MedGen

Developmental and epileptic encephalopathy-55 (DEE55) is an autosomal recessive neurologic disorder characterized by onset of refractory seizures in the first weeks or months of life. Affected individuals have an extremely poor outcome, with profoundly impaired intellectual development, absent speech, spastic quadriplegia, and dyskinetic movements. Most have cortical visual impairment and require a feeding tube. Brain imaging shows nonspecific abnormalities, including cerebral atrophy, thin corpus callosum, and abnormal signals in the white matter. Death in childhood may occur. Biochemically, the disorder is associated with impaired synthesis of GPI-anchored proteins (summary by Vetro et al., 2020). For a general phenotypic description and a discussion of genetic heterogeneity of DEE, see 308350. For a discussion of genetic heterogeneity of GPI biosynthesis defects, see GPIBD1 (610293). [from OMIM]

Vissers-Bodmer syndrome (VIBOS) is characterized by global developmental delay with variably impaired intellectual development, speech delay, motor delay, and behavioral abnormalities apparent from infancy. The phenotype is highly variable: some individuals have only mild learning difficulties, whereas others have severe cognitive impairment with IQ in the 50s. Many patients have behavioral abnormalities, including autism spectrum disorder, ADD, ADHD, obsessive-compulsive disorder, and impulsivity. Other common features include growth impairment abnormalities, hypotonia, and distal skeletal defects, such as foot and hand deformities. Less common features include seizures, brain abnormalities on MRI, feeding problems, and joint hypermobility. Most individuals have dysmorphic facial features, but there is no recognizable gestalt (summary by Vissers et al., 2020). [from OMIM]

Al Kaissi syndrome (ALKAS) is an autosomal recessive developmental disorder characterized by growth retardation, spine malformation, particularly of the cervical spine, dysmorphic facial features, and delayed psychomotor development with moderate to severe intellectual disability (summary by Windpassinger et al., 2017). [from OMIM]

An abnormally reduced head circumference in a growing child. Head circumference is measured with a nonelastic tape and comprises the distance from above the eyebrows and ears and around the back of the head. The measured HC is then plotted on an appropriate growth chart. Microcephaly is defined as a head circumference (HC) that is great than two standard deviations below the mean of age- and gender-matched population based samples. Severe microcephaly is defined with an HC that is three standard deviations below the mean. [from HPO]