A small-for-gestational-age infant is born prematurely to a 38-year-old woman who had inconsistent prenatal care. Physical examination shows a small head and eyes as well as a cleft lip and palate. There is a small, round punched-out lesion with an overlying thin membrane on the patient's scalp. A small, membranous sac with a loop of bowel protrudes from the patient's abdominal midline. The infant is transferred to the neonatal intensive care unit for further workup and management. Which of the following is most likely responsible for this patient's condition?

Question

A small-for-gestational-age infant is born prematurely to a 38-year-old woman who had inconsistent prenatal care.  Physical examination shows a small head and eyes as well as a cleft lip and palate.  There is a small, round punched-out lesion with an overlying thin membrane on the patient's scalp.  A small, membranous sac with a loop of bowel protrudes from the patient's abdominal midline.  The infant is transferred to the neonatal intensive care unit for further workup and management.  Which of the following is most likely responsible for this patient's condition?

Quizplus · Accepted Answer

11ec160b_3780_c52d_9249_63ea3512a20d_MD0001_00 Patau syndrome, or trisomy 13, is a severe genetic disorder with phenotypic features reflecting a defect in the fusion of the prechordal mesoderm, an integral embryological structure affecting growth of the midface, eyes, and forebrain. This results in catastrophic midline defects, including holoprosencephaly, microcephaly, microphthalmia, cleft lip/palate, and omphalocele. Abnormal brain development results in intellectual disability and seizures. Additional abnormalities include polydactyly and cutis aplasia (focal skin defect of the scalp). The majority of patients with Patau syndrome die in utero; only 5% survive beyond 6 months. Cytogenetic studies usually demonstrate meiotic nondisjunction, which is the failure of chromosomal separation during meiosis, causing inheritance of a chromosome pair from 1 parent rather than a single chromatid. Maternal age >35 is an important risk factor for this abnormality of oocyte division. Nondisjunction results in a fetus with 3 complete copies of chromosome 13 (47, XX, +13). (Choice A) Patients with Down syndrome (trisomy 21) typically have a flat facial profile, upslanting palpebral fissures, low-set small ears, redundant skin at the nape of the neck, single transverse palmar crease, and hypotonia. Increased rates of duodenal atresia and Hirschsprung disease are seen in these patients. (Choice B) Clinical manifestations of Edwards syndrome (trisomy 18) include fetal growth retardation, hypertonia, micrognathia, and congenital heart defects. Additional features include clenched hands with overlapping fingers, Meckel's diverticulum, and malrotation. (Choice C) Nicotine use during pregnancy increases the risk of prematurity and low birth weight. Related pregnancy complications include placenta previa and abruption. (Choice D) Fetal exposure to maternal phenytoin has been associated with several congenital anomalies (eg, cardiac defects, cleft lip/palate, hypoplastic nails). It is not associated with cutis aplasia or omphalocele. (Choice E) Congenital rubella syndrome typically occurs after a first trimester maternal rubella infection. Abnormalities classically include hearing loss, cataracts, and cardiac defects. (Choice G) Williams syndrome is a genetic disorder classically associated with "elfin" facies, supravalvular aortic stenosis, and an extroverted personality. Educational objective: Patau syndrome (trisomy 13) usually occurs secondary to meiotic nondisjunction in mothers of advanced maternal age. Key physical findings reflect defective prechordal mesoderm fusion resulting in midline defects (eg, holoprosencephaly, microphthalmia, cleft lip/palate, omphalocele) as well as polydactyly and cutis aplasia. __________ References: Clinical features and prognosis of a sample of patients with trisomy 13 (Patau syndrome) from Brazil. (http://www.ncbi.nlm.nih.gov/pubmed/23613355) Phenotypic variability in Patau syndrome. (http://www.ncbi.nlm.nih.gov/pubmed/24340511)

A Small-For-Gestational-Age Infant Is Born Prematurely to a 38-Year-Old Woman