MEDNIK syndrome is a severe multisystem disorder characterized by impaired intellectual development, enteropathy, deafness, peripheral neuropathy, ichthyosis, and keratoderma (summary by Montpetit et al., 2008). Patients with MEDNIK exhibit distinct dysmorphic features, including high forehead, upslanting palpebral fissures, depressed nasal bridge, and low-set ears, as well as growth retardation and moderate to severe intellectual disability, with brain atrophy on imaging. Other features include sensorineural deafness, enteropathy with congenital diarrhea, abnormalities of copper metabolism associated with liver disease, and ichthyosis, hyperkeratosis, and erythroderma. Peripheral neuropathy has also been observed in adult patients (Martinelli et al., 2013). MEDNIK syndrome shows phenotypic similarities to CEDNIK syndrome (609528).

A rare, syndromic diabetes mellitus characterized by partial pancreatic agenesis, diabetes mellitus, and heart anomalies (including transposition of the great vessels, ventricular or atrial septal defects, pulmonary stenosis, or patent ductus arteriosis).

An extremely rare autosomal recessive gastroenterological disorder reported in three families so far characterized by meconium ileus without any further stigmata of cystic fibrosis including pulmonary or pancreatic manifestations. Two of the reported patients developed chronic diarrhea in infancy. Homozygous mutations in the GUCY2C gene (12p12) leading to marked reduction or absence of enzymatic activity of guanylate cyclase 2C were found in the affected patients. The disease was reported to show partial penetrance.

ACTG2 visceral myopathy is a disorder of smooth muscle dysfunction of the bladder and gastrointestinal system with phenotypic spectrum that ranges from mild to severe. Bladder involvement can range from neonatal megacystis and megaureter (with its most extreme form of prune belly syndrome) at the more severe end, to recurrent urinary tract infections and bladder dysfunction at the milder end. Intestinal involvement can range from malrotation, neonatal manifestations of microcolon, megacystis microcolon intestinal hypoperistalsis syndrome, and chronic intestinal pseudoobstruction (CIPO) in neonates at the more severe end to intermittent abdominal distention and functional intestinal obstruction at the milder end. Affected infants (with or without evidence of intestinal malrotation) often present with feeding intolerance and findings of non-mechanical bowel obstruction that persist after successful surgical correction of malrotation. Individuals who develop manifestations of CIPO in later childhood or adulthood often experience episodic waxing and waning of bowel motility. They may undergo frequent abdominal surgeries (perhaps related to malrotation or adhesions causing mechanical obstruction) resulting in resection of dilated segments of bowel, often becoming dependent on total parenteral nutrition (TPN).

Megacystis-microcolon-intestinal hypoperistalsis syndrome-2 (MMIHS2) is characterized by prenatal bladder enlargement, neonatal functional gastrointestinal obstruction, and chronic dependence on total parenteral nutrition and urinary catheterization. The majority of cases have a fatal outcome due to malnutrition and sepsis, followed by multiorgan failure (summary by Wang et al., 2019). For a discussion of genetic heterogeneity of MMIHS, see 249210.

Megacystis microcolon intestinal hypoperistalsis syndrome (MMIHS) is a rare congenital defect of visceral smooth muscle, primarily affecting females who present at birth with functional obstruction of the intestine, microcolon, dilation of the bladder, and secondary hydronephrosis. Total parenteral nutrition, adequate intermittent catheterization of bladder, and surgical corrections for intestinal malrotation are frequent modes of treatment for this disease without which rapid death ensues. In some instances, multivisceral organ transplantation has been undertaken with some success. Despite these clinical interventions, MMIHS often leads to premature death due to complications of therapy (summary by Halim et al., 2017). For a discussion of genetic heterogeneity of MMIHS, see 249210.

Megacystis-microcolon-intestinal hypoperistalsis syndrome-5 (MMIHS5) is a form of visceral myopathy characterized by significant inter- and intrafamilial variability, with the most severely affected patients exhibiting prenatal bladder enlargement, intestinal malrotation, neonatal functional gastrointestinal obstruction, and chronic dependence on total parenteral nutrition (TPN) and urinary catheterization (Wangler et al., 2014). For a general phenotypic description and discussion of genetic heterogeneity of MMIHS, see MMIHS1 (249210).