7640 The first description of an MC4R variant in a patient with Kallmann syndrome and obesity

Abstract Disclosure: A.A. Aslam: None. S. Lim: None. R. Willemsen: None. K. Koysombat: None. M. Young: None. W.S. Dhillo: None. A. Abbara: None. S. Howard: None. E.F. Gevers: None. Introduction: Pathogenic MC4R gene variants result in hyperphagia and early onset obesity but puberty is not usually affected. We describe an MC4R variant in a patient with Kallmann syndrome and obesity. A 16 year old male with repaired Tetralogy of Fallot, anosmia, autism and anxiety, was referred with obesity and delayed puberty. His birth weight was 3360 g (-0.26 SDS). Height was -1.31 SDS, BMI 30.7 kg/m2. He had high arched palate, normal skin and hair colour, mild hypertelorism and upward slanting palpebral fissures. Pubertal staging was A2P1G1 5ml testes bilaterally. Results: LHRH test showed borderline low peaks (LH 5.0 U/L, FSH 2.6 U/L) and inhibin B 108 pg/mL (25-325 pg/mL). MRI brain showed hypoplastic olfactory bulbs, absent olfactory sulci and normal pituitary anatomy. CGH microarray, karyotype and the UK hypogonadism gene panel were normal. He underwent whole genome sequencing in the Genetic Factors Affecting the Timing of Puberty Study; no abnormalities in 52 known genes associated with GnRH deficiency were found but a previously described heterozygous variant was detected, MC4R c.542G>A, p.Gly181Asp, classified pathogenic and absent in control databases. Management: He was commenced on Testosterone but showed progression of testicular size to 10 mL and testosterone was stopped but required restarting. Repeat investigations off treatment, aged 22 years (height 178 cm, BMI 42 kg/m2, testes 15 mL): inhibin B 66 pg/mL, testosterone 2 nmol/L, baseline LH 2.4 U/L, stimulated peak 24.9 U/L, baseline FSH 1.2 U/L, stimulated peak 4.2 U/L. Cortisol and IGF1 were in the normal range. He also developed autoimmune hypothyroidism with raised TPO antibodies (TSH 24.7 mU/L, FT4 5.6 pmol/L). Discussion: Previous in vitro work has shown complete loss of function of MC4R p.Gly181Asp due to reduced cell surface expression and reduced binding to a-MSH. Heterozygous p.Gly181Asp variants have been described in several children/adults with obesity; but hypogonadism in heterozygous carriers has not. Homozygous MC4R p.Gly181Asp was found in a male with obesity and partial HH thought to be due to abnormal GnRH production but with normal olfactory bulbs. We are the first to describe a heterozygous MC4R p.Gly181Asp variant in a patient with partial hypogonadism and anosmia with hypoplastic bulbs in addition to obesity. Interaction between POMC-MC-leptin circuits and Kisspeptin-GnRH circuits is recognised although not completely understood. Previous work has shown that a subset of kisspeptin neurons express MC4R and that KNDy neurones receive synaptic input from POMC neurons. In addition, inhibition of MC4R/MC3R results in delayed onset of puberty in rats. Our results support a role for MC4R in GnRH secretion and potentially olfactory /GnRH neuronal migration. Assessment of spontaneous gonadotrophin production and response of gonadotrophin production to kisspeptin stimulation is currently in progress. Presentation: 6/1/2024