Sebold et al. (2010) summarized the phenotype of tetrasomy 18p with a list of findings reported in more than 25% of theretofore published cases: neonatal feeding problems, growth retardation, microcephaly, strabismus, muscle tone abnormalities, scoliosis/kyphosis, and variants on ... Sebold et al. (2010) summarized the phenotype of tetrasomy 18p with a list of findings reported in more than 25% of theretofore published cases: neonatal feeding problems, growth retardation, microcephaly, strabismus, muscle tone abnormalities, scoliosis/kyphosis, and variants on brain MRI. Developmental delay and cognitive impairment are universally present. To more fully describe the molecular features and clinical presentation of tetrasomy 18p, Sebold et al. (2010) performed array CGH on samples from 42 individuals with tetrasomy 18p, and reviewed the medical records of these individuals. Forty-one of these individuals had an isochromosome 18p in all cells examined; the remaining individual had mosaicism. In addition, 31 of these 42 individuals underwent a series of clinical and genetic evaluations at the Chromosome 18 Clinical Research Center in the University of Texas Health Science Center at San Antonio. Sebold et al. (2010) also reviewed 65 patients reported in the literature. Developmental delay/mental retardation was found in every individual. A clear majority had neonatal complications including feeding difficulties and respiratory distress, and jaundice in about half of the chart-reviewed cohort. Hypoglycemia and bradycardia were rarely seen. Growth retardation was present in about 30%, and microcephaly in about 50%, of all individuals. Palatal anomalies were rare. Strabismus was present in about 50% of cases with refractive errors present in about one-third. A significant proportion of patients suffered from hearing loss or recurrent otitis media, or had small or narrow ear canals. The majority had abnormal muscle tone and about 20% had seizures. Myelomeningocele was present in 6%, and among the 12 patients who underwent MRI, 3 had enlarged lateral ventricles and 3 thin or small corpus callosum. Cardiac defects were present in one-quarter of all patients. Cryptorchidism was seen in 39% of males. Hypospadias and other congenital malformations were rare. History of constipation was present in one-third of patients. Other GI abnormalities were less common. Congenital abnormalities of the bones were present in 22%, with scoliosis and kyphosis developing in 37% and foot abnormalities present in about 23%. No patient had a thyroid abnormality. Four of the 31 patients who underwent clinical assessment had growth hormone deficiency, and 4% had IgA deficiency. About 4% of all patients suffered stillbirth or early death. Dysmorphic features noted during genetic evaluation included ptosis in one-third; posteriorly rotated ears in one-third; simple helices in less than one-third; small ears in half; abnormal columella in half; smooth philtrum in the vast majority; small mouth in half; thin upper lip in one-third; and abnormal Cupid's bow (smooth, ill-defined, or narrow) in about one-third. A high, arched, or narrow palate was present in 25 of 31 patients examined. More than half had a prominent or pointed chin and sloping shoulders or trapezius muscles; about one-third had partial or mild syndactyly of the toes and narrow feet; two-thirds had clinodactyly; and slightly more than half had camptodactyly or finger contractures. Shawl scrotum and proximally placed anus were rarely seen.