Six novel mutations detected in the GALC gene in 17 Japanese patients with Krabbe disease, and new genotype–phenotype correlation

Abstract

Krabbe disease is an autosomal recessive leukodystrophy. It is pathologically characterized by demyelination of the central and peripheral nervous systems and the accumulation of globoid cells in brain white matter. It is caused by a deficiency of galactocerebrosidase (GALC) activity. We investigated mutations of the GALC gene in 17 Japanese patients with Krabbe disease, the largest subject number of Japanese patients to date, and found 27 mutations. Of these mutations, six were novel, including two nonsense mutations, W115X and R204X, two missense mutations, S257F and L364R, a small deletion, 393delT, and a small insertion, 1719-1720insT. Our findings, taken with the reported mutations in Japanese patients, confirm several mutations common to Japanese patients, the two most frequent being 12Del3Ins and I66M+I289V, which account for 37% of all mutant alleles. With two additional mutations, G270D and T652P, these account for up to 57% of genetic mutations in Japanese patients. Distribution of the mutations within the GALC gene indicated some genotype-phenotype correlation. I66M+I289M, G270D, and L618S contributed to a mild phenotype. Screening for these mutations may provide an effective method with which to predict the clinical phenotype.

Altered Trafficking and Processing ofGALCMutants Correlates with Globoid Cell Leukodystrophy Severity

“…In the lysosome, GALC catabolizes galactolipids, such as galactosylceramide and psychosine (Suzuki, 2004). Because clinical laboratories use total cell lysates from blood cells or skin fibroblasts to measure GALC activity, it is possible that GALC present in other subcellular organelles could falsely skew the enzymatic activity measured in total cells after lysis but would not reflect the useful activity of GALC in vivo in the lysosome.…”

“…The mutations are numbered according to HGVS, which have elsewhere been described as G41S, D528N, and L618S, respectively. G57S is responsible for the majority of later-onset GLD in the Catania region of Italy (Lissens et al, 2007), D544N is found in the infantile-onset Muslim Arab population of Israel , and L634S is a prominent later-onset mutation in Japan (Xu et al, 2006;Hossain et al, 2014). All of these mutations are sometimes found in homozygosity among GLD patients, and in the homozygous state they cause later-or infantile-onset GLD respectively, suggesting they are clearly associated with the age of onset of GLD.…”

“…Three factors have been suggested as potential contributors to clinical variability: cis-polymorphisms (Raghavan et al, 2005), environmental influences including diet (Pannuzzo et al, 2010), and modifier genes such as saposinA/Psap (Yagi et al, 2004) or others (Lattanzi et al, 2010). The GALC precursor protein is generated in the endoplasmic reticulum (ER) and is transported to the lysosome, where it is processed into 50 and 30 kDa subunits (Nagano et al, 1998).…”

Newborn screening for Krabbe disease in New York State: the first eight years’ experience

“…Functional studies would be necessary to determine whether p.V320M and others (such as p.D94=) are indeed pseudodeficiency alleles. p.L618S was found in cis with several other variants in our population (Supplementary Table S3 online), and those who carried two copies of p.L618S were categorized as being at high (1; case 9, 3,28,29,32 Nearly all of the 348 infants referred carried at least one of the three common activity-attenuating polymorphisms (p.R168C, p.D232N, p.I546T). The frequency of each was elevated in the referral population compared with published data.…”

Newborn Screening for Krabbe Disease and Other Lysosomal Storage Disorders: Broad Lessons Learned

“…Another example, p.Leu634Ser (legacy p.Leu618Ser) is primarily found in infants with Japanese ethnicity. Infants homozygous for these variants have been assigned to the high risk category, but in the literature there are only two cases of individuals homozygous for p.Leu634Ser, and both patients were adults when diagnosed with KD [41]. There are no known cases of Krabbe disease homozygous for p.Tyr319Cys.…”