Distal monosomy 13q is a rare chromosomal anomaly syndrome, resulting from a partial deletion of the long arm of chromosome 13, with a highly variable phenotype typically characterized by varying degrees of intellectual disability and developmental delay, as well as CNS malformations (e.g. holoprosencephaly, anencephaly, ventriculomegaly, Dandy-Walker malformation), ocular abnormalities (e.g. hypertelorism, microphthalmia, strabismus, aniridia, retinal dysplasia) and craniofacial dysmorphism (microcephaly, trigonocephaly, large and malformed ears, broad prominent nasal bridge, micrognathia). Cardiac, genitourinary, gastrointestinal and skeletal manifestations have also been reported.
Detailed analysis of neural tube defects (NTD) in publications about distal monosomy 13q showed that most defects affect cranial aspect of the neural tube (anencephaly, exencephaly, encephaloceles) with a relative small proportion of spina bifida.