摘要:

The biology of the X chromosome is unique, as there are two Xs in females and only a single X in males, whereas the autosomes are present in duplicate in both sexes. The presence of only a single autosome, which can occur as a result of an error in meiotic segregation, is invariably an embryonic lethal event. Monosomy for the X chromosome is viable because of dosage compensation, a system found in all organisms with an X:Y form of sex determination, which brings about equality of expression of most X-linked genes in females and males. In mammals, the dosage compensation system involves silencing of most of the genes on one X chromosome; it is called X chromosome inactivation. In this review, we focus first on recent advances in our understanding of the molecular basis of the X inactivation mechanism. Then we consider an unusual feature of X inactivation, the mosaic nature of the female and subsequent exposure to somatic cell selection.

ISSN:1040-8703    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Because of the increasing population of childhood cancer survivors, there is a need to focus on the late effects of cancer therapy. After discharge by their pediatric oncologists, it is essential that patients are not lost to the health system but rather are under continued surveillance with access to the appropriate physicians. Endocrine and metabolic consequences may impact the life of the patient both soon after cancer treatment and for many years in the future. The purpose of this article is to explore the current literature in the following areas: growth hormone (GH) deficiency, gonadotropin-releasing hormone (GnRH) analogues with GH therapy in childhood, safety of GH replacement, cardiovascular risk factors, osteopenia, thyroid problems, and gonadal damage resulting in infertility.

ISSN:1040-8703    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Circadian rhythms are endogenously generated rhythms with a period length of about 24 hours. A biologic clock in the hypothalamic suprachiasmatic nuclei is responsible for the generation of circadian rhythms. Notable examples of the circadian rhythms include the sleep-wake cycle and rhythms in hormone production. Abnormalities of the circadian system include biologic clock lesions that result in arrhythmic behavior and irregular sleep patterns. Abnormalities of the circadian system also occur when there is desynchronization of clock phase with that of the outside world, resulting in conditions such as “jet-lag.” Numerous aspects of human physiology are greatly influenced by the time of day, as is the pathogenesis of illness. During development, the circadian system becomes functional at early stages and is regulated by photic information. With the continued elucidation of circadian system influences on human physiology and illness, it is anticipated that circadian biology will have an increasingly important impact on the clinical care of children.

ISSN:1040-8703    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Normal thyroid function is essential for development, growth, and metabolic homeostasis. The prerequisites for an euthyroid metabolic state include a normally developed thyroid gland, a properly functioning system for thyroid hormone synthesis, and sufficient iodine intake.Defects in any of the essential steps in thyroid development or thyroid hormone synthesis may result in morphologic abnormalities and impaired hormonogenesis. These defects can be partial or complete, leading to varying degrees of hypothyroidism. Morphologic alterations associated with congenital hypothyroidism include the absence of detectable thyroid tissue, ectopic tissue, thyroid hypoplasia, or a goitrous thyroid. However, in some patients with hypothyroidism, the thyroid is of normal size. This article focuses on defects in thyroid development. Recent insights into the developmental regulation of the calcitonin-producing C cells will not be discussed, and defects in hormone synthesis are discussed in an accompanying article[1].

ISSN:1040-8703    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Thyroid hormone synthesis requires a normally developed thyroid gland, a properly functioning hypothalamic-pituitary-thyroid axis, and sufficient iodine intake. This article focuses on genetic defects in this axis. Defects that are primarily of developmental origin are discussed in our associated article in this issue[1].Defects in hormone synthesis usually are associated with the development of a goiter, provided that the bioactivity and action of thyrotropin (TSH) are not impaired. In contrast, hypoplasia of the gland may be caused by developmental defects, bioinactive TSH, or resistance to TSH at the level of the receptor or its signaling pathway. At the other end of the spectrum, hyperthyroidism may result from gain of function mutations in genes regulating growth and function.

ISSN:1040-8703    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

An adolescent with hypophosphatemic rickets developed cardiac calcifications in the absence of hypercalcemia or elevation of the phosphocalcic product (the product of the total serum calcium and phosphorus concentrations). Cardiac calcifications led to aortic and mitral valve dysfunction, myocardial calcification, and arrhythmia. Hyperparathyroidism probably played a significant role in the development of this complication, which emphasizes the necessity for intermittent assessment of parathyroid status in individuals receiving medical therapy for hypophosphatemic rickets.

ISSN:1040-8703    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

The authors describe recent developments in three areas of pediatrics commonly encountered by the office practitioner. First, clinical assessment of jaundice remains critically important as “early discharge” of newborns continues. Practitioners constantly balance clinical realities with an evidence-based approach in the management and follow-up of neonatal hyperbilirubinemia. Second, given the frequent exposure of children to animals, a thorough understanding of animal bites, pet-borne infections, and rabies prophylaxis is essential for every pediatrician. Finally, immunization status remains one of our leading health indicators. Recent changes in the routine immunization schedule and a renewed emphasis on vaccine safety provide insight into the future direction of vaccinology.

ISSN:1040-8703    

出版商:OVID    

年代:2001

数据来源: OVID