pregnancy course was regular , except for maternal consumption of mebendazol at 5 weeks ' gestation to treat a pinworm infection . maternal history was negative for consumption of any known teratogenic class drug during the whole pregnancy . clinical examination at birth was normal , except for complete congenital anonychia of left middle finger ( fig.1 ) . x - ray was performed , showing an absence of the left middle finger distal phalanx ( fig.2).the rest of the nails on the fingers and toes were normal . parents were not consanguineous and have normal fingernails and toenails . the baby was discharged on the third day of life , and was found healthy and thriving at three - month follow - up visit . final diagnosis was that of a sporadic co. x - ray showing absence of left middle finger distal phalanx . congenital onychodystrophy ( co ) , also called as iso  kikuchi syndrome , was first described by iso in 1969 1 and later by kikuchi in 1974 2 as a clinical syndrome involving dysplasia / absence of fingernails with underlying bone abnormalities . since these first observations , clinical criteria have been expanded to include a number of additional associated conditions derived from small series , case reports , and retrospective reviews over the next 30 years . co clinical criteria are the following : 

 unilateral or bilateral hypoplasia of the index fingernails and/or other fingers including toenails 3 ( up to total anonychia of hands and feet ) ; 

 radiographic abnormalities of the distal bony phalanx of the affected fingers ; 

 congenital occurrence , which can be both sporadic or hereditary 4,5 . unilateral or bilateral hypoplasia of the index fingernails and/or other fingers including toenails 3 ( up to total anonychia of hands and feet ) ; 
 
 radiographic abnormalities of the distal bony phalanx of the affected fingers ; 
 
 congenital occurrence , which can be both sporadic or hereditary 4,5 . genetic loci responsible for the condition are still under investigation : linkage to the known keratin gene clusters on 12q12 and 17q21 has been excluded by krebsova et  al . in 2000 ; 7 a putative isolated congenital nail dysplasia locus , designated ndic , has been identified on 17p13 , although the identified region harbors no genes known to be involved in skin or nail abnormalities 7 . several acquired isolated nail disorders which may represent differential diagnoses of co are presented in table1 
 8 . differently from all these conditions , co presents as a congenital hypoplasia , dysplasia , or absence of one or more fingernails , and is typically accompanied by underlying phalanx bone disease . acquired isolated nail disorders 8 several heterogeneous multisystem pathologies may also come with ungueal abnormalities ; these are summarized in table2 
 813 . 813 
 triangular nail lunula 
 
 fingernails and toenails hypoplasia 8 
 
 absent or hypoplastic patellae 
 
 elbow dysplasia , often involving posterior subluxation of the radial head 
 
 iliac horns dysplasia 
 
 arrested or reduced nail growth 
 
 thickened and over - curved nails with absence of cuticle 
  differently from the above - mentioned conditions , classic co does not come with involvement of systems other than nails and relative phalanges . kikuchi originally suggested fetal grip as a causative mechanism of nail and phalanx ischemia , leading to dysplasia or even complete resorption of such structures 14 . this theory , however , is not consistent with the recent acquisitions on developmental biology stating that limbs and bones develop early in fetal life , prior to fetus ' ability to exert a significant grip . more recently , several pathogenetic mechanisms have been proposed for this condition : 

 selective abnormal fetal vascular supply from palmar digital artery causing in utero ischemic injury : the ischemic damage would mainly be seen on the radial side of the affected finger due to the smaller caliber of the artery on that side 15 , which should be more protected than the ulnar one;16 

 in utero dysplastic change in the crescent - shaped cap of the distal phalanx , a theory that would account for the frequent  y  shape of the dysplastic distal phalanx , when present;17 

 genetic mutations causing impairment of the wnt signaling pathway , an evolutionarily conserved signal transduction pathway that plays a pivotal role in embryonic development , growth regulation of multiple tissues , and cancer development;18 

 fetal exposure to teratogens , particularly antiepilectic drugs : phenytoin 19 , valproate , and carbamazepine20 
 
 selective abnormal fetal vascular supply from palmar digital artery causing in utero ischemic injury : the ischemic damage would mainly be seen on the radial side of the affected finger due to the smaller caliber of the artery on that side 15 , which should be more protected than the ulnar one;16 
 
 in utero dysplastic change in the crescent - shaped cap of the distal phalanx , a theory that would account for the frequent  y  shape of the dysplastic distal phalanx , when present;17 
 
 genetic mutations causing impairment of the wnt signaling pathway , an evolutionarily conserved signal transduction pathway that plays a pivotal role in embryonic development , growth regulation of multiple tissues , and cancer development;18 
 
 fetal exposure to teratogens , particularly antiepilectic drugs : phenytoin 19 , valproate , and carbamazepine20 
  a literature research showed no proven association between the use of mebendazole during pregnancy and co. conversely , helminth infection during pregnancy is associated with poor cognitive and gross motor outcomes in infants , so that measures to prevent helminth infection during pregnancy should be reinforced;21 anthelminthic therapy is actually recommended in infected pregnant women , and it has been associated to a decreased rate of maternal anemia and low birth weight 22 . nevertheless , clinical follow - up is needed in order to exclude other conditions associated with multisystem pathology ; a  complete family history may also be warranted to determine sporadic or hereditary transmission of such a condition .
key clinical messageclassic co ( also called iso  kikuchi syndrome ) represents a benign , isolated condition associated with normal patient outcome . 
 nevertheless , clinical follow - up and/or further clinically - based tests are needed to exclude other nail diseases associated with multisystem pathology ; complete family history is also important to determine sporadic or hereditary transmission of such condition .