In a series of Pierre Robin syndrome (PRS) and isolated cleft palate patients (ICP) both U- and V-formed clefts were observed with equal frequency, but the PRS clefts were in average slightly wider. There were totally submucous clefts among the PRS patients. There was no statistical difference between the groups in the prevalence of clefts in the relatives of the patients. The incidence of (genetically influenced) conical elevations in the lower lip was lowest in the noncleft subjects, high in ICP and highest in PRS children. The incidence of hypodontia, which acceptedly is genetically influenced, was also highest in the PRS group. Thus the foetal malposition with the tongue between the palatal shelves does not seem to play any decisive role in the pathogenesis of most PRS clefts. The cause for the PRS is more likely a genetically influenced growth disturbance in the maxilla and the mandible, which due to the organogenetic differences leads to diverging end results, micrognathia and cleft.

The treatment of cleft lip and/or palate [CL(P), CP] in Finland has been centralized to one unit since 1947. Since 1963 all congenital malformations are reported to a central register. Comparison of these two materials showed that altogether 3928 children with clefts, born from 1948 to 1975, were registered in a total of 2 258 850 live born children in Finland, corresponding an incidence of 1.74%. There was a constant registered rise in the incidence from 1.31% in 1948-52 to 2.16% in 1969-75, indicating a corrected "true" increase in the incidence by 33% in 28 years, or approximately by over one percent per year. Of all registered clefts born 1963-75 23.5% were lacking from the Register of Congenital Malformations, and 10.3% from the hospital records. In 1948-75 55.8% of the clefts belonged to the group CP and 44.2% to CL(P). The incidence of CP increased from 0.78% in 1948-52 to 1.21% in 1969-75, and that of CL(P) from 0.53 to 0.95%. An average of 13,8% of the CP-cases were submucous clefts. Their registered incidence in all live born children increased from 0.08% in 1948-52 to 0.19% in 1969-75.

Comparison of the patient records of the Finnish Red Cross National Cleft Center and the Central Register of Congenital Malformations showed a statistically significant yearly fluctuation as well as an increasing trend in the incidence of both cleft lip (and palate) and isolated cleft palate during the period 1948-1975. Almost significant difference was found in the monthly incidence of CL(P) with the peak in children born in April, while no such difference could be noticed in CP or both groups combined. The rapid increase and similarity of the incidence curves of both CL(P) and CP is suggestive of the action of simultaneous and similar exogenous agents in the pathogenesis of both types. In patients with CL(P) the etiological factor was considered to have been active 35 weeks and in CP 31 weeks before delivery. The monthly number of clefts was compared to the number of serologically verified infections (influenza A, respiratory syncytical, mumps, measles, rubeola, parainfluenza, adenoviruses as well as Mycoplasma pneumoniae) in the years 1971-75. No statistically significant correlation was found in this respect.