Christine R. Bryke

Distinct Missense Mutations of the FGFR3 Lys650 Codon Modulate Receptor Kinase Activation and the Severity of the Skeletal Dysplasia Phenotype

The fibroblast growth factor-receptor 3 (FGFR3) Lys650 codon is located within a critical region of the tyrosine kinase-domain activation loop. Two missense mutations in this codon are known to result in strong constitutive activation of the FGFR3 tyrosine kinase and cause three different skeletal dysplasia syndromes-thanatophoric dysplasia type II (TD2) (A1948G [Lys650Glu]) and SADDAN (severe achondroplasia with developmental delay and acanthosis nigricans) syndrome and thanatophoric dysplasia type I (TD1) (both due to A1949T [Lys650Met]). Other mutations within the FGFR3 tyrosine kinase domain (e.g., C1620A or C1620G [both resulting in Asn540Lys]) are known to cause hypochondroplasia, a relatively common but milder skeletal dysplasia. In 90 individuals with suspected clinical diagnoses of hypochondroplasia who do not have Asn540Lys mutations, we screened for mutations, in FGFR3 exon 15, that would disrupt a unique BbsI restriction site that includes the Lys650 codon. We report here the discovery of three novel mutations (G1950T and G1950C [both resulting in Lys650Asn] and A1948C [Lys650Gln]) occurring in six individuals from five families. Several physical and radiological features of these individuals were significantly milder than those in individuals with the Asn540Lys mutations. The Lys650Asn/Gln mutations result in constitutive activation of the FGFR3 tyrosine kinase but to a lesser degree than that observed with the Lys540Glu and Lys650Met mutations. These results demonstrate that different amino acid substitutions at the FGFR3 Lys650 codon can result in several different skeletal dysplasia phenotypes.

Chromothriptic Cure of WHIM Syndrome

Chromothripsis is a catastrophic cellular event recently described in cancer in which chromosomes undergo massive deletion and rearrangement. Here, we report a case in which chromothripsis spontaneously cured a patient with WHIM syndrome, an autosomal dominant combined immunodeficiency disease caused by gain-of-function mutation of the chemokine receptor CXCR4. In this patient, deletion of the disease allele, CXCR4(R334X), as well as 163 other genes from one copy of chromosome 2 occurred in a hematopoietic stem cell (HSC) that repopulated the myeloid but not the lymphoid lineage. In competitive mouse bone marrow (BM) transplantation experiments, Cxcr4 haploinsufficiency was sufficient to confer a strong long-term engraftment advantage of donor BM over BM from either wild-type or WHIM syndrome model mice, suggesting a potential mechanism for the patients cure. Our findings suggest that partial inactivation of CXCR4 may have general utility as a strategy to promote HSC engraftment in transplantation.

Cytogenetic and molecular characterization of marker chromosomes in patients with mosaic 45,X karyotypes.

SummaryCytogenetic and molecular techniques were employed to determine the origin of marker chromosomes in five patients with mosaic 45,X karyotypes. The markers were shown to be derived from the X chromosome in three female patients and from the Y chromosome in one female and one male. One of the female patients, with a very small, X-derived ring chromosome, had additional phenotypic abnormalities not typically associated with Turner syndrome. In this patient, both the ring and the normal X chromosomes replicated early; perhaps the unusual phenotype is the result of both chromosomes remaining transcriptionally active. These studies illustrate the power of resolution and utility of combined cytogenetic and molecular approaches to some clinical cases.

Myeloproliferative disorder with eosinophilia and ETV6-ABL gene rearrangement: Efficacy of second-generation tyrosine kinase inhibitors

ETV6/ABL is a rare gene rearrangement that has rarely been detected in Philadelphia-negative chronic myeloproliferative disorders (C-MPD) and found to have tyrosine kinase activity similar to the BCR/ABL fusion protein. We describe a case of a 61-year-old female with a C-MPD associated with an ETV6/ABL gene rearrangement. She achieved complete cytogenetic remission on imatinib 400mg daily for 17 months, but then developed morphologic and cytogenetic relapse. After starting nilotinib 400mg orally twice daily, she achieved CCyR at 3, 6, and 11 months, suggesting that second-generation TKIs can result in favorable responses in patients with ETV6/ABL rearrangement who relapse after imatinib.

Incidence and patterns of ALK FISH abnormalities seen in a large unselected series of lung carcinomas

BackgroundAnaplastic lymphoma receptor tyrosine kinase (ALK) gene rearrangements have been reported in 2-13% of patients with non-small cell lung cancer (NSCLC). Patients with ALK rearrangements do not respond to EGFR-specific tyrosine kinase inhibitors (TKIs); however, they do benefit from small molecule inhibitors targeting ALK.ResultsIn this study, fluorescence in situ hybridization (FISH) using a break-apart probe for the ALK gene was performed on formalin fixed paraffin-embedded tissue to determine the incidence of ALK rearrangements and hybridization patterns in a large unselected cohort of 1387 patients with a referred diagnosis of non-small cell lung cancer (1011 of these patients had a histologic diagnosis of adenocarcinoma). The abnormal FISH signal patterns varied from a single split signal to complex patterns. Among 49 abnormal samples (49/1387, 3.5%), 32 had 1 to 3 split signals. Fifteen samples had deletions of the green 5′ end of the ALK signal, and 1 of these 15 samples showed amplification of the orange 3′ end of the ALK signal. Two patients showed a deletion of the 3′ALK signal. Thirty eight of these 49 samples (38/1011, 3.7%) were among the 1011 patients with confirmed adenocarcinoma. Five of 8 patients with ALK rearrangements detected by FISH were confirmed to have EML4-ALK fusions by multiplex RT-PCR. Among the 45 ALK-rearranged samples tested, only 1 EGFR mutation (T790M) was detected. Two KRAS mutations were detected among 24 ALK-rearranged samples tested.ConclusionsIn a large unselected series, the frequency of ALK gene rearrangement detected by FISH was approximately 3.5% of lung carcinoma, and 3.7% of patients with lung adenocarcinoma, with variant signal patterns frequently detected. Rare cases with coexisting KRAS and EGFR mutations were seen.

Solitary rectal ulcer syndrome in a teenaged boy.

Since the original description of solitary rectal ulcer by Cruveilheir in 1830, about 250 cases have been reported (1). The condition most frequently presents in adults between 30 and 50 years of age. There are very few pediatric case reports and none have come from North America. We report here a 13-year-old boy with solitary rectal ulcer syndrome and a review of the pediatric experience with this rare condition.

Clinical and Molecular Characterization of Overlapping Interstitial Xp21-p22 Duplications in Two Unrelated Individuals

Development and implementation of high‐density DNA arrays demonstrated the important role of copy number changes on the X chromosome in the etiology of developmental delay and mental retardation (MR). We describe two unrelated patients with developmental delay due to similar interstitial duplications at Xp21‐p22. The first patient is a 6‐month‐old male with multiple affected family members including many females. The second patient is a 5‐year‐old adopted female. In both patients, chromosome analysis and array comparative genomic hybridization (aCGH) showed duplications of overlapping regions at Xp21‐p22. The duplicated segments contain numerous genes associated with MR, including AP1S2, NHS, CDKL5, RPS6KA3, SMS, and ARX. Except for developmental delay, there is little phenotypic overlap between the male and the female patient. Additionally, the female patient and affected female relatives of the male patient have variable severities of cognitive impairment, likely due to different X‐inactivation patterns and effects of other, nonduplicated genes important for normal development. These cases illustrate that increased gene dosage of X‐linked MR genes lead to cognitive impairment. Precise delineation of chromosome rearrangements by aCGH and identification of genes within duplicated segments helped in establishing genotype–phenotype correlations for each of our patients, in comparing them to each other, as well as with previously reported cases of Xp21‐p22 duplications. However, we show that even with detailed molecular characterization, phenotype prediction remains challenging in patients with structural abnormalities of the X chromosome.

Marfan Syndrome Type II: There Is More to Marfan Syndrome than Fibrillin 1

Marfan syndrome is a well-described autosomal dominant syndrome with widely variable clinical manifestations. Cardiovascular complications include mitral valve prolapse with or without associated mitral valve insufficiency, aortic root dilatation, and most importantly the occasional development of aortic aneurysms or rupture. Given the inconsistent phenotype along with the potentially life-threatening implications, clinicians are increasingly turning to genetic testing for definitive diagnostic confirmation. It has been well established that mutations in the FBN1 gene encoding the structural protein Fibrillin 1 is the molecular etiology of Marfan syndrome. However, there are numerous patients who meet the Ghent clinical diagnostic criteria for Marfan syndrome who do not have identifiable FBN1 mutations. Recently, mutations in TGFBR1 and TGFBR2 (transforming growth factor beta receptors 1 and 2, respectively) have been shown to result in Loeys-Dietz syndrome, a connective tissue disorder with significant phenotypic overlap with Marfan syndrome. Individuals with this Marfanoid disorder lack the ocular findings of Marfan syndrome and often have dysmorphic features such as unusual facies, cleft palate, and contractures. In addition, Loeys-Dietz syndrome patients often present in childhood with significant cardiovascular problems. This article serves to report an illustrative case of Loeys-Dietz syndrome and reviews the phenotypic consequences of FBN1 and TGFBR1 and TGFBR2 gene mutations.

Low expression of Abelson interactor-1 is linked to acquired drug resistance in Bcr-Abl-induced leukemia.

The basis for persistence of leukemic stem cells in the bone marrow microenvironment remains poorly understood. We present evidence that signaling cross-talk between α4 integrin and Abelson interactor-1 (Abi-1) is involved in the acquisition of an anchorage-dependent phenotype and drug resistance in Bcr-Abl-positive leukemia cells. Comparison of Abi-1 (ABI-1) and α4 integrin (ITGA4) gene expression in relapsing Bcr-Abl-positive CD34+progenitor cells demonstrated a reduction in Abi-1 and an increase in α4 integrin mRNA in the absence of Bcr-Abl mutations. This inverse correlation between Abi-1 and α4 integrin expression, as well as linkage to elevated phospho-Akt and phospho-Erk signaling, was confirmed in imatinib mesylate -resistant leukemic cells. These results indicate that the α4-Abi-1 signaling pathway may mediate acquisition of the drug-resistant phenotype of leukemic cells.

Desbuquois syndrome in three sisters with significantly different lengths of survival

Desbuquois syndrome is a rare, autosomal recessive, well-delineated genetic disorder. It is characterized by severe micromelic dwarfism, thoracic hypoplasia, broad proximal femora with enlarged lesser trochanters resembling a ‘‘Swedish key,’’ advanced carpal and tarsal bone age, and spondyloarticular problems. Severe joint laxity and dislocation overlap with Larsen syndrome. The narrow chest cavity and concurrent kyphoscoliosis often contribute to respiratory infections and respiratory failure resulting indeath soonafter birth [Desbuquois et al., 1966; Meinecke et al., 1989; Shohat et al., 1994; Hall, 1999; Faivre et al., 2003, 2004a,b]. We report three sisters with significantly different lengths of survival. Patients 1 and 2 were briefly mentioned and listed as case 6 and 7 of Shohat et al. [1994].