MRD22 is characterized by impaired intellectual development with frequent cooccurrence of corpus callosum anomalies, hypotonia, microcephaly, growth problems, and variable facial dysmorphism. Chromosome 1q43-q44 deletion syndrome is characterized by moderate to severe mental retardation, limited or no speech, and variable but characteristic facial features, including round face, prominent forehead, flat nasal bridge, hypertelorism, epicanthal folds, and low-set ears. Other features may include hypotonia, poor growth, microcephaly, agenesis of the corpus callosum, and seizures. The phenotype is variable, and not all features are observed in all patients, which may be explained in some cases by incomplete penetrance or variable expressivity. [From OMIM]