The combination of Dandy-Walker malformation and occipital cephalocele is a rare autosomal dominant condition, known as ADDWOC, and caused by mutations in NID1 or LAMC1. We present a three-generation family with variable manifestations of Dandy-Walker malformation and occipital cephalocele. They all have normal psychomotor development and lack neurological manifestations. Mutation analysis revealed a likely pathogenic missense variant in NID1 (c.3336T > G, p.Asn1112Lys), affecting an amino acid residue crucial in the nidogen/laminin interaction.

Autosomal dominant Dandy-Walker malformation and occipital cephalocele (ADDWOC) is a rare, congenital, and incompletely penetrant malformation that is considered to be part of the Dandy-Walker spectrum of disorders. Affected individuals often present with an occipital cephalocele with a bony skull defect, but typically have normal neurological development. Here, we report on a three-generation family in which individuals have variable phenotypes that are consistent with the ADDWOC spectrum: arachnoid cysts in the proband and his maternal grandfather, an occipital cephalocele in the proband and his brother, and a small bony defect in the proband\'s mother. Whole exome sequencing identified a rare heterozygous variant in NID1 (NM_002508.2:c.1162C>T, (p.Gln388Ter)) in the proband, his brother, and his mother. Sanger sequencing confirmed the presence of this variant in the maternal grandfather. The identical c.1162C>T variant was previously identified in variably affected members of a three-generation family with ADDWOC. This case report provides further evidence that variants in NID1 may be clinically relevant for the development of a phenotype that is consistent with ADDWOC, and extends the phenotype of NID1-associated ADDWOC to include arachnoid cysts. Given that the Dandy-Walker malformation itself is not a pre-requisite to this spectrum of phenotypes, we also suggest a novel term for the NID1-associated disorder in order to give emphasis to this phenotypic variability: \"Autosomal Dominant Posterior Fossa Anomalies with Occipital Cephaloceles.\"