Purpose or Case Report: Introduction:
Smith-Lemli-Opitz syndrome (SLOS) is a rare autosomal recessive metabolic disorder caused by deficiency of 7-dehydrocholesterol reductase, leading to impaired cholesterol biosynthesis (Kelley & Hennekam, 2000). It has associations with multiple congenital anomalies, including craniofacial, cardiac, and genitourinary malformations. Renal abnormalities, including renal agenesis, affect around 25% of individuals with SLOS (Nowaczyk, 2020), yet little literature is available on how this manifests clinically.

Case:
We report a 6-month-old infant with a background of known SLOS admitted with vomiting, fever, and persistent electrolyte derangements despite IV fluids. Initial ultrasound of the urinary tract demonstrated increased echogenicity and moderate pelvicalyceal dilatation of the right kidney with mild ureteric dilatation. The left kidney was not visualised in the renal fossa, and a small elongated echogenic structure adjacent to the spleen was suggestive of an atrophic kidney. Follow-up ultrasound at 7 months confirmed absence of the left kidney, with compensatory hypertrophy of the right kidney and mild hydronephrosis. Serial chest radiographs revealed concurrent cardiomegaly and recurrent respiratory infections. The case was discussed in a multidisciplinary setting, and urology input confirmed the diagnosis of unilateral renal agenesis in the context of SLOS.

Discussion:
While renal anomalies such as hypoplasia, duplication, and vesicoureteric reflux have been reported in SLOS (Nowaczyk & Irons, 2012), more data is needed to explore how this may clinically present. This case highlights the importance of systematic renal evaluation in children with SLOS, particularly when presenting with acute kidney injury or electrolyte imbalance (Porter, 2008) as a result of unilateral or bilateral kidney agenesis. This report builds the case for early urological screening of all children with SLOS, allowing for early detection and longitudinal monitoring, which is essential for guiding management, anticipating complications, and counselling families.

References:
Kelley RI, Hennekam RC. Smith-Lemli-Opitz syndrome. J Med Genet. 2000;37(5):321–335.
Nowaczyk MJ, Wassif CA. Smith-Lemli-Opitz Syndrome. In: Adam MP, Feldman J, Mirzaa GM, et al., eds. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1998
Nowaczyk MJ, Irons MB. Smith-Lemli-Opitz syndrome: phenotype, natural history, and epidemiology. Am J Med Genet C Semin Med Genet. 2012
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