The prevalence of autosomal dominant mental retardation-56 is unknown. So far, 27 individuals were described in the literature.

Clinical characteristics
Individuals with autosomal dominant mental retardation-56 have a variable degree of developmental delay / intellectual disability, ranging from mild to severe. Microcephaly, hypoplasia of the corpus callosum and epilepsy may also be observed.

Molecular characteristics
A spectrum of pathogenic variants were detected, in heterozygosity, in the CLTC gene, including nonsense, frameshift, missense, and splice site variants and in-frame deletions.

Genetic Counselling
The recurrence risk in siblings of individuals with a de novo CLTC variant is estimated to be low, i.e. <1% (although higher than in the general population due to the theoretical possibility of germline mosaicism). Since the patients’ phenotype may be mild, it is recommended to test both parents to exclude inherited variants.

Treatment is symptomatic and multidisciplinary.