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Mol Genet Metab. 2017 Sep;122(1-2):60-66. doi: 10.1016/j.ymgme.2017.06.011. Epub 2017 Jun 29.

Milder clinical and biochemical phenotypes associated with the c.482G>A (p.Arg161Gln) pathogenic variant in cobalamin C disease: Implications for management and screening.

Author information

1
Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA; Department of Molecular and Human Genetics, Texas Children's Hospital, Houston, TX, USA.
2
Department of Molecular and Human Genetics, Texas Children's Hospital, Houston, TX, USA.
3
Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA; Department of Molecular and Human Genetics, Texas Children's Hospital, Houston, TX, USA. Electronic address: Burrage@bcm.edu.
4
Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA; Department of Molecular and Human Genetics, Texas Children's Hospital, Houston, TX, USA. Electronic address: bgraham@bcm.edu.

Abstract

INTRODUCTION:

Cobalamin C disease is a multisystemic disease with variable manifestations and age of onset. Genotype-phenotype correlations are well-recognized in this disorder. Here, we present a large cohort of individuals with cobalamin C disease, several of whom are heterozygous for the c.482G>A pathogenic variant (p.Arg161Gln). We compared clinical characteristics of individuals with this pathogenic variant to those who do not have this variant. To our knowledge, this study represents the largest single cohort of individuals with the c.482G>A (p.Arg161Gln) pathogenic variant.

METHODS:

A retrospective chart review of 27 individuals from 21 families with cobalamin C disease who are followed at our facility was conducted.

RESULTS:

13 individuals (48%) are compound heterozygous with the c.482G>A (p.Arg161Gln) on one allele and a second pathogenic variant on the other allele. Individuals with the c.482G>A (p.Arg161Gln) pathogenic variant had later onset of symptoms and easier metabolic control. Moreover, they had milder biochemical abnormalities at presentation which likely contributed to the observation that 4 individuals (31%) in this group were missed by newborn screening.

CONCLUSION:

The c.482G>A (p.Arg161Gln) pathogenic variant is associated with milder disease. These individuals may not receive a timely diagnosis as they may not be identified on newborn screening or because of unrecognized, late onset symptoms. Despite the milder presentation, significant complications can occur, especially if treatment is delayed.

KEYWORDS:

Cobalamin C; Genotype-phenotype; Hydroxocobalamin; Late-onset; R161Q

PMID:
28693988
PMCID:
PMC5612879
DOI:
10.1016/j.ymgme.2017.06.011
[Indexed for MEDLINE]
Free PMC Article

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