Molecular approaches to dysmorphology.

The biochemical and physiological defects underlying human dysmorphic syndromes can now be approached using techniques of molecular biology. The genetic component of the causation of the dysmorphology can be studied in isolation from the environmental component by using large, rare families which exhibit the same phenotype as more complex multifactorial disorders, but inherit the mutation in a monogenic fashion. Such an analysis starts with the determination of linkage to a gene probe, followed by the use of newer techniques of molecular biology to enable cloning and sequencing of the mutated gene. Analysis of the gene product by amino acid sequence homology to other known proteins, and tissue specific expression, may place the defect within the cascade of events associated with development and differentiation. Once cloned, the gene can also be manipulated in transgenic laboratory animals and the effect of its mutation studied directly. The use of techniques of molecular biology to study the genetic aspects of dysmorphic syndromes will allow insight to be gained both into normal fetal development and into the causes of congenital malformations.