we report on the inheritance of a familial t(x;15)(p22.3;p10 ) translocation in a fetus referred for short long bones .
these events lead to partial nullosomy of x chromosome genes in males and to premature ovarian failure and lri - weill syndrome ( mim 127300 ) in females ( due to nonrandom inactivation of the undeleted x chromosome ) . here
, we report on what we believe to be the first prenatal diagnosis of a der(x)t(x;15)(p22.33;p10 ) translocation in a fetus with shortened long bones at a second trimester ultrasound examination .
we also demonstrated the utility of array comparative genomic hybridization ( acgh ) analysis for clearly defining the size of the x chromosome nullosomy and thus enabling appropriate genetic counseling .
a 30-year - old woman ( gravida 2 para 1 , iii:1 ) was referred to our unit at 26 weeks of gestation because her male fetus ( iv:2 ) had abnormally short long bones ( below the third percentile at 23 weeks ) .
the patient 's previous pregnancy had been uneventful and her second pregnancy had been conceived naturally with a 30-year - old man .
the mother presented with madelung deformity and relatively short stature ( 1.53 m , which is two standard deviations ( sds ) below the mean ) .
no dysmorphic features or mental disabilities were apparent in and the family 's medical history was unremarkable .
the first - trimester ultrasound scan was normal , with a crown  rump length of 60.0 mm and a nuchal translucency measurement of 1.2 mm .
the second - trimester , integrated risk screening for trisomy 21 yielded a value of 1/5000 ( hcg : 0.41 multiple of the median ( mom ) and fp ( feto protein ) : 1.21 mom ) .
a post referral ultrasound scan confirmed these findings but did not identify other anomalies ( other than asymmetric ears ) . a two - dimensional ultrasound examination confirmed the abnormally short femur length , with a value corresponding to 2223 weeks of gestation .
there were no feature suggestive of achondroplasia or incomplete osteogenesis ( i.e. , fracture , curvature or cupping of the edge in the long bones ) .
the couple agreed to undergo an amniocentesis for chromosome analysis . on the basis of ( i ) a conventional cytogenetic analysis of the fetus , the parents , the maternal grandparents , and the maternal grandmother 's parents and ( ii ) an acgh analysis of the fetus and the mother
, we diagnosed a 46,y , der(x)t(x;15)(p22.33;q10)mat associated with a terminal par1 deletion and a partial xp22.33 short nullosomy ( encompassing the xg , gyg2 , and arsd genes ) . on the basis of the literature and in accordance with the french legislation , our institution 's clinicians , cytogeneticists , and obstetricians provided the parents with extensive genetic counseling .
they notably explained the characteristics of lri - weill syndrome and idiopathic short stature ( iss ) associated with deletion of the short stature homeobox - containing ( shox ) gene ( mim : 312865 ) , the high probability of infertility and the lack of knowledge concerning the partial nullosomy . under french law , parents may choose to continue or terminate the pregnancy at any time ( regardless of the gestational age ) ; after thought , the parents in this case decided to continue with the pregnancy .
after an uneventful pregnancy , a male infant was born at term ( birth weight : 3.270 kg [ 0.5 sd ] ; birth length : 47 cm [ 1 sd ] ) .
the boy 's weight was 7.4 kg ( 1 sd ) and his height was 67 cm ( 1 sd ) .
the boy is of short stature ( height : 86 cm ( 1.5 sd ) , with short limbs ; weight : 12 kg ( 1 sd ) due to shox haploinsufficiency but does not have madelung deformity .
given that abnormally short long bones on ultrasound are suggestive of a chromosomal abnormality , fluorescent in situ hybridization ( fish ) was performed on 100 interphase nuclei with an aneuvysion kit ( vysis , abbott molecular , des plaines , il ) .
an analysis of amniotic fluid cells ( using standard gtg , rhg , cbg and nor banding ) revealed a 46,y , der(x ) fetal karyotype , with an acrocentric satellite at the top of the short arm of the der(x ) chromosome ( fig.1a ) . further fish analysis ( using probes for wcpx [ metasystems , altlussheim , germany ] , shox [ kreatech ; amsterdam , the netherlands ] and dxys130 [ kreatech ] ) enabled us to better define the fetal karyotype .
we hypothesized that the fetus had inherited an unbalanced translocation between an acrocentric satellite and the top of the short arm of the x chromosome ( combined with shox gene deletion ) .
( a ) the proband 's derivative x chromosome , with r and g banding : fluorescent in situ hybridization on the maternal derivative x chromosome using ( b ) cep x ( dxz1 ) sg and telvysion xp / ypter ( so ) probes ( abbott molecular , vysis ) , ( c ) shox ( so ) and cep x ( sg ) probes ( abbott molecular , vysis ) and ( d ) a wcp x probe ( sg ) ( abbott molecular , vysis ) and a nor probe ( so ) .
the results of parental karyotyping and fish analyses ( fig.1b  d ) prompted us to diagnose a maternally inherited , unbalanced , derivated chromosome ( iii:1 ) .
karyotyping of the maternal grandparents then enabled us to confirm the unbalanced inheritance of a t(x;15)(p22.3;q10 ) translocation from the maternal grandmother ( ii:2 ) with normal stature ( 1.61 m ) .
this resulted in a 46,x , t(x;15)(p22.3;q10)dn karyotype , since the great - grandparents ' karyotypes were normal ( fig.2 ) .
we then performed an acgh analysis , in order to define ( i ) the size of the fetal deletion and the potentially associated nullosomy and ( ii ) the mother 's deletion on the x chromosome .
genomic dna was extracted from cultured amniotic cells and from the mother 's blood using a perfect pure dna blood kit ( magna pure , roche , indianapolis , in ) , according to the manufacturer 's instructions . using a 180-oligonucleotide array ( agilent , santa clara , ca
; mean resolution : 5 kb ) , dna analytix software ( agilent ) and the hg 19 build , a maternal deletion was confirmed ( fig.3a ) .
it spanned from 0 ( probe : a_18_p17041097 ( 61,091 - 61,138 ) ) to 2,822,216 ( probe : a_16_p03642083 ( 2,822,157 - 2,822,216 ) ) and encompassed the whole par1 region ( a 2.6 mb region containing 24 genes ) and its three most proximal genes : xg ( chrx : 2,670,093 - 2,707,747 ) , gyg2 ( chrx:2,746,863 - 2,800,861 ) , and part of arsd ( 2,822,011 - 2,847,416 pdb ) .
180k array cgh analysis ( agilent ) ( a ) the mother ( iii:1 ) ( b ) the proband ( iv:2 ) .
it was associated with a nullosomy encompassing the three above - mentioned genes ( fig.3b ) .
the final fetal karyotype was , therefore , 46,y , der(x)t(x;15)(p22.3;q10)mat.arrxp22.33(0 - 2,689,408)x1mat , xp22.33(2,701,273 - 2,822,216)x0mat .
translocations between chromosomes x and 15 are rare . as is the case for all translocations , different breakpoints lead to the inheritance of unbalanced chromosomes .
inheritance of der(x ) ( an x chromosome derived from an x - autosome translocation ) results in deletion of the x chromosome and duplication of chromosome 15 .
when unbalanced chromosomes are inherited in males , der(x ) might lead to the partial nullosomy of x chromosome genes  as is observed for the inheritance of partial x chromosome deletions .
the nullosomies described to date result in a variety of contiguous gene syndromes , all of which are associated with mental retardation . in general , females with this type of deletion are phenotypically normal , since biased inactivation of the deleted x chromosome is frequently found in this context .
however , premature ovarian failure can be caused by haploinsufficiency of genes that are essential for oogenesis and that probably escaped x inactivation .
when the deletion encompasses the par1 region , lri - weill syndrome or iss results from the shox deletion . here , we report on what we believe to be the first prenatal diagnosis of a der(x),t(x;15)(p22.33;p10 ) in a fetus with abnormally short long bones in a second - trimester ultrasound examination .
a conventional cytogenetic analysis of the family clearly showed that the der(x ) was maternally inherited from a t(x;15)(p22.33;p10 ) .
next , acgh analysis enabled us to define the size of the x chromosome nullosomy , interpret the karyotype and to provide in - depth genetic counseling .
however , there was still doubt as to the impact of the partial nullosomy , with a 2.6 mb deletion and a 200 kb nullosomy encompassing the three most proximal genes in the par1 region ( xg , gyg2 and arsd ) .
par1 and par2 are short , pseudoautosomal ( par ) , homologous regions on mammalian x and y chromosomes ( at the top of the short and long arms of these chromosomes , respectively ) .
par1 encompasses 2.6 mb of the short - arm tips of both x and y chromosomes in humans and other great apes . to date , 24 genes have been assigned to par1 and half of these have a known function . in particular
par1 is required for pairing of the x and y chromosomes during male meiosis and is the only crossing - over point for the gonosomes .
when par1 ( and thus the shox gene ) is absent , the fetus presents iss ( explaining the ultrasound findings ) and short femur length  both of which are classical features of lri - weill syndrome .
furthermore , deletion of par1 on the x chromosome makes meiotic pairing of the x and y chromosomes impossible ; in turn , meiotic arrest occurs at the pachytene stage .
spermatozoa are unlikely to be retrieved with a testicular biopsy ( with a view to use in intracytoplasmic sperm injection ) . for these affected individuals ,
the xg gene is located within the xp22.32 locus at position 2,670,093 - 2,734,541 , which is at the pseudoautosomal boundary on the short arm of the x chromosome .
the three 5 exons are inside the pseudoautosomal region and the remaining exons are within the x - specific end region .
the xg gene encodes the homo sapiens xg blood antigen ( a cell - surface antigen with 48% homology with cd99 and one of the 34 currently known human blood group antigens ) .
no disease or syndrome has been linked to abnormalities in the xg locus , even though the latter reportedly escapes x chromosome inactivation .
the copy on the y chromosome is truncated ( xgpy2 : homo sapiens xg pseudogene , y - linked 2 ( genomic sequence : chry:2,620,337 - 2,643,037 ) ) and transcribed but is not expected to yield a y chromosome - specific gene product .
in fact , the genes on the y chromosome ( other than those in the pars ) can be classified into three categories , ( i ) x - transposed genes with 99% sequence identity with the homolog on chromosome x , ( ii ) x - degenerated genes ( mainly pseudogenes and relics of autosomal sequences ) , and ( iii ) amplicon genes .
this x - linked gene is preferentially expressed in liver , heart , and pancreas .
the other gene in the family is located on chromosome 3 ( gyg1 , on 3q24 ) and encodes muscle glycogenin .
both glycogenins are involved in blood glucose homeostasis . to date , no diseases have been linked to gyg2 abnormalities .
a short , 3 truncated version ( homo sapiens glycogenin 2 pseudogene 1 ( gyg2p1 ) , non - coding rna ) has been identified on the y chromosome ( 14,517,915 - 14,533,389 pdb ) .
the lysosomal protein encoded by arsd is a member of the arylsulfatase ( ars ) family , which is essential for the correct composition of bone and cartilage matrix .
the arsd gene ( encoding a lysosomal protein ) is the most distal in the ars cluster ( arsd , arse , arsf , and arsh ) and has not been linked to a human disease .
arsd has the typical features of genes that map to the pseudoautosomal region of the x chromosome : ( i ) it escapes x inactivation and ( ii ) it has a related pseudogene ( assigned to yq11 ) .
in contrast , abnormalities in the arse gene in same cluster have been associated with x - linked recessive punctata chondrodysplasia , ( omim 302950 ) .
our genetic counseling took account of the absence of reported abnormalities for xg , gyg2 , and arsd and the pregnancy was uneventful .
he is healthy and the only apparent clinical sign is short stature . this case has been entered in the ecaruca database .
 key clinical messagetranslocations between x and acrocentric chromosomes are rare . 
 we report on the inheritance of a familial t(x;15)(p22.3;p10 ) translocation in a fetus referred for short long bones . 
 cytogenetic analysis revealed an unbalanced translocation combined with a three - gene nullosomy . 
 after genetic counseling , a prognosis was established and a healthy boy was delivered . 
Key Clinical Message
Introduction
Case Report
Cytogenetic Analysis
Discussion
Conflict of Interest