Celia's encephalopathy and c.974dupG in BSCL2 gene: a hidden change in a known variant

Abstract

Celia's encephalopathy (progressive encephalopathy with/without lipodystrophy (PELD)) is a childhood neurodegenerative disorder with a fatal prognosis before the age of 10, due to the variant c.985C>T in the BSCL2 gene that causes a cryptic splicing site leading to skipping of exon 7. For years, different authors have reported cases of congenital generalized lipodystrophy due to the variant c.974dupG in BSCL2 associated with neurological manifestations of variable severity, although some of them clearly superimposable to PELD. To identify the molecular mechanisms responsible for these neurological alterations in two patients with c.974dupG. Clinical characterization, biochemistry, and neuroimaging studies of two girls carrying this variant. In silico analysis, PCR amplification, and BSCL2 cDNA sequencing. BSCL2-201 transcript expression, which lacks exon 7, by qPCR in fibroblasts from the index case, from a healthy child as a control and from two patients with PELD, and in leukocytes from the index case and her parents. One with a severe encephalopathy including a picture of intellectual deficiency, severe language impairment, myoclonic epilepsy, and lipodystrophy as described in PELD, dying at 9 years and 9 months of age. The other 2-year-old patient showed incipient signs of neurological involvement. In silico and cDNA sequencing studies showed that variant c.974dupG gives rise to skipping of exon 7. The expression of BSCL2-201 in fibroblasts was significantly higher in the index case than in the healthy child, although less than in the case with homozygous PELD due to c.985C>T variant. The expression of this transcript was approximately half in the healthy carrier parents of this patient. The c.974dupG variant leads to the skipping of exon 7 of the BSCL2 gene and is responsible for a variant of Celia's encephalopathy, with variable phenotypic expression.

Keywords: BSCL2; Congenital generalized lipodystrophy; Cryptic splicing; Neurodegeneration; PELD.

Figure 1.

A. Results of the amplification of a 573 bp region of cDNA from leukocytes from the index case and different subjects. Samples from the 974dupG index case and 985C>T PELD index case show the presence of an additional 431 base pair-long band. B. Sequencing of the 431 base pair band showed complete skipping of exon 7.

Figure 2.

A. Relative expression of BSCL2-201 transcript in fibroblasts from a control children, a homozygous PELD patient (c.985C>T), a compound heterozygous patient (c.[985C>T];[509_5013del] and case #1 (c.974dupG). *: p<0.05 compared with control; #: p<0.05 compared with homozygous PELD patient. B. Relative expression of BSCL2-201 transcript in leukocytes from case #1, her mother (simple heterozygous), her father (simple heterozygous) and brother (wt).

Figure 3.

BSCL2-203 transcript sequence surrounding the c.974dupG (purple shading) and c.985C>T (red shading) variants, and the incorrectly annotated c.975dupG variant (grey shading).