Tetrasomy 5p mosaicism due to an extra i(5p) in a severely affected girl

Abstract

We present a case of mosaic 5p tetrasomy. The mosaicism 46,XX/47,XX,+i(5p) was found at different ratios in blood lymphocytes, skin fibroblasts, and chondrocytes. The origin of the extra isochromosome was confirmed by FISH. The clinical picture corresponds to that described in trisomy 5p patients, although it was more severe than the two previously reported cases of mosaic 5p tetrasomy. No correlation between clinical severity and proportion of tetrasomic cells in blood or fibroblasts was found in these cases.

Unusual isochromosome 5p marker chromosome

“…However they are well known by cytogeneticists because of the Pallister–Killian syndrome where mosaic tetrasomy 12p due to an isochromosome 12p or i(12p) is present in fibroblasts of affected cases. More rarely mosaic tetrasomies 5p due to a supernumerary i(5p) have been found either postnatally in blood lymphocytes and fibroblasts [Sijmons et al, ; Stanley et al, ; Lorda‐Sanchez et al, ; Hansen et al, ; Brock et al, ] or prenatally in amniotic fluid [Reddy and Huang, ] and in chorion villous sampling [Paulick et al, ]. A recent paper describing a new case focused on the issue of i(5p) and compared the different reported cases [Brock et al, ].…”

“…A recent paper describing a new case focused on the issue of i(5p) and compared the different reported cases [Brock et al, ]. The most common features observed in affected patients are: psychomotor delay and seizures [Sijmons et al, ; Stanley et al, ; Lorda‐Sanchez et al, ; Hansen et al, ; Brock et al, ], ventriculomegaly and hypotonia with short stature or growth delay, [Sijmons et al, ; Stanley et al, ; Lorda‐Sanchez et al, ; Brock et al, ], fifth finger clinodactyly [Sijmons et al, ; Lorda‐Sanchez et al, ; Hansen et al, ; Brock et al, ]. More rarely were described mosaic pigmentary changes [Sijmons et al, ; Hansen et al, ; Brock et al, ], macrocephaly and overlapping toes [Stanley et al, ; Lorda‐Sanchez et al, ; Brock et al, ].…”

“…The most common features observed in affected patients are: psychomotor delay and seizures [Sijmons et al, ; Stanley et al, ; Lorda‐Sanchez et al, ; Hansen et al, ; Brock et al, ], ventriculomegaly and hypotonia with short stature or growth delay, [Sijmons et al, ; Stanley et al, ; Lorda‐Sanchez et al, ; Brock et al, ], fifth finger clinodactyly [Sijmons et al, ; Lorda‐Sanchez et al, ; Hansen et al, ; Brock et al, ]. More rarely were described mosaic pigmentary changes [Sijmons et al, ; Hansen et al, ; Brock et al, ], macrocephaly and overlapping toes [Stanley et al, ; Lorda‐Sanchez et al, ; Brock et al, ]. The dysmorphic facial features comprised upslanting palpebral fissures [Sijmons et al, ; Stanley et al, ] and hypertelorism [Stanley et al, ], anteverted nasal tip [Sijmons et al, ; Lorda‐Sanchez et al, ], abnormal auricles with preauricular pits [Stanley et al, ; Lorda‐Sanchez et al, ], and midface hypoplasia [Lorda‐Sanchez et al, ].…”

“…More rarely were described mosaic pigmentary changes [Sijmons et al, ; Hansen et al, ; Brock et al, ], macrocephaly and overlapping toes [Stanley et al, ; Lorda‐Sanchez et al, ; Brock et al, ]. The dysmorphic facial features comprised upslanting palpebral fissures [Sijmons et al, ; Stanley et al, ] and hypertelorism [Stanley et al, ], anteverted nasal tip [Sijmons et al, ; Lorda‐Sanchez et al, ], abnormal auricles with preauricular pits [Stanley et al, ; Lorda‐Sanchez et al, ], and midface hypoplasia [Lorda‐Sanchez et al, ]. A normal phenotype associated with a i(5)(p10) confined in blood has also been reported [Venci and Bettio, ].…”

Pigmentary mosaicism with mosaic chromosome 5p tetrasomy

“…However, only a few cases with tetraploid mosaicism have been described. The tetrasomy 5p mosaicism is a rare constitutional chromosome aberration described in a few cases with a variety of associated clinical findings 1–5 . The condition of pigmentary mosaicism was formerly known as linear and whorled naevoid hypermelanosis or hypomelanosis of Ito, when associated with neurological deficits.…”