The following are descriptions of diagnostic molecular genetics tests available to qualified professionals in the medical community. For more information, call Theresa Herman, CLS at (510) 428-3623.
Fragile-X Syndrome
We screen all patients first using a PCR test. Unaffected males will show a normal size PCR fragment, and unaffected females with two normal size fragments will be determined by this PCR test alone. Males with a null PCR result and females who show a single size normal fragment by PCR will need further analysis by Southern blotting with a FraXA probe. (We recommend submitting an additional Na heparin blood specimen at the same time as this DNA testing is performed if a general karyotype analysis has not been done on the patient).
Prader-Willi / Angelman Syndrome
We use a methylation-specific polymerase chain reaction assay (M-PCR) for the detection of Prader-Willi (PWS) and Angelman (AS) syndromes on patients' bisulfite-modified DNA. M-PCR will distinguish methylated from unmethylated DNA at a CpG island of SNRPN, a candidate gene for PWS. This method will detect either a deletion or uniparental disomy as the cause of the disease but does not distinguish between the two. (We recommend submitting an additional Na heparin blood specimen at the same time as this DNA testing is performed if a general karyotype analysis has not been done on the patient, see above.).
UPD chromosome 7
A similar method to Prader-Willi syndrome testing is used to diagnose UPD for chromosome 7, which is found in ~ 10% of Russell-Silver syndrome cases.
Spinal Muscular Atrophy Types 1, 2, and 3
This PCR/RE assay will detect homozygous deletions in exons 7 and 8 of the SMN gene that confirm a diagnosis of SMA Types 1 and 2 in up to 95% of patients and in ~80% of patients with SMA Type 3. This method cannot be used for carrier testing.
Cystic Fibrosis Mutation Screen
We test for 32 CF mutations by the reverse dot blot method, using membrane-bound oligonucleotides which hybridize to complementary sequences in PCR-amplified patient DNA. This 32 mutation panel picks up about 88% of CF mutations in the Caucasian population. Mutations tested: DF508, G551D, R553X, G542X, N1303K, R117H, 621+1, DI507, 1717-1, G85E, 3905insT, R347H, R347P, 3659delC, R334W, Q493X, 1898+1, 3849+10kb, 2184delA, 2183AA«G, R560T, 3849+4, 2789+5, 711+1, W1282X, A455E, V520F, R1162X, S549N, Y1092X, Y122X, S549R For families in which the CF affected patient's mutations have not been identified, we can use linkage analysis to determine inheritance of the CF chromosomes for prenatal diagnosis. Blood specimens are also required from the patient and the parents for this analysis.
Hemoglobin S, C, E, D
PCR and restriction enzyme digestion is used to detect the b globin gene mutation.
Medium Chain Acyl Co-A Dehydrogenase Deficiency
This assay detects the presence or absence of the primary MCAD mutation site at position 985 of the coding region, using PCR and restriction enzyme digestion.
Achondroplasia G380R mutation of FGFR3
This PCR/RE assay will detect the presence or absence of the G-to-A substitution or the G-to-C transition at nucleotide 1138 in the FGFR3 gene, causing autosomal dominant short-limbed dwarfism.
Y microdeletions
About 10-20% of men requesting ICSI who have severe oligospermia or azoospermia have small deletions within one of the AZF (azoospermia factor) regions associated with infertility. We offer a PCR-based test for 18 sequence-tagged sites in the AZF regions.
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