Chromosomal Abnormalities George E Tiller, MD, PhD Regional Chief, Dept. Genetics Southern California Permanente Medical Group Los Angeles, CA Objectives of Lecture list several indications for karyotyping describe clinical features of common chromosomal anomalies contrast routine karyotyping with FISH and CGH explain the phenomena of genetic imprinting & UPD Chromosomal Disorders found in >7% human conceptuses responsible for >50% miscarriages (trisomy 16 > 45,XO > others) 1/200 liveborn with chromosomal disorder Types of Chromosomal Anomalies numerical changes of sets: triploidy, tetraploidy of individual: trisomy, monosomy mosaicism structural changes deletions duplications translocations inversions 1
Indications for Chromosomal Analysis birth and infancy suspicious phenotype ambiguous genitalia multiple congenital anomalies childhood mental retardation suspicious phenotype adolescence primary amenorrhea abnormal stature adulthood: several incidence: 1/750 Down Syndrome features: characteristic facial features, hypotonia, developmental delay, simian creases, brachydactyly, short stature, increased risk for CHD (>50%), duodenal obstruction, hypothyroidism 1 o defect: Trisomy 21 (>95% 47,XS +21) Trisomy 18 incidence: 1/3,000 features: IUGR, FTT, hypertonia, CHD, CL/P, malformed ears, micrognathia, overlapping digits, hernias, renal anomalies, severe developmental delay <10% survive 1 year 2
Trisomy 13 incidence: 1/5,000 features: IUGR, FTT, hypotonia, CHD, CL/P, apnea, seizures, malformed ears, polydactyly, microcephaly, microphthalmia, CNS defects, renal anomalies, cutis aplasia, severe developmental delay <10% survive 1 year Turner Syndrome incidence: 1/2,500 features: webbed neck, low hairline, infantile lymphedema, CHD (CoA), widely spaced nipples, cubitus valgus, ovarian dysgenesis 1 o defect: 45,X (50%); ringx or isox (25%); mosaic 25% (45,X/46,XX or XY) Rx: GH tx, hormone replacement tx Klinefelter Syndrome incidence: 1/800 (most common sex chromosome anomaly) features: tall, thin stature; mild learning d/o, scant facial/pubic hair, hypogonadism, gynecomastia, sterility 1 o defect: 47,XXY Rx: testosterone replacement tx 3
Fragile X Syndrome incidence: 1/4,000 males features: delayed motor development, large ears and long faces, severe speech delay, autism, loose joints, large testicles cytogenetics: fragile site at Xq27 molecular: >200 (CCG) n expansion in FMR1 1/3 carrier females mildly symptomatic Prader-Willi Syndrome incidence: 1/20,000 features: hypotonia, hypogonadism, small hands & feet, almond-shaped eyes, polyphagia, obesity, short stature, MR cytogenetics: deletion 15q11 by karyotype or FISH (70%); matupd (25%) molecular: abnormal DNA methylation pattern of genes at 15q11 Angelman Syndrome incidence: 1/20,000 features: microcephaly, broad mouth, large jaw, seizures, ataxia ( puppet-like gait), inappropriate laughter, autism cytogenetics: deletion 15q11 by karyotype or FISH (70%); patupd (7%) molecular: abnormal DNA methylation pattern of genes at 15q11; UBE3A mutation (10%) 4
Imprinting identical genes may be marked differently during germ cell development gene expression may be influenced by imprinting, leading to variable phenotypes examples: Prader-Willi sx, Angelman sx, familial paragangliomas, Beckwith-Wiedemann sx Williams Syndrome incidence: 1/7,500 features: short stature; developmental delay; cocktail party personality; stellate irides, long philtrum, full lips; hoarse voice; SVAS, PS; +/- hypercalcemia 1 o defect: contiguous gene syndrome (microdeletion on 7q) Contiguous Gene Syndrome abnormalities of >2 adjacent genes deletion, duplication, or uniparental disomy microdeletions detected by FISH examples: Prader-Willi, Angelman, Beckwith-Wiedemann, Williams, digeorge, Miller-Dieker lissencephaly, Smith-Magenis, Langer-Giedion sxs 5
CATCH 22 Syndrome includes: digeorge sx, Shprintzen sx, some isolated CHD incidence: 1/5,000 features: Cardiac defects (esp. TOF); Abnormal facies; Thymic hypoplasia; Cleft palate; Hypocalcemia 1 o defect: 22q11 microdeletion; underdevelopment 4th branchial arch and 3rd/4th pharyngeal pouches Cri du Chat Syndrome incidence: 1/20,000 features: SGA, hypotonia with weak, high-pitched cry, microcephaly, hypertelorism, epicanthal folds, downslanting palpebral fissures, small jaw, CHD 1 o defect: 5p- (terminal deletion of short arm of chromosome 5) Beckwith-Wiedemann Syndrome incidence: 1/15,000 inheritance: 85% sporadic; rare AD features: large for gestational age; hypoglycemia, macroglossia, ear pits/creases, organomegaly, omphalocele, umbilical hernia, Wilms tumor (5%) 1 o defect: gene dosage defect at 11p15 6
Comparative Genomic Hybridization (CGH) a molecular karyotype may detect deletions & insertions as small as 50Kb will not detect balanced translocations cost is coming down Cytogenetic References Down syndrome. Pediatrics 1072):442, 2001 Fragile X syndrome. Pediatrics 98(2):297, 1996 Turner syndrome. Pediatrics 111(3):692, 2003 Williams syndrome. Pediatrics 107(5):1192, 2001 all can be found online at http://aappolicy.aappublications.org Jones, KL. Smith s Recognizable Patterns of Human Malformation, 6th ed. New York: Elsevier, 2005. The bible of dysmorphology 7