Malformed Frogs: The Collapse of Aquatic Ecosystems

6. Human Malformations and Causes

six HUMAN MALFORMATIONS AND CAUSES The question that he frames in all but words Is what to make of a diminished thing? ROBERT FROST1 The fear that what was happening to frogs could happen to humans is the major reason why the malformed frog problem tipped in 1996. As with many ways of thinking about malformed frogs, the logic behind this concern is sound. Something in the water is causing frog malformations; developmental systems are conserved across vertebrates; therefore, if it’s happening to frogs it could happen to us. Given this, it becomes useful to review human malformations (congenital anomalies) in light of frog malformations. The rate of congenital anomalies in humans varies slightly from continent to continent and region to region, but globally it is remarkably constant , somewhere between 1.5 and 3.5% of live births.2 This rate increases with age up to about five years, when other problems (e.g., heart defects, deafness, epilepsy, growth deficiencies, and mental deficiencies) not apparent at birth get noticed. Serious problems in the development of the brain, internal organs, and glands often have no adverse effect on prenatal growth but can cause serious postnatal secondary growth deficiencies.2 TYPES OF HUMAN MALFORMATIONS This list of human congenital anomalies, along with their numeric codes, is known as the International Classifications of Diseases, 9th Revision, 179 Clinical Modification (ICD-9-CM Codes).3 This system is used by hospital staff to standardize the reporting of birth defects. XIV . Congenital Anomalies (ICD-9-CM Codes 740.0–759.9) 740 Anencephalus and similar anomalies 741 Spina bifida 742 Other congenital anomalies of the nervous system 743 Congenital anomalies of the eye(s) 744 Congenital anomalies of the ear(s), face, and neck 745 Bulbus cordis anomalies and anomalies of cardiac septal closure 746 Other congenital anomalies of heart 747 Other congenital anomalies of circulatory system 748 Congenital anomalies of respiratory system 749 Cleft palate 750 Other congenital anomalies of upper alimentary tract 752 Congenital anomalies of genital organs 753 Congenital anomalies of urinary system 754 Certain congenital musculoskeletal deformities 755 Other congenital anomalies of the limbs 756 Other congenital musculoskeletal anomalies 757 Congenital anomalies of the integument 758 Chromosomal anomalies 759 Other and unspecified congenital anomalies Each of the list’s whole number codes has subdivisions. For example, Code 755, Other congenital anomalies of limbs, is divided as follows: 755.0 Polydactyly 755.1 Syndactyly 755.2 Reduction deformities of the upper limb 755.3 Reduction deformities of the lower limb 755.4 Reduction deformities, unspecified limb 755.5 Other anomalies of upper limb, including the shoulder girdle 755.6 Other anomalies of lower limb, including the pelvic girdle 755.8 Other specified anomalies of an unspecified limb 755.9 Unspecified anomalies of an unspecified limb 180 human malformations and cause s The most common types of congenital anomalies are chromosomal abnormality syndromes (primarily ICD-9-CM code 758, but malformations encompassed in other codes can be produced by chromosomal abnormalities ).2 Chromosomal abnormality syndromes occur in about 5% of human pregnancies; many fetuses displaying chromosomal abnormalities are spontaneously aborted, and thus do not show up in statistics based on birth rates. Triploidy occurs where three (rather than the expected two) copies of each chromosome are present (frequency of occurrence 1:100, with the majority of embryos spontaneously aborted).4 Many chromosomal abnormalities consist of triplicate copies of particular chromosomes (humans normally have 23 pairs of chromosomes, each pair is labeled with a number ) including: Trisomy 21 (Down Syndrome; frequency of occurrence 1:630–750 live births),2 Trisomy 18 (Edwards syndrome or Trisomy E; frequency of occurrence 1:3,300–11,000 live births),2 Trisomy 13 (Patau Syndrome or Trisomy D; frequency of occurrence 1:5,000 live births),2 and Trisomy 8 (few reported cases).2 Both Trisomy 21 and Trisomy 18 can occur in population clusters, and can co-occur in affected populations . Trisomies 2, 14, 15, 16, and 22 result in spontaneous abortions. Additional chromosomal syndromes occur rarely and include 4p (WolfHirschhorn ) syndrome (frequency of occurrence 1:50,000 live births);2 5p (cri-du-chat or cry of the cat syndrome; frequency of occurrence 1:50,000 live births),2 13q (frequency of occurrence 1:12,000–22,000 live births),2 18p and 18q (frequency of occurrence 1:40,000 live births),2 and 21q (perhaps 1:4,000 live births).2 These...