KANSAS CITY, MO—Newborn screening for Krabbe disease, also known as globoid-cell leukodystrophy (GLD), may help researchers evaluate potential therapies for this condition, according to an overview presented at the 46th Annual Meeting of the Child Neurology Society. Early diagnosis likely is needed to effectively intervene, especially in rapidly progressive forms of the disease, said Gustavo H. B. Maegawa, MD, PhD, Associate Professor of Neuroscience in the Department of Pediatrics at the University of Florida’s College of Medicine in Gainesville.
A Severe Condition
Krabbe disease is a lysosomal storage disorder caused by mutations in the galactosylceramidase (GALC) gene. The incidence is approximately one in 100,000 births. The carrier frequency is approximately one in 150. Krabbe disease is panethnic, and high incidence has been observed in inbred populations.
In the United States, 85% to 90% of patients with Krabbe disease have the infantile form, with onset of symptoms occuring before age 6 months. Stage I symptoms of infantile Krabbe disease include irritability, stiffness, developmental delay, feeding problems, and seizures. Stage II symptoms include rapid neurodegeneration with hypertonicity of the upper and lower extremities, optic atrophy, wheel-chair bound, hyporeflexia, and worsening of dysphagia requiring tube feeding. During stage III, affected patients become immobile, go blind, and eventually enter a vegetative state. Most cases are infantile and progress “so fast that the child dies before 10 or 12 months of age,” said Dr. Maegawa.
Late-onset forms of Krabbe disease include late-infantile Krabbe disease, with onset between age 6 months and 2 years; juvenile onset, which occurs between ages 3 and 8; and adult-onset, which occurs after age 8. “No consistent correlation has been observed between age of onset and residual GALC enzyme activity measured in peripheral leukocytes,” said Dr. Maegawa.
However, some correlations are observed when GALC enzymatic activity is measured from culture primary fibroblasts (derived from skin biopsies) from patients with different clincial forms of GLD. In GALC from these cells, a higher residual GALC activity is detected in cultured fibroblasts from patients with late-onset forms of GLD.
EEGs for patients with Krabbe disease initially appear normal, although they can have background activity that is slow and disorganized. Given that in GLD, the myelin-forming cells are severely affected in both central and peripheral nervous systems (oligodendrocytes and Schwann cells, respectively), nerve conduction velocities are consistently low, especially in patients with peripheral neuropathy, said Dr. Maegawa. In addition, visual and auditory evoked responses are severely abnormal in patients with early-infantile onset.
Current Treatment and Newborn Screening
In 2005, Escolar et al reported that hematopoietic stem cell transplantation (HSCT) favorably altered the natural history of the disease in asymptomatic newborns with infantile Krabbe disease, whereas HSCT after symptoms had developed did not result in substantive neurologic improvement. This finding set the stage for newborn screening programs for Krabbe disease.
New York State began screening all newborns for Krabbe disease in 2006. Wasserstein et al examined the clinical outcomes of infants screened for Krabbe disease in the state. Of the nearly two million infants screened, five were diagnosed with early-infantile Krabbe disease, and three died. Two babies died from HSCT-related complications, and one died from untreated disease. In addition, screening identified 92 infants with low risk of the disease, 37 with moderate risk, and 14 with high risk.
Initially, infants with confirmatory residual GALC activities between 0.30 and 0.5 nmol/hour/mg protein were considered to be at low-risk. Later on, with the experience of repeating the GALC activity, infants with activities greater than 0.3 nmol/hour/mg are now considered to not be at risk unless they carry two potentially pathogenic variants, which would classify them as moderate risk. In the moderate-risk category, newborns present confirmatory GALC activity of 0.16 to 0.29 nmol/hour/mg protein or GALC activity in the low-risk range but two known or potentially pathogenic mutations in the GALC gene.
In the high-risk category, newborns show high risk for Krabbe disease based on very low confirmatory GALC activity of 0.0 to 0.15-nmol/hour/mg protein. All infants in this group underwent urgent neurodiagnostic evaluation that included a neurologic exam every month, neuroimaging at 0, four, eight, and 12 months until 12 months. Between 13 and 36 months of age, the neurologic exams are every three months and brain imaging as needed.
The incidence of infantile Krabbe disease in New York, one in 394,000, was lower than anticipated. Researchers also observed significant overlap between risk categories. A few children switched from high to moderate risk groups. Finally, there was low compliance with the Krabbe Consortium protocol.