Idiopathic pulmonary hemorrhage was diagnosed in 37 infants in the Cleveland, Ohio, area between 1993 and 1998. This rare disorder has been related to 12 deaths, including 7 originally thought to be sudden infant death syndrome. Thirty of the infants were African American, all of whom lived in a limited geographic area of eastern metropolitan Cleveland, an area of older housing stock. An investigation led by the Centers for Disease Control and Prevention has found an association with household exposure to a toxigenic mold, Stachybotrys chartarum, and other fungi. The rapidly growing lungs of young infants appear to be especially vulnerable to the toxins made by toxigenic molds. Environmental tobacco smoke was frequently present in the infants' homes and may be a trigger precipitating the acute bleeding. Stachybotrys, although not thought to be a common mold, is known to have a wide geographic distribution. An additional 101 cases of acute, idiopathic pulmonary hemorrhage have been reported in infants in the United States over the past 5 years. In this overview, the investigations are summarized, the clinical profile is described, the toxicity of S. chartarum is discussed, and pathophysiologic concepts are presented.

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Pelizaeus Merzbacher disease is an X-linked dysmyelinating disorder of the CNS, resulting from mutations in the proteolipid protein (PLP) gene. An animal model for this disorder, the myelin-deficient (MD) rat, carries a point mutation in the PLP gene and exhibits a phenotype similar to the fatal, connatal disease, including extensive dysmyelination, tremors, ataxia, and death at approximately postnatal day 21 (P21). We postulated that early death might result from disruption of myelinated neural pathways in the caudal brainstem and altered ventilatory response to oxygen deprivation or hypercapnic stimulus. Using barometric plethysmography to measure respiratory function, we found that the MD rat develops lethal hypoxic depression of breathing at P21, but hypercapnic ventilatory response is normal. Histologic examination of the caudal brainstem in the MD rat at this age showed extensive dysmyelination and downregulation of NMDA and to a lesser extent GABA(A) receptors on neurons in the nucleus tractus solitarius, hypoglossal nucleus, and dorsal motor nucleus of the vagus. Unexpectedly, immunoreactive PLP/DM20 was detected in neurons in the caudal brainstem. Not all biosynthetic functions and structural elements were altered in these neurons, because phosphorylated and nonphosphorylated neurofilament and choline acetyltransferase expression were comparable between MD and wild-type rats. These findings suggest that PLP is expressed in neurons in the developing brainstem and that PLP gene mutation can selectively disrupt central processing of afferent neural input from peripheral chemoreceptors, leaving the central chemosensory system for hypercapnia intact.

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Infants referred for apnea monitoring studies because of persistent bedside monitor alarms have very infrequent prolonged apnea but a higher frequency of desaturation and bradycardia in response to short respiratory pauses than infants without persistent bedside monitor alarms. Referral infants also exhibit a lower baseline Sao2. These abnormalities in oxygenation and cardiorespiratory control may be markers for subtle residual lung disease or functional central nervous system abnormalities.