Diagnostic screening identifies a wide range of mutations involving the SHOX gene, including a common 47.5 kb deletion 160 kb downstream with a variable phenotypic effect.

Léri-Weill dyschondrosteosis (LWD) results from heterozygous mutations of the SHOX gene, with homozygosity or compound heterozygosity resulting in the more severe form, Langer mesomelic dysplasia (LMD). These mutations typically take the form of whole or partial gene deletions, point mutations within the coding sequence, or large (>100 kb) 3' deletions of downstream regulatory elements. We have analyzed the coding sequence of the SHOX gene and its downstream regulatory regions in a cohort of 377 individuals referred with symptoms of LWD, LMD or short stature. A causative mutation was identified in 68% of the probands with LWD or LMD (91/134). In addition, a 47.5 kb deletion was found 160 kb downstream of the SHOX gene in 17 of the 377 patients (12% of the LWD referrals, 4.5% of all referrals). In 14 of these 17 patients, this was the only potentially causative abnormality detected (13 had symptoms consistent with LWD and one had short stature only), but the other three 47.5 kb deletions were found in patients with an additional causative SHOX mutation (with symptoms of LWD rather than LMD). Parental samples were available on 14/17 of these families, and analysis of these showed a more variable phenotype ranging from apparently unaffected to LWD. Breakpoint sequence analysis has shown that the 47.5 kb deletion is identical in all 17 patients, most likely due to an ancient founder mutation rather than recurrence. This deletion was not seen in 471 normal controls (P<0.0001), providing further evidence for a phenotypic effect, albeit one with variable penetration.

Diagnosing Smith-Magenis syndrome and duplication 17p11.2 syndrome by RAI1 gene copy number variation using quantitative real-time PCR.

Smith-Magenis syndrome (SMS) and duplication 17p11.2 (dup17p11.2) syndrome are multiple congenital anomalies/mental retardation disorders resulting from either a deletion or duplication of the 17p11.2 region, respectively. The retinoic acid induced 1 (RAI1) gene is the causative gene for SMS and is included in the 17p11.2 region of dup17p11.2 syndrome. Currently SMS and dup17p11.2 syndrome are diagnosed using a combination of clinically recognized phenotypes and molecular cytogenetic analyses such as fluorescent in situ hybridization (FISH). However, these methods have proven to be highly expensive, time consuming, and dependent upon the low resolving capabilities of the assay. To address the need for improved diagnostic methods for SMS and dup17p11.2 syndrome, we designed a quantitative real-time PCR (Q-PCR) assay that measures RAI1 copy number using the comparative C(t) method, DeltaDeltaC(t). We tested our assay with samples blinded to their previous SMS or dup17p11.2 syndrome status. In all cases, we were able to determine RAI1 copy number status and render a correct diagnosis accordingly. We validated these results by both FISH and multiplex ligation-dependent probe amplification (MLPA). We conclude that Q-PCR is an accurate, reproducible, low-cost, and reliable assay that can be employed for routine use in SMS and dup17p11.2 diagnosis.

The Icarus effect: the influence of diluent warming on dantrolene sodium mixing time.

Prompt administration of intravenous (i.v.) dantrolene sodium (DS) is the primary determinant of successful treatment of malignant hyperthermia (MH) syndrome. Because DS has a long reconstitution time for use in treating an MH crisis, we evaluated an alternative technique for hastening the reconstitution. Simulating real-world conditions, with equipment common to the operating room environment, we conducted a randomized, controlled, single-blind study dividing 16 DS vials into 2 equal groups: warm (41 degrees C) and ambient temperature (22 degrees C). With an i.. fluid warmer at 41 degrees C, primed with a 1-L bag of preservative-free sterile water, attached to a 60-mL syringe via a 3-way stopcock, we aspirated and injected the diluent directly into each DS vial. The Icarus effect was clearly demonstrated: warmed diluent vs ambient temperature hastened the reconstitution time for DS. The mean time to particulate-free DS solution suitable for i.v. injection with the warm diluent was 58.88 seconds compared with 93.87 seconds for the ambient temperature group (P <.001). A practical method using a reliable and safe warming device readily available to anesthetists and ubiquitous to the operating room environment speeds the time to administration of DS ultimately reducing morbidity and mortality associated with MH.