A patient with microbrachycephaly, high forehead, long philtrum, thin upper lip, 
downturned corners of the mouth, low set ears with overlapping helix, 
fifth-finger clinodactyly, small hands and feet, bilateral transverse palmar 
crease, low total finger ridge count, hypotonia, severe growth and psychomotor 
delay, mild hypoplasia of corpus callosum, and Arnold-Chiari type 1 malformation 
is reported. The karyotype showed 46, XY, del(1)(q23q31.2). Coagulation factor V 
(F5, 1q23) and coagulation factor XIII (F13B, 1q31-q32.1) levels were normal. As 
expected, antithrombin III (AT3, 1q23-q25.1) serum level and activity were half 
of normal. We performed a review of the literature on proximal and intermediate 
deletion 1q syndrome, and we hypothesize the existence of only one 1q 
interstitial deletion syndrome, clinically characterized by ATIII deficiency.