Severe Congenital Neutropenia Type 4: A Rare Disease Harboring a G6pc3 Gene Pathogenic Variant Particular to the Mexican Population.

Background: Severe congenital neutropenia type 4 (SCN4) is a rare autosomal recessive granulopoiesis disorder caused by G6PC3 gene pathogenic variants. The estimated prevalence is 1/10,000,000 people. Over 90% of patients present a syndromic form with variable multisystemic involvement, including congenital heart defects, increased visibility of superficial veins (IVSV), inflammatory bowel disease, and congenital urogenital defects as prominent symptoms.

Objectives: The objective of the study was to study non-hematological phenotypic findings that suggest a clinical diagnosis of SCN4.

Methods: We examined medical records of patients diagnosed with neutropenia from January 2000 to December 2020, selecting cases with non-hematologic manifestations for phenotypic description and G6PC3 gene sequencing.

Results: We found 11 cases with non-hematologic features: congenital heart defects in 8, IVSV in 6, inflammatory bowel disease in 4, urogenital defects in 4, and similar facial appearance. In addition, Sanger sequencing confirmed 3 homozygous cases for the c.210delC variant, a compound heterozygous harboring this variant, and a c.199_218+1 deletion.

Conclusions: Our findings of the c.210delC variant in very close geographical settings, to date, have only been reported among Mexicans, and a mutual uncommon surname in two families strongly supports a founder effect for the variant in the studied population. Furthermore, the described non-hematologic symptoms in patients with severe primary neutropenia should be explored, confirming SCN4 by investigating G6PC3 gene mutations.