Respiratory distress can be caused by an underdeveloped trachea which collapses on inhalation or by insufficient rib cage development. Genetics
CMD is commonly caused by chromosomal abnormalities in or around the gene SOX9 on the long arm of chromosome 17, specifically at position 17q24, generally spontaneously arising or de novo mutations. Also, numerous single nucleotide variants been identified involving the SOX9 gene that cause some form of CMD. The SOX9 gene codes for a protein transcription factor which, when expressed at the embryonic stage, plays an important role in determining sexual characteristics and greatly influences skeletal development. When the SRY gene of the Y chromosome is expressed in human embryos, a cascade of gene interactions controlled by SOX9 begins and ultimately leads to male gender.. Any mutation within the coding region of SOX9 can cause campomelic dysplasia and 75% of the reported mutations lead to sex reversal. Four major classes of heterozygous SOX9 mutations can cause CMD: amino acid substitutions in the HMG-box, truncations or frameshifts that alter the C-terminal end, mutations at the splice junction, and chromosomal translocations. Additionally, mutations upstream from SOX9 can also cause CMD. Several researchers have reported cis-acting control elements upstream of SOX9. Translocation breakpoints scattered over 1Mb proximal to SOX9 indicate the presence of an extended control region.The lack of correlation between specific genetic mutations and observed phenotype, particularly with regard to sex reversal, give clear evidence of the variable expressivity of the disease.
Cooks syndrome is a hereditary disorder which is characterized in the hands by bilateral nail hypoplasia on the thumb, index finger, and middle finger, absence of fingernails (anonychia) on the ring finger and little finger, lengthening of the thumbs, and bulbousness of the fingers. In the feet, it is characterized by absence of toenails and absence/hypoplasia of the distal phalanges. In the second study of this disorder, it was found that the intermediate phalanges, proximal phalanges, and metacarpals were unaffected.The disorder was first described by Cooks et al. in 1985 after being discovered in two generations of one family. It was proposed that the inheritance of the disorder is autosomal dominant. A second family, this with three affected generations, confirmed that the inheritance of the disorder is autosomal dominant. Although several genetic disorders exist which can cause anonychia and onychodystrophy, such disorders often cause other anomalies such as deafness, mental retardation, and defects of the hair, eyes, and teeth. Cooks syndrome is not known to cause any such anomalies.In 1999, a pair of siblings was found with brachydactyly type B. Because the disorder primarily affected the nails and distal phalanges, the research group concluded that brachydactyly type B and Cooks syndrome are the same disorder. However, in 2007, a 2-year-old girl was found with symptoms consistent with both brachydactyly type B and Cooks syndrome. It was found that the two syndromes were distinct clinically, radiologically, and genetically. Notes


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