Peroxisomal acyl-CoA oxidase deficiency is a disorder of peroxisomal fatty acid beta-oxidation. See also D-bifunctional protein deficiency (261515), caused by mutation in the HSD17B4 gene (601860) on chromosome 5q2. The clinical manifestations of these 2 deficiencies are similar to those of disorders of peroxisomal assembly, including Zellweger cerebrohepatorenal syndrome (see 214100) and neonatal adrenoleukodystrophy (see 601539) (Watkins et al., 1995).

An X-linked dominant condition caused by mutation(s) in the IQSEC2 gene, encoding IQ motif and SEC7 domain-containing protein 2. It is characterized by substantially impaired intellectual functioning and behavioral abnormalities.

Focal segmental glomerulosclerosis and neurodevelopmental syndrome (FSGSNEDS) is characterized by global developmental delay and renal dysfunction manifest as proteinuria and nephrotic syndrome apparent from infancy or early childhood. Some patients present with renal disease, whereas others present with developmental delay and develop renal disease later in childhood. Renal biopsy shows focal segmental glomerulosclerosis (FSGS), but the course of the disease is variable: some patients have transient proteinuria and others require renal transplant. Neurodevelopmental features are also variable, with some patients having only mildly impaired intellectual development, and others having a severe developmental disorder associated with early-onset refractory seizures or epileptic encephalopathy. Additional features, including feeding difficulties, poor overall growth, and nonspecific dysmorphic facial features, are commonly observed (summary by Assoum et al., 2018 and Weng et al., 2021).