ESPE Abstracts

Background: Congenital leptin deficiency (CLD) is an extremely rare condition due to homozygous pathogenic mutations in the leptin (LEP) gene. The clinical manifestation of patients with CLD is severe early-onset obesity and hyperphagia. Most patients with pathogenic homozygous leptin gene mutations have low or undetectable leptin levels, whereas few cases show high bio-inactive circulating leptin levels. To date, around 20 variants in the LEP gene have been described in the literature.

Objective: To identify genetic causes implicated in the development of severe early-onset obesity using Next-Generation Sequencing (NGS)

Method: Whole exome sequencing (WGS) was performed in two severely obese patients and their parents using Illumina HiSeq 2000 sequencer and reads were aligned to hg19 human genome reference. Sanger sequencing was used for confirmation of the variant identified in WGS.

Case 1: A seven-year-old girl born by normal delivery with birth weight of 3.4 Kg, who started to gain weight from the age of five months. She presented with severe childhood obesity, 78 kg, BMI of 48 Kg/m² at the age of five years. The patient had extreme hyperphagia, obstructive sleep apnea, and fatty liver disease.

Case 2: A nine-year-old girl with birth weight of 3 Kg, who started to gain weight around one year of age. At the time of diagnosis her weight was 98 Kg with BMI of 44.2 Kg/m² at the age of seven years. The patient like her sibling had morbid obesity, hyperphagia and fatty liver disease.

Results: A novel homozygous variant in the LEP gene splice region was found in these two siblings, c.-29+1G>A. The variant was inherited from clinically healthy parents who were heterozygous for the variant. This rare variant was not found in public databases. In-silico analysis predicted the pathogenicity of the variant due to intron retention in the LEP gene. Serum leptin measured by ELISA were undetectable.

Conclusions: A novel homozygous splice site mutation was identified in two severely obese sisters. Undetectable serum leptin levels indicate a complete loss of function of the gene. This genotype is highly likely to explain the phenotype of our patients. The pathogenicity of splice site variants should not be underestimated in routine genetic sequence analysis. Early detection of LEP gene mutations could help patients benefit from leptin replacement therapy, hence patients with childhood obesity should undergo genetic testing. Further functional studies of the variant are underway to elucidate the mechanism by which this variant causes early onset obesity.