[Analysis of clinical manifestation and genetic mutation in a child with X-linked chondrodysplasia punctata 2].

OBJECTIVE: To analyze clinical manifestations and genetic mutation in a child with severe short stature and other malformations. METHODS: The child has undergone history taking and physical examination. Genome DNA was extracted from peripheral blood samples of the proband and her family members. Candidate genes were captured with Agilent SureSelect and sequenced on an Illumina platform. Suspected mutation was verified by Sanger sequencing. RESULTS: The patient, a six-year-and-10-month old girl, presented with non-symmetrical short stature, dysmorphism, abnormalities of limbs and spine, amblyopia of left eye, and cataract of right eye, in addition with frequent respiratory infection and micturition. Laboratory testing suggested 25-hydroxy vitamin D deficiency (18.9 ng/mL). Spine X-ray showed multiple malformations with centrums. Her mother also featured short stature (138 cm). Her aunt had short stature (130 cm) and limb-length discrepancy. Her little brother was 2.5 years old, and his height was 81 cm (-3.4 SD). Exome sequencing revealed a heterozygous mutation c.184C to T (p.Arg62Trp) in the proband and her mother. The same mutation was not found in her father and brother. CONCLUSION: The patient was diagnosed with X-linked chondrodysplasia punctata 2. Mutation of the EBP gene probably underlied the disease in this family.

Characterization of six missense mutations in the tissue-nonspecific alkaline phosphatase (TNSALP) gene in Chinese children with hypophosphatasia.

AIMS: Hypophosphatasia, a rare inherited disease characterized by defective mineralization of bone and teeth, is caused by various mutations in the tissue-nonspecific isoenzyme of alkaline phosphatase (TNSALP) gene. Our aim was to determine the mutations on TNSALP gene in three Chinese children diagnosed as having hypophosphatasia. METHODS: Genomic DNA was extracted from whole blood samples of patients and their parents. The TNSALP coding regions were then sequenced. Plasmids expressing wild-type or various mutants were built and in vitro studies were performed in order to determine whether these amino acid replacements could affect the TNSALP enzymatic activity. RESULTS: Six missense mutations were identified from three independent pedigrees. Of the six missense mutations, four were novel and two had been previously reported. The Y28D, A111T and T389N mutants displayed only negligible ALP activity in vitro compared to the wild-type (WT) TNSALP. The defect was mainly due to the significantly decreased protein expression in the 66 KD immature forms and the nearly undetectable protein expression in the 80 KD mature forms. Moreover, all three mutants had a dominant negative effect on the WT protein when co-transfected with TNSALP (WT). M219V and R136L mutants both exhibited partial enzymatic activities which were consistent with reduced protein expression in both forms of TNSALP which further exhibited moderate dominant-negative effect. In addition, Y388H mutant showed weak ALP activity. Western blot analysis indicated that the extreme reduction in signal from the mature forms of TNSALP could be the main cause of decreased enzymatic activity, since a strong signal was observed in the immature forms. CONCLUSION: Six missense mutations were identified in three Chinese hypophosphatasia pedigrees with subnormal serum ALP activity. Our results show that the low activity of serum ALP in the three patients is due mainly to a defect in the protein expression of the mutants. This may be the underling molecular mechanism for hypophosphatasia in these patients.

Identification of TCIRG1 and CLCN7 gene mutations in a patient with autosomal recessive osteopetrosis.

Osteopetrosis is a heritable bone disorder that exhibits highly clinical and genetical heterogeneity, and is caused by defective osteoclastic resorption. The three main forms are the autosomal recessive severe (ARO), the intermediate autosomal and the autosomal dominant benign osteopetrosis forms. In the present study, the clinical, biochemical and radiological manifestations were described in a patient with osteopetrosis. Sequence analysis identified the compound heterozygous mutations, c.909C>A (p.Tyr303X) and c.2008C>T (p.Arg670X), in TCIRG1, and a heterozygous splicing mutation, c.1798­1G>T, in the chloride channel 7 gene (CLCN7). Two aberrant forms of the CLCN7 transcripts, c.1798_1883 (exon 20) deletion predicted to cause p.Leu601GlyfsX13, and the c.1798_1821 deletion, the first 24 bp of the exon 20, predicted to cause p.Gly600_Gln607del, were detected by further analysis of the splicing patterns in the leukocytes. The patient's asymptomatic mother carried the TCIRG1 c.909C>A (p.Tyr303X) and CLCN7 c.1798­1G>T mutations, while the asymptomatic father carried the TCIRG1 c.2008C>T (p.Arg670X) mutation only. The patient was finally diagnosed with ARO on the basis of clinical and biochemical parameters, radiological changes and genetic defects. To the best of our knowledge, this is the first reported case of a patient with osteopetrosis who carries TCIRG1 and CLCN7 mutations. In addition, among the three mutations, TCIRG1 c.909C>A and CLCN7 c.1798­1G>T were novel mutations.

Molecular defects identified by whole exome sequencing in a child with Fanconi anemia.

Fanconi anemia is a rare genetic disease characterized by bone marrow failure, multiple congenital malformations, and an increased susceptibility to malignancy. At least 15 genes have been identified that are involved in the pathogenesis of Fanconi anemia. However, it is still a challenge to assign the complementation group and to characterize the molecular defects in patients with Fanconi anemia. In the current study, whole exome sequencing was used to identify the affected gene(s) in a boy with Fanconi anemia. A recurring, non-synonymous mutation was found (c.3971C>T, p.P1324L) as well as a novel frameshift mutation (c.989_995del, p.H330LfsX2) in FANCA gene. Our results indicate that whole exome sequencing may be useful in clinical settings for rapid identification of disease-causing mutations in rare genetic disorders such as Fanconi anemia.

A unique combination of 17pter trisomy and 21qter monosomy in a boy with developmental delay, severe intellectual disability, growth retardation and dysmorphisms.

BACKGROUND: Microduplication at 17p13.3 and microdeletion at 21q22 are both rare chromosomal aberrations. The presence of both genomic imbalances in one patient has not been previously reported in literature. In this study, we performed a molecular diagnostic testing with a whole genome microarray on a 3-year-old boy with developmental delay, mental retardation and multiple malformations. METHODS: A routine G-banding karyotype analysis was performed using peripheral lymphocytes. Chromosome microarray analysis (CMA) was done using Affymetrix CytoScan™ HD array. Genomic imbalances were further confirmed by multiple ligation-dependent probe amplification (MLPA). RESULTS: The result of karyotyping was normal but CMA detected a 9.8 Mb microduplication at 17p13.3-13.1 (chr17: 1-9,875,545) and a 2.8 Mb microdeletion involving 21q22.3-qter (chr21: 45,239,077-48,097,372). The imbalances were due to a balanced translocation present in patient's mother. The patient was characterized with short stature, profound developmental delay, non-verbal, intellectual disability as well as craniofacial dysmorphism, subtle brain structural anomaly and sparse scalp hair. CONCLUSIONS: This is the first patient reported with a combination of a microduplication at 17p13.3-13.1 and a microdeletion at 21q22.3-qter. Both genomic imbalances were undetected by conventional karyotyping but were delineated with CMA test. Synergistic effect from the two rare genomic imbalances is likely responsible for the severe clinical phenotypes observed in this patient.

[Overview of clinical occurrence of primary immunodeficiency disorders in children].

OBJECTIVE: More than one hundred primary immunodeficiency disorders have been discovered so far. But the incidence of these disorders in our country is still not clear, so we analyzed the clinical data of 93 children with primary immunodeficiency disorders seen in our hospital in recent 30 years to understand the occurrence of primary immunodeficiency disorders in children, to promote the clinicians to become familiar with these disorders, to improve the nationwide registry system and to establish the basis for the treatment and prevention in future. METHODS: To analyze the constituent ratio of the 93 children with primary immunodeficiency disorders seen in our hospital from 1974 to 2003, diagnostic and classification criteria were set by taking the proposal by International Union of Immunological Societies (IUIS) PID classification committee in 2003 into account. All the data were analyzed retrospectively. RESULTS: In the 93 children with primary immunodeficiency disorders, antibody deficiencies were the most frequent (39.8%) finding, followed by combined immunodeficiency, combined T- and B-cell disorders (22.6%), and T lymphocytic deficiencies alone (14.0%). Immunodeficiency with other major defects accounted for 12.9%, phagocytic disorders 9.7%, and complement deficiencies 1.1%. Thus, there seemed to be a tendency that the incidence increased with time. The incidence of these disorders has increased significantly as shown by 50 diagnosed cases in children with these disorders since 1996. Sixteen children died, with the highest mortality occurred with combined immunodeficiency. Seven children developed bronchiectasis. Two children suffered from persistent diarrhea while one of the two was complicated with persistent intestinal fistula. One child developed juvenile rheumatoid arthritis, another one with granulocytopenia and iridocyclitis, and the other with allergic purpura. The boys: girls ratio for all disorders was 3:1. The age of onset ranged from 10 days to 37 years of age. CONCLUSIONS: There are vast variety of primary immunodeficiency disorders in our area and antibody deficiency is the most common abnormality. Combined immunodeficiency has early onset age and high mortality rate. With the great improvement of the diagnostic techniques, these disorders have become a group of important disorders and all the clinicians should pay great attention to these disorders.

[Low dose methotrexate combined with GM-CSF induced differentiation of U937 cells].

OBJECTIVE: To explore the effect of methotrexate on acute monoblastic leukemia cells, and the potential role of low-dose methotrexate in the treatment of monoblastic leukemia. METHODS: By using U937 cell line as a model, the induced differentiation of MTX or GM-CSF or their combination was detected by NBT reduction test, morphological observation and CD(14) expression. TRAP-ELISA was used for measuring telomerase activity. RESULTS: After incubation with 20 nmol/L methotrexate for 24, 48, 72 and 96 hours, the size of the U937 cells increased, the nuclear/plasma ratio gradually decreased, NBT reductive test became positive, and CD(14) positive cells increased from 3% to 20% after 72 hours incubation, indicating partial differentiation. Treatment of U937 cells with 100 U/ml GM-CSF alone failed to induce differentiation. However, GM-CSF combined with low-dose methotrexate resulted in 63% of differentiated cells after 72 hours incubation, and telomerase activity of the U937 cells decreased from 2.11 (before treatment) to 1.48, 0.77, 0.24 (after treatment for 24, 48, 72 hrs respectively). The extent of the decrease of telomerase activity was in proportion with the degree of differentiation. CONCLUSION: Monoblastic leukemia might be treated with low-dose methotrexate plus GM-CSF as a differentiation induction regimen.

[Primary study on establishment of namalwa 12/MTX resistant cell strain and its mechanism].

BACKGROUND & OBJECTIVE: Methotrexate has been used to treat malignant tumor for 50 years. Different mechanisms of methotrexate resistance has been known in various kinds of leukemias. Because of individualized chemotherapy according to different drug metabolism in different leukemia patients, the treatment became more reasonable and scientific and the treatment effect has been gradually improved. However, there was few report about its drug resistance mechanism in lymphoma. This study was designed to establish Burkitt's lymphoma methotrexate resistant cell strain--Namlwa 12/MTX and study its resistant mechanism. METHODS: Namlwa 12/MTX resistant cell strain was established by repeated impulsed exposure to methotrexate. The difference of the methotrexate effect on Namlwa 12/MTX and Namlwa cell strains were evaluated with MTT method. The level of dihydrofolate reductase (DHFR) mRNA expression was assayed with RT-PCR. The function of the reduced folate carrier (RFC) were tested with 3H-MTX labeling and counted with beta-liquid scintillation counter. The capacity to form the polyglutamate methotrexate (MTXPG) in these cell strains was assayed with 3H-MTX labeling and high pressure liquid chromatography (HPLC) separation. RESULTS: More than 20 times methotrexate resistance was found in Namalwa 12/MTX cell strain in comparison with the Namalwa cell strain. This resistance was not associated with the dysfunction of the RFC, but was closely associated with the amount of MTXPG formed. The amount of total MTXPG (MTXPG1-6) formed in these 2 cell strains was (1583 +/- 26) pmol/10(9) tumor cells and (4453 +/- 236) pmol/10(9) tumor cells, respectively (P < 0.05), while the amount of long chain MTXPG (MTXPG4-6) formed only accounted for 5.5% and 25.4% of the MTXPG1-6, respectively (P < 0.05). The level of DHFR mRNA expression was gradually increased with the formation of the drug resistance in Namalwa 12/MTX. CONCLUSION: Synthesizing difficulty of MTXPG and over-expression of DHFR mRNA level result in methotrexate resistance in Namalwa 12/MTX cell strain.