Background
Methods
Key questions to be addressed (Fig. 1)
Results
Question 1: Newborn screening for Krabbe disease using DBS
Initial screening tests
Assay Platform | MS/MS | MS/MS | Fluorometry |
---|---|---|---|
Marker | GALC activity | GALC activity | GALC activity |
Substrate | Synthetic analog of galactosylceramide containing a C8-fatty acyl chain; after incubation with GALC, releases novel ceramide | Synthetic analog of galactosylceramide containing a C7-fatty acyl chain; after incubation with GALC, releases novel ceramide | Artificial fluorogenic compound; after incubation with GALC, releases 4-MU analog that is measured fluorometrically |
States using assay | -* | IL, KY, NY, OH | MO |
Reference | [17] |
Test Method | Rationale | Advantages | Disadvantages |
---|---|---|---|
30 kb deletion testing | Known pathogenic mutation, common in IKD patients | Low complexity, rapid assay. When found homozygous indicates IKD. | Rare mutation, whose presence is more likely to indicate carrier status (i.e. “false positive”) and where the absence will still not avoid possible IKD (“false negative”) |
Psychosine testing | Appears to be associated with active disease in KD patients | Rapid test that when elevated indicates IKD. | Requires MS/MS equipment with higher sensitivity than that typically used in NBS labs but testing can be regionalized while still ensuring rapid turnaround time. |
GALC Genotyping | With 30kbDel, it is traditionally considered the “gold standard” 2nd tier testing in KD-NBS, but there may still be GALC deletions missed, leading to false negative results. | Can identify those infants at highest risk for IKD. Provides some reassurance to those who are carriers, have only enzyme lowering polymorphisms, or known “mild” mutations. | Instrumentation and expertise required are beyond the capabilities of most NBS labs. Many GALC mutations identified through KD-NBS are of uncertain clinical significance. Database of all known KD genotypes not available to support genotype interpretations. |
Second tier screening tests
Patienta | GALC mutations (simplified, allele1//allele2)a | WBC GALCa(nmol/h/mg) | psychosineb (nmol/L) | Age at HSCTa | HSCT Centerc | Outcomea | |
---|---|---|---|---|---|---|---|
IKD | 1 | 30kbDel//p.I546T + p.X670Qext*42 | 0.01 | 28.0 | 32 days | A | Alive, significant delays but interactive |
2 | 30kbDel//30kbDel | 0.05 | 32.2 | 31 days | A | Death | |
3 | 30kbDel//30kbDel | 0.02 | 38.1 | refused | – | Death | |
4 | 30kbDel// p.G360Dfs*2 | 0.12 | 60 | 41 days | B | Alive, severe delays, minimally interactive | |
5 | 30kbDel//30kbDel | 0.05 | 53.1 | 24 days | B | Death | |
High risk for KDa | N = 8 | Bi-allelic pathogenic GALC mutations | Range: 0.03-0.12 | Range: 0.21-2.7 | Currently, all continue to do well and have had no symptoms requiring additional referrals (follow-up ranging from 1 to 9 years, J. Orsini, personal communication) |
Question 2: Confirmatory diagnostic testing of newborns referred after abnormal KD-NBS
Question 3. Selection of HSCT centers and timely referral
1. Refer to transplant center ASAP (DOL 5-6) (Fig. 1) |
2. HSCT Center helps to arrange insurance coverage, lodging, admission for work up |
3.Baby admitted to HSCT Center (DOL 7-8): |
a. Blood drawn for stat HLA typing (high resolution Class I ABC, Class II DRB1), and studies, including, blood type, and psychosine |
b. Maternal blood for donor screening tests |
c. CSF for protein, cell count |
d. Neuroimaging tests: MRI brain with DTI |
e. Neurophysiological tests: EEG, BAER, VEP, nerve conduction tests |
f. Neurology and neurodevelopmental consult |
g. Hearing and vision evaluations |
h. Echocardiogram to check for PFO or PDA. If present, filter IV lines to prevent air emboli |
i. Physical therapy consultation |
j. When HLA typing is available, search for an unrelated cord blood unit donor, select units (> 4/6 match and > 5×10e7 cells/kg for HLA-confirmatory typing and GAL-C enzyme levels) to be used for final unit selection |
k. Proceed with insurance/third party payer authorization for transplantation |
l. Place central line and consider G-Tube placement for supplemental feeding |
m. Administer chemotherapy (currently 9 days) |
n. Make final cord blood unit selection during chemotherapy |
o. Administer transplant (DOL 21+) |