A classification of genes involved in normal and delayed male puberty

Case Report: Multiple prolactinomas in a young man with Kallmann syndrome and familial hypocalciuric hypercalcemia

Introduction

The occurrence of prolactinomas in sex hormone treated patients with central hypogonadism is extremely rare.

Case presentation

We present a Caucasian male patient who was diagnosed with Kallmann syndrome (KS) at age 15 years. Testosterone treatment was started. At age 26 the patient presented with mild headache. MRI revealed two separate pituitary adenomas along with the absence of the olfactory bulbs. Given the presence of marked hyperprolactinemia (17x upper limit of the reference range) the diagnosis prolactinoma was made and treatment with cabergoline was started which resulted in a complete biochemical response and in marked reduction of both adenomas in size. Hypogonadism persisted and testosterone replacement therapy was continued. Genetic testing of genes associated with pituitary tumors, Kallmann syndrome and idiopathic hypogonadotropic hypogonadism was negative. Mild concomitant hypercalcemia in accordance with familial hypocalciuric hypercalcemia (FHH) prompted mutation analysis of the calcium receptor (CASR) gene which yielded a pathogenic inactivating variant.

Discussion/conclusion

The presence of two separate prolactinomas in a patient with KS has not yet been reported in the literature. The effect of sex hormone treatment of KS patients on the possible development of prolactinoma is unknown at present. The occurance of multiple prolactinomas in our patient suggests increased susceptibility. Although CaSR is expressed in GnRH neurons in mouse brain and CaSR deficient mice have a reduced hypothalamic GnRH neuronal population, the relevance of the CASR gene variant in our patient for the KS phenotype is unclear at present.

Genetic analysis of failed male puberty using whole exome sequencing

OBJECTIVES

Although at least 598 genes are involved in the development of the hypothalamo-pituitary-testicular (HPT) axis, mutations in only 75 genes have so far been shown to cause delayed puberty.

METHODS

Six male patients with failed puberty, manifested as absence of pubertal changes by 18 years of age, underwent whole exome sequencing of genomic DNA with subsequent bioinformatics analysis and confirmation of selected variants by Sanger sequencing. Genes having plausibly pathogenic non-synonymous variants were characterized as group A (previously reported to cause delayed puberty), group B (expressed in the HPT-axis but no mutations therein were reported to cause delayed puberty) or group C (not reported previously to be connected with HPT-axis).

RESULTS

We identified variants in genes involved in GnRH neuron differentiation (2 in group A, 1 in group C), GnRH neuron migration (2 each in groups A and C), development of GnRH neural connections with supra-hypothalamic and hypothalamic neurons (2 each in groups A and C), neuron homeostasis (1 in group C), molecules regulating GnRH neuron activity (2 each in groups B and C), receptors/proteins expressed on GnRH neurons (1 in group B), signaling molecules (3 in group C), GnRH synthesis (1 in group B), gonadotropins production and release (1 each in groups A, B, and C) and action of the steroid hormone (1 in group A).

CONCLUSIONS

Non-synonymous variants were identified in 16 genes of the HPT-axis, which comprised 4 in group A that contains genes previously reported to cause delayed puberty, 4 in group B that are expressed along HPT-axis but no mutations therein were reported previously to cause delayed puberty and 8 in group C that contains novel candidate genes, suggesting wider genetic causes of failed male puberty.