Case of the Week
Section Editors: Matylda Machnowska1 and Anvita Pauranik2
1University of Toronto, Toronto, Ontario, Canada
2BC Children's Hospital, University of British Columbia, Vancouver, British Columbia, Canada
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March 3, 2014
Semilobar Holoprosencephaly
- Holoprosencephaly affects 1 in 8,000 live births and is the most common structural anomaly of the developing forebrain, resulting in facial dysmorphism, neurologic impairment, and additional clinical sequelae. Given the increasing relative contribution of genetic diseases to perinatal morbidity and mortality, proper recognition and management of holoprosencephaly can improve care for a significant number of affected children.
- Holoprosencephaly is divided into four types, based on the degree of nonseparation of the prosencephalon. These types, in order of increasing cortical separation, include the alobar form, characterized by diffuse cortical nonseparation; the semilobar form, characterized by nonseparation of the frontal lobes; the lobar form, characterized by nonseparation of the basal aspect of the frontal lobes; and the middle interhemispheric variant, characterized by nonseparation of the posterior frontal and parietal lobes. Despite the identification of several genetic loci and other etiologic agents involved in pathogenesis, additional causes are elusive. Moreover, satisfactory explanations for phenomena such as incomplete penetrance and variable expressivity are lacking.
- For each patient, pediatricians should follow a diagnostic protocol including dysmorphology examination, complete family history and ascertainment of risk factors, and neuroimaging. Many medical issues, including hypothalamic dysfunction, endocrinologic dysfunction, motor impairment, respiratory issues, seizures, and hydrocephalus should be prioritized in management. Pediatricians should work with genetic specialists to identify syndromic forms and to perform cytogenetic investigation, molecular screening, and genetic counseling in order to fully characterize prognosis and recurrence risk.
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