**4. Epidemiological aspects of dysmorphisms**

On its own, a certain type of congenital defect may be rare, but congenital defects as a whole are relatively common in all domestic species and their different breeds and are a significant cause of neonatal and infant mortality and morbidity. Preliminary data suggest that the frequency of dysmorphisms is greater in pigs, followed in descending order by dogs, horses, cattle and cats6 (Hámori, 1983).

#### **4.1 Frequency, mortality and morbidity**

The *frequency* of major dysmorphisms in humans is estimated at 3% of live births (Marden et al, 1964). This number practically doubles by the end of the first year of life, with the identification of defects that manifest later (Kumar & Burton, 2008). In domestic animals, these numbers must be similar or even higher because inbreeding is common in selective breeding both for companion animals and for farm animals, increasing the coefficient of consanguinity. One study (Priester et al, 1970), which included all domestic species, analyzed almost 138,000 individuals and found a rate of 4.68%. However, minor dysmorphisms are not always identified and are seldom included in statistics. The same may occur in the case of major dysmorphisms when they affect internal structures and cause intrauterine or neonatal death and are not always reported. Rates of occurrence vary according to each abnormality and can also vary according to species, breed and geographical location. *Mortality* varies a great deal from one dysmorphism to another. Some are so serious that they cause intrauterine or perinatal death, such as combined heart-lung defects; others are incompatible with life and the affected individual dies soon after birth, as is the case with anencephaly. However, a large number of major dysmorphisms can be corrected surgically or be given some form of treatment, making life viable. Furthermore, minor dysmorphisms have no meaning in terms of mortality. Like mortality, *morbidity* also varies according to the dysmorphism. In many cases, treatment definitively cures the defect and the individual goes on to live a normal life; in other cases, treatment can improve the quality of life, but the individual will have chronic difficulties until the end of his days.

#### **4.2 Risk factors**

The artificial selection in breeding to obtain animals with a new or better appearance or for financial gain often means consanguineous unions, increasing the risk of the recurrence of a given defect in future generations. The environment also poses many risk factors during pregnancy, such as: 1) residue from pesticides in water, pasture and other foods; 2) certain toxic plants7 in the pasture; 3) inadequate conservation of animal feed and other foodstuff

<sup>6</sup> Cats are generally under-represented in samples involving several species. However, veterinarians of small animals often come across congenital defects in purebred cats, which are suggestive of a relatively high rate of dysmorphisms in this species, which is not always reported in journals. They have seen conjoined twins, poliotia, radial agenesis, frontonasal dysplasia, cyclopia, diprosopia, meningocele, anencephaly, spina bifida, hydrocephaly, polydactyly, syndactyly, anal atresia, hypospadias, true hermaphroditism, pseudohermaphroditism and others.

<sup>7</sup> Examples include certain species of the genus *Lupinus* (lupines) that contain teratogenic alkaloids (anagyrine, ammodendrine) that cause a form of congenital arthrogryposis in calves, known as "crooked calf disease". This disease occurs when pregnant cows ingest the plants between the fortieth

serious angular deviation of the thoracic limbs and polydactyly (Bowling & Millon, 1990); 6) *structural chromosomal aberrations*, such as the translocation between the X chromosome and

an autosome described by Schelling et al., (2001) in an intersex Yorkshire terrier.

Fig. 4. X-linked hypohidrotic ectodermal dysplasia: A) Congenital absence of hair

Laboratory of Pathology, Faculty of Veterinary Medicine, FEPAR.

**5.1.2 Environmental etiology** 

(congenital alopecia); B) Dental defects (conical teeth and oligodontia); C) Microphotograph of the skin (from an alopecic area) showing absence of hair follicles, sebaceous glands and sweat glands. Shorr stain, X10 objective. Photograph **C** courtesy of Dr. Silvana M. Cirio,

The environment can be a source of numerous potential teratogens, an important cause of congenital defects in both humans and animals because their presence is not always obvious or the harmful effect of certain products is unknown to the public at large, which increases the risk of maternal exposure to them. *Environmental teratogens* are agents in the *environment*  that can negatively impact embryonic development, causing congenital defects. Many chemical products and medicines have been considered potentially teratogenic for decades. Some have been confirmed as such and others have been refused, while the potential of others is doubtful or has been mistakenly confirmed (Koren & Nickel, 2010; 2011). In principle, the risk of a defect is related to the frequency and degree of maternal exposure (Holmes, 2011). Agents that are commonly considered as potentially teratogenic can be separated into four groups: 1) *environmental contaminants,* such as mercury10, lead, polychlorinated biphenyls, organochlorines and dioxins. There is also considerable doubt

10 Mercury does not cause gross birth defects, but rather lesions in the central nervous system which cause psychomotor retard, convulsions and other neurological signs (Lancaster, 2011). The sad history of *Minamata disease* was first reported in 1953, but its cause was identified only three years later: a chemical plant discharged water containing inorganic mercury into Minamata Bay in Japan, and this was transformed into organic mercury (methylmercury) by marine microorganisms. Contaminated fish and clams with mythylmercury were consumed as food by the inhabitants of the town of Minamata and this was the source of poisoning which, in the case of pregnant women, affected the fetus, causing *congenital Mimata disease* (Moura, 1993). The number of people affected by the disease was officially

established as 2,252, of whom 1,043 had already died 36 years later (Harada, 1995).

which results in mycotoxins; 4) excessive levels of nitrogen-containing food preservatives8 in low quality animal feed; 5) medicine9 in the early stages of pregnancy; 6) medicines for continuous use during pregnancy, such as some anticonvulsants; 7) occurrence of certain infectious or metabolic diseases during pregnancy.
