Abnormalities: Special Syndromes – Primary and Secondary Palate Development

by John McLachlan, PhD

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    00:01 genetic components. Two examples are Treacher Collins and Pierre Robin syndromes.

    00:05 This is an image of Treacher Collins syndrome, and here we can see that there is malar hypoplasia that’s underdevelopment of the bones of the face, particularly, the zygomatic bones.

    00:17 There’s also underdevelopment of the jaw, mandibular hypoplasia. And the palpebral fissures of the eyes are downward slanting, and the ears themselves are malformed and in a slightly abnormal position overall. This represents an autosomal dominant trait and is present in something like one in 10,000 live births. Another condition for which we do not have an image is Pierre Robin syndrome. Here, we have hypoplasia of the mandible, and that can lead to a displacement of the tongue and may be associated with a bilateral cleft palate.

    00:54 There will also be defects of the external eye and ear under these conditions.

    00:59 And it may be sporadic although it may also have a genetic basis. The incidence is not entirely clear, but may be something of the other one per 8,500 live births. Di George syndrome, by contrast, is a third and fourth arch phenomenon, where the development of the third and fourth pharyngeal pouches has been significantly affected. As a result, what we’d expect to see is hypoplasia or even complete absence of the thymus and malformation or absence of the parathyroid glands, and that may have some disturbances to the blood vessel system as well. Again, we’d expect to see ear abnormalities and reduction in the size of the jaw.

    01:44 Because of the reduction or absence of a thymus, the baby may be more susceptible to infections since the thymus plays a significant role in the immune system in early development.

    01:56 One particular example, we can trace exactly where the process has gone wrong, is we can identify a particular deletion on chromosome 22. Incidents would appear to be something of the order of one in 4,000. But for these rare and sometimes hard to recognize conditions is always an element of uncertainty in the exact frequency. If an abnormality of the head and neck is observed, there are a number of things which we can look at to explore what might have happened. We can list these structures that are affected, and then we can look back to the embryology to explore which arches or pouches or grooves would normally give rise to those particular structures in the embryo and looking back in time in this way might suggest the genes that could be involved, and that could be something that could be explored through genetic analysis. And if they are indeed affected, then this gives suggestions as to how best this condition might be treated. So then in summary, we’ve looked at the appearance of the pharyngeal arches as we briefly reviewed face development and since this contain muscle, cartilage, nerves, and blood vessels, each of these may be affected by abnormalities. Initially, the arches are separated by grooves, and the process of normal face development is one of growth and fusion of these structures together.

    03:23 If something happens to interrupt this process, then complex clefts may arise in ways which are relatively predictable given the nature of the underlying processes. Of course, genetic defects can contribute in significant ways to all of these kinds of abnormalities.

    03:41 Thank you very much.

    About the Lecture

    The lecture Abnormalities: Special Syndromes – Primary and Secondary Palate Development by John McLachlan, PhD is from the course System-Specific Embryology with John McLachlan.

    Author of lecture Abnormalities: Special Syndromes – Primary and Secondary Palate Development

     John McLachlan, PhD

    John McLachlan, PhD

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