G6PC3 deficiency is characterized by severe congenital neutropenia which occurs in a phenotypic continuum that includes the following: Isolated severe congenital neutropenia (nonsyndromic). Classic G6PC3 deficiency (severe congenital neutropenia plus cardiovascular and/or urogenital abnormalities). Severe G6PC3 deficiency (classic G6PC3 deficiency plus involvement of non-myeloid hematopoietic cell lines, additional extra-hematologic features, and pulmonary hypertension; known as Dursun syndrome). Neutropenia usually presents with recurrent bacterial infections in the first few months of life. Intrauterine growth restriction (IUGR), failure to thrive (FTT), and poor postnatal growth are common. Other findings in classic and severe G6PC3 deficiency can include inflammatory bowel disease (IBD) resembling Crohn's disease, and endocrine disorders (growth hormone deficiency, hypogonadotropic hypogonadism, and delayed puberty).

Biliary, renal, neurologic, and skeletal syndrome (BRENS) is an autosomal recessive complex ciliopathy with multisystemic manifestations. The most common presentation is severe neonatal cholestasis that progresses to liver fibrosis and cirrhosis. Most patients have additional clinical features suggestive of a ciliopathy, including postaxial polydactyly, hydrocephalus, retinal abnormalities, and situs inversus. Additional features of the syndrome may include congenital cardiac defects, echogenic kidneys with renal failure, ocular abnormalities, joint hyperextensibility, and dysmorphic facial features. Some patients have global developmental delay. Brain imaging typically shows dilated ventricles, hypomyelination, and white matter abnormalities, although some patients have been described with abnormal pituitary development (summary by Shaheen et al., 2020 and David et al., 2020).