Open Access Research article

Adult siblings with homozygous G6PC3 mutations expand our understanding of the severe congenital neutropenia type 4 (SCN4) phenotype

Bridget A Fernandez123, Jane S Green1, Ford Bursey23, Brendan Barrett23, Andrée MacMillan3, Sarah McColl3, Sara Fernandez3, Proton Rahman23, Krista Mahoney1, Sergio L Pereira4, Stephen W Scherer4, Kym M Boycott5, Michael O Woods1* and FORGE Canada Consortium

Author Affiliations

1 Discipline of Genetics, Memorial University of Newfoundland, Health Sciences Centre, Rm 4333, 300 Prince Philip Drive, St. John’s, Newfoundland and Labrador, A1B 3V6, Canada

2 Discipline of Medicine, Memorial University of Newfoundland, St John’s, Newfoundland and Labrador, A1B 3V6, Canada

3 Eastern Health, St John’s, NL, A1B 3V6, Canada

4 The Centre for Applied Genomics and Program in Genetics and Genome Biology, The Hospital for Sick Children, Toronto, Ontario, M5G 1L7, Canada

5 Children’s Hospital of Eastern Ontario Research Institute, University of Ottawa, Ottawa, Ontario, K1H 8L1, Canada

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BMC Medical Genetics 2012, 13:111  doi:10.1186/1471-2350-13-111

Published: 21 November 2012

Abstract

Background

Severe congenital neutropenia type 4 (SCN4) is an autosomal recessive disorder caused by mutations in the third subunit of the enzyme glucose-6-phosphatase (G6PC3). Its core features are congenital neutropenia and a prominent venous skin pattern, and affected individuals have variable birth defects. Oculocutaneous albinism type 4 (OCA4) is caused by autosomal recessive mutations in SLC45A2.

Methods

We report a sister and brother from Newfoundland, Canada with complex phenotypes. The sister was previously reported by Cullinane et al., 2011. We performed homozygosity mapping, next generation sequencing and conventional Sanger sequencing to identify mutations that cause the phenotype in this family. We have also summarized clinical data from 49 previously reported SCN4 cases with overlapping phenotypes and interpret the medical histories of these siblings in the context of the literature.

Results

The siblings’ phenotype is due in part to a homozygous mutation in G6PC3, [c.829C > T, p.Gln277X]. Their ages are 38 and 37 years respectively and they are the oldest SCN4 patients published to date. Both presented with congenital neutropenia and later developed Crohn disease. We suggest that the latter is a previously unrecognized SCN4 manifestation and that not all affected individuals have an intellectual disability. The sister also has a homozygous mutation in SLC45A2, which explains her severe oculocutaneous hypopigmentation. Her brother carried one SLC45A2 mutation and was diagnosed with “partial OCA” in childhood.

Conclusions

This family highlights that apparently novel syndromes can in fact be caused by two known autosomal recessive disorders.

Keywords:
Albinism; Exome sequencing; G6PC3 protein; Inflammatory bowel disease; Oculocutaneous albinism type 4 (OCA4); Neutropenia; Severe congenital neutropenia type 4 (SCN4); SLC45A2 protein