomegalovirus (CMV) promoter driving the transgene is replaced with the synthetic "CAG" promoter used in several clinically approved gene therapy agents. AAV-SPL 2.0 infection of human embryonic kidney (HEK) cells led to 30% higher SPL expression and enzyme activity compared to AAV-SPL. Newborn Sgpl1 knockout mice receiving AAV-SPL 2.0 survived ≥ 5 months and showed normal neurodevelopment, 85% of normal weight gain over the first four months, and delayed onset of proteinuria. Over time, treated mice developed nephrosis and glomerulosclerosis, which likely resulted in their demise. Our overall findings show that AAV-SPL 2.0 performs equal to or better than AAV-SPL. However, improved kidney targeting may be necessary to achieve maximally optimized gene therapy as a potentially lifesaving SPLIS treatment.

Sphingosine phosphate lyase insufficiency syndrome: a systematic review

BACKGROUND

Sphingosine-1-phosphate lyase insufficiency syndrome (SPLIS) or nephrotic syndrome type-14 is caused by biallelic mutations in SGPL1. Here, we conducted a systematic review to delineate the characteristics of SPLIS patients.

METHODS

A literature search was performed in PubMed, Web of Science, and Scopus databases, and eligible studies were included. For all patients, demographic, clinical, laboratory, and molecular data were collected and analyzed.

RESULTS

Fifty-five SPLIS patients (54.9% male, 45.1% female) were identified in 19 articles. Parental consanguinity and positive family history were reported in 70.9% and 52.7% of patients, respectively. Most patients (54.9%) primarily manifested within the first year of life, nearly half of whom survived, while all patients with a prenatal diagnosis of SPLIS (27.5%) died at a median [interquartile (IQR)] age of 2 (1.4-5.3) months (P = 0.003). The most prevalent clinical feature was endocrinopathies, including primary adrenal insufficiency (PAI) (71.2%) and hypothyroidism (32.7%). Kidney disorders (42, 80.8%) were mainly in the form of steroid-resistant nephrotic syndrome (SRNS) and progressed to end-stage kidney disease (ESKD) in 19 (36.5%) patients at a median (IQR) age of 6 (1.4-42.6) months. Among 30 different mutations in SGPL1, the most common was c.665G > A (p.Arg222Gln) in 11 (20%) patients. Twenty-six (49.1%) patients with available outcome were deceased at a median (IQR) age of 5 (1.5-30.5) months, mostly following ESKD (23%) or sepsis/septic shock (23%).

CONCLUSION

In patients with PAI and/or SRNS, SGPL1 should be added to diagnostic genetic panels, which can provide an earlier diagnosis of SPLIS and prevention of ESKD and other life-threatening complications.

Advancements on the Multifaceted Roles of Sphingolipids in Hematological Malignancies

Dysregulation of sphingolipid metabolism plays a complex role in hematological malignancies, beginning with the first historical link between sphingolipids and apoptosis discovered in HL-60 leukemic cells. Numerous manuscripts have reviewed the field including the early discoveries that jumpstarted the studies. Many studies discussed here support a role for sphingolipids, such as ceramide, in combinatorial therapeutic regimens to enhance anti-leukemic effects and reduce resistance to standard therapies. Additionally, inhibitors of specific nodes of the sphingolipid pathway, such as sphingosine kinase inhibitors, significantly reduce leukemic cell survival in various types of leukemias. Acid ceramidase inhibitors have also shown promising results in acute myeloid leukemia. As the field moves rapidly, here we aim to expand the body of literature discussed in previously published reviews by focusing on advances reported in the latter part of the last decade.