May 3, 2006
BIO 2233 Heredity
CRI-DU-CHAT SYNDROME (CDCS)
Cri-du-chat syndrome (CDCS) refers to a unique combination of physical and mental characteristics associated with a loss of genetic material on the distal short arm of the fifth chromosome. This loss of genetic material is referred to as a deletion. CDCS is also called 5p- syndrome (5p-S), 5p monosomy, or Cat Cry syndrome which was first identified by Dr. Jerome Lejeune in 1963. He named so because of the distinctive cry in infancy that resembles to the mewing of a cat. This characteristic cry in the infancy is caused by structural abnormalities of the larynx (such as laryngeal hypoplasia) and CNS dysfunction (Chen, 2005). The laryngeal appearance may be normal or may exhibit remarkable anatomical abnormalities such as floppy epiglottis, small larynx, and asymmetric vocal cords. In addition to that, developmental field connecting the brain and the affected clivus region of the cranial base with the laryngeal region from which the characteristic cry derives may exist (Chen 2005). Its high-pitched, monochromatic cry usually makes a physician decide to obtain a chromosome study and the definitive test required to confirm the diagnosis of CDCS (Campbell, 2005). The characteristic cry usually disappears by the time they are aged two year. Other features evident in infancy include characteristic physical features such as a small moon-shaped face, epicanthic folds, wide spaced, down-slanting eyes, and a small mouth and chin (Campbell, 2005). These infants also exhibit low muscle tone (hypotonia), slow growth, and significant developmental delays. As children with CDCS grow, the face usually elongates and becomes thinner and more triangular in shape with a broad forehead and a somewhat small pointed and receding lower jaw and chin.. The epicantal folds remain and the nasal bridge widens and remains flattened. Baby teeth are often delayed in erupting, are small, and have multiple spaces (diastemas). The growth rate may be normal in the early months or years but frequently slows somewhat during the toddler and schools years resulting in growth parameters that are below average (Campbell, 2005). Developmental milestones usually emerge slowly and show increasing delays with both the increasing age of the child and the complexity of the task. As well as a delay in expressive language, high rates of hyperactivity and inattention are often noted clinically, and symptoms of attention deficit hyperactivity disorder are also found. By looking at their behaviors, the majority of the individuals exhibited some form of self-injurious behavior such as predominantly head banging and vomiting or rumination). Sixty-five per cent were reported as displaying some form of aggressive behavior; for example, hitting others or pulling others’ hair (Sarimski, 2005).
Almost 80-85% cases are caused by sporadic de novo deletion of 5p which are mostly paternal in origin (Chen, 2005). Most of the remaining cases result from unbalanced translocations, which may be either maternally or paternally derived. According to the study of Anju et el, the telomerase reverse transcriptase (hTERT) gene which is localizing chromosome fifth is relating to CDCS. hTERT is responsible for the rate-limiting of telomerase activity that is essential for telomere-length maintenance and sustained cell proliferation (Anju et el, 2003). Anju et el found that the CDCS patients had shorter telomeres than age-matched unaffected individuals and had a reduction in replicative life span and a high rate of chromosome fusions in cultured patient’s fibroblasts. Therefore Anju et el are hypothysing that “one allele of hTERT should be deleted in this syndrome, and, a deletion of one hTERT copy occurs with in CDCS, consequently allowing hTERT expression and causing haploinsufficiency for...