Characterization of a prenatally assessed de novo supernumerary minute ring chromosome 20 in a phenotypically normal male

Abstract

Background: The heterogeneous group of small supernumerary marker chromosomes (sSMCs) presents serious counseling problems, especially if they are present de novo and diagnosed prenatally. The incidence has been estimated at 1 in 1000 prenatal samples. We present a case of mosaic sSMC diagnosed prenatally after amniocentesis. The sSMC was characterized by various molecular cytogenetic techniques and determined to be a r(20) chromosome. After genetic counseling, the parents decided to continue the pregnancy, and a boy with minor phenotypic variants was born after 39 weeks of pregnancy. The case is compared with four other cases of prenatally detected r(20) mosaicism.

Chromosomal breakpoints characterization of two supernumerary ring chromosomes 20

“…To our knowledge, 13 cases of supernumerary r(20) have been reported so far. Of these, 8 cases were ascertained postnatally [Callen et al, 1991; Blennow et al, 1993; Van Langen et al, 1996; Viersbach et al, 1997; Crolla et al, 1998; Austin‐Ward et al, 2000; Pinto et al, 2005] and 5 prenatally [Batista et al, 1995; Viersbach et al, 1997; Cotter et al, 2005; Kitsiou‐Tzeli et al, 2009].…”

“…Previously described patients with an extra r(20) showed varying degrees of phenotypic abnormality. Among these descriptions, the most frequently noted manifestations are growth and psychomotor retardation, low‐set ears, hands and feet anomalies, and micrognathia [Callen et al, 1991; Blennow et al, 1993; Batista et al, 1995; Van Langen et al, 1996; Viersbach et al, 1997; Crolla et al, 1998; Austin‐Ward et al, 2000; Pinto et al, 2005; Kitsiou‐Tzeli et al, 2009] (Table I). In our study, Patient 1 had intrauterine growth retardation associated with some facial dysmorphism.…”

Clinical, cytogenetic and molecular study of a case of ring chromosome 10

“…Ring chromosome 10 is a rare disorder. Only seventeen cases of ring chromosome 10 have been reported in literature and mostly defined by G banding [ 3 - 15 ] and only four cases with molecular cytogenetic definition [ 2 , 16 , 17 ]. This is the fifth case with precisely defined r(10) helping to better establish a karyotype-phenotype correlation.…”

A systematic analysis of small supernumerary marker chromosomes using array CGH exposes unexpected complexity

“…Among these descriptions, the most frequently noted manifestations were growth and psychomotor retardation, low-set ears, hand and foot anomalies, and micrognathia. [32][33][34][35][36][37][38][39][40] In patient 2, 30 a supernumerary marker was found in 43% of amniocytes and fetal lymphocytes. At 15 months of age, except for obesity, her psychomotor development was normal and no dysmorphic features were noted.…”