Collaborators: Anil Mukherjee (right) and co-author Zhongjian (Gary) Zhang

Infantile neuronal ceroid lipofuscinosis (INCL) is the tongue-twisting name for a horrific, but fortunately rare, lysosomal storage disease, also known as childhood Batten disease. Children born with the defect are normal at birth, but by around 1 year, show symptoms of retinal damage and neurodegeneration that will leave them blind by age 2 and brain dead by age 4. Children with INCL persist in a vegetative state until death at age 8 to 12 years.

Into this hopelessness NICHD’s Anil Mukherjee and his colleagues have brought a tiny ray of light, thanks to a pilot project spawned by a Bench-to-Bedside Award. Very preliminary results from their treatment of two infants with INCL indicate that an experimental drug, cysteamine bitartrate (Cystagon), may stop the disease’s progressive retinal and brain damage. Definitive data will be collected over the pilot study’s four years of observation on five infants.

"The Bench-to-Bedside Award helped us enormously," Mukherjee told The NIH Catalyst in an interview. "We used the award to complete some of our basic laboratory research (Z. Zhang, J.DeB. Butler, S.W. Levin, K.E. Wisniewski, S.S. Brooks, and A.B. Mukherjee. Nature Medicine 7:478–484, 2001) and then embarked on this protocol." Mukherjee says the B-to-B award "provided an added incentive to initiate the pilot study," which evaluates Cystagon for the treatment of INCL.

Mukherjee worked on the study with Zhongjian (Gary) Zhang from his laboratory, James Sidbury, Jr., former NICHD scientific director (now retired), Rafael Caruso of NEI, Andrea Gropman and Kenneth Fischbeck of NINDS, and the CC’s Zenadie Quezado and Nicholas Patronas. Extramural collaborators included Sondra Levin from Walter Reed Army Medical Center, Sandra Hofmann of the University of Texas Southwestern Medical Center in Dallas, Krystyna Wisniewski of the New York State Institute for Basic Research on Staten Island, and Pirkko Santavuori of the University of Helsinki, who first described INCL.

In a recent lecture, NICHD cell biologist Juan Bonifacino said that, from the outset, serendipity has played a leading role in research on lysosomes and lysosomal storage diseases. INCL is no exception. In 1997, as Mukherjee’s lab was trying to isolate and characterize a mouse phospholipase A2 gene, they also came upon the gene for another enzyme—palmitoyl-protein thioesterase (PPT). As it turned out, Hofmann’s group had already snared the human PPT gene. She and others went on to link mutations in the PPT gene to INCL as Mukherjee and his colleagues went to work on a therapy to replace or compensate for the defective enzyme.

Mukherjee explains that many proteins are modified, post-translationally, by the addition of lipids such as palmitic acid. These adornments may anchor proteins in membranes or be essential for their function in other ways. But once the proteins have served their purposes, "the thioester linkage must be disrupted and the lipid must be cleaved from these proteins for recycling or degradation," Mukherjee says. "Thus PPT plays a critical role." Unable to degrade the protein-lipid complexes (ceroid), the cells of INCL patients—including key retinal and brain cells—just keep accumulating ceroid in lysosomes.

Mukherjee saw INCL’s Achilles’ heel in PPT’s flimsy thioester linkage, which he and his colleagues rationalized would be susceptible to nucleophilic chemicals. They screened a list of such drugs, tested three for their ability to cleave the thioester linkage, and picked two with very few side effects—cysteamine and N-acetyl cysteine—to test in vitro in cells from nine INCL patients. Serendipity again had a role in the choices. Just down the hall, Mukherjee’s NICHD neighbor, Bill Gahl, had been using cysteamine bitartrate for more than 20 years to treat cystinosis, another hereditary lysosomal storage disease. Gahl’s data showed that cysteamine could enter the lysosomes and was likely to cross the blood-brain barrier—properties that would be essential for an INCL therapy.

Results of the lab experiments were spectacular—biochemical and electron microscopic inspections of the cells showed that Cystagon cleared ceroid deposits from the cells. This result paved the way for a clinical trial. "There is no effective treatment for these patients, and INCL is uniformly fatal," Mukherjee says. "Cystagon is definitely worth trying." The scientists fired off their B-to-B proposal.

INCL is a rare disease (1 in 100,000 births) and, thus far, Mukherjee and his colleagues have treated just two of the five patients permitted for their Cystagon protocol. The signs are as positive as could be hoped at this early stage (6 months for one patient, almost a year for the other). Patients’ white blood cells are free of ceroid inclusions and, within the 6 months of treatment, the babies show no signs of further retinal and brain deterioration. "The biology of this disease predicts that retinas and the brain would degenerate further during this period," Mukherjee says, leaving him guardedly optimistic.

Because some damage to the babies’ eyes and brains had already occurred before the disease was recognized and the infants were brought in for treatment at age 2 years, Mukherjee and his colleagues do not know the extent to which the infants will achieve normal developmental milestones. "If they still have brain function at age 4, then we have achieved something," says Mukherjee. "And if they regain eyesight, that would indicate the drug is effective."

Ultimately, the key to real success with the drug may lie in the earliest possible treatment—before the onset of symptoms. Scientists in Finland are now giving this twist to the NIH experimental approach. They have given Cystagon treatment to a days-old infant whose parents had previously had a baby with INCL.

Mukherjee says the infant’s circumstances are unusual—generally INCL is not anticipated (heterozygous carriers have no symptoms) or recognized until an affected infant shows symptoms later in its first year of life.

As word gets out about the Cystagon clinical trial, Mukherjee keenly awaits results from the next visits of his small patients and the recruitment of additional new patients. But he says that despite the drug’s encouraging signs, he’s not putting all his eggs in one basket. The research team is now starting to develop strategies for INCL gene therapy.

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