Intellectual disability in LFS usually ranges from mild to moderate, but severe cases have also been reported. A relatively common brain anomaly seen with LFS is agenesis of the corpus callosum, an error of embryonic development in which the corpus callosum (a structure of the mammalian brain composed of nerves that allows communication between the left and right cerebral hemispheres) is not present. Among a number of adverse neurological effects sometimes found with an absence of the corpus callosum, intellectual disability has been shown to occur at a rate of approximately 73 percent. A correlation between agenesis of the corpus callosum and intellectual disability in LFS, however, has not been suggested. Psychiatric Psychopathology and related behavioral abnormalities are typically seen in LFS, and they may be considered in the diagnosis of the disorder. The most common of these in LFS is an autism-like spectrum disorder, and LFS is considered one of a number of genetic disorders associated with autism. Additional alterations of psychopathology with behavioral manifestations that have been observed in LFS include: psychotic behavior, schizophrenia, hyperactivity and attention-deficit hyperactivity disorder, aggression, oppositional defiant disorder, obsessive compulsive disorder, extreme shyness, learning disability, cognitive impairment, short-term memory deficit, low frustration tolerance, social dysfunction, lack of impulse control, eating disorder and associated malnutrition, attributed to psychogenic loss of appetite; and pyromania. While psychiatric conditions like these are to be expected with LFS, there have also been cases of the disorder with some preservation of mental and behavioral abilities, such as problem solving, reasoning and normal intelligence. The psychopathology of LFS usually exhibits schizophrenia. When schizophrenia is diagnosed in an individual known to be affected by intellectual disability, LFS may be considered in the differential diagnosis of schizophrenia, with confirmation of cause through appropriate psychiatric and genetic evaluation methods. Marfanoid habitus LFS is clinically distinguished from other X-linked forms of intellectual disability by the accompanying presence of marfanoid habitus. Marfanoid habitus describes a group of physical features common to Marfan<unk> . Including Marfan<unk>  and LFS, marfanoid features of this type have also been observed with several other disorders, one of which is multiple endocrine neoplasia type 2. In LFS, specific features identified as marfanoid include: a long, narrow face; tall, thin stature; long, slender limbs, fingers and toes (not unlike arachnodactyly) with joint hyperextensibility, shortened halluces (the big toes) and long second toes. The diagnosis of marfanoid habitus in LFS is often delayed because many of the physical features and characteristics associated with it are usually not evident until adolescence. Head and face Craniofacial and other features of LFS include: maxillary hypoplasia (underdevelopment of the upper jaw bone), a small mandible (lower jaw bone) and receding chin, a high-arched palate (the roof of the mouth), with crowding and misalignment of the upper teeth; macrocephaly (enlarged skull) with a prominent forehead, hypernasal speech (voice), a long nose with a high, narrow nasal bridge; a deep, short philtrum (the indentation in the upper lip, beneath the nose), low-set ears with some apparent retroversion, hypotonia (decreased muscle tone), pectus excavatum (a malformity of the chest), slightly enlarged to normal testicular size in males, and seizures. Hypernasal speech, or , is primarily the result of velopharyngeal insufficiency, a sometimes congenital aberration in which the velopharyngeal sphincter allows too much air into the nasal cavity during speech. In LFS, hypernasality may also be caused by failure of the soft palate and uvula to reach the back wall of the pharynx (the interior cavity of the throat where swallowing generally occurs) during speech, a condition that can be associated with a submucosal cleft palate. Heart A number of features involving the heart have been noted in several LFS cases, the most significant being dilation of the aortic root, a section of the ascending aorta. Aortic root dilation (enlargement) is associated with a greatly increased risk of dissection of the aortic wall, resulting in aortic aneurysm. As this presents a possible life-threatening consequence of LFS, routine cardiac evaluation methods such as echocardiogram are implemented when the disorder is first diagnosed, along with MRI scans of the brain to screen for suspected agenesis of the corpus callosum. Additional effects on the heart that have been reported with LFS are ventricular and atrial septal defect.
Lujan–Fryns syndrome
McKittrick-Wheelock syndrome
Smith–Fineman–Myers syndrome
Fox–Fordyce disease
McGillivray syndrome
Townes–Brocks syndrome
Kearns–Sayre syndrome
Flynn–Aird syndrome