Transcription factor 7-like 1 is involved in hypothalamo-pituitary axis development in mice and humans.

Aberrant embryonic development of the hypothalamus and/or pituitary gland in humans results in congenital hypopituitarism (CH). Transcription factor 7-like 1 (TCF7L1), an important regulator of the WNT/ß-catenin signaling pathway, is expressed in the developing forebrain and pituitary gland, but its role during hypothalamo-pituitary (HP) axis formation or involvement in human CH remains elusive. Using a conditional genetic approach in the mouse, we first demonstrate that TCF7L1 is required in the prospective hypothalamus to maintain normal expression of the hypothalamic signals involved in the induction and subsequent expansion of Rathke's pouch progenitors. Next, we reveal that the function of TCF7L1 during HP axis development depends exclusively on the repressing activity of TCF7L1 and does not require its interaction with ß-catenin. Finally, we report the identification of two independent missense variants in human TCF7L1, p.R92P and p.R400Q, in a cohort of patients with forebrain and/or pituitary defects. We demonstrate that these variants exhibit reduced repressing activity in vitro and in vivo relative to wild-type TCF7L1. Together, our data provide support for a conserved molecular function of TCF7L1 as a transcriptional repressor during HP axis development in mammals and identify variants in this transcription factor that are likely to contribute to the etiology of CH.

Diagnosis and evaluation of hypogonadism.

Hypogonadism is defined as defects in gonadal response to gonadotropins or sex hormone biosynthesis. Clinical evaluation and diagnosis of patients is challenging, particularly before puberty. Basal determinations of the gonadotropins luteinizing hormone, follicle-stimulating hormone, the gonadal sex steroids testosterone and/or estrogen and markers of gonadal function including inhibin B and anti-Müllerian hormone are useful, but only at specific ages, thus necessitating combined hormonal tests with meticulous physical examination. GnRH testing can be useful, and may be used in combination with hCG testing to discriminate between isolated hypogonadotropic hypogonadism and constitutional delay of growth and puberty. Urine steroid profiles may be helpful in the diagnosis of androgen biosynthetic defects. Also increasingly important is genotypic screening for genetic or chromosomal abnormalities, together with detailed family and medical histories including antecedent substance abuse, chronic disease, and exposure to chemotherapy or radiotherapy. This chapter explores the diagnosis and evaluation of patients with hypogonadism and reviews the genetic/chromosomal factors involved in the condition.

Pituitary gland development: an update.

The embryonic development of the pituitary gland involves a complex and highly spatio-temporally regulated network of integrating signalling molecules and transcription factors. Genetic mutations in any of these factors can lead to congenital hypopituitarism in association with a wide spectrum of craniofacial/midline defects ranging from incompatibility with life to holoprosencephaly (HPE) and cleft palate and septo-optic dysplasia (SOD). Increasing evidence supports a genotypic overlap with hypogonadotrophic hypogonadal disorders such as Kallmann syndrome, which is consistent with the known overlap in phenotypes between these disorders. This chapter reviews the cascade of events leading up to the successful development of the pituitary gland and to highlight key areas where genetic variations can occur thus leading to congenital hypopituitarism and associated defects.