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MAN1B-CDG: Novel variants with a distinct phenotype and review of literature.

Balasubramanian M. and al. Eur J Med Genet. 2018 Jun 14.


Abstract

BACKGROUND:

Congenital disorders of glycosylation (CDG) are a group of rare metabolic diseases due to impaired lipid and protein glycosylation. It comprises a characteristic high frequency of intellectual disability (ID) and a wide range of clinical phenotypes.

OBJECTIVE:

To identify the underlying diagnosis in two families each with two siblings with variable level of ID through trio whole exome sequencing.

METHODS:

Both the families were recruited to the Deciphering Developmental Disorders (DDD) study to identify the aetiology for their ID. Further work-up included isoelectric focusing (IEF) of serum transferrin done to add evidence to the molecular diagnosis.

RESULTS:

These patients were found to have three novel variants in MAN1B1 inherited from their healthy parents. Serum transferrin IEF showed a type 2 pattern.

DISCUSSION:

MAN1B1 variants were initially described in association with non-syndromic ID; subsequent literature suggested that variants in MAN1B1 resulted in a CDG-type II syndrome. However, there remains a paucity of literature on detailed clinical phenotyping and it still remains a rare form of CDG. The present patients showed the phenotype previously reported in MAN1B1-CDG: a characteristic facial dysmorphism, hypotonia, truncal obesity and in some, behavioural problems.

CONCLUSIONS:

In unexplained ID, serum transferrin should be included in the first-line screening. With advances in genomic medicine, it is important to diagnose CDG as this has implications for management and recurrence risk counselling.

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