Sphingosine 1- Phosphate Lyase Insufficiency Syndrome (SPLIS); A Role in Multiple Endocrinopathies

Abstract

Sphingosine 1-phosphate lyase insufficiency syndrome (SPLIS) was described in 2017 as a novel condition affecting sphingolipid metabolism. There is a multisystemic phenotype including nephrotic syndrome and primary adrenal insufficiency (PAI) and to a lesser extent ichthyosis, neurological disease and lymphopenia. A proportion of patients also presented with hypothyroidism and hypogonadism. To interrogate the endocrine aspect of the syndrome we reviewed clinical data within our patient cohort with SPLIS and those within the wider literature. To date there have been 45 patients identified with SPLIS with significant associated mortality (n=23/45, 51%; 4 of these in utero). There is no clear genotype-phenotype correlation. Whilst nephrotic syndrome is most prevalent (n=34/45; 76%), a significant proportion of patients (n=27/45, 60%) also presented with glucocorticoid deficiency, some with additional mineralocorticoid deficiency (n=7/27). Five further patients were noted to have adrenal calcifications though biochemistry was not undertaken. Most patients presented with PAI in the first 2 years of life (n=21/27), with the oldest presentation being 11 years of age. Adrenal calcifications are a common finding in those who had documented imaging (n=13/15, 87%). Primary gonadal failure has been reported in 8 male cases, all with concomitant PAI. Presenting features included microphallus (n=7/8) and cryptorchidism (n=8/8), indicating reduced in utero androgen exposure. All who had biochemical evaluation demonstrated raised basal LH and FSH/ exaggerated response to LHRH stimulation, a lack of testosterone response to HCG stimulation and low antimullerian hormone (AMH) levels. To date there are no reports of pubertal delay in female patients, and those of age within our cohort have normal ovarian reserve as evidenced by AMH levels (n=2). Primary hypothyroidism, with mildly raised TSH and low Free T4 is reported in 12 patients. Most did not have goiters and had concomitant PAI and nephrotic syndrome (n=11/12). SPLIS is unique amongst sphingolipid disorders in presenting with significant endocrinopathy. This may be the consequence of the particular sphingolipid signature of the disease and the pathogenic mechanisms need to be explored further. It is clear that endocrine dysfunction needs to be considered at diagnosis and surveillance undertaken to detect evolving disease which could have a significant impact on morbidity and mortality.