The primary goal of this project is to understand the molecular and biochemical processes that underlie birth defects. Although individually rare, genetic syndromes and malformations have a large impact on childhood morbidity and mortality. We study both dysmorphic mouse and human malformation syndromes. Our laboratory's focus is the Smith-Lemli-Opitz syndrome (SLOS) and other inborn errors of cholesterol biosynthesis. SLOS is a human autosomal recessive multiple congenital anomaly/mental retardation syndrome characterized by facial dysmorphology, mental retardation with a characteristic behavioral phenotype, growth retardation, and variable structural anomalies of the heart, lungs, brain, gastrointestinal tract, limbs, genitalia and kidneys. SLOS also has a distinct behavioral phenotype which includes self-injurious and autistic features. Biochemically patients with SLOS have an inborn error of cholesterol biosynthesis. Specifically they have a defect in the conversion of 7-dehydrocholesterol to cholesterol. We do not know why these children have such a variety of congenital malformations, and neurological problems. We cloned the gene encoding the 7-dehydrocholesterol reductase, and have subsequently identified mutations in this gene in more than fifty patients with Smith-Lemli-Opitz syndrome. Our laboratory continues to identify mutations in SLOS patients, and to determine residual enzymatic function in patient fibroblasts. This information is being used to establish genotype/enzymatic activity/phenotype correlations for this disorder. We have also isolated the mouse gene encoding this enzyme, and have produced a mouse model for this disorder. We are using this mouse model to further our understanding of how the malformations seen in this syndrome develop, and to further our understanding of the neurophysiological basis of the neurological problems associated with this syndrome. Hypomorphic mouse models of SLOS have now been developed. These mouse models are being used to investigate therapeutic interventions including dietary cholesterol supplementation, simvastatin therapy and gene therapy. In addition to SLOS, we have identified a patient with lathosterolosis. This human syndrome has not previously been described. Like SLOS, lathosterolosis is due to an inborn error of cholesterol synthesis. In lathosterolosis, there is a defect in the conversion of lathosterol to 7-dehydrocholesterol. A mouse model of lathosterolosis has been produced. This mouse replicates many of the findings found in the human patient, and will be used to further our understanding of the biological processes which cause the birth defects found in these syndromes. Most recently a mouse model of desmosterolosis has been developed. A clinical protocol to evaluate endocrine and neurological aspects of SLOS has made significant progress. In collaboration with a group of investigators at the Kennedy Krieger Institute in Baltimore, we continue to characterize the behavioral phenotype associated with SLOS. This behavioral phenotype includes autistic features, and the effect of dietary cholesterol therapy on this clinical problem is being studied. Characterization of adrenal function in SLOS patients demonstrated that many of our patients have compensated adrenal insufficiency. This finding will impact medical management of these patients. A protocol to investigate the safety and efficacy of simvastatin therapy in SLOS has been initiated and has enrolled half of the patients needed for this clinical trial. A new protocol to investigate the short term behavioral effects of dietary cholesterol supplementation in SLOS was initiated this past year. SLOS is thought to be more common in individuals of Northern European descent with a carrier frequency of the most common mutant allele of about 1%. Very few patients of African descent have been described; however, we have shown that the carrier frequency of this same mutation in African Canadians and African Americans appears to be relatively high (0.7%). Our laboratory is also studying two mouse models in which we have disrupted Lhx2 and Lhx9. Lhx2 and Lhx9 are two closely related LIM homeodomain proteins that regulate the expression of other genes during development. They appear to have individual and redundant functions during development. The Lhx2 mutant mouse has forebrain malformations, anophthalmia, and severe anemia. Lhx9 mutant mice do not develop gonads. The combined Lhx2/Lhx9 mutant mouse has a limb reduction malformation that we are characterizing at the molecular level.
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