Lesson of the week: Turner's syndrome mosaicism in patients with a normal blood lymphocyte karyotype

Variable degree of mosaicism for tetrasomy 18p in phenotypically discordant monozygotic twins-Diagnostic implications

Background

Phenotypically discordant monozygotic twins (PDMZTs) offer a unique opportunity to study post‐zygotic genetic variation and provide insights into the linkage between genotype and phenotype. We report a comprehensive analysis of a pair of PDMZTs.

Methods

Dysmorphic features and delayed neuro‐motor development were observed in the proband, whereas her twin sister was phenotypically normal. Four tissues (blood, skin, hair follicles, and buccal mucosa) from both twins were studied using four complementary methods, including whole‐exome sequencing, karyotyping, array CGH, and SNP array.

Results

In the proband, tetrasomy 18p affecting all studied tissues except for blood was identified. Karyotyping of fibroblasts revealed isochromosome 18p [i(18p)] in all metaphases. The corresponding analysis of the phenotypically normal sister surprisingly revealed low‐level mosaicism (5.4%) for i(18p) in fibroblasts.

Conclusion

We emphasize that when mosaicism is suspected, multiple tissues should be studied and we highlight the usefulness of non‐invasive sampling of hair follicles and buccal mucosa as a convenient source of non‐mesoderm‐derived DNA, which complements the analysis of mesoderm using blood. Moreover, low‐level mosaic tetrasomy 18p is well tolerated and such low‐level mosaicism, readily detected by karyotyping, can be missed by other methods. Finally, mosaicism for low‐level tetrasomy 18p might be more common in the general population than it is currently recognized, due to detection limitations.

Monozygotic twin discordant for Down syndrome: mos 47,XX,+21/46,XX and 46,XX

Monozygotic twins, developed from a single zygote, are almost identical in clinical phenotype and concordant karyotypes. Monozygotic twins with discordant karyotypes are thought to be quite rare. Here, we report monochorionic-diamniotic twins discordant for Down syndrome. On findings of prenatal ultrasonography, nuchal translucency thickness was different between twins, and suggested that one of the twins was at high risk for having chromosomal abnormalities including Down syndrome. The twins were monochorionic-diamniotic; therefore, chorionic villi sampling of the common placenta was performed. The karyotype of the chorionic villi cells was 46,XX, and pregnancy was maintained. After delivery, dysmorphic clinical features suggesting Down syndrome were found in one of the twins, while the other twin showed a morphologically normal appearance. Karyotypes of peripheral blood leukocytes were repeatedly normal in the dysmorphic twin; however, the karyotype of skin fibroblasts from the dysmorphic twin indicated Down syndrome mosaicism; 47,XX,+21[99]/46,XX[2]. The karyotype of skin fibroblasts from the morphologically normal twin was 46,XX. Monozygosity of the twins was confirmed by a short tandem repeat analysis using 16 polymorphic markers. A mitotic nondisjunction followed by the twinning would explain the discordant karyotypes between monozygotic twins.

Chromosome abnormalities in Indonesian patients with short stature

Background

Short stature is associated with several disorders including wide variations of chromosomal disorders and single gene disorders. The objective of this report is to present the cytogenetic findings in Indonesian patients with short stature.

Methods

G-banding and interphase/metaphase FISH were performed on short stature patients with and without other clinical features who were referred by clinicians all over Indonesia to our laboratory during the year 2003–2009.

Results

The results of chromosomal analysis of ninety seven patients (mean age: 10.7 years old) were collected. The group of patients with other clinical features showed sex chromosome abnormalities in 45% (18/40) and autosomal abnormalities in 10% (4/40), whereas those with short stature only, 42.1% (24/57) had sex chromosome abnormalities and 1.75% (1/57) had autosomal abnormalities. The autosomal chromosomal abnormalities involved mostly subtelomeric regions. Results discrepancies between karyotype and FISH were found in 10 patients, including detection of low-level monosomy X mosaicism in 6 patients with normal karyotype, and detection of mosaic aneuploidy chromosome 18 in 1 patient with 45,XX,rob(13;14)(q10;q10).

Statistical analysis showed no significant association between the groups and the type of chromosomal abnormalities.

Conclusion

Chromosome abnormalities account for about 50% of the short stature patients. Wide variations of both sex and autosomal chromosomes abnormalities were detected in the study. Since three out of five patients had autosomal structural abnormalities involving the subtelomeric regions, thus in the future, subtelomeric FISH or even a more sensitive method such as genomic/SNP microarray is needed to confirm deletions of subtelomeric regions of chromosome 9, 11 and 18. Low-level mosaicism in normal karyotype patients indicates interphase FISH need to be routinely carried out in short stature patients as an adjunct to karyotyping.

JC, Almeida JC. Investigação clínica e genética em meninas com baixa estatura idiopática

Em 10 meninas com diagnóstico de baixa estatura idiopática (BEI), realizamos avaliação citogenética após revisão clínica. Dois cariótipos foram anormais: mos 45,X/46,XX; mos 45,X/46,X,der(Xp)/46,X,r(X), e para sua elucidação foram aplicadas técnicas de citogenética molecular e análise de microssatélites, incluindo SHOX CA repeat. Os resultados confirmaram a origem dos cromossomos anômalos e a identificação da haploinsuficiência do gene SHOX. Nos oito casos com cariótipo normal, a pesquisa de mosaicismos crípticos pela técnica FISH através da sonda centromérica (DXZ1) em células de mucosa oral (nuc ish) evidenciou a presença de dois mosaicos verdadeiros (DXZ1x2/DXZ1x1). A revisão clínica da paciente com anomalia estrutural de X e das 2 meninas com mosaicismo detectados pelo nuc ish, mostrou a presença de 3 ou mais sinais clínicos observados na síndrome de Turner (ST). Estes resultados reafirmam a importância da análise citogenética em meninas com diagnóstico de BEI e sinais clínicos da ST. Os resultados do estudo molecular para o gene SHOX confirmam sua relação com estigmas da ST. Sendo normal o cariótipo, a pesquisa de mosaicismos crípticos em outros tecidos deve ser considerada. O diagnóstico mais preciso poderá modificar a conduta terapêutica, como indicação do GH nessas meninas.

Antiangiogenic activity of synthetic dihydrobenzofuran lignans

A series of synthetic dihydrobenzofuran lignans, obtained by biomimetic oxidative dimerization of caffeic or ferulic acid methyl ester followed by derivatization reactions, was tested for its antiangiogenic activity in the CAM (chorioallantoic membrane) assay. The dimerization product of caffeic acid methyl ester (2a) (methyl (E)-3-[2-(3,4-dihydroxyphenyl)-7-hydroxy-3-methoxycarbonyl-2,3-dihydro-1-benzofuran-5-yl]prop-2-enoate) showed a pronounced antiangiogenic activity, especially the 2R,3R-enantiomer.

Turner's syndrome in adulthood

Turner's syndrome is the most common chromosomal abnormality in females, affecting 1:2,500 live female births. It is a result of absence of an X chromosome or the presence of a structurally abnormal X chromosome. Its most consistent clinical features are short stature and ovarian failure. However, it is becoming increasingly evident that adults with Turner's syndrome are also susceptible to a range of disorders, including osteoporosis, hypothyroidism, and renal and gastrointestinal disease. Women with Turner's syndrome have a reduced life expectancy, and recent evidence suggests that this is due to an increased risk of aortic dissection and ischemic heart disease. Up until recently, women with Turner's syndrome did not have access to focused health care, and thus quality of life was reduced in a significant number of women. All adults with Turner's syndrome should therefore be followed up by a multidisciplinary team to improve life expectancy and reduce morbidity.

Turner's syndrome mosaicism 45X/47XXX: an interesting natural history

Mosaicism 45X/47XXX is a sporadic form of ovarian dysgenesis. Many of the cases previously described were characterized by a variable phenotype expression. We here report the case of a 33-yr-old woman with recent secondary amenorrhea, weight loss and breast regression. Her menarche had occurred at the age of 11 yr and 6 months and her menstrual cycles had been regular until the age of 28; then, oligomenorrhea and hypertricosis developed. A pelvic ultrasound showed enlarged polycystic-like ovaries and normal uterus. She was treated with ethynil-estradiol and cyproterone acetate for one year. At the age of 31 yr, she underwent a pelvic ultrasound--which revealed normal volume of the ovaries--and hormonal assays including FSH (69 UI/l), LH (113 UI/l), 17beta-estradiol (88 pg/ml), plasma androgens and cortisol levels within normal ranges. No organ-specific autoantibodies toward ovaries, steroid-producing cells or adrenals were found. At the age of 33 yr, there was ultrasound evidence of streak-like ovaries. The patient's height was 145 cm and her weight 45 kg. She had normal female external genitalia, abnormal upper-to-lower body segment ratio, webbed neck, low posterior hair line, cubitus valgus, short and asymmetrical 4th metacarpi, hallux with lateral deviation and moderate scoliosis. No increase in ovarian steroids were found after GnRH-analogue triptorelin (0,1 mg sc) administration. The karyotype analysis on peripheral blood lymphocytes showed a mosaic 45X (90% cells) and 47XXX (10% cells). Diagnostic pelviscopy confirmed streak gonads. Chronic lymphocytic thyroiditis was diagnosed but no cardiovascular or kidney abnormalities were found. A neuro-psychological evaluation revealed emotional and social immaturity, disorders in motorial coordination, visual-spatial organization, as well as reading difficulties and impaired complex phrase construction. The presence of several somatic features of Turner's syndrome, neuro-psychological disorders and an interesting natural history probably depended on the quantitative proportion of 45X to 47XXX cell-lines in different tissues and organs. Estrogen and progestin replacement therapy led to weight gain, re-appearance of secondary sexual characteristics and a mild improvement in mental equilibrium.

Phenotypic expression of tissue mosaicism in a 45,X/46,X,dicY(q11.2) female

We describe a girl who presented at the age of 11 years with short stature. She had female external genitalia and some clinical features of Turner syndrome. At laparotomy a uterus and Fallopian tubes and small gonad-like tissue masses in the region of the Fallopian fimbria were found. The tissue masses were removed and histological examination revealed no organized testicular or ovarian morphology. Remnants of Fallopian tubes, epididymis, and clusters of Leydig cells were seen but no Sertoli cells were found. Endocrine studies showed levels of sex hormones consistent with primary gonadal failure. G-banding analysis of 16 blood lymphocytes revealed the karyotype 46,X,dicY(q11.2) in all cells. Varying proportions of X and Y centromeres in blood lymphocytes, skin fibroblasts, and in the incompletely formed Wolffian and Müllerian duct derivatives were demonstrated by FISH. Molecular studies confirmed the absence of most of the long arm of the Y chromosome and an intact short arm. The SRY gene was shown to be present, but we presume that due to the mosaicism the dose was insufficient to allow normal testicular development.