An individual with a point mutation affecting the gene responsible for neurophysin synthesis is most likely to suffer from:

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11ec160b_3ca8_cf57_9249_4d64d8885c99_MD0001_00 Neurophysins are carrier proteins for oxytocin and vasopressin (antidiuretic hormone, ADH), hormones produced within the paraventricular and supraoptic nuclei, respectively, and released from the posterior pituitary. Like the hormones they accompany, neurophysins are produced within the neuronal cell bodies of hypothalamic nuclei. Neurophysins bind oxytocin and vasopressin and act as chaperone molecules as they are shuttled toward the nerve terminals in the posterior pituitary. Neurophysin II has a binding site specific for vasopressin and is thought to be involved in the transport and packaging of vasopressin through the endoplasmic reticulum (ER) and Golgi apparatus into neurosecretory granules. A point mutation in neurophysin II could result in abnormal protein folding and removal from the ER along with bound vasopressin, thereby decreasing availability of vasopressin for neurosecretory release. Such a mechanism may be responsible for some cases of autosomal dominant hereditary hypothalamic diabetes insipidus. (Choice A) Short stature may result from a growth hormone deficiency. Neither hypothalamic GHRH release nor anterior pituitary growth hormone secretion involves neurophysins. (Choice B) Generalized hyperpigmentation is a manifestation of Addison's disease, where a primary defect in adrenal cortisol production reduces feedback inhibition of anterior pituitary pro-opiomelanocortin (POMC) synthesis. As a result, POMC cleavage products, including ACTH and melanocyte-stimulating hormone (MSH), are secreted in excess. High MSH levels cause increased melanin synthesis by melanocytes. (Choice D) The synthesis and release of TRH and TSH do not involve neurophysins. TRH stimulates the release of both TSH and prolactin. Dopamine tonically inhibits prolactin release. (Choice E) Infertility can result from inadequate hypothalamic release of GnRH or decreased anterior pituitary production of FSH or LH. Educational Objective: Neurophysins are carrier proteins for oxytocin and vasopressin (ADH). Oxytocin and vasopressin are carried by unique neurophysins from their site of production in the cell bodies of the paraventricular and supraoptic nuclei to their site of release in the axon terminals of the posterior pituitary. Point mutations in neurophysin II underlie most cases of hereditary hypothalamic diabetes insipidus, a disorder resulting from insufficient ADH release into the systemic circulation.

An Individual with a Point Mutation Affecting the Gene Responsible