Recognizable patterns of human malformation : genetic, embryologic, and clinical aspects / by David W. Smith.

  • Smith, David W., 1926-1981.
Date:
1970
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Recognizable patterns of human malformation : genetic, embryologic, and clinical aspects / by David W. Smith. Source: Wellcome Collection.

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    Chapter One 5 a variety of teratogenic agents in animals^ and has occurred in sheep as a consequence of the pregnant ewe ingesting the plant Veratrum cali- fornicum between the fifth and fifteenth days of gestation.^ There is no known environmental teratogen associated with this defect in man. The anomaly has been a frequent feature of the 13 trisomy syndrome and an occasional feature of the short arm 18 deletion syndrome; for most other cases the etiology has not been determined. The prognosis for central nervous system function in individuals with this type of defect is very poor, and the author recommends limita¬ tion of medical assistance toward survival in such patients. 5. Sirenomelia (Mermaid), Caudal Regression Anomaly —Primary Defect in Mid-posterior Axis Mesoderm^^ (see Fig. 8) The most severe form of this defect, sireno¬ melia or sympodia, is presumably the conse¬ quence of a wedge-shaped early deficit of the posterior axis mesoderm, allowing for fusion of the early limb buds at their fibular margins with absence or incomplete development of the inter¬ vening caudal structures. The embryonic defect apparently dates back to the primitive streak stage during the third week, prior to develop¬ ment of the allantois, for there is usually an absence of allantoic vessels. The single umbilical artery arises directly from the aorta, rather than the usual two umbilical arteries arising from the hypogastric vessels. This defect, occurring in about one in 60,000 newborns, has a 2.7 : 1 male sex preponderance. All degrees of severity are observed, presumably dependent on the relative length and width of the early caudal deficit. The variable consequences are often called the caudal regression syndrome.'- Conceivably, imperforate anus might represent a minor degree of this type of defect. It is important to appreciate that the fol¬ lowing defects of the caudal axis may be present in an individual with imperforate anus: lower vertebral defects, 40 per cent; urological defects other than fistulas, 19 per cent; genital anom¬ alies, 17 per cent; and lower limb defect, 10 per cent. 6. Potter's Syndrome'^ '^ —Primary Defect of Renal Agenesis or Other Anomaly Leading to a Lack of Urine Flow into the Amniotic Space (see Fig. 9) Renal agenesis, which must have occurred prior to 31 days, will secondarily limit the amount of amniotic fluid and thereby result in further anomalies during prenatal life. The renal agene¬ sis may be the only primary defect, or it may be one feature of a more extensive caudal axis anom¬ aly (see condition 5). The anomaly occurs more frequently in anatomical males, 17 of 20 in Pot¬ ter's series,'^ and this might be partially ex¬ plained by the observations of Schlegel et al.^'^ They noted masculinization of the external geni¬ talia in an XX female with Potter's syndrome and raised the possibility of the genital develop¬ ment being secondary to limited androgen excre¬ tion and degradation in this female with renal agenesis. 7. Abdominal Muscle Deficiency, Renal and Urinary Tract Dysplasia, and Cryptorchidism; the So-Called Triad Syndrome —Possibly an Early Defect of Mesoderm Contributing to Abdominal Musculature, Renal Parenchyma, Urinary Tract Musculature, and Descent of the Testicles'^^' (see Fig. 10) The remarkable similarity among affected individuals with abdominal muscle deficiency suggests that this syndrome may be the conse¬ quence of a single localized defect in early meso¬ derm which eventually contributes to the forma¬ tion of the abdominal musculature, the urinary tract musculature, the renal parenchyma, and possibly the gubernaculum testis. The condition occurs predominantly in males who occasionally have defects of the lower limbs as well. The prog¬ nosis for these patients is mainly dependent on the degree of renal insufficiency and complica¬ tions arising from poor drainage of the urinary tract. Abdominal binding will often improve respiratory exchange and assist in the patient's having bowel movements. Some improvement in abdominal muscle mass and function may occur with age; because these patients are usually of normal intelligence all supportive measures seem indicated. 8. Exstrophy of Bladder^• —Defect in Development of Infraumbilical Mesenchyme (Mesoderm) (see Fig. 11) Normally the bladder portion of the cloaca and the overlying ectoderm are in direct contact (the cloacal membrane) until the infraumbilical mesenchyme migrates into the area around the sixth to seventh week, giving rise to the lower abdominal wall, genital tubercles, and pubic rami. A failure of the infraumbilical mesen¬ chyme to invade the area allows for a breakdown in the cloacal membrane, in similar fashion to that which normally occurs at the oral, anal and urogenital areas where mesoderm does not inter¬ cede between ectoderm and endoderm. Thus the posterior bladder wall is exposed in conjunction with defects in structures derived from the infra¬ umbilical mesenchyme. This anomaly, six times as likely to occur in the male as in the female, continues to be a diffi¬ cult one to correct, though encouraging results have followed immediate postnatal primary closure of both the bladder and the pubic rami.