Beta-propeller Protein-Associated Neurodegeneration (BPAN) via the WDR45 Gene

Beta-propeller protein-associated neurodegeneration (BPAN) was also described as static encephalopathy of childhood with neurodegeneration in adulthood (SENDA). Phenotypes include early onset global developmental delay during early childhood and development of Parkinsonism, dystonia, and dementia during adolescence or early adulthood. Seizures, spasticity and disordered sleep are also common features. Brain MRI reveals iron accumulation in the globus pallidus and substantia nigra. A characteristic finding is T1-weighted hyperintensity surrounding a central band of hypointensity in the substantia nigra. Cerebral and cerebellar atrophy are also present (Haack et al. 2012; Okamoto et al. 2014; Ozawa et al 2014; Hogarth 2015; Arber et al. 2016).

Beta-propeller protein-associated neurodegeneration is inherited in an X-linked dominant manner and is caused by pathogenic variants in the WDR45 gene which encodes WD repeat-containing protein. This protein plays a putative role in the autophagy pathway, a lysosomal process to degrade cellular components such as damaged organelles, or protein aggregation (Okamoto et al. 2014; Arber et al. 2016).

The majority of patients are females, suggesting that beta-propeller protein-associated neurodegeneration is lethal in most males. However, in male patients, their phenotype is similar to that in females, indicating somatic mosaicism in surviving males. Females may also show mosaicism, as well as skewing of X chromosome inactivation (Haack et al. 2012; Arber et al. 2016).

Pathogenic variants in WDR45 for this disease cover missense, nonsense, small deletion/insertion, and splice variants, as well as large deletions in the WDR45 locus (Haack et al. 2012; Hayflick et al. 2013; Human Gene Mutation Database). These pathogenic variants can occur de novo.

Pathogenic variants in the WDR45 gene account for 7% of Neurodegeneration with brain iron accumulation (Hogarth 2015).

This test provides full coverage of all coding exons of the WDR45 gene, plus ~10 bases of flanking noncoding DNA. We define full coverage as >20X NGS reads or Sanger sequencing.