Leukoencephalopathies and metabolic diseases

Compound heterozygous pathogenic variants in the GALC gene cause infant-onset Krabbe disease

BACKGROUND

Krabbe disease, also called globoid cell leukodystrophy, is an autosomal recessive disease caused by a deficiency of lysosomal galactocerebrosidase. Infantile Krabbe occurring before 12 months of age accounts for most cases. Typical clinical features include irritability, seizures, peripheral neuropathy, and progressive neurodegeneration.

METHODS

We collected and summarized the clinical and genetic data of an 8-month-old boy who demonstrated Krabbe disease onset at around 6 months. Potential pathogenic variants were screened by whole exome sequencing, and effects of candidate variants on alternative transcript and truncated protein were further validated at the RNA and protein level.

RESULTS

Galactocerebrosidase activity was nearly absent in his blood, and whole exome sequencing revealed compound heterozygous variants [NM_000153.4: (c.658C>T); (c.328+5G>T)] in galactosylceramidase (GALC). The variant c.328+5G>T was predicted to alter splicing, and the abnormal isoform transcript was validated by observation of abnormal RNA isoforms. The variant c.658C>T was predicted to cause truncation of the protein, which was validated by western blotting.

CONCLUSIONS

Our findings revealed compound heterozygous variants with solid experimental results for Krabbe disease and provides strong evidence for further Krabbe disease screening and clinical consulting. As a rare inherited systemic disorder, genetic variants in Krabbe disease should be investigated, as experimental validation for clinical diagnosis is needed.

A novel homozygous GALC variant has been associated with Krabbe disease in a consanguineous family

Krabbe disease (KD) or globoid cell leukodystrophy is an autosomal recessive lysosomal storage disorder involving the white matter of the peripheral and the central nervous systems. It is caused by a deficiency of galactocerebrosidase enzyme activity. The most common manifestation is the classical early onset KD that leads to patient's loss before the age of 2. Herein, we report the evaluation of a consanguineous family with three affected children manifesting severe neurological findings that ended with death before the age of 2, in an attempt to provide genetic diagnosis to the family. One of the children underwent detailed physical and neurological examinations, including brain magnetic resonance imaging (MRI) and scalp electroencephalography (EEG) evaluations. GALC genetic testing on this child enabled identification of a novel homozygous variant (NM_000153.3: c.1394C>T; p.(Thr465Ile)), which confirmed diagnosis as KD. Familial segregation of this variant was performed by PCR amplification and Sanger sequencing that revealed the parents as heterozygous carriers. We believe this novel GALC variant will not only help in genetic counseling to this family but will also aid in identification of future KD cases.