Porth's Essentials of Pathophysiology, 4e

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Cell and Tissue Function

U N I T 1

mutations, characteristic patterns exist. First, multifac- torial congenital malformations tend to involve a single organ or tissue derived from the same embryonic devel- opmental field. Second, the risk of recurrence in future pregnancies is for the same or a similar defect. This means that parents of a child with a cleft palate defect have an increased risk of having another child with a cleft palate, but not with spina bifida. Third, the increased risk (com- pared with the general population) among first-degree relatives of the affected person is 2% to 7%, and among second-degree relatives, it is approximately one-half that amount. 4 The risk increases with increasing incidence of the defect among relatives. This means that the risk is greatly increased when a second child with the defect is born to a couple. The risk also increases with severity of the disorder and when the defect occurs in the sex not usually affected by the disorder. Cleft Lip and Cleft Palate Cleft lip with or without cleft palate is one of the most common birth defects. 25–28 It is also one of the more conspicuous, resulting in an abnormal facial appearance and defective speech. The incidence varies among eth- nic groups, ranging from 2 per 1000 live births among Native Americans and Asians, 1 per 1000 among people of European ancestry, to 1 per 2500 among Africans. 27 Cleft lip with or without cleft palate is more frequent among boys, whereas isolated cleft palate is twice as common among girls. Developmentally, the defect has its origin at about the 35th day of gestation when the frontal prominences of the craniofacial structures fuse with the maxillary pro- cess to form the upper lip. 2 This process is under the con- trol of many genes, and disturbances in gene expression (hereditary or environmental) at this time may result in cleft lip with or without cleft palate (Fig. 6-7). The defect may also be caused by teratogens (e.g., rubella,

anticonvulsant drugs) and is often encountered in children with chromosomal abnormalities. Cleft lip and palate defects may vary from a small notch in the vermilion border of the upper lip to com- plete separation involving the palate and extending into the floor of the nose. The clefts may be unilateral or bilateral and may involve the alveolar ridge. The condi- tion may be accompanied by deformed, supernumerary, or absent teeth. Isolated cleft palate occurs in the mid- line and may involve only the uvula or may extend into or through the soft and hard palates. Children with cleft lip or palate commonly have prob- lemswithfeedingandspeech.Theimmediateprobleminan infant with cleft palate is feeding. Nursing at the breast or nipple depends on suction developed by pressing the nipple against the hard palate with the tongue. Although infants with cleft lip usually have no problems with feeding, those with cleft palate usually require specially constructed, soft artificial nipples with large openings and a squeezable bottle. A specially constructed plastic obturator that fits over the palate defect may be used to facilitate sucking for some infants. 25 Cleft lip and palate can also cause speech defects. The muscles of the soft palate and the lateral and posterior walls of the naso- pharynx constitute a valve that separates the nasophar- ynx from the oropharynx during swallowing and in the production of certain vocal sounds such as p, b, d, t, h, and y , or the sibilants s, sh, and ch . A child with cleft lip or palate may require years of special treatment by health care professionals, including a plastic surgeon, pediatric dentist, orthodontist, speech therapist, and nurse specialist. 25 Surgical closure of the lip is usually performed by 3 months of age, with closure of the palate usually done before 1 year of age. Depending on the extent of the defect, additional surgery may be required as the child grows. Displacement of the maxil- lary arches and malposition of the teeth usually require orthodontic correction. ■■ Genetic disorders can be caused by single gene (mendelian) or multiple gene (polygenic) inheritance. In single gene disorders the defective gene may be present on an autosome or on the X chromosome and they may be expressed as a dominant or recessive trait. In autosomal dominant disorders, a single mutant allele from an affected parent is transmitted to an offspring regardless of sex.The affected parent has a 50% chance of transmitting the disorder to each offspring. Autosomal recessive disorders are manifested only when both members of the gene pair are affected. Usually, both parents are unaffected but are carriers of the defective gene.Their chances of having an affected child are one in four. SUMMARY CONCEPTS

Unilateral

Bilateral

FIGURE 6-7. Cleft lip and cleft palate.